Astrophysics, abstract
astro-ph/0406104

From: Patrick Morris [view email]
Date: Thu, 3 Jun 2004 23:32:53 GMT   (189kb)

MARCS-Model Stellar Atmospheres, and Their Application to the Photometric Calibration of the Spitzer-IRS

Authors: L. Decin (KUL), P. W. Morris (Caltech), P. N. Appleton (Caltech), V. Charmandaris (Cornell), L. Armus (Caltech), J. R. Houck (Cornell)
Comments: 6 pages, 3 figures, accepted for publication in the ApJSS Spitzer edition

We describe state-of-the-art MARCS-code model atmospheres generated for a group of A dwarf, G dwarf, and late-G to mid-K giant standard stars, selected to photometrically calibrate the Spitzer-IRS, and compare the synthetic spectra to observations of HR 6688, HR 6705, and HR 7891. The general calibration processes and uncertainties are briefly described, and the differences between various templated composite spectra of the standards are addressed. In particular, a contrast between up-to-date model atmospheres and previously published composite and synthetic spectra is illustrated for wavelength ranges around 8um (where the SiO Delta(v) = 1 band occurs for the cooler standards) and lambda greater than 20um, where the use of the Engelke function will lead to increasingly large discrepancies due to the neglect of gravity in cool stars. At this point, radiometric requirements are being met, absolute flux calibration uncertainties (1-sigma) are ~20% in the SH and LH, and ~15% in the SL and LL data, and order-to-order flux uncertainties are ~10% or less. Iteration between the MARCS model atmosphere inputs and the data processing will improve the S/N ratios and calibration accuracies.

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Astrophysics, abstract
astro-ph/0406222

From: Thomas Roellig [view email]
Date: Wed, 9 Jun 2004 00:28:57 GMT   (109kb)

Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs

Authors: T. L. Roellig, J. E. Van Cleve, G. C. Sloan, J. C. Wilson, D. Saumon, S. K. Leggett, M. S. Marley, M. C. Cushing, J. D. Kirkpatrick, A. K. Mainzer, J. R. Houck
Comments: 4 pages, 2 figures

We present the first mid-infrared spectra of brown dwarfs, together with observations of a low-mass star. Our targets are the M3.5 dwarf GJ 1001A, the L8 dwarf DENIS-P J0255-4700, and the T1/T6 binary system epsilon Indi Ba/Bb. As expected, the mid-infrared spectral morphology of these objects changes rapidly with spectral class due to the changes in atmospheric chemistry resulting from their differing effective temperatures and atmospheric structures. By taking advantage of the unprecedented sensitivity of the Infrared Spectrograph on the Spitzer Space Telescope we have detected the 7.8 micron methane and 10 micron ammonia bands for the first time in brown dwarf spectra.

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Astrophysics, abstract
astro-ph/0412272

From: James Muzerolle [view email]
Date: Sat, 11 Dec 2004 20:54:55 GMT   (54kb)

The Outburst of V1647 Ori Revealed by Spitzer

Authors: J. Muzerolle, S. T. Megeath, K. M. Flaherty, K. D. Gordon, G. H. Rieke, E. T. Young, C. J. Lada
Comments: 12 pages, 3 figures, accepted by ApJ Letters
Journal-ref: Astrophys.J. 620 (2005) L107-L110

We present Spitzer Space Telescope observations of V1647 Ori, the outbursting source lighting McNeil's nebula, taken near the optical peak of the outburst in early March 2004. The source is easily detected in all Spitzer imaging bands from 3.6 - 70 microns. The fluxes at all wavelengths are roughly a factor of 15 brighter than pre-outburst levels; we measure a bolometric luminosity of 44 Lsun. We posit that this event is due to an increase in the accretion luminosity of the source. Simple models of an accretion disk plus tenuous envelope can qualitatively explain the observed pre- and post-outburst spectral energy distributions. The accretion activity implied by our results indicates that the outburst may be intermediate between FUor and EXor-type events. We also report the discovery of a previously unknown mid-infrared counterpart to the nearby Herbig-Haro object HH 22.

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Astrophysics, abstract
astro-ph/0502100

From: Kevin Luhman [view email]
Date: Fri, 4 Feb 2005 13:30:21 GMT   (29kb)

Spitzer Identification of the Least Massive Known Brown Dwarf with a Circumstellar Disk

Authors: K. L. Luhman, Paola D'Alessio, Nuria Calvet, Lori E. Allen, Lee Hartmann, S. T. Megeath, P. C. Myers, G. G. Fazio
Comments: 9 pages, 1 figure
Journal-ref: Astrophys.J. 620 (2005) L51-L54

Using the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope, we have obtained mid-infrared photometry of the least massive known brown dwarf in the Chamaeleon I star-forming region. For this young brown dwarf, OTS 44, we have constructed a spectral energy distribution (SED) from 0.8-8 um by combining the measurements at 3.6, 4.5, 5.8, and 8.0 um from IRAC with ground-based photometry at I, J, H, and K. The resulting SED for OTS 44 exhibits significant excess emission longward of 3 um relative to the SED expected from the photosphere of the brown dwarf. We have successfully modeled the source of this excess emission in terms of an irradiated viscous accretion disk with M'<=10^-10 M_sun/year. With a spectral type of M9.5 and a mass of ~15 M_Jup, OTS 44 is now the coolest and least massive brown dwarf observed to have a circumstellar disk. These measurements demonstrate that disks exist around brown dwarfs even down to the deuterium burning mass limit and the approximate upper mass limit of extrasolar planetary companions.

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Astrophysics, abstract
astro-ph/0502527

From: Adam J. Burgasser [view email]
Date (v1): Thu, 24 Feb 2005 22:33:09 GMT   (81kb)
Date (revised v2): Tue, 1 Mar 2005 14:53:37 GMT   (79kb)

Spitzer Studies of Ultracool Subdwarfs: Metal-poor Late-type M, L and T Dwarfs

Authors: Adam J. Burgasser (AMNH)
Comments: 4 pages, 4 figures, contribution to "The Spitzer Space Telescope: New Views of the Cosmos" meeting held 9-12 November 2004; v2 fixes some botched references (thanks to R. Scholz for pointing them out)

Recent discoveries from red optical proper motion and wide-field near-infrared surveys have uncovered a new population of ultracool subdwarfs, metal-poor stars and brown dwarfs extending into the late-type M, L and possibly T spectral classes. These objects are among the first low-mass stars and brown dwarfs formed in the Galaxy, and are valuable tracers of metallicity effects in low-temperature atmospheres. Like solar metallicity late-type dwarfs, ultracool subdwarfs emit the majority of their emergent flux at infrared wavelengths. Here I discuss how Spitzer observations will contribute to the study of these objects, enabling measurement of the temperature scale, tests for dust formation and the identification of surface gravity and metallicity diagnostics in the coldest brown dwarfs.

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Astrophysics, abstract
astro-ph/0503326

From: Martin Cohen [view email]
Date: Tue, 15 Mar 2005 20:49:57 GMT   (239kb)

G313.3+00.3: A New Planetary Nebula discovered by the Australia Telescope Compact Array and the Spitzer Space Telescope

Authors: Martin Cohen, Anne J. Green, Mallory S.E. Roberts, Marilyn R. Meade, Brian Babler, Remy Indebetouw, Barbara A. Whitney, Christer Watson, Mark Wolfire, Mike J. Wolff, John S. Mathis, Edward B. Churchwell
Comments: 18 pages, LaTeX (aastex), incl. 8 PostScript (eps) figures and 1 table. Accepted by ApJ (Part 1)
Journal-ref: Astrophys.J. 627 (2005) 446-453

We present a new planetary nebula, first identified in images from the Australia Telescope Compact Array, although not recognized at that time. Recent observations with the Spitzer Space Telescope during the GLIMPSE Legacy program have rediscovered the object. The high-resolution radio and infrared images enable the identification of the central star or its wind, the recognition of the radio emission as thermal, and the probable presence of polycylic aromatic hydrocarbons in and around the source. These lead to the conclusion that G313.3+00.3 is a planetary nebula. This object is of particular interest because it was discovered solely through radio and mid-infrared imaging, without any optical (or near-infrared) confirmation, and acts as a proof of concept for the discovery of many more highly extinguished planetary nebulae. G313.3+00.3 is well-resolved by both the instruments with which it was identified, and suffers extreme reddening due to its location in the Scutum-Crux spiral arm.

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Astrophysics, abstract
astro-ph/0504086

From: Kate Y. L. Su [view email]
Date: Mon, 4 Apr 2005 21:33:42 GMT   (776kb)

The Vega Debris Disk -- A Surprise from Spitzer

Authors: K. Y. L. Su (1), G. H. Rieke (1), K. A. Misselt (1), J. A. Stansberry (1), A. Moro-Martin (1,3), K. R. Stapelfeldt (2), M. W. Werner (2), D. E. Trilling (1), G. J. Bendo (1), K. D. Gordon (1), D. C. Hines (4), M. C. Wyatt (5), W. S. Holland (5), M. Marengo (6), S. T. Megeath (6), G. G. Fazio (6) ((1) Steward Observatory, (2) JPL/Caltech, (3) Max-Planck-Institut fur Astronomie, (4) Space Science Institute, (5) Royal Observatory, (6) CfA)
Comments: 13 pages, 17 figures, accepted for publication in ApJ. (Figures 2, 3a, 3b and 4 have been degraded to lower resolutions.)
Journal-ref: Astrophys.J. 628 (2005) 487-500

We present high spatial resolution mid- and far-infrared images of the Vega debris disk obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The disk is well resolved and its angular size is much larger than found previously. The radius of the disk is at least 43" (330 AU), 70"(543 AU), and 105" (815 AU) in extent at 24, 70 and 160 um, respectively. The disk images are circular, smooth and without clumpiness at all three wavelengths. The radial surface brightness profiles imply an inner boundary at a radius of 11"+/-2" (86 AU). Assuming an amalgam of amorphous silicate and carbonaceous grains, the disk can be modeled as an axially symmetric and geometrically thin disk, viewed face-on, with the surface particle number density following an r^-1 power law. The disk radiometric properties are consistent with a range of models using grains of sizes ~1 to ~50 um. We find that a ring, containing grains larger than 180 um and at radii of 86-200 AU from the star, can reproduce the observed 850 um flux, while its emission does not violate the observed MIPS profiles. This ring could be associated with a population of larger asteroidal bodies analogous to our own Kuiper Belt. Cascades of collisions starting with encounters amongthese large bodies in the ring produce the small debris that is blown outward by radiation pressure to much larger distances where we detect its thermal emission. The dust production rate is >~10^15 g/s based on the MIPS results. This rate would require a very massive asteroidal reservoir for the dust to be produced in a steady state throughout Vega's life. Instead, we suggest that the disk we imaged is ephemeral and that we are witnessing the aftermath of a large and relatively recent collisional event, and subsequent collisional cascade.

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Astrophysics, abstract
astro-ph/0505492

From: Pedro Garcia-Lario [view email]
Date: Tue, 24 May 2005 14:41:50 GMT   (8kb)

From ISO to Spitzer: a new view of the AGB-PN transition phase

Authors: P. Garcia-Lario, J.V. Perea Calderon
Comments: To appear in the conference proceedings "Spitzer Space Telescope: New Views of the Universe, held Nov. 2004 in Pasadena, 2 pages, 0 figures

We present a novel classification scheme for stars evolving in the transition phase between the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) stage based on the results obtained with ISO-SWS. With the better sensitivity and higher spatial resolution of Spitzer this analysis can now be extended to a larger number of sources located in the Galactic Bulge, in the Magellanic Clouds and in other Galaxies of the Local Group, offering an excellent opportunity to study the validity of the proposed scheme in environments which are free of the distance scale bias that hinder the observations made with ISO on galactic sources located at uncertain distances. The new observations will be used to test the current evolutionary models which predict the dredge-up of processed material to the surface of low- and intermediate-mass stars as a function of the progenitor mass and of the metallicity.

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Astrophysics, abstract
astro-ph/0506407

From: Rubina Kotak [view email]
Date: Fri, 17 Jun 2005 10:31:08 GMT   (124kb)

Early-time Spitzer observations of the type II-Plateau supernova, 2004dj

Authors: Rubina Kotak (Imperial College London), Peter Meikle (Imperial College London), Schuyler van Dyk (Spitzer Science Cente), Peter Hoeflich (Uni. of Texas), Seppo Mattila (Stockholm Observatory)
Comments: ApJ Letters (accepted)
Journal-ref: Astrophys.J. 628 (2005) L123-L126

We present mid-infrared observations with the Spitzer Space Telescope of the nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have obtained the first mid-IR spectra of any supernova apart from SN 1987A. A prominent [NiII] 6.64 micron line is observed, from which we deduce that the mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red wing of the CO-fundamental band. We relate our findings to possible progenitors and favour an evolved star, most likely a red supergiant, with a probable initial mass between ~10 and 15 Msun.

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Astrophysics, abstract
astro-ph/0506473

From: Ciska Markwick-Kemper [view email]
Date: Mon, 20 Jun 2005 20:51:06 GMT   (97kb)

Spitzer detections of new dust components in the outflow of the Red Rectangle

Authors: F. Markwick-Kemper, J. D. Green, E. Peeters
Comments: accepted by ApJL; 5 pages; 4 figures
Journal-ref: Astrophys.J. 628 (2005) L119-L122

We present Spitzer high spectral resolution IRS spectroscopy of three positions in the carbon-rich outflow of post-AGB star HD 44179, better known as the Red Rectangle. Surprisingly, the spectra show some strong unknown mid-infrared resonances, in the 13-20 micron range. The shape and position of these resonances varies with position in the nebula, and are not correlated with the PAH features. We conclude these features are due to oxygen-rich minerals, located in a region which is believed to be predominantly carbon-rich. We provide possible explanations for the presence of oxygen-rich dust in the carbon-rich outflows. Simple Mg-Fe-oxides are suggested as carriers of these unidentified features.

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Astrophysics, abstract
astro-ph/0506743

From: Michael R. Meyer [view email]
Date: Wed, 29 Jun 2005 21:31:43 GMT   (67kb)

Spitzer Observations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

Authors: J.R. Stauffer, L. Rebull (Spitzer Science Center), J. Carpenter, L. Hillenbrand (Caltech), D. Backman (NASA-Ames), M.R. Meyer, J.S. Kim, M.D. Silverstone, E. Young (Steward Observatory, UofA), D.C. Hines (SSI), D.R. Soderblom (STScI), E.E. Mamajek (Harvard-Smithsonian CfA), P. Morris (SSC), J. Bouwman (MPIA-Heidelberg), S.E. Strom (NOAO)
Comments: 32 postscript pages including 8 figues and 3 tables. To appear in the Astronomical Journal

Fluxes and upper limits in the wavelength range from 3.6 to 70 microns from the Spitzer Space Telescope are provided for twenty solar-mass Pleiades members. One of these stars shows a probable mid-IR excess and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS wavelengths, HII1101, we derive Log(L[dust]/L[Sun]) ~ -3.8 and an estimated debris disk mass of 4.2 x 10^-5 M(Earth) for an assumed uniform dust grain size of 10 microns If the stars with detected excesses are interpreted as stars with relatively recent, large collision events producing a transient excess of small dust particles, the frequency of such disk transients is about ~ 10 % for our ~ 100 Myr, Pleiades G dwarf sample. For the stars without detected 24-70 micron excesses, the upper limits to their fluxes correspond to approximate 3 sigma upper limits to their disk masses of 6 x 10^-6 M(Earth) using the MIPS 24 micron upper limit, or 2 x 10^-4 M(Earth) using the MIPS 70 micron limit. These upper limit disk masses (for "warm" and "cold" dust, respectively) are roughly consistent, but somewhat lower than, predictions of a heuristic model for the evolution of an "average" solar-mass star's debris disk based on extrapolation backwards in time from current properties of the Sun's Kuiper belt.

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Astrophysics, abstract
astro-ph/0506743

From: Michael R. Meyer [view email]
Date: Wed, 29 Jun 2005 21:31:43 GMT   (67kb)

Spitzer Observations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

Fluxes and upper limits in the wavelength range from 3.6 to 70 microns from the Spitzer Space Telescope are provided for twenty solar-mass Pleiades members. One of these stars shows a probable mid-IR excess and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS wavelengths, HII1101, we derive Log(L[dust]/L[Sun]) ~ -3.8 and an estimated debris disk mass of 4.2 x 10^-5 M(Earth) for an assumed uniform dust grain size of 10 microns If the stars with detected excesses are interpreted as stars with relatively recent, large collision events producing a transient excess of small dust particles, the frequency of such disk transients is about ~ 10 % for our ~ 100 Myr, Pleiades G dwarf sample. For the stars without detected 24-70 micron excesses, the upper limits to their fluxes correspond to approximate 3 sigma upper limits to their disk masses of 6 x 10^-6 M(Earth) using the MIPS 24 micron upper limit, or 2 x 10^-4 M(Earth) using the MIPS 70 micron limit. These upper limit disk masses (for "warm" and "cold" dust, respectively) are roughly consistent, but somewhat lower than, predictions of a heuristic model for the evolution of an "average" solar-mass star's debris disk based on extrapolation backwards in time from current properties of the Sun's Kuiper belt.

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Astrophysics, abstract
astro-ph/0509199

From: Geoffrey Bryden [view email]
Date: Wed, 7 Sep 2005 20:04:44 GMT   (116kb)

Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer/MIPS Survey

Authors: G. Bryden, C. A. Beichman, D. E. Trilling, G. H. Rieke, et al
Comments: 11 figures
Journal-ref: Astrophys.J. 636 (2006) 1098-1113

We have searched for infrared excesses around a well defined sample of 69 FGK main-sequence field stars. These stars were selected without regard to their age, metallicity, or any previous detection of IR excess; they have a median age of ~4 Gyr. We have detected 70 um excesses around 7 stars at the 3-sigma confidence level. This extra emission is produced by cool material (< 100 K) located beyond 10 AU, well outside the ``habitable zones'' of these systems and consistent with the presence of Kuiper Belt analogs with ~100 times more emitting surface area than in our own planetary system. Only one star, HD 69830, shows excess emission at 24 um, corresponding to dust with temperatures > 300 K located inside of 1 AU. While debris disks with Ld/L* > 10^-3 are rare around old FGK stars, we find that the disk frequency increases from 2+-2% for Ld/L* > 10^-4 to 12+-5% for Ld/L* > 10^-5. This trend in the disk luminosity distribution is consistent with the estimated dust in our solar system being within an order of magnitude, greater or less, than the typical level around similar nearby stars.

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Astrophysics, abstract
astro-ph/0509507

From: G. C. Sloan [view email]
Date: Fri, 16 Sep 2005 18:01:45 GMT   (70kb)

R CrB Candidates in the Small Magellanic Cloud: Observations of Cold, Featureless Dust with the Spitzer Infrared Spectrograph

Authors: Kathleen E. Kraemer, G.C. Sloan, P.R. Wood, Stephan D. Price, Michael P. Egan
Comments: Accepted by ApJ Letters 25 August, 2005, 4 pages (emulateapj), 5 figures
Journal-ref: Astrophys.J. 631 (2005) L147-L150

We observed 36 evolved stars in the Small Magellanic Cloud (SMC) using the low-resolution mode of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. Two of these stars, MSX SMC 014 and 155, have nearly featureless spectral energy distributions over the IRS wavelength range (5.2-35 um) and F_nu peaking at ~8-9 um. The data can be fit by sets of amorphous carbon shells or by single 600-700 K blackbodies. The most similar spectra found in extant spectral databases are of R CrB, although the spectral structure seen in R CrB and similar stars is much weaker or absent in the SMC sources. Both SMC stars show variability in the near-infrared. Ground-based visual spectra confirm that MSX SMC 155 is carbon-rich, as expected for R CrB (RCB) stars, and coincides with an object previously identified as an RCB candidate. The temperature of the underlying star is lower for MSX SMC 155 than for typical RCB stars. The strength of the C_2 Swan bands and the low temperature suggest that it may be a rare DY Per-type star, only the fifth such identified. MSX SMC 014 represents a new RCB candidate in the SMC, bringing the number of RCB candidates in the SMC to six. It is the first RCB candidate discovered with Spitzer and the first identified by its infrared spectral characteristics rather than its visual variability.

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Astrophysics, abstract
astro-ph/0509695

From: Jacco van Loon [view email]
Date: Thu, 22 Sep 2005 18:55:35 GMT   (531kb)

ESO-VLT and Spitzer spectroscopy of IRAS05328-6827: a massive young stellar object in the Large Magellanic Cloud

Authors: Jacco Th. van Loon (Keele University, UK), J.M. Oliveira (Keele), P.R. Wood (ANU), A.A. Zijlstra (Manchester), G.C. Sloan (Cornell), M. Matsuura (Manchester), P.A. Whitelock (SAAO), M.A.T. Groenewegen (Leuven), J.A.D.L. Blommaert (Leuven), M.-R.L. Cioni (ROE), S. Hony (Leuven), C. Loup (IAP), L.B.F.M. Waters (Amsterdam, Leuven)
Comments: Accepted for publication in MNRAS Letters. 5 pages, 5 figures

We present the first thermal-infrared spectra of an extra-galactic Young Stellar Object (YSO), IRAS05328-6827 in the HII region LHA 120-N148 in the Large Magellanic Cloud. The observed and modelled spectral energy distribution reveals a massive YSO, M=20 Msun, which is heavily-embedded and probably still accreting. The reduced dust content as a consequence of the lower metallicity of the LMC allows a unique view into this object, and together with a high C/O ratio may be responsible for the observed low abundance of water ice and relatively high abundances of methanol and CO2 ices.

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Astrophysics, abstract
astro-ph/0509786

From: Snezana Stanimirovic [view email]
Date: Mon, 26 Sep 2005 22:56:05 GMT   (227kb)

Spitzer Space Telescope detection of the young supernova remnant 1E 0102.2-7219

Authors: Snezana Stanimirovic (1), Alberto D. Bolatto (1), Karin Sandstrom (1), Adam K. Leroy (1), Joshua D. Simon (1,2), B. M. Gaensler (3), Ronak Y. Shah (4), James M. Jackson (4) ((1) UC Berkeley, (2) Caltech, (3) CfA, (4) Boston University)
Comments: 5 pages, accepted by ApJL
Journal-ref: Astrophys.J. 632 (2005) L103-L106

We present infrared observations of the young, oxygen-rich supernova remnant 1E 0102.2-7219 (E0102) in the Small Magellanic Cloud, obtained with the Spitzer Space Telescope. The remnant is detected at 24 um but not at 8 or 70 um and has a filled morphology with two prominent filaments. We find evidence for the existence of up to 8x10^-4 Msolar of hot dust (T~120 K) associated with the remnant. Most of the hot dust is located in the central region of E0102 which appears significantly enhanced in infrared and radio continuum emission relative to the X--ray emission. Even if all of the hot dust was formed in the explosion of E0102, the estimated mass of dust is at least 100 times lower that what is predicted by some recent theoretical models.

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Astrophysics, abstract
astro-ph/0510518

From: Ho-Gyu Lee [view email]
Date (v1): Tue, 18 Oct 2005 11:37:17 GMT   (965kb)
Date (revised v2): Mon, 23 Jan 2006 09:45:13 GMT   (973kb)

Infrared Supernova Remnants in the Spitzer GLIMPSE Field

Authors: Ho-Gyu Lee
Comments: 30 pages including 24 figures, published in JKAS (Journal of the Korean Astronomical Society)
Journal-ref: JKAS, 2005, 38, 385

We have searched for infrared emission from supernova remnants (SNRs) included in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) field. At the positions of 100 known SNRs, we made 3.6, 4.5, 5.8, and 8.0 um band images covering the radio continuum emitting area of each remnant. In-depth examinations of four band images based on the radio continuum images of SNRs result in the identification of sixteen infrared SNRs in the GLIMPSE field. Eight SNRs show distinct infrared emission in nearly all the four bands, and the other eight SNRs are visible in more than one band. We present four band images for all identified SNRs, and RGB-color images for the first eight SNRs. These images are the first high resolution (<2") images with comparative resolution of the radio continuum for SNRs detected in the mid-infrared region. The images typically show filamentary emission along the radio enhanced SNR boundaries. Most SNRs are well identified in the 4.5 and 5.8 um bands. We give a brief description of the infrared features of the identified SNRs.

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Astrophysics, abstract
astro-ph/0510630

From: William T. Reach [view email]
Date: Thu, 20 Oct 2005 21:26:28 GMT   (870kb)

A Spitzer Space Telescope Infrared Survey of Supernova Remnants in the Inner Galaxy

Authors: William T. Reach, Jeonghee Rho, Achim Tappe, Thomas G. Pannuti, Crystal L. Brogan, Edward B. Churchwell, Marilyn R. Meade, Brian Babler, Remy Indebetouw, Barbara A. Whitney
Comments: Accepted 10/18/2005 for publication in "The Astronomical Journal". The figures in this astro-ph submission are drastically reduced in quality in order to fit within its limits

Using Infrared Array Camera (IRAC) images at 3.6, 4.5, 5.8, and 8 microns from the GLIMPSE Legacy science program on the Spitzer Space Telescope, we searched for infrared counterparts to the 95 known supernova remnants that are located within galactic longitudes 65>|l|>10 degrees and latitudes |b|<1 degree. Eighteen infrared counterparts were detected. Many other supernova remnants could have significant infrared emission but are in portions of the Milky Way too confused to allow separation from bright HII regions and pervasive mid-infrared emission from atomic and molecular clouds along the line of sight. Infrared emission from supernova remnants originates from synchrotron emission, shock-heated dust, atomic fine-structure lines, and molecular lines. The detected remnants are G11.2-0.3, Kes 69, G22.7-0.2, 3C 391, W 44, 3C 396, 3C 397, W 49B, G54.4-0.3, Kes 17, Kes 20A, RCW 103, G344.7-0.1, G346.6-0.2, CTB 37A, G348.5-0.0, and G349.7+0.2. The infrared colors suggest emission from molecular lines (9 remnants), fine-structure lines (3), and PAH (4), or a combination; some remnants feature multiple colors in different regions. None of the remnants are dominated by synchrotron radiation at mid-infrared wavelengths. The IRAC-detected sample emphasizes remnants interacting with relatively dense gas, for which most of the shock cooling occurs through molecular or ionic lines in the mid-infrared.

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Astrophysics, abstract
astro-ph/0511094

From: Brad Hansen [view email]
Date: Thu, 3 Nov 2005 00:43:11 GMT   (772kb)

A Spitzer Search for Infrared Excesses around Massive Young White Dwarfs

Authors: Brad M. S. Hansen, Shri Kulkarni, Sloane Wiktorowicz
Comments: 39 pages, 21 figures, 3 tables, 0 carbs. to appear in the Astronomical Journal (Feb 2006)

We examine 14 hot white dwarfs for signs of infrared excess using the Spitzer Space Telescope. Twelve of the objects are massive white dwarfs which have been suggested to be the result of binary mergers. The remaining two objects are undermassive white dwarfs which again may be the result of mergers or the inspiral of a substellar companion. In no case do we find any evidence for significant infrared excesses out to wavelengths of 8 microns. This places strong constraints on the presence of orbiting dust and weaker constraints on the presence of close substellar companions.

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Astrophysics, abstract
astro-ph/0511314

From: S. T. Megeath [view email]
Date: Thu, 10 Nov 2005 16:49:28 GMT   (93kb)

Spitzer/IRAC Photometry of the Eta Chameleontis Association

Authors: S. T. Megeath (1), L. Hartmann (2), K. L. Luhman (3), G. G. Fazio (1)
Comments: Accepted to ApJ letters
Journal-ref: Astrophys.J. 634 (2005) L113-L116

We present IRAC 3.6, 4.5, 5.8 and 8 micron photometry for the 17 A, K and M type members of the Eta Chameleontis association. These data show infrared excesses toward six of the 15 K and M stars, indicating the presence of circumstellar disks around 40% of the stars with masses of 0.1-1 solar mass. The two A-stars show no infrared excesses. The excess emission around one of the stars is comparable to the median excess for classical T Tauri stars in the Taurus association; the remaining five show comparatively weak excess emission. Taking into account published Halpha spectroscopy that shows that five of the six stars are accreting, we argue that the disks with weak mid-infrared excesses are disks in which the inner disks have been largely depleted of small grains by grain growth, or, in one case, the small grains have settled to the midplane. This suggests that Eta Cha has a much higher fraction of disks caught in the act of transitioning into optically thin disks than that measured in younger clusters and associations.

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Astrophysics, abstract
astro-ph/0601305

From: Mukremin Kilic [view email]
Date: Fri, 13 Jan 2006 22:16:53 GMT   (60kb)

The Mystery Deepens: Spitzer Observations of Cool White Dwarfs

Authors: Mukremin Kilic, Ted von Hippel, Fergal Mullally (Texas), William T. Reach, Marc J. Kuchner, D. E. Winget, Adam Burrows
Comments: 17 pages, 4 figures, ApJ in press, 10 May 2006
Journal-ref: Astrophys.J. 642 (2006) 1051-1056

We present 4.5$\mu$m and 8$\mu$m photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with T_eff< 6000 K show slightly depressed mid-infrared fluxes relative to white dwarf models. In addition, another white dwarf with a peculiar optical and near-infrared spectral energy distribution (LHS 1126) is found to display significant flux deficits in Spitzer observations. These mid-infrared flux deficits are not predicted by the current white dwarf models including collision induced absorption due to molecular hydrogen. We postulate that either the collision induced absorption calculations are incomplete or there are other unrecognized physical processes occuring in cool white dwarf atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with effective temperature well in excess of 10$^5$ K. This implies that the source of this flux deficit is probably not molecular absorption but some other process.

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Astrophysics, abstract
astro-ph/0601314

From: Karl D. Gordon [view email]
Date: Sun, 15 Jan 2006 19:05:37 GMT   (280kb)

Spitzer/MIPS Infrared Imaging of M31: Further Evidence for a Spiral/Ring Composite Structure

Authors: Karl D. Gordon, J. Bailin, C. W. Engelbracht, G. H. Rieke, K. A. Misselt, W. B. Latter, E. T. Young, M. L. N. Ashby, P. Barmby, B. K. Gibson, D. C. Hines, J. Hinz, O. Krause, D. A. Levine, F. R. Marleau, A. Noriega-Crespo, S. Stolovy, D. A. Thilker, M. W. Werner
Comments: 7 pages, 4 figures, ApJ Letters, in press (preprint with full resolution images available at this http URL)
Journal-ref: Astrophys.J. 638 (2006) L87-L92

New images of M31 at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) reveal the morphology of the dust in this galaxy. This morphology is well represented by a composite of two logarithmic spiral arms and a circular ring (radius ~10 kpc) of star formation offset from the nucleus. The two spiral arms appear to start at the ends of a bar in the nuclear region and extend beyond the star forming ring. As has been found in previous work, the spiral arms are not continuous but composed of spiral segments. The star forming ring is very circular except for a region near M32 where it splits. The lack of well defined spiral arms and the prominence of the nearly circular ring suggests that M31 has been distorted by interactions with its satellite galaxies. Using new dynamical simulations of M31 interacting with M32 and NGC 205 we find that, qualitatively, such interactions can produce an offset, split ring like that seen in the MIPS images.

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Astrophysics, abstract
astro-ph/0601495

From: Patrice Bouchet J.. [view email]
Date (v1): Mon, 23 Jan 2006 01:45:09 GMT   (761kb)
Date (revised v2): Tue, 12 Sep 2006 14:31:56 GMT   (372kb)
Date (revised v3): Wed, 13 Sep 2006 10:42:31 GMT   (474kb)

SN 1987A After 18 Years: Mid-Infrared GEMINI and SPITZER Observations of the Remnant

Authors: Patrice Bouchet, Eli Dwek, I. John Danziger, Richard G. Arendt, I. James M. De Buizer, Sangwook Park, Nicholas B. Suntzeff, Robert P. Kirshner, Peter Challis
Comments: 50 pages; 3 tables; 18 figures. New version significantly modified. New figures (all of them appended). To appear in ApJ v648n1, October 10, 2006

We present high resolution 11.7 and 18.3um mid-IR images of SN 1987A obtained on day 6526 with T-ReCS attached to the Gemini telescope. The 11.7um flux has increased significantly since our last observations on day 6067. The images clearly show that all the emission arises from the equatorial ring (ER). Spectra obtained with Spitzer, on day 6184 with MIPS at 24um, on day 6130 with IRAC in the 3.6-8um region, and on day 6190 with IRS in the 12-37um region show that the emission consists of thermal emission from silicate dust that condensed out in the red giant wind of the progenitor star. The dust temperature is ~166K, and the emitting dust mass is ~2.6 x 10-6 Msun. Lines of [Ne II]12.82um and [Ne III]15.56um are clearly present, as well as a weak [Si II]34.8um line. We also detect two lines near 26um which we tentatively ascribe to [Fe II]25.99um and [O IV]25.91um. Comparison of the Gemini 11.7um image with X-ray images from Chandra, UV-optical images from HST, and radio synchrotron images obtained by the ATCA show generally good correlation of the images across all wavelengths. Because of the limited resolution of the mid-IR images we cannot uniquely determine the location or heating mechanism of the dust giving rise to the emission. The dust could be collisionally heated by the X-ray emitting plasma, providing a unique diagnostic of plasma conditions. Alternatively, the dust could be radiatively heated in the dense UV-optical knots that are overrun by the advancing supernova blast wave. In either case the dust-to-gas mass ratio in the circumstellar medium around the supernova is significantly lower than that in the general ISM of the LMC, suggesting either a low condensation efficiency in the wind of the progenitor star, or the efficient destruction of the dust by the SN blast wave.

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Astrophysics, abstract
astro-ph/0602531

From: Albert Zijlstra [view email]
Date: Fri, 24 Feb 2006 09:12:10 GMT   (571kb)

A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud

Authors: Albert A. Zijlstra, Mikako Matsuura, Peter R. Wood, G.C. Sloan, Eric Lagadec, Jacco Th. van Loon, M.A.T. Groenewegen, M.W. Feast, J.W. Menzies, P.A. Whitelock, J.A.D.L. Blommaert, M.-RL. Cioni, H.J. Habing, S. Hony, C. Loup, L.B.F.M. Waters
Comments: Submitted to MNRAS. 22 pages
Journal-ref: Mon.Not.Roy.Astron.Soc. 370 (2006) 1961-1978

We present a Spitzer Space Telescope spectroscopic survey of mass-losing carbon stars (and one oxygen-rich star) in the Large Magellanic Cloud. The spectra cover the wavelength range 5--38 micron. They show varying combinations of dust continuum, dust emission features (SiC, MgS) and molecular absorption bands (C2H2, HCN). A set of four narrow bands, dubbed the Manchester system, is used to define the infrared continuum for dusty carbon stars. The relations between the continuum colours and the strength of the dust and molecular features are studied, and are compared to Galactic stars of similar colours. The circumstellar 7-micron C2H2 band is found to be stronger at lower metallicity, from a comparison of stars in the Galaxy, the LMC and the SMC. This is explained by dredge-up of carbon, causing higher C/O ratios at low metallicity (less O). A possible 10-micron absorption feature seen in our spectra may be due to C3. This band has also been identified with interstellar silicate or silicon-nitrite dust. The line-to-continuum ratio of theSiC and MgS bands shows some indication of being lower at low metallicity. The MgS band is only seen at dust temperatures below 600 K. We discuss the selection of carbon versus oxygen-rich AGB stars using the J-K vs. K-A colours, and show that these colours are relatively insensitive to chemical type. Metal-poor carbon stars form amorphous carbon dust from self-produced carbon. The formation efficiency of oxygen-rich dust depends more strongly on metallicity. We suggest that in lower-metallicity environments, the dust input into the Interstellar Medium by AGB stars is efficient but may be strongly biassed towards carbonaceous dust, as compare to the Galaxy.

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Astrophysics, abstract
astro-ph/0602552

From: Patrick Morris [view email]
Date: Fri, 24 Feb 2006 23:55:45 GMT   (752kb)

Tentative Discovery of a New Supernova Remnant in Cepheus: Unveiling an Elusive Shell in the Spitzer Galactic First Look Survey

Authors: Patrick W. Morris, Susan Stolovy, Stefanie Wachter, Alberto Noriega-Crespo, Thomas G. Pannuti, D.W. Hoard
Comments: 11 pages; accepted for publication in Astrophysical Journal Letters
Journal-ref: Astrophys.J. 640 (2006) L179-L182

We have discovered an axially symmetric, well-defined shell of material in the constellation of Cepheus, based on imaging acquired as part of the Galactic First Look Survey with the Spitzer Space Telescope. The 86'' x 75'' object exhibits brightened limbs on the minor axis, and is clearly visible at 24 microns, but is not detected in the 3.6, 4.5, 5.8, 8.0, 70, or 160 micron images. Followup with 7.5 - 40 micron spectroscopy reveals the shell to be composed entirely of ionized gas, and that the 24 micron imaging traces solely [O IV] 25.89 micron emission. The spectrum also exhibits weaker [Ne III], [S III], and very weak [Ne V] emission. No emission from warm dust is detected. Spectral cuts through the center of the shell and at the northern limb are highly consistent with each other. The progenitor is not readily identified, but with scaling arguments and comparison to well-known examples of evolved stellar objects, we find the observations to be most straightforward to interpret in terms of a young supernova remnant located at a distance of at least 10 kpc, some 400 pc above the Galactic disk. If confirmed, this would be the first SNR discovered initially at infrared wavelengths.

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Astrophysics, abstract
astro-ph/0603443

From: Catherine Buchanan [view email]
Date: Thu, 16 Mar 2006 23:16:09 GMT   (41kb)

Spitzer IRS Spectra of Luminous 8 micron Sources in the Large Magellanic Cloud

Authors: Catherine L. Buchanan (1), Joel H. Kastner (1), William J. Forrest (2), Bruce J. Hrivnak (3), Raghvendra Sahai (4), Michael Egan (5), Adam Frank (2), Cecilia Barnbaum (6)
Comments: 4 pages, 4 figures, uses ASP style file. To appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 2005

We have produced an atlas of Spitzer Infrared Spectrograph (IRS) spectra of mass-losing, evolved stars in the Large Magellanic Cloud. These stars were selected to have high mass-loss rates and so contribute significantly to the return of processed materials to the ISM. Our high-quality spectra enable the determination of the chemistry of the circumstellar envelope from the mid-IR spectral features and continuum. We have classified the spectral types of the stars and show that the spectral types separate clearly in infrared color-color diagrams constructed from 2MASS data and synthetic IRAC/MIPS fluxes derived from our IRS spectra. We present diagnostics to identify and classify evolved stars in nearby galaxies with high confidence levels using Spitzer and 2MASS photometry. Comparison of the spectral classes determined using IRS data with the IR types assigned based on NIR colors also revealed a significant number of misclassifications and enabled us to refine the NIR color criteria resulting in more accurate NIR color classifications of dust-enshrouded objects.

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Astrophysics, abstract
astro-ph/0604115

From: Geoffrey Bryden [view email]
Date: Wed, 5 Apr 2006 22:08:54 GMT   (35kb)

Spitzer/MIPS Limits on Asteroidal Dust in the Pulsar Planetary System PSR B1257+1

Authors: G. Bryden, C. A. Beichman, G. H. Rieke, J. A. Stansberry, K. R. Stapelfeldt, D. E. Trilling, N. J. Turner, A. Wolszczan

With the MIPS camera on Spitzer, we have searched for far-infrared emission from dust in the planetary system orbiting pulsar PSR 1257+12. With accuracies of 0.05 mJy at 24 um and 1.5 mJy at 70 um, photometric measurements find no evidence for emission at these wavelengths. These observations place new upper limits on the luminosity of dust with temperatures between 20 and 1000 K. They are particularly sensitive to dust temperatures of 100-200 K, for which they limit the dust luminosity to below $3 \times 10^{-5}$ of the pulsar's spin-down luminosity, three orders of magnitude better than previous limits. Despite these improved constraints on dust emission, an asteroid belt similar to the Solar System's cannot be ruled out.

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Astrophysics, abstract
astro-ph/0605051

From: Simone Migliari [view email]
Date: Tue, 2 May 2006 03:12:33 GMT   (203kb)

Spitzer Reveals Infrared Optically-Thin Synchrotron Emission from the Compact Jet of the Neutron Star X-Ray Binary 4U 0614+091

Authors: S. Migliari (UCSD), J.A. Tomsick (UCSD), T.J. Maccarone (Southampton), E. Gallo (UCSB), R.P. Fender (Southampton), G. Nelemans (Nijmegen), D.M. Russell (Southampton)
Comments: Accepted for publication in ApJ Letters
Journal-ref: Astrophys.J. 643 (2006) L41-L44

Spitzer observations of the neutron star (ultra-compact) X-ray binary (XRB) 4U 0614+091 with the Infrared Array Camera reveal emission of non-thermal origin in the range 3.5-8 um. The mid-infrared spectrum is well fit by a power law with spectral index of alpha=-0.57+/-0.04 (where the flux density is F_nu \propto nu^(alpha)). Given the ultra-compact nature of the binary system, we exclude the possibility that either the companion star or the accretion disk can be the origin of the observed emission. These observations represent the first spectral evidence for a compact jet in a low-luminosity neutron star XRB and furthermore of the presence, already observed in two black hole (BH) XRBs, of a `break' in the synchrotron spectrum of such compact jets. We can derive a firm upper limit on the break frequency of the spectrum of nu_thin=3.7x10^(13) Hz, which is lower than that observed in BH XRBs by at least a factor of 10. Assuming a high-energy cooling cutoff at ~1 keV, we estimate a total (integrated up to X-rays) jet power to X-ray bolometric luminosity ratio of \~5%, much lower than that inferred in BHs.

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Astrophysics, abstract
astro-ph/0605167

From: Karl Misselt [view email]
Date: Fri, 5 May 2006 17:31:37 GMT   (986kb)

Spitzer Observations of V838 Monocerotis: Detection of a Rare Infrared Light Echo

Authors: D.P.K. Banerjee, K.Y.L. Su, K.A. Misselt, N.M. Ashok
Comments: Accepted ApJL. 6 pages including two plates. Emulateapj style. Hi-Res figures available on request
Journal-ref: Astrophys.J. 644 (2006) L57-L62

We present Spitzer observations of the unusual variable V838 Monocerotis. Extended emission is detected around the object at 24, 70 and 160um. The extended infrared emission is strongly correlated spatially with the HST optical light echo images taken at a similar epoch. We attribute this diffuse nebulosity to be from an infrared light echo caused by reprocessed thermal emission from dust heated by the outward-propagating radiation from the 2002 eruption. The detection of an IR light echo provides an opportunity to estimate the mass in dust of the echo material and hence constrain its origin. We estimate the dust mass of the light echo to be on the order of a solar mass - thereby implying the total gas plus dust mass to be considerably more - too massive for the echo material to be the ejecta from previous outburst/mass-losing events. This is therefore suggestive that a significant fraction of the matter seen through the light echo is interstellar in origin. Unresolved emission at 24 and 70um is also seen at the position of the central star possibly indicating the presence of hot dust freshly condensed in the outburst ejecta.

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Astrophysics, abstract
astro-ph/0605187

From: Massimo Marengo [view email]
Date: Sat, 6 May 2006 23:54:31 GMT   (962kb)

A Spitzer/IRAC Search for Substellar Companions of the Debris Disk Star epsilon Eridani

Authors: M. Marengo, S. T. Megeath, G. G. Fazio, K. R. Stapelfeldt, M. W. Werner, D. E. Backman
Comments: 36 pages, to be published on The Astrophysical Journal, vol. 647, August 2006

We have used the InfraRed Array Camera (IRAC) onboard the Spitzer Space telescope to search for low mass companions of the nearby debris disk star epsilon Eridani. The star was observed in two epochs 39 days apart, with different focal plane rotation to allow the subtraction of the instrumental Point Spread Function, achieving a maximum sensitivity of 0.01 MJy/sr at 3.6 and 4.5 um, and 0.05 MJy/sr at 5.8 and 8.0 um. This sensitivity is not sufficient to directly detect scattered or thermal radiation from the epsilon Eridani debris disk. It is however sufficient to allow the detection of Jovian planets with mass as low as 1 MJ in the IRAC 4.5 um band. In this band, we detected over 460 sources within the 5.70 arcmin field of view of our images. To test if any of these sources could be a low mass companion to epsilon Eridani, we have compared their colors and magnitudes with models and photometry of low mass objects. Of the sources detected in at least two IRAC bands, none fall into the range of mid-IR color and luminosity expected for cool, 1 Gyr substellar and planetary mass companions of epsilon Eridani, as determined by both models and observations of field M, L and T dwarf. We identify three new sources which have detections at 4.5 um only, the lower limit placed on their [3.6]-[4.5] color consistent with models of planetary mass objects. Their nature cannot be established with the currently available data and a new observation at a later epoch will be needed to measure their proper motion, in order to determine if they are physically associated to epsilon Eridani.

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Astrophysics, abstract
astro-ph/0605365

From: Joel Green [view email]
Date: Mon, 15 May 2006 17:37:09 GMT   (882kb)

Spitzer-IRS Observations of FU Orionis Objects

Authors: J. D. Green, L. Hartmann, N. Calvet, D. M. Watson, M. Ibrahimov, E. Furlan, B. Sargent, W. J. Forrest
Comments: 30 pages, 8 figures, accepted by ApJ

We present 5-35 $\mu$m spectra, taken with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope, of five FU Orionis objects: FU Ori, V1515 Cyg, V1057 Cyg, BBW 76, and V346 Nor. All but V346 Nor reveal amorphous silicate grains in emission at 10 $\mu$m and 20 $\mu$m, and show water-vapor absorption bands at 5.8 and 6.8 $\mu$m and SiO or possibly methane absorption at 8 $\mu$m. These absorption features closely match these bands in model stellar photospheres -- signs of the gaseous photospheres of the inner regions of these objects' accretion disks. The continuum emission at 5-8 $\mu$m is also consistent with such disks, and, for FU Orionis and BBW 76, longer-wavelength emission may be fit by a model which includes moderate disk flaring. V1057 Cyg and V1515 Cyg have much more emission at longer wavelengths than the others, perhaps evidence of substantial remnant of their natal, infalling envelopes.

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Astrophysics, abstract
astro-ph/0605584

From: Peter Meikle [view email]
Date (v1): Tue, 23 May 2006 10:42:35 GMT   (255kb)
Date (revised v2): Mon, 31 Jul 2006 12:35:14 GMT   (254kb)

A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova

Authors: W. P. S. Meikle (1), S. Mattila (2), C. L. Gerardy (1), R. Kotak (3), M. Pozzo (1), S. D. van Dyk (4), D. Farrah (5), R. A. Fesen (6), A. V. Filippenko (7), C. Fransson (8), P. Lundqvist (8), J. Sollerman (9), J. C. Wheeler (10) ((1) Imperial College London, (2) Queen's University Belfast, (3) European Southern Observatory, (4) IPAC, California Institute of Technology, (5) Cornell University, (6) Dartmouth College, (7) University of California, Berkeley, (8) Stockholm University (9) University of Copenhagen, (10) The University of Texas at Austin)
Comments: 41 pages, 11 figures, 4 tables, accepted for publication in Astrophysical Journal (References corrected)

We present late-time (590-994 d) mid-IR photometry of the normal, but highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star-formation region or molecular cloud along the line-of-sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly-condensed dust and/or an ejecta/CSM impact but their contributions are likely to be small. For the case of a CSM-IR echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio. Such a CSM would have resulted from episodic mass loss whose rate declined significantly about 28,000 years ago. Alternatively, an IR echo from a surrounding, dense, dusty molecular cloud might also have been responsible for the fading component. Either way, this is the first time that an IR echo has been clearly identified in a Type IIP supernova. We find no evidence for or against the proposal that Type IIP supernovae produce large amounts of dust via grain condensation in the ejecta. However, within the CSM-IR echo scenario, the mass of dust derived implies that the progenitors of the most common of core-collapse supernovae may make an important contribution to the universal dust content.

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Astrophysics, abstract
astro-ph/0605639

From: Michael Cushing [view email]
Date: Wed, 24 May 2006 20:51:56 GMT   (190kb)

A Spitzer Infrared Spectrograph (IRS) Spectral Sequence of M, L, and T Dwarfs

Authors: M.C. Cushing, T.L. Roellig, M.S. Marley, D. Saumon, S.K. Leggett, J. D. Kirkpatrick, J.C. Wilson, G.C. Sloan, A.K. Mainzer, J.E. Van Cleve, J.R. Houck
Comments: Accepted for publication in the Astrophysical Journal

We present a low-resolution (R = 90), 5.5-38 micron spectral sequence of a sample of M, L, and T dwarfs obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The spectra exhibit prominent absorption bands of H_2O at 6.27 microns, CH_4 at 7.65 microns, and NH_3 at 10.5 microns and are relatively featureless at lambda > 15 microns. Three spectral indices that measure the strengths of these bands are presented; H_2O absorption features are present throughout the MLT sequence while the CH_4 and NH_3 bands first appear at roughly the L/T transition. Although the spectra are, in general, qualitatively well matched by synthetic spectra that include the formation of spatially homogeneous silicate and iron condensate clouds, the spectra of the mid-type L dwarfs show an unexpected flattening from roughly 9 to 11 microns. We hypothesize that this may be a result of a population of small silicate grains that are not predicted in the cloud models. The spectrum of the peculiar T6 dwarf 2MASS J0937+2931 is suppressed from 5.5-7.5 microns relative to typical T6 dwarfs and may be a consequence of its mildly metal-poor/high surface gravity atmosphere. Finally, we compute bolometric luminosities of a subsample of the M, L, and T dwarfs by combining the IRS spectra with previously published 0.6-4.1 micron spectra and find good agreement with the values of Golimowski et al. who use L'- and M'-band photometry and to account for the flux emitted at lambda > 2.5 microns.

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Astrophysics, abstract
astro-ph/0605731

From: Letizia Stanghellini [view email]
Date: Tue, 30 May 2006 23:41:33 GMT   (29kb)

Spitzer Spectra of Magellanic Cloud PNe

Authors: L. Stanghellini, P. Garcia Lario, A. Manchado, J. V. Perea Calderon, D. A. Garcia-Hernandez, R. A. Shaw, E. Villaver
Comments: IAU Symposium 234, Proceedings, in press

Planetary nebulae (PNe) in the Magellanic Clouds (LMC, SMC) offer a unique opportunity to study both the population and evolution of low- and intermediate-mass stars in an environment which is free of the distance scale bias that hinder Galactic PN studies. The emission shown by PNe in the 5-40 $\mu$m range is characterized by the presence of a combination of solid state features (from the dust grains) and nebular emission lines over-imposed on a strong dust continuum. We acquired low resolution IRS spectroscopy of a selected sample of LMC and SMC PNe whose morphology, size, central star brightness, and chemical composition are known. The data have been acquired and reduced, and the IRS spectra show outstanding quality as well as very interesting features. The preliminary analysis presented here allows to determine strong correlations between gas and dust composition, and nebular morphology. More detailed analysis in the future will deepen our knowledge of mass-loss mechanism, its efficiency, and its relation to PN morphology.

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Astrophysics, abstract
astro-ph/0606202

From: Steve B. Howell [view email]
Date: Thu, 8 Jun 2006 18:34:14 GMT   (21kb)

First Spitzer Space Telescope Observations of Magnetic Cataclysmic Variables: Evidence for Excess Emission at 3--8 microns

Authors: Steve B. Howell, Carolyn Brinkworth, D. W. Hoard, Stefanie Wachter, Thomas Harrison, Howard Chun Beth Thomas, Linda Stefaniak, David R. Ciardi, Paula Szkody, Gerard van Belle
Comments: Accepted to ApJ Letters

We present the first observations of magnetic cataclysmic variables with the Spitzer Space Telescope. We used the Infrared Array Camera to obtain photometry of the polars EF Eri, GG Leo, V347 Pav, and RX J0154.0-5947 at 3.6, 4.5, 5.8, and 8.0 $\mu$m. In all of our targets, we detect excess mid-infrared emission over that expected from the component stars alone. We explore the origin of this IR excess by examining bremsstrahlung, cyclotron emission, circumbinary dust, and L/T brown dwarf secondary stars. Bremsstrahlung and cyclotron emission appear unlikely to be significant contributors to the observed fluxes. At present, the most likely candidate for the excess emission is dust that is probably located in a circumbinary disk with an inner temperature near 800 K. However, a simple dust disk plus any reasonable low mass or brown dwarf-like secondary star is unable to fully explain the observed flux densities in the 3--8 $\mu$m region.

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Astrophysics, abstract
astro-ph/0606236

From: Martha Boyer [view email]
Date: Fri, 9 Jun 2006 16:03:06 GMT   (691kb)

Stellar Populations and Mass-Loss in M15: A Spitzer Detection of Dust in the Intra-Cluster Medium

Authors: Martha L. Boyer (1), Charles E. Woodward (1), Jacco Th. van Loon (2), Karl D. Gordon (3), A. Evans (2), Robert D. Gehrz (1), L. A. Helton (1), Elisha F. Polomski (1) ((1) Department of Astronomy, University of Minnesota, (2) Astrophysics Group, School of Physical & Geographical Sciences, Keele University, (3) Steward Observatory, University of Arizona)
Comments: Accepted for publication in AJ. 20 pages, 10 figures, 6 tables. Full resolution versions of figures 1, 5, 7, and 8 are available in a PDF version of this manuscript at this http URL

We present Spitzer Space Telescope IRAC and MIPS observations of the galactic globular cluster M15 (NGC 7078), one of the most metal-poor clusters with a [Fe/H] = -2.4. Our Spitzer images reveal a population of dusty red giants near the cluster center, a previously detected planetary nebula (PN) designated K648, and a possible detection of the intra-cluster medium (ICM) arising from mass loss episodes from the evolved stellar population. Our analysis suggests 9 (+/-2) x 10^-4 solar masses of dust is present in the core of M15, and this material has accumulated over a period of approximately 10^6 years, a timescale ten times shorter than the last galactic plane crossing event. We also present Spitzer IRS follow up observations of K648, including the detection of the [NeII] 12.81 micron line, and discuss abundances derived from infrared fine structure lines.

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Astrophysics, abstract
astro-ph/0606296

From: Mikako Matsuura [view email]
Date: Tue, 13 Jun 2006 07:23:42 GMT   (280kb)

Spitzer observations of acetylene bands in carbon-rich AGB stars in the Large Magellanic Cloud

Authors: M. Matsuura, P.R. Wood, G.C. Sloan, A.A. Zijlstra, J.Th. van Loon, M.A.T. Groenewegen, J.A.D.L. Blommaert, M.-R.L. Cioni, M.W. Feast, H.J. Habing, S. Hony, E. Lagadec, C. Loup, J.W. Menzies, L.B.F.M. Waters, P.A. Whitelock
Comments: 7 pages, accepted by MNRAS
Journal-ref: Mon.Not.Roy.Astron.Soc. 371 (2006) 415-420

We investigate the molecular bands in carbon-rich AGB stars in the Large Magellanic Cloud (LMC), using the InfraRed Spectrograph (IRS) on board the Spitzer Space Telescope (SST) over the 5--38 micron range. All 26 low-resolution spectra show acetylene (C2H2) bands at 7 and 14 micron. The hydrogen cyanide (HCN) bands at these wavelengths are very weak or absent. This is consistent with low nitrogen abundances in the LMC. The observed 14 micron C2H2 band is reasonably reproduced by an excitation temperature of 500 K. There is no clear dilution of the 14 micron band by circumstellar dust emission. This 14 micron band originates from molecular gas in the circumstellar envelope in these high mass-loss rate stars, in agreement with previous findings for Galactic stars. The C2H2,column density, derived from the 13.7 micron band, shows a gas mass-loss rate in the range 3x10^-6 to 5x10^{-5} Msun yr-1. This is comparable with the total mass-loss rate of these stars estimated from the spectral energy distribution. Additionally, we compare the line strengths of the 13.7 micron C2H2 band of our LMC sample with those of a Galactic sample. Despite the low metallicity of the LMC, there is no clear difference in the C2H2 abundance among LMC and Galactic stars. This reflects the effect of the 3rd dredge-up bringing self-produced carbon to the surface, leading to high C/O ratios at low metallicity.

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Astrophysics, abstract
astro-ph/0606321

From: Tea Temim [view email]
Date (v1): Tue, 13 Jun 2006 19:18:14 GMT   (482kb)
Date (revised v2): Fri, 23 Jun 2006 20:10:00 GMT   (482kb)

Spitzer Space Telescope Infrared Imaging and Spectroscopy of the Crab Nebula

Authors: Tea Temim (1), Robert D. Gehrz (1), Charles E. Woodward (1), Thomas L. Roellig (2), Nathan Smith (3 and 6), Lawrence R. Rudnick (1), Elisha F. Polomski (1), Kris Davidson (1), Lunming Yuen (4), Takashi Onaka (5) ((1) Department of Astronomy, University of Minnesota, (2) NASA Ames Research Center, Moffett Field, CA, (3) Center for Astrophysics and Space Astronomy, University of Colorado, (4) Technosciences Corp., Moffett Field, CA, (5) University of Tokyo, Tokyo, Japan, (6) Visiting Astronomer, Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory (NOAO))
Comments: 21 pages, 4 tables, 16 figures

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II]1.644 micron. The 8.0 micron image, made with a bandpass that includes [Ar II]7.0 micron, resembles the general morphology of visible H-alpha and near-IR [Fe II] line emission, while the 3.6 and 4.5 micron images are dominated by continuum synchrotron emission. The 24 micron and 70 micron images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 micron images reveals a spatial variation in the synchrotron power law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum jet and torus with the steeper diffuse nebula, and suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and polar jet structures seen in Chandra and HST images (Hester et al. 2002) can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of approximately 1264 km/s.

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Astrophysics, abstract
astro-ph/0606356

From: Margaret Meixner Dr. [view email]
Date: Wed, 14 Jun 2006 18:59:49 GMT   (8833kb)

Spitzer Survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (SAGE) I: Overview and Initial Results

Authors: Margaret Meixner, Karl D. Gordon, Remy Indebetouw, Joseph L. Hora, Barbara Whitney, Robert Blum, William Reach, Jean-Philippe Bernard, Marilyn Meade, Brian Babler, Charles W. Engelbracht, Bi-Qing For, Karl Misselt, Uma Vijh, Claus Leitherer, Martin Cohen, Ed B. Churchwell, Francois Boulanger, Jay A. Frogel, Yasuo Fukui, Jay Gallagher, Varoujan Gorjian, Jason Harris, Douglas Kelly, Akiko Kawamura, SoYoung Kim, William B. Latter, Suzanne Madden, Ciska Markwick-Kemper, Akira Mizuno, Norikazu Mizuno, Jeremy Mould, Antonella Nota, M.S. Oey, Knut Olsen, Toshikazu Onishi, Roberta Paladini, Nino Panagia, Pablo Perez-Gonzalez, Hiroshi Shibai, Sato Shuji, Linda Smith, Lister Staveley-Smith, A.G.G.M. Tielens, Toshiya Ueta, Schuyler Van Dyk, Kevin Volk, Michael Werner, Dennis Zaritsky
Comments: Accepted by the Astronomical Journal
Journal-ref: Astron.J. 132 (2006) 2268-2288

We are performing a uniform and unbiased, ~7x7 degrees imaging survey of the Large Magellanic Cloud (LMC), using the IRAC and MIPS instruments on board the Spitzer Space Telescope in order to survey the agents of a galaxy's evolution (SAGE), the interstellar medium (ISM) and stars in the LMC. The detection of diffuse ISM with column densities >1.2x10^21 H cm^-2 permits detailed studies of dust processes in the ISM. SAGE's point source sensitivity enables a complete census of newly formed stars with masses >3 solar masses that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass loss rates >1x10^-8 solar masses per year will quantify the rate at which evolved stars inject mass into the ISM of the LMC. The observing strategy includes two epochs in 2005, separated by three months, that both mitigate instrumental artifacts and constrain source variability. The SAGE data are non-proprietary. The data processing includes IRAC and MIPS pipelines and a database for mining the point source catalogs, which will be released to the community in support of Spitzer proposal cycles 4 and 5. We present initial results on the epoch 1 data with a special focus on the N79 and N83 region. The SAGE epoch 1 point source catalog has ~4 million sources. The point source counts are highest for the IRAC 3.6 microns band and decrease dramatically towards longer wavelengths consistent with the fact that stars dominate the point source catalogs and that the dusty objects, e.g. young stellar objects and dusty evolved stars that detected at the longer wavelengths, are rare in comparison. We outline a strategy for identifying foreground MW stars, that may comprise as much as 18% of the source list, and background galaxies, that may comprise ~12% of the source list.

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Astrophysics, abstract
astro-ph/0606432

From: Brian Patten [view email]
Date (v1): Sun, 18 Jun 2006 19:07:23 GMT   (182kb)
Date (revised v2): Tue, 27 Jun 2006 15:38:54 GMT   (183kb)

Spitzer/IRAC Photometry of M, L, and T Dwarfs

Authors: Brian M. Patten, John R. Stauffer, Adam Burrows, Massimo Marengo, Joseph L. Hora, Kevin L. Luhman, Sarah M. Sonnett, Todd J. Henry, Deepak Raghavan, S. Thomas Megeath, James Liebert, Giovanni G. Fazio
Comments: 32 pages, 18 figures, accepted for publication to ApJ: revised to adjust acknowledgments, add a few more references, and the correct typographical errors in text and tables 1 and 3 (note as binaries sds0926+5847 and 2ma1553+1532)

We present the results of a program to acquire photometry for eighty-six late-M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M_5.8 versus [5.8]-[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one parameter family in Teff. Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of five (~70 M_Jup to ~15 M_Jup), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 micron fluxes to be lower than expected, from which we infer a stronger CO fundamental band at ~4.67 microns. This suggests that equilibrium CH_4/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of Ks, IRAC 3.6 micron, and 4.5 micron bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the M_Ks versus Ks-[4.5] relation, which shows a smooth progression over spectral type and splits the M, L, and T types cleanly.

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Astrophysics, abstract
astro-ph/0606532

From: Toshiya Ueta [view email]
Date: Wed, 21 Jun 2006 19:58:21 GMT   (126kb)

Spitzer/MIPS Imaging of NGC 650: Probing the History of Mass Loss on the Asymptotic Giant Branch

Authors: Toshiya Ueta
Comments: 9 pages in the emulated ApJ format with 6 figures, to appear in ApJ

We present the far-infrared (IR) maps of a bipolar planetary nebula (PN), NGC 650, at 24, 70, and 160 micron taken with the Multiband Imaging Photometer for Spitzer (MIPS) on-board the Spitzer Space Telescope. While the two-peak emission structure seen in all MIPS bands suggests the presence of a near edge-on dusty torus, the distinct emission structure between the 24 micron map and the 70/160 micron maps indicates the presence of two distinct emission components in the central torus. Based on the spatial correlation of these two far-IR emission components with respect to various optical line emission, we conclude that the 24 micron emission is largely due to the [O IV] line at 25.9 micron arising from highly ionized regions behind the ionization front, whereas the 70 and 160 micron emission is due to dust continuum arising from low-temperature dust in the remnant asymptotic giant branch (AGB) wind shell. The far-IR nebula structure also suggests that the enhancement of mass loss at the end of the AGB phase has occurred isotropically, but has ensued only in the equatorial directions while ceasing in the polar directions. The present data also show evidence for the prolate spheroidal distribution of matter in this bipolar PN. The AGB mass loss history reconstructed in this PN is thus consistent with what has been previously proposed based on the past optical and mid-IR imaging surveys of the post-AGB shells.

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Astrophysics, abstract
astro-ph/0606563

From: Michael Werner [view email]
Date (v1): Thu, 22 Jun 2006 18:24:49 GMT   (2861kb)
Date (revised v2): Thu, 22 Jun 2006 21:15:34 GMT   (844kb)

First Fruits of the Spitzer Space Telescope: Galactic and Solar System Studies

Authors: M.Werner, G.Fazio, G.Rieke, T.Roellig, D.Watson
Comments: Review article to appear in slightly different format in Vol.44 of Annual Reviews of Astronomy and Astrophysics, 2006
Journal-ref: Ann.Rev.Astron.Astrophys. 44 (2006) 269-321

This article provides a brief overview of the Spitzer Space Telescope and discusses its initial scientific results on galactic and solar system science.

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Astrophysics, abstract
astro-ph/0606666

From: Basmah Riaz [view email]
Date: Tue, 27 Jun 2006 21:29:47 GMT   (87kb)

Spitzer Observations of two TW Hydrae Association Brown Dwarfs

Authors: Basmah Riaz, John E. Gizis, Abraham Hmiel
Comments: 13 pages, 3 figures, published in ApJ
Journal-ref: Astrophys.J. 639 (2006) L79

We present Spitzer Space Telescope observations of two TW Hydrae Association brown dwarfs, 2MASSW J1207334-393254 and 2MASSW J1139511-315921, in the IRAC and MIPS 24 micron bands. Based on their IRAC colors, we have classified them as Classical and Weak-line T Tauri stars, respectively. For 2MASSW J1207334-393254, we have found that a flat disk model fits the data very well. This brown dwarf shows the presence of warm (T > 100 K) circumstellar dust close (R < 0.2 AU) to it, and does not display any signs of cleansing of dust within several AU of the star. In comparison with other TWA members that show excess in IR, we suggest that there exists a different disk evolution/dust processing mechanism for stellar and sub-stellar objects. 2MASSW J1139511-315921 does not show any significant excess in any of the IRAC bands, but a small one at 24 micron, which is not significant enough to suggest the presence of warm dust around this star. It shows signs of dust cleansing in the inner several AU, similar to most of the other TWA members.

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Astrophysics, abstract
astro-ph/0606756

From: Catherine Buchanan [view email]
Date: Fri, 30 Jun 2006 19:38:28 GMT   (533kb)

A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud

Authors: Catherine L. Buchanan (1), Joel H. Kastner (1), William J. Forrest (2), Bruce J. Hrivnak (3), Raghvendra Sahai (4), Michael Egan (5), Adam Frank (2), Cecilia Barnbaum (6), ((1) Center for Imaging Science, Rochester Institute of Technology, (2) University of Rochester, (3), Valparaiso University, (4) NASA/JPL, (5) Air Force Research Laboratory, (6) Valdosta University)
Comments: 46 pages, 9 figures; accepted for publication in AJ; abstract abridged

We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of highly luminous, compact mid-infrared sources in the Large Magellanic Cloud. Sources were selected on the basis of infrared colors and 8 micron (MSX) fluxes indicative of highly evolved, intermediate- to high-mass stars with current or recent mass loss at large rates. We determine the chemistry of the circumstellar envelope from the mid-IR continuum and spectral features and classify the spectral types of the stars. In the sample of 60 sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch (AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB stars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find that the overwhelming majority of the sample AGB stars (with typical IR luminosities ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects are predominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine mean bolometric corrections to the stellar K-band flux densities and find that for carbon stars, the bolometric corrections depend on the infrared color, whereas for RSGs, the bolometric correction is independent of IR color. Our results reveal that objects previously classified as PNe on the basis of IR colors are in fact compact HII regions with very red IRS spectra that include strong atomic recombination lines and PAH emission features. We demonstrate that the IRS spectral classes in our sample separate clearly in infrared color-color diagrams that use combinations of 2MASS data and synthetic IRAC/MIPS fluxes derived from the IRS spectra. On this basis, we suggest diagnostics to identify and classify, with high confidence levels, IR-luminous evolved stars and HII regions in nearby galaxies using Spitzer and near-infrared photometry.

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Astrophysics, abstract
astro-ph/0607405

From: Basmah Riaz [view email]
Date: Tue, 18 Jul 2006 04:25:41 GMT   (458kb)

Spitzer Observations of Nearby M Dwarfs

Authors: Basmah Riaz, D. J. Mullan, John E. Gizis
Comments: 20 pages, 5 figures, accepted in ApJ

We present Spitzer IRAC and MIPS observations for a sample of eight M dwarfs: six dMe, one dM, and one sdMe star. All of our targets are found to have SEDs which are fitted within the error bars by a purely photospheric spectrum out to 24 micron. We find no evidence for IR excess. None of our targets is detected in the MIPS 70 and 160 micron bands. The estimated ages for all are >10 Myr, suggesting that enough disk dissipation has occurred within the inner several AU of the star. For four of these, Mullan et al. (1989) had reported IRAS detections at 12 micron, although the reported fluxes were below the 5-sigma IRAS detection limit (~0.2 Jy). Mullan et al. also pointed out that V-K colors in dMe stars are larger than those in dM stars, possibly because of the presence of a chromosphere. Here we suggest that metallicity effects provide a better explanation of the V-K data.
For reasons of observational selection, our targets are not the most active flare stars known, but being dMe stars indicates the presence of a chromosphere. Scaling from Houdebine's model of the AU Mic chromosphere, we have computed the free-free infrared excesses for a range of densities. Our Spitzer 24 micron data shows that the chromospheres in two of our targets are less dense than in AU Mic by a factor of 10 or more. This is consistent with the fact that our sample includes the less active flare stars. Our models also indicate that the chromospheric contribution to the observed AU Mic emission at submillimeter wavelengths is only about 2%.

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Astrophysics, abstract
astro-ph/0608083

From: David Ciardi [view email]
Date: Thu, 3 Aug 2006 15:38:37 GMT   (199kb)

Spitzer Observations of Var Her 04: Possible Detection of Dust Formation in a Super-Outbursting TOAD

Authors: David R. Ciardi, Stefanie Wachter, D. W. Hoard, Steve B. Howell, Gerard T. van Belle
Comments: Accepted for publication in The Astronomical Journal

We present four MIPS (24 \micron) and two IRAC (3.6, 4.5, 5.8, and 8.0 \micron) Spitzer observations of the newly discovered Tremendous Outburst Amplitude Dwarf nova (TOAD) Var Her 04 during decline from super-outburst. The four MIPS observations span 271 days and the two IRAC observations span 211 days. Along the line-of-sight to Var Her 04, there is a foreground M-star within 1\arcsec of the variable; as a result, all of the Spitzer photometry presented in this paper is a blend of the foreground M-star and Var Her 04. We estimate the quiescent level of the TOAD to be $\Delta V=4-5$ magnitudes below that of the M-star. Based upon the spectral energy distribution and the 2MASS colors, we find the M-star to be an M3.5V dwarf at a distance of 80-130 pc. Based upon its outburst amplitude and quiescent apparent magnitude, we estimate the distance to Var Her 04 to be 200-400 pc, suggesting that the line-of-sight foreground star is physically unrelated to the cataclysmic variable. All of the Spitzer photometry is consistent with the photospheric emission of the line-of-sight M3.5V star, except for one 24 \micron observation obtained after the variable re-brightened. This 24 \micron flux density is 75 $\mu$Jy ($4\sigma$) above the preceding and following MIPS observations. We tentatively suggest that the mid-infrared brightening of 75 $\mu$Jy may be associated with a dust formation event in the super-outburst ejecta. Assuming a dust temperature of 100-400 K, we have estimated the amount of dust required. We find $10^{-13}-10^{-11}$ M$_\odot$ of dust is needed, consistent with amounts of mass ejection in TOADs expected during super-outburst, and possibly making TOADs important contributors to the recycling of the interstellar medium.

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Astrophysics, abstract
astro-ph/0608189

From: Robert Blum [view email]
Date: Tue, 8 Aug 2006 23:22:11 GMT   (387kb)

Spitzer SAGE survey of the Large Magellanic Cloud II: Evolved Stars and Infrared Color Magnitude Diagrams

Authors: R. D. Blum, J. R. Mould, K. A. Olsen, J. A. Frogel, M. Werner, M. Meixner, F. Markwick-Kemper, R. Indebetouw, B. Whitney, M. Meade, B. Babler, E. B. Churchwell, K. Gordon, C. Engelbracht, B. -Q. For, K. Misselt, U. Vijh, C. Leitherer, K. Volk, S. Points, W. Reach, J. L. Hora, J. -P. Bernard, F. Boulanger, S. Bracker, M. Cohen, Y. Fukui, J. Gallagher, V. Gorjian, J. Harris, D. Kelly, A. Kawamura, W. B. Latter, S. Madden, A. Mizuno, N. Mizuno, A. Nota, M. S. Oey, T. Onishi, R. Paladini, N. Panagia, P. Perez-Gonzalez, H. Shibai, S. Sato, L. Smith, L. Staveley-Smith, A. G. G. M. Tielens, T. Ueta, S. Van Dyk, D. Zaritsky
Comments: LaTex, 31 pages, 10 figures. Accepted for publication in the Astronomical Journal
Journal-ref: Astron.J. 132 (2006) 2034-2045

Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 um epoch one data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the 2MASS survey, the diagrams are used to delineate the evolved stellar populations in the Large Magellanic Cloud as well as Galactic foreground and extragalactic background populations. Some 32000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17500 are classified as oxygen-rich, 7000 carbon-rich, and another 1200 as ``extreme'' asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called ``obscured'' AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen--rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 um MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass loss budget of the LMC (1200 such sources are identified).

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Astrophysics, abstract
astro-ph/0608561

From: Alberto D. Bolatto [view email]
Date: Fri, 25 Aug 2006 20:01:13 GMT   (869kb)

The Spitzer Survey of the Small Magellanic Cloud: S3MC Imaging and Photometry in the Mid- and Far-Infrared Wavebands

Authors: Alberto D. Bolatto, Joshua D. Simon, Snezana Stanimirovic, Jacco Th. van Loon, Ronak Y. Shah, Kim Venn, Adam K. Leroy, Karin Sandstrom, James M. Jackson, Frank P. Israel, Aigen Li, Lister Staveley-Smith, Caroline Bot, Francois Boulanger, Monica Rubio
Comments: Accepted for publication in The Astrophysical Journal. Given the draconian figure file-size limits implemented in astro-ph, readers are encouraged to download the manuscript with full quality images from this http URL
Journal-ref: Astrophys.J. 655 (2007) 212-232

We present the initial results from the Spitzer Survey of the Small Magellanic Cloud (S3MC), which imaged the star-forming body of the Small Magellanic Cloud (SMC) in all seven MIPS and IRAC wavebands. We find that the F_8/F_24 ratio (an estimate of PAH abundance) has large spatial variations and takes a wide range of values that are unrelated to metallicity but anticorrelated with 24 um brightness and F_24/F_70 ratio. This suggests that photodestruction is primarily responsible for the low abundance of PAHs observed in star-forming low-metallicity galaxies. We use the S3MC images to compile a photometric catalog of ~400,000 mid- and far-infrared point sources in the SMC. The sources detected at the longest wavelengths fall into four main categories: 1) bright 5.8 um sources with very faint optical counterparts and very red mid-infrared colors ([5.8]-[8.0]>1.2), which we identify as YSOs. 2) Bright mid-infrared sources with mildly red colors (0.16<[5.8]-[8.0]<0.6), identified as carbon stars. 3) Bright mid-infrared sources with neutral colors and bright optical counterparts, corresponding to oxygen-rich evolved stars. And, 4) unreddened early B stars (B3 to O9) with a large 24 um excess. This excess is reminiscent of debris disks, and is detected in only a small fraction of these stars (<5%). The majority of the brightest infrared point sources in the SMC fall into groups one to three. We use this photometric information to produce a catalog of 282 bright YSOs in the SMC with a very low level of contamination (~7%).

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Astrophysics, abstract
astro-ph/0609083

From: Nye Evans [view email]
Date: Mon, 4 Sep 2006 14:50:57 GMT   (173kb)

The Spitzer IRS view of V4334 Sgr (Sakurai's Object)

Authors: A. Evans (Keele University), V. H. Tyne, J. Th. van Loon, B. Smalley (Keele), T. R. Geballe (Gemini), R. D. Gehrz, C. E. Woodward (Minnesota), A. A. Zijlstra (Manchester), E. Polomski (Minnesota), M. T. Rushton (Keele), S. P. S. Eyres (Central Lancs), S. G. Starrfield (Arizona), J. Krautter (Heidelberg), R. M. Wagner (LBT)
Comments: 5 pages, 6 figures. Accepted for publication in MNRAS
Journal-ref: Mon.Not.Roy.Astron.Soc.Lett. 373 (2006) L75-L79

We present an observation of the very late thermal pulse object V4334 Sgr (Sakurai's Object) with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. The emission from 5-38 microns is dominated by the still-cooling dust shell. A number of features are seen in absorption against the dust shell, which we attribute to HCN and polyyne molecules. We use these features to determine the 12C/13C ratio for the absorbing gas to be ~ 3.2 (+3.2,-1.6}; this implies that, despite the H-content of the molecules, the hydrocarbon-bearing gas must have originated in material produced in the very late thermal pulse. We see no evidence of emission lines, despite the recently-reported optical and radio observations that suggest the effective temperature of the stellar remnant is rising.

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Astrophysics, abstract
astro-ph/0609141

From: Nick Siegler [view email]
Date: Wed, 6 Sep 2006 18:11:36 GMT   (456kb)

Spitzer 24 Micron Observations of Open Cluster IC 2391 and Debris Disk Evolution of FGK Stars

Authors: Nick Siegler (1), James Muzerolle (1), Erick T. Young (1), George H. Rieke (1), Eric E. Mamajek (2), David E. Trilling (1), Nadya Gorlova (1), Kate Y. L. Su (1) ((1) Steward Observatory, University of Arizona, (2) Harvard-Smithsonian Center for Astrophysics)
Comments: total 23 pages including 7 figures, accepted for publication in ApJ

We present 24 micron Spitzer/MIPS photometric observations of the ~50 Myr open cluster IC 2391. Thirty-four cluster members ranging in spectral type from B3-M5 were observed in the central square degree of the cluster. Excesses indicative of debris disks were discovered around 1 A star, 6 FGK stars, and possibly 1 M dwarf. For the cluster members observed to their photospheric limit, we find a debris disk frequency of 10 (-3,+17)% for B-A stars and 31 (-9,+13)% for FGK stars using a 15% relative excess threshold. Relative to a model of decaying excess frequency, the frequency of debris disks around A-type stars appears marginally low for the cluster's age while that of FGK stars appears consistent. Scenarios that may qualitatively explain this result are examined. We conclude that planetesimal activity in the terrestrial region of FGK stars is common in the first ~50 Myr and decays on timescales of ~100 Myr. Despite luminosity differences, debris disk evolution does not appear to depend strongly on stellar mass.

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Astrophysics, abstract
astro-ph/0609299

From: Jeronimo Bernard-Salas [view email]
Date: Mon, 11 Sep 2006 20:00:38 GMT   (47kb)

The Spitzer-IRS spectrum of SMP LMC 11

Authors: J. Bernard-Salas, E. Peeters, G.C. Sloan, J. Cami, S. Guiles, J.R. Houck
Comments: 5 pages (in emulateapj), 1 table, 2 figures. Accepted for publication in ApJ Letters

We present the first mid-infrared spectra of SMP LMC 11 in the Large Magellanic Cloud. While this object resembles a planetary nebula in the optical, its infrared properties are more similar to an object in transition from the asymptotic giant branch to the planetary nebula phase. A warm dust continuum dominates the infrared spectrum. The peak emission corresponds to a mean dust temperature of 330 K. The spectrum shows overlapping molecular absorption bands from 12 to 17 um corresponding to acetylene and polyacetylenic chains and benzene. This is the first detection of C4H2, C6H2, C6H6 and other molecules in an extragalactic object. The infrared spectrum of SMP LMC 11 is similar in many ways to that of the pre-planetary nebula AFGL 618. The IRS spectrum shows little evidence of nitrogen-based molecules which are commonly seen in Galactic AGB stars. Polycyclic aromatic hydrocarbons are also absent from the spectrum. The detection of the [NeII] 12.8 um line in the infrared and other forbidden emission lines in the optical indicates that an ionized region is present.

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Astrophysics, abstract
astro-ph/0609464

From: Kevin Luhman [view email]
Date: Sat, 16 Sep 2006 11:41:40 GMT   (488kb)

Discovery of Two T Dwarf Companions with the Spitzer Space Telescope

Authors: K. L. Luhman (Penn State), B. M. Patten (CfA), M. Marengo (CfA), M. T. Schuster (CfA), J. L. Hora (CfA), R. G. Ellis (CfA), J. R. Stauffer (SSC), S. M. Sonnett (CfA), E. Winston (CfA), R. A. Gutermuth (CfA), S. T. Megeath (Toledo), D. E. Backman (SOFIA), T. J. Henry (George State), M. W. Werner (JPL), G. G. Fazio (CfA)
Comments: Astrophysical Journal, in press

We report the discovery of T dwarf companions to the nearby stars HN Peg (G0V, 18.4 pc, ~0.3 Gyr) and HD 3651 (K0V, 11.1 pc, ~7 Gyr). During an ongoing survey of 5'x5' fields surrounding stars in the solar neighborhood with IRAC aboard the Spitzer Space Telescope, we identified these companions as candidate T dwarfs based on their mid-IR colors. Using near-IR spectra obtained with SpeX at the NASA IRTF, we confirm the presence of methane absorption that characterizes T dwarfs and measure spectral types of T2.5+/-0.5 and T7.5+/-0.5 for HN Peg B and HD 3651 B, respectively. By comparing our Spitzer data to images from 2MASS obtained several years earlier, we find that the proper motions of HN Peg B and HD 3651 B are consistent with those of the primaries, confirming their companionship. HN Peg B and HD 3651 B have angular separations of 43.2" and 42.9" from their primaries, which correspond to projected physical separations of 795 and 476 AU, respectively. A comparison of their luminosities to the values predicted by theoretical evolutionary models implies masses of 0.021+/-0.009 and 0.051+/-0.014 Msun for HN Peg B and HD 3651 B. In addition, the models imply an effective temperature for HN Peg B that is significantly lower than the values derived for other T dwarfs at similar spectral types, which is the same behavior reported by Metchev & Hillenbrand for the young late-L dwarf HD 203030 B. Thus, the temperature of the L/T transition appears to depend on surface gravity. Meanwhile, HD 3651 B is the first substellar companion directly imaged around a star that is known to harbor a close-in planet from RV surveys. The discovery of this companion supports the notion that the high eccentricities of close-in planets like the one near HD 3651 may be the result of perturbations by low-mass companions at wide separations.

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Astrophysics, abstract
astro-ph/0610101

From: Jay Farihi [view email]
Date: Wed, 4 Oct 2006 07:31:23 GMT   (57kb)

Spitzer Observations of GD 362 and Other Metal-Rich White Dwarfs

Authors: J. Farihi, B. Zuckerman, E.E. Becklin, M. Jura
Comments: 6 pages, 3 figures, to appear in the ASP Conference Series for the 15th European White Dwarf Workshop

A {\em Spitzer} IRAC survey of 17 nearby metal-rich white dwarfs, nominally DAZ stars, reveals excess emission from only 3 targets: G29-38, GD 362 and G167-8. Observations of GD 362 with all three {\em Spitzer} instruments reveals a warm ($\approx1000$ K) dust continuum, very strong silicate emission, and the likely presence of cooler ($\approx500$ K) dust. While there is a general similarity between the mid-infrared spectral energy distributions of G29-38 and GD 362, the IRAC fluxes of G167-8 are so far unique among white dwarfs. However, further observations of G167-8 are required before the measured excess can be definitely associated with the white dwarf.

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Astrophysics, abstract
astro-ph/0610384

From: Klaus Martin Pontoppidan [view email]
Date: Thu, 12 Oct 2006 22:09:08 GMT   (201kb)

Modeling Spitzer observations of VV Ser. I. The circumstellar disk of a UX Orionis star

Authors: Klaus M. Pontoppidan, Cornelis P. Dullemond, Geoffrey A. Blake, A. C. Adwin Boogert, Ewine F. van Dishoeck, Neal J. Evans, Jacqueline Kessler-Silacci, Fred Lahuis
Comments: 12 pages, accepted for publication in ApJ

We present mid-infrared Spitzer-IRS spectra of the well-known UX Orionis star VV Ser. We combine the Spitzer data with interferometric and spectroscopic data from the literature covering UV to submillimeter wavelengths. The full set of data are modeled by a two-dimensional axisymmetric Monte Carlo radiative transfer code. The model is used to test the prediction of (Dullemond et al. 2003) that disks around UX Orionis stars must have a self-shadowed shape, and that these disks are seen nearly edge-on, looking just over the edge of a puffed-up inner rim, formed roughly at the dust sublimation radius. We find that a single, relatively simple model is consistent with all the available observational constraints spanning 4 orders of magnitude in wavelength and spatial scales, providing strong support for this interpretation of UX Orionis stars. The grains in the upper layers of the puffed-up inner rim must be small (0.01-0.4 micron) to reproduce the colors (R_V ~ 3.6) of the extinction events, while the shape and strength of the mid-infrared silicate emission features indicate that grains in the outer disk (> 1-2 AU) are somewhat larger (0.3-3.0 micron). From the model fit, the location of the puffed-up inner rim is estimated to be at a dust temperature of 1500 K or at 0.7-0.8 AU for small grains. This is almost twice the rim radius estimated from near-infrared interferometry. A best fitting model for the inner rim in which large grains in the disk mid-plane reach to within 0.25 AU of the star, while small grains in the disk surface create a puffed-up inner rim at ~0.7-0.8 AU, is able to reproduce all the data, including the near-infrared visibilities. [Abstract abridged]

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Astrophysics, abstract
astro-ph/0610385

From: Klaus Martin Pontoppidan [view email]
Date: Thu, 12 Oct 2006 22:09:40 GMT   (892kb)

Modeling Spitzer observations of VV Ser. II. an extended quantum heated nebula and a disk shadow

Authors: Klaus M. Pontoppidan, Cornelis P. Dullemond, Geoffrey A. Blake, Neal J. Evans, Vincent C. Geers, Paul M. Harvey, William Spiesman
Comments: 11 pages, accepted for publication in ApJ

We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6--70 micron images show bright, localized and nebulous emission extended over 4 arcmin centered on VV Ser. We interpret the nebulosity as being due to transiently heated grains excited by UV photons emitted by VV Ser. A companion paper describes how the physical structure of the VV Ser disk has been constrained using a wide range of observational data modeled by an axisymmetric Monte Carlo radiative transfer code. In this paper we employ the model to study the nebulosity surrounding VV Ser using quantum-heated PAH molecules and Very Small Grains (VSGs) consisting of amorphous carbon in the thermal cooling approximation. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this dark wedge as the shadow cast by the inner regions of a near-edge-on disk in UV light, allowing the PAHs to be excited only outside of this shadow. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. Although depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5+/-2% of the total dust mass, given the opacity. The extent of the nebulosity constrains the density of the gas surrounding the VV Ser disk to 500+/-200 cm-3 for a gas-to-dust ratio of 100. This low density suggests that the quantum heated material is not part of the original envelope of VV Ser and that it is rather a quiescent part of the Serpens molecular cloud that the star has passed into after being formed. [Abstract abridged]

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Astrophysics, abstract
astro-ph/0610838

From: Jessica Ennis [view email]
Date (v1): Fri, 27 Oct 2006 19:58:54 GMT   (1900kb)
Date (revised v2): Sun, 29 Oct 2006 19:04:26 GMT   (1334kb)
Date (revised v3): Wed, 1 Nov 2006 23:08:37 GMT   (1334kb)

Spitzer IRAC Images and Sample Spectra of Cassiopeia A's Explosion

Authors: J. A. Ennis (1), L. Rudnick (1), W. T. Reach (2), J. D. Smith (3), J. Rho (2), T. DeLaney (4), H. Gomez (5), T. Kozasa (6) ((1) University of Minnesota, (2) California Institute of Technology, (3) Steward Observatory, (4) Harvard-Smithsonian Center for Astrophysics, (5) University of Wales, (6) Hokkaido University)
Comments: 28 pages, 10 figures, accepted in to the Astrophysical Journal. For full-resolution images, please see this http URL Revised to correct an error in references
Journal-ref: Astrophys.J. 652 (2006) 376-386

We present Spitzer IRAC images, along with representative 5.27 to 38.5 micron IRS spectra of the Cassiopeia A supernova remnant. We find that various IRAC channels are each most sensitive to a different spectral and physical component. Channel 1 (3.6 micron) matches radio synchrotron images. Where Channel 1 is strong with respect to the other channels, the longer-wavelength spectra show a broad continuum gently peaking around 26 micron, with weak or no lines. We suggest that this is due to un-enriched progenitor circumstellar dust behind the outer shock, processed by shock photons and electrons. Where Channel 4 (8 micron) is bright relative to the other IRAC channels, the long-wavelength spectra show a strong, 2-3 micron-wide peak at 21 micron, likely due to silicates and proto-silicates, as well as strong ionic lines of [Ar II], [Ar III], [S IV] and [Ne II]. In these locations, the dust and ionic emission originate from the explosion's O-burning layers. The regions where Channels 2 (4.5 micron) and 3 (5.6 micron) are strongest relative to Channel 4 show a spectrum that rises gradually to 21 micron, and then flattens or rises more slowly to longer wavelengths, along with higher ratios of [Ne II] to [Ar II]. Dust and ionic emission in these locations arise primarily from the C- and Ne- burning layers. These findings are consistent with asymmetries in the explosion producing variations in the velocity structure in different directions, but preserving the nucleosynthetic layers. At each location, the dust and ionic lines in the mid-infrared, and the hotter and more highly ionized optical and X-ray emission are then dominated by the layer currently encountering the reverse shock in that direction.

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Astrophysics, abstract
astro-ph/0610856

From: Fergal Mullally [view email]
Date: Sat, 28 Oct 2006 22:38:18 GMT   (29kb)

Spitzer White Dwarf Planet Limits

Authors: F. Mullally, Ted von Hippel, D. E. Winget
Comments: 4 pages, 3 figures, to appear in Proceedings of 15th European White Dwarf Workshop

We present preliminary limits on the presence of planets around white dwarf stars using the IRAC photometer on the Spitzer space telescope. Planets emit strongly in the mid-infrared which allows their presence to be detected as an excess at these wavelengths. We place limits of $5 M_J$ for 8 stars assuming ages of $1 Gyr$, and $10 M_J$ for 23 stars.We describe our survey, present our results and comment on approaches to improve our methodology.

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Astrophysics, abstract
astro-ph/0610953

From: Kevin France [view email]
Date: Tue, 31 Oct 2006 18:24:45 GMT   (965kb)

A Cometary Bow Shock and Mid-Infrared Emission Variations Revealed in Spitzer Observations of HD 34078 and IC 405

Authors: Kevin France (1,2), Stephan R. McCandliss (1), Roxana E. Lupu (1) (1-JHU, 2-CITA/U Toronto)
Comments: ApJ accepted, uses emulateapj, images compressed for astro-ph

We present new infrared observations of the emission/reflection nebula IC 405 obtained with the Spitzer Space Telescope. Infrared images in the four IRAC bands (3.6, 4.5, 5.8, and 8.0 um) and two MIPS bands (24 and 70 um) are complemented by IRS spectroscopy (5-30 um) of two nebular filaments. The IRAC (8.0 um) and MIPS imaging shows evidence of a bow shock associated with the runaway O9.5V star, HD 34078, created by the interaction between the star and nebular material. The ratio of emission at 24 to 70 um is higher in the immediate vicinity of HD 34078 than in the outer filaments, providing evidence for elevated dust temperatures (T_d > 90 K) in the shock region. The nebular imaging reveals that the morphology is band dependent, with varying contributions from aromatic emission features, H2, and dust emission. Nebular spectroscopy is used to quantify these contributions, showing several aromatic emission bands between 6-14 um, the S(5), S(3), S(2), and S(1) pure rotational emission lines of H2, and atomic fine structure lines of Ne, S, and Ar. The low-dispersion spectra provide constraints on the ionization state of the large molecules responsible for the aromatic infrared features. H2 rotational temperatures of the two bright nebular filaments are determined from the observed line strengths. An average T(H2) ~ 400 K is inferred, with evidence for additional non-uniform excitation by UV photons in the intense radiation field of HD 34078. The photoexcitation hypothesis is supported by direct measurement of the far-UV H2 fluorescence spectrum, obtained with FUSE.

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Astrophysics, abstract
astro-ph/0611026

From: Thomas E. Harrison [view email]
Date: Wed, 1 Nov 2006 15:28:20 GMT   (186kb)

Spitzer IRS Spectroscopy of Intermediate Polars: Constraints on Mid-Infrared Cyclotron Emission

Authors: Thomas E. Harrison, Ryan K. Campbell, Steve B. Howell, France A. Cordova, Axel D. Schwope
Comments: 43 pages, including 17 figures, accepted by the Astrophysical Journal

We present Spitzer Infrared Spectrograph (IRS) observations of eleven intermediate polars (IPs). Spectra covering the wavelength range from 5.2 to 14 $\mu$m are presented for all eleven objects, and longer wavelength spectra are presented for three objects (AE Aqr, EX Hya, and V1223 Sgr). We also present new, moderate resolution (R $\sim$ 2000) near-infrared spectra for five of the program objects. We find that, in general, the mid-infrared spectra are consistent with simple power laws that extend from the optical into the mid-infrared. There is no evidence for discrete cyclotron emission features in the near- or mid-infrared spectra for any of the IPs investigated. If cyclotron emission is occurring in the 5.2 to 14.0 $\mu$m bandpass it constitutes less than 1% of the bolometric luminosity of any of the IPs. We discuss our results in the context of the standard model for IPs.

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Astrophysics, abstract
astro-ph/0611071

From: Eric Lagadec [view email]
Date: Thu, 2 Nov 2006 19:58:23 GMT   (1664kb)

Spitzer spectroscopy of carbon stars in the Small Magellanic Cloud

Authors: Eric Lagadec, Albert A. Zijlstra, G.C. Sloan, Mikako Matsuura, Peter Wood, G.J. Harris, Jacco Th. van Loon, J.A.D.L. Blommaert, S. Hony, M.A.T. Groenewegen, M.W. Feast, P.A. Whitelock, J.W. Menzies, M.-R. Cioni, L.B.F.M. Waters
Comments: 17 pages, 17 figures

We present Spitzer Space telescope spectroscopic observations of 14 carbon-rich AGB stars in the Small Magellanic Cloud. SiC dust is seen in most of the carbon-rich stars but it is weak compared to LMC stars. The SiC feature is strong only for stars with significant dust excess, opposite to what is observed for Galactic stars. We argue that in the SMC, SiC forms at lower temperature than graphite dust, whereas the reverse situation occurs in the Galaxy where SiC condenses at higher temperatures and forms first. Dust input into the interstellar medium by AGB stars consists mostly of carbonaceous dust, with little SiC or silicate dust. Only the two coolest stars show a 30-micron band due to MgS dust. We suggest that this is due to the fact that, in the SMC, mass-losing AGB stars generally have low circumstellar (dust) optical depth and therefore effective heating of dust by the central star does not allow temperatures below the 650 K necessary for MgS to exist as a solid. Gas phase C$_2$H$_2$ bands are stronger in the SMC than in the LMC or Galaxy. This is attributed to an increasing C/O ratio at low metallicity. We present a colour-colour diagram based on Spitzer IRAC and MIPS colours to discriminate between O- and C-rich stars. We show that AGB stars in the SMC become carbon stars early in the thermal-pulsing AGB evolution, and remain optically visible for $\sim 6 \times 10^5$ yr. For the LMC, this lifetime is $\sim 3 \times 10^5$ yr. The superwind phase traced with Spitzer lasts for $\sim 10^4$ yr. Spitzer spectra of a K supergiant and a compact HII region are also given.

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Astrophysics, abstract
astro-ph/0611095

From: Dale Jackson [view email]
Date: Thu, 2 Nov 2006 21:33:32 GMT   (312kb)

A Spitzer/IRAC Census of the Asymptotic Giant Branch Populations in Local Group Dwarfs. I. WLM

Authors: Dale C. Jackson, Evan D. Skillman, Robert D. Gehrz, Elisha Polomski, Charles E. Woodward
Comments: Accepted by ApJ, 34 pages, 13 figures, version with high-resolution figures available at: this http URL

We present Spitzer/IRAC observations at 3.6 and 4.5 microns along with optical data from the Local Group Galaxies Survey to investigate the evolved stellar population of the Local Group dwarf irregular galaxy WLM. These observations provide a nearly complete census of the asymptotic giant branch (AGB) stars. We find 39% of the infrared-detected AGB stars are not detected in the optical data, even though our 50% completeness limit is three magnitudes fainter than the red giant branch tip. An additional 4% of the infrared-detected AGBs are misidentified in the optical, presumably due to reddening by circumstellar dust. We also compare our results with those of a narrow-band optical carbon star survey of WLM, and find the latter study sensitive to only 18% of the total AGB population. We detect objects with infrared fluxes consistent with them being mass-losing AGB stars, and derive a present day total mass-loss rate from the AGB stars of 0.7-2.4 x 10^(-3) solar masses per year. The distribution of mass-loss rates and bolometric luminosities of AGBs and red supergiants are very similar to those in the LMC and SMC and the empirical maximum mass-loss rate observed in the LMC and SMC is in excellent agreement with our WLM data.

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Astrophysics, abstract
astro-ph/0611100

From: Zhongxiang Wang [view email]
Date: Thu, 2 Nov 2006 23:05:48 GMT   (55kb)

Spitzer Mid-infrared Upper Limits on Anomalous X-Ray Pulsars 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197

Authors: Z. Wang, V. M. Kaspi, S. J. U. Higdon
Comments: 7 pages, 5 figures, submitted to ApJ

We report on mid-infrared imaging observations of the anomalous X-ray pulsars (AXPs) 1E 1048.1-5937, 1RXS J170849-400910, and XTE J1810-197. The observations were carried out at 4.5 and 8.0 microns with the Infrared Array Camera and at 24 microns with the Multiband Imaging Photometer on the Spitzer Space Telescope. No mid-infrared counterparts were detected. As infrared emission from AXPs may be related to their X-ray emission either via the magnetosphere or via a dust disk, we compare the derived upper limits on the infrared/X-ray flux ratios of the AXPs to the same ratio for 4U 0142+61, an AXP previously detected in the mid-infrared range. The comparison indicates that our three non-detections are consistent with their relatively low X-ray fluxes. For XTE J1810-197, our upper limits set a constraint on its rising radio/millimeter energy spectrum, suggesting a spectral break between 1.5$\times 10^{11}$--6$\times10^{13}$ Hz.

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Astrophysics, abstract
astro-ph/0611127

From: Kathleen Kraemer [view email]
Date: Fri, 3 Nov 2006 19:45:11 GMT   (32kb)

A Post-AGB Star in the Small Magellanic Cloud Observed with the Spitzer Infrared Spectrograph

Authors: Kathleen E. Kraemer, G. C. Sloan, J. Bernard-Salas, Stephan D. Price, Michael P. Egan, P. R. Wood
Comments: 4 figures, Fig. 4 color; to appear in the 20 November 2006 Astrophysical Journal Letters

We have observed an evolved star with a rare combination of spectral features, MSX SMC 029, in the Small Magellanic Cloud (SMC) using the low-resolution modules of the Infrared Spectrograph on the Spitzer Space Telescope. A cool dust continuum dominates the spectrum of MSX SMC 029. The spectrum also shows both emission from polycyclic aromatic hydrocarbons (PAHs) and absorption at 13.7 micron from C2H2, a juxtaposition seen in only two other sources, AFGL 2688 and IRAS 13416-6243, both post-asymptotic giant branch (AGB) objects. As in these sources, the PAH spectrum has the unusual trait that the peak emission in the 7-9 micron complex lies beyond 8.0 micron. In addition, the 8.6 micron feature has an intensity as strong as the C-C modes which normally peak between 7.7 and 7.9 micron. The relative flux of the feature at 11.3 micron to that at 8 micron suggests that the PAHs in MSX SMC 029 either have a low ionization fraction or are largely unprocessed. The 13-16 micron wavelength region shows strong absorption features similar to those observed in the post-AGB objects AFGL 618 and SMP LMC 11. This broad absorption may arise from the same molecules which have been identified in those sources: C2H2, C4H2, HC3N, and C6H6. The similarities between MSX SMC 029, AFGL 2688, and AFGL 618 lead us to conclude that MSX SMC 029 has evolved off the AGB in only the past few hundred years, making it the third post-AGB object identified in the SMC.

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Astrophysics, abstract
astro-ph/0611346

From: Massimo Marengo [view email]
Date: Fri, 10 Nov 2006 18:22:48 GMT   (160kb)

Spitzer/IRAC Characterization of Galactic AGB Stars

Authors: M. Marengo, J.L. Hora, P. Barmby, S.P. Willner, L.E. Allen, M.T. Schuster, G.G. Fazio
Comments: 5 pages, to appear in proceedings of "Why Galaxy care about AGB Stars", Vienna August 7-11, 2006

The Spitzer Space Telescope and in particular its InfraRed Array Camera (IRAC) is an ideal facility to study the distribution of AGB stars in our own and other galaxies because of its efficiency in surveying vast areas of the sky and its ability to detect sources with infrared excess. The IRAC colors of AGB stars, however, are not well known because cool stars have numerous molecular absorption features in the spectral region covered by the IRAC photometric system. The presence and strength of these features depends on the chemistry of the stellar atmosphere and the mass loss rate and can change with time due to the star's variability. To characterize the IRAC colors of AGB stars, we are carrying out a Spitzer Guaranteed Time Observation program to observe a sample of AGB stars with IRAC. The results will be made available to the community in the form of template magnitudes and colors for each target with the goal of aiding the identification of AGB stars in already available and future IRAC surveys. We present here the first results of this project.

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Astrophysics, abstract
astro-ph/0611511

From: Susanne Friedrich [view email]
Date: Thu, 16 Nov 2006 08:45:08 GMT   (349kb)

Search for Giant Planets around White Dwarfs with HST, Spitzer, and VLT

Authors: S. Friedrich (1 and 2), H. Zinnecker (1), S. Correia (1), W. Brandner (3), M. Burleigh (4), M. McCaughrean (5) ((1) Astrophysikalisches Institut Potsdam, (2) Max-Planck-Institut f. Extraterrestrische Physik, (3) Max-Planck-Institut f. Astronomie, (4) Department of Physics & Astronomy, University of Leicester, (5) School of Physics, University of Exeter)
Comments: 6 pages, 4 figures, 15th European Workshop on White Dwarfs

For the last three years we have performed a survey for young (<3 Gyrs) giant planets around nearby white dwarfs with HST, Spitzer, and VLT. Direct HST/NICMOS imaging of the seven white dwarfs in the Hyades gave no evidence for companions down to about 10 Jupiter masses and separations larger than 0.5 arcsec (about 25 AU), while VLT/NACO observations revealed a putative companion to a field white dwarf. Second epoch observations with SINFONI on the VLT, however, showed that it is most probably a background star. With IRAC on Spitzer we also found no indications of cool, very low mass companions in our sample of field white dwarfs. The implications of these non-detections are briefly discussed.

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Astrophysics, abstract
astro-ph/0611588

From: Fergal Mullally [view email]
Date: Fri, 17 Nov 2006 23:11:05 GMT   (207kb)

A Spitzer White Dwarf Infrared Survey

Authors: F. Mullally, Mukremin Kilic, William T. Reach, Marc J. Kuchner, Ted von Hippel, Adam Burrows, D. E. Winget
Comments: 24 pages. Accepted by Astrophysical Journal Supplement Series

We present mid-infrared photometry of 124 white dwarf stars with Spitzer Space Telescope. Objects were observed simultaneously at 4.5 and 8.0um with sensitivities better than 1 mJy. This data can be used to test models of white dwarf atmospheres in a new wavelength regime, as well as to search for planetary companions and debris disks.

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Astrophysics, abstract
astro-ph/0611899

From: Pier-Emmanuel Tremblay [view email]
Date: Wed, 29 Nov 2006 15:00:07 GMT   (235kb)

Infrared Photometric Analysis of White Dwarfs from The Two Micron All Sky Survey and the Spitzer Space Telescope

Authors: P.-E. Tremblay, P. Bergeron
Comments: 41 pages, 9 figures, accepted for publication in the Astrophysical Journal

We review the available near- and mid-infrared photometry for white dwarfs obtained from the Two Micron All-Sky Survey (2MASS) and by the Spitzer Space Telescope. Both data sets have recently been used to seek white dwarfs with infrared excesses due to the presence of unresolved companions or circumstellar disks, and also to derive the atmospheric parameters of cool white dwarfs. We first attempt to evaluate the reliability of the 2MASS photometry by comparing it with an independent set of published JHK CIT magnitudes for 160 cool white dwarf stars, and also by comparing the data with the predictions of detailed model atmosphere calculations. The possibility of using 2MASS to identify unresolved M dwarf companions or circumstellar disks is then discussed. We also revisit the analysis of 46 binary candidates from Wachter et al. using the synthetic flux method and confirm the large near-infrared excesses in most objects. We perform a similar analysis by fitting Spitzer 4.5 and 8 micron photometric observations of white dwarfs with our grid of model atmospheres, and demonstrate the reliability of both the Spitzer data and the theoretical calculations up to 8 micron. Finally, we search for massive disks resulting from the merger of two white dwarfs in a 2MASS sample composed of 57 massive degenerates, and show that massive disks are uncommon in such stars.

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Astrophysics, abstract
astro-ph/0612161

From: Arne Rau [view email]
Date (v1): Wed, 6 Dec 2006 20:57:45 GMT   (252kb)
Date (revised v2): Tue, 9 Jan 2007 21:25:39 GMT   (222kb)

Spitzer Observations of the New Luminous Red Nova M85OT2006-1

Authors: A. Rau, S.R. Kulkarni, E.O. Ofek, L. Yan
Comments: manuscript after minor revisions, accepted for ApJ

M85OT2006-1 is the latest and most brilliant addition to the small group of known Luminous Red Novae (LRNe). An identifying characteristic of the previously detected events (M31 RV, V4322 Sgr & V838 Mon) was a spectral red-ward evolution connected with an emerging infrared component following the optical decay. Here we report on the discovery of a similar feature in Keck/NIRC and Spitzer photometry of M85OT2006-1 six months post-eruption. We find that its 2.1-22 micrometer spectral energy distribution is best described by a black body with effective temperature T_eff=950+-150 K and bolometric luminosity L=2.9+-0.5x10^5 L_sun. Assuming spherical geometry, the black body effective radius, R=2.0+-0.5x10^4 R_sun, and corresponding expansion velocity, v=870+-260 km/s, are remarkably similar to the properties of M31 RV 70 days after its eruption. Furthermore, we propose a search strategy for LRNe in the local Universe making use of the longevity of their infrared excess emission and discuss the expected number of events in the Spitzer Infrared Nearby Galaxies Survey.

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Astrophysics, abstract
astro-ph/0701307

From: Carolyn Brinkworth [view email]
Date: Wed, 10 Jan 2007 18:00:56 GMT   (93kb)

Spitzer Space Telescope observations of magnetic cataclysmic variables: possibilities for the presence of dust in polars

Authors: C. S. Brinkworth, D. W. Hoard, S. Wachter, S. B. Howell, D. R. Ciardi, P. Szkody, T. E. Harrison, G. T. van Belle, A. A. Esin
Comments: 58 pages, 14 figures, ApJ accepted

We present Spitzer Space Telescope photometry of six short-period polars, EF Eri, V347 Pav, VV Pup, V834 Cen, GG Leo, and MR Ser. We have combined the Spitzer Infrared Array Camera (3.6 -8.0 microns) data with the 2MASS J, H, K_s photometry to construct the spectral energy distributions of these systems from the near- to mid-IR (1.235 - 8 microns). We find that five out of the six polars have flux densities in the mid-IR that are substantially in excess of the values expected from the stellar components alone. We have modeled the observed SEDs with a combination of contributions from the white dwarf, secondary star, and either cyclotron emission or a cool, circumbinary dust disk to fill in the long-wavelength excess. We find that a circumbinary dust disk is the most likely cause of the 8 micron excess in all cases, but we have been unable to rule out the specific (but unlikely) case of completely optically thin cyclotron emission as the source of the observed 8 micron flux density. While both model components can generate enough flux at 8 microns, neither dust nor cyclotron emission alone can match the excess above the stellar components at all wavelengths. A model combining both cyclotron and dust contributions, possibly with some accretion-generated flux in the near-IR, is probably required, but our observed SEDs are not sufficiently well-sampled to constrain such a complicated model. If the 8 micron flux density is caused by the presence of a circumbinary dust disk, then our estimates of the masses of these disks are many orders of magnitude below the mass required to affect CV evolution.

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Astrophysics, abstract
astro-ph/0701398

From: Amanda K. Mainzer [view email]
Date: Sat, 13 Jan 2007 02:00:12 GMT   (440kb)

Moderate Resolution Spitzer Infrared Spectrograph (IRS) Observations of M, L, and T Dwarfs

Authors: A. K. Mainzer, Thomas L. Roellig, D. Saumon, Mark S. Marley, Michael C. Cushing, G. C. Sloan, J. Davy Kirkpatrick, S. K. Leggett, John C. Wilson
Comments: 19 pages, 7 figures, accepted ApJ 1/12/07

We present 10 - 19 um moderate resolution spectra of ten M dwarfs, one L dwarf, and two T dwarf systems obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope. The IRS allows us to examine molecular spectroscopic features/lines at moderate spectral resolution in a heretofore untapped wavelength regime. These R~600 spectra allow for a more detailed examination of clouds, non-equilibrium chemistry, as well as the molecular features of H2O, NH3, and other trace molecular species that are the hallmarks of these objects. A cloud-free model best fits our mid-infrared spectrum of the T1 dwarf epsilon Indi Ba, and we find that the NH3 feature in epsilon Indi Bb is best explained by a non-equilibrium abundance due to vertical transport in its atmosphere. We examined a set of objects (mostly M dwarfs) in multiple systems to look for evidence of emission features, which might indicate an atmospheric temperature inversion, as well as trace molecular species; however, we found no evidence of either.

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Astrophysics, abstract
astro-ph/0701441

From: Thayne Currie [view email]
Date: Mon, 15 Jan 2007 23:59:55 GMT   (819kb)

Spitzer/IRAC and JHKs Observations of h & chi Persei: Constraints on Protoplanetary Disk and Massive Cluster Evolution at ~ 10^7 yr

Authors: Thayne Currie (1), Zoltan Balog (2), S. J. Kenyon (1), , G. Rieke (2), L. Prato (3), E. T. Young (2), J. Muzerolle (2), D.P. Clemens (4), M. Buie (3), D. Sarcia (4), A. Grabau (4), E. V. Tollestrup (4), B. Taylor (3), E. Dunham (3), G. Mace (3) ((1) Harvard-Smithsonian Center for Astrophysics, (2) Steward Observatory/University of Arizona, (3) Lowell Observatory, (4) Boston University)
Comments: 26 pages, 18 figures, accepted for publication in the Astrophysical Journal (April 10, 2007)

We describe IRAC 3.6-8 mu_m observations and ground-based near-IR JHKs photometry from Mimir and 2MASS of the massive double cluster h & chi Persei complete to J=15.5 (M ~ 1.3 Msun. Within 25' of the cluster centers we detect \~11,000 sources with J < 15.5, ~7,000 sources with [4.5] < 15, and ~ 5000 sources with [8] < 14.5. In both clusters, the surface density profiles derived from the 2MASS data decline with distance from the cluster centers as expected for a bound cluster. Within 15' of the cluster centers, ~ 50% of the stars lie on a reddened ~ 13 Myr isochrone; at 15'-25' from the cluster centers, ~ 40% lie on this isochrone. Thus, the optical/2MASS color-magnitude diagrams indicate that h & chi Per are accompanied by a halo population with roughly the same age and distance as the two dense clusters. The double cluster lacks any clear IR excess sources for J < 13.5 (~ 2.7 Msun). Therefore, disks around high-mass stars disperse prior to ~ 10^{7} yr. At least 2-3% of the fainter cluster stars have strong IR excess at both [5.8] and [8]. About 4-8% of sources slightly more massive than the Sun (~ 1.4 Msun) have IR excesses at [8]. Combined with the lack of detectable excesses for brighter stars, this result suggests that disks around lower-mass stars have longer lifetimes. The IR excess population also appears to be larger at longer IRAC bands ([5.8], [8]) than at shorter IRAC/2MASS bands ($K_{s}$, [4.5]), a result consistent with an inside-out clearing of disks.

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Astrophysics, abstract
astro-ph/0701476

From: Jesus Hernandez PhD [view email]
Date: Tue, 16 Jan 2007 19:30:08 GMT   (864kb)

Spitzer Space Telescope study of disks in the young $\sigma$ Orionis cluster

Authors: Jesus Hernandez, L. Hartmann, T. Megeath, R. Gutermuth, J. Muzerolle, N. Calvet, A. K. Vivas, C. Briceno, L. Allen, J. Stauffer, E. Young, G. Fazio
Comments: 44pages, 17 figures. Sent to ApJ

We report new Spitzer Space Telescope observations from the IRAC and MIPS instruments of the young (~ 3 Myr) sigma Orionis cluster. We identify 336 stars as members of the cluster using optical and near-infrared color magnitude diagrams. Using the spectral energy distribution (SED) slopes in the IRAC spectral range, we place objects in several classes: non-excess stars, stars with optically thick disks(like classical T Tauri stars), class I (protostellar) candidates, and stars with ``evolved disks''; the last exhibit smaller IRAC excesses than optically thick disk systems. In general, this classification agrees with the location expected in IRAC-MIPS color-color diagrams for these objects. We find that the evolved disk systems are mostly a combination of objects with optically thick but non-flared disks, suggesting grain growth and/or settling, and transition disks, systems in which the inner disk is partially or fully cleared of small dust. In all, we identify 7 transition disk candidates and 3 possible debris disk systems. As in other young stellar populations, the fraction of disks depends on the stellar mass, ranging from ~10% for stars in the Herbig Ae/Be mass range (>2 msun) to ~35% in the T Tauri mass range (1-0.1 msun). We find that the disk fraction does not decrease significantly toward the brown dwarf candidates (<0.1 msun). The IRAC infrared excesses found in stellar clusters and associations with and without central high mass stars are similar, suggesting that external photoevaporation is not very important in many clusters. Finally, we find no correlation between the X-ray luminosity and the disk infrared excess, suggesting that the X-rays are not strongly affected by disk accretion.

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Astrophysics, abstract
astro-ph/0701703

From: Alexander Scholz [view email]
Date (v1): Wed, 24 Jan 2007 20:46:12 GMT   (104kb)
Date (revised v2): Wed, 24 Jan 2007 21:00:54 GMT   (104kb)

Evolution of brown dwarf disks: A Spitzer survey in Upper Scorpius

Authors: Alexander Scholz (Toronto, St. Andrews), Ray Jayawardhana (Toronto), Kenneth Wood (St. Andrews), Gwendolyn Meeus (AIP), Beate Stelzer (Palermo), Christina Walker, Mark O'Sullivan (St. Andrews)
Comments: 39 pages, 7 figures, accepted for publication in ApJ

We have carried out a Spitzer survey for brown dwarf (BD) disks in the ~5 Myr old Upper Scorpius (UpSco) star forming region, using IRS spectroscopy from 8 to 12\mu m and MIPS photometry at 24\mu m. Our sample consists of 35 confirmed very low mass members of UpSco. Thirteen objects in this sample show clear excess flux at 24\mu m, explained by dust emission from a circum-sub-stellar disk. Objects without excess emission either have no disks at all or disks with inner opacity holes of at least ~5 AU radii. Our disk frequency of 37\pm 9% is higher than what has been derived previously for K0-M5 stars in the same region (on a 1.8 sigma confidence level), suggesting a mass-dependent disk lifetime in UpSco. The clear distinction between objects with and without disks as well as the lack of transition objects shows that disk dissipation inside 5 AU occurs rapidly, probably on timescales of <~10^5 years. For the objects with disks, most SEDs are uniformly flat with flux levels of a few mJy, well modeled as emission from dusty disks affected by dust settling to the midplane, which also provides indirect evidence for grain growth. The silicate feature around 10\mu m is either absent or weak in our SEDs, arguing for a lack of hot, small dust grains. Compared with younger objects in Taurus, BD disks in UpSco show less flaring. Taken together, these results clearly demonstrate that we see disks in an advanced evolutionary state: Dust settling and grain growth are ubiquituous in circum-sub-stellar disks at ages of 5 Myr, arguing for planet forming processes in BD disks. For almost all our targets, results from high-resolution spectroscopy and high-spatial resolution imaging have been published before, thus providing a large sample of BDs for which information about disks, accretion, and binarity is available. (abridged)

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Astrophysics, abstract
astro-ph/0701741

From: Zoltan Balog [view email]
Date: Thu, 25 Jan 2007 20:16:48 GMT   (2069kb)

SPITZER/IRAC-MIPS Survey of NGC2244: Protostellar Disk Survival in the Vicinity of Hot Stars

Authors: Zoltan Balog, James Muzerolle, G. H. Rieke, Kate Y. L. Su, Eric T. Young
Comments: 10 pages, 9 figures accepted for publication in Astrophysical Journal

We present the results from a survey of NGC 2244 from 3.6 to 24 micron with the Spitzer Space Telescope. The 24micron-8micron-3.6micron color composite image of the region shows that the central cavity surrounding the multiple O and B stars of NGC2244 contains a large amount of cool dust visible only at 24micron. Our survey gives a detailed look at disk survivability within the hot-star-dominated environment in this cavity. Using mid infrared two color diagrams ([3.6]-[4.5] vs [5.8]-[8.0]) we identified 337 class II and 25 class I objects out of 1084 objects detected in all four of these bands with photometric uncertainty better than 10%. Including the 24 micron data, we found 213 class II and 20 class I sources out of 279 stars detected also at this latter band. The center of the class II density contours is in very good agreement with the center of the cluster detected in the 2MASS images. We studied the distribution of the class II sources relative to the O stars and found that the effect of high mass stars on the circumstellar disks is significant only in their immediate vicinity.

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Astrophysics, abstract
astro-ph/0701906

From: Marc Audard [view email]
Date: Wed, 31 Jan 2007 15:17:16 GMT   (545kb)

A Mid-Infrared Spitzer Study of the Herbig Be Star R Mon and the Associated HH 39 Herbig-Haro Object

Authors: M. Audard (1), S. Skinner (2), M. Guedel (3), T. Lanz (4), F. Paerels (5), H. Arce (6) ((1) University of Geneva, (2) University of Colorado, (3) Paul Scherrer Institut, (4) University of Maryland, (5) Columbia University, (6) American Museum of Natural History)
Comments: to appear in Astrophysics and Space Science, special issue of "Science with ALMA: a new era for Astrophysics" conference, ed. Dr. Bachiller

We report on initial results of our Spitzer Cycle 2 program to observe the young massive star R Mon and its associated HH 39 Herbig-Haro object in the mid-infrared. Our program used all instruments on-board Spitzer to obtain deep images with IRAC of the HH 39 complex and of R Mon and its surroundings, a deep image of HH 39 at 24 and 70 $\mu$m with MIPS, and mid-infrared spectra with the SH, LH, and LL modules of IRS. The aim of this program is to study the physical links in a young massive star between accretion disk, outflows and jets, and sh ocks in the associated HH object. Our preliminary analysis reveals that several knots of HH 39 are clearly detected in most IRAC bands. In IRAC4 (8 $\mu$m), diffuse emission, probably from PAHs, appears as foreground emission covering the HH 39 emission. The HH 39 knots are detected at 24 microns, despite the fact that dust continuum emission covers the knots and shows the same structure as observed with IRAC4. The IRS spectra of HH 39 show weak evidence of [Ne II] 12.8 $\mu$m and 0--0 S(1) H$_2$ 17.0 $\mu$m lines. A more detailed analysis is, however, required due to the faintness of the Herbig-Haro knots. Finally, we obtained the SH and MIPS SED spectra of R Mon. A PAH emission feature at 11.3 $\mu$m is detected on top of the strong continuum; although no strong emission or absorption lines are observed, we will seek to detect faint lines. The combined IRAC, IRS, and MIPS data of the R Mon/HH 39 system will help us to understand circumstellar disk processing, and the connection between jets, outflows, and HH objects.

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arXiv.org > astro-ph > astro-ph/0406104

Astrophysics, abstractastro-ph/0406104

MARCS-Model Stellar Atmospheres, and Their Application to the Photometric Calibration of the Spitzer-IRS

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arXiv.org > astro-ph > astro-ph/0406222

Astrophysics, abstractastro-ph/0406222

Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs

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arXiv.org > astro-ph > astro-ph/0412272

Astrophysics, abstractastro-ph/0412272

The Outburst of V1647 Ori Revealed by Spitzer

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arXiv.org > astro-ph > astro-ph/0502100

Astrophysics, abstractastro-ph/0502100

Spitzer Identification of the Least Massive Known Brown Dwarf with a Circumstellar Disk

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arXiv.org > astro-ph > astro-ph/0502527

Astrophysics, abstractastro-ph/0502527

Spitzer Studies of Ultracool Subdwarfs: Metal-poor Late-type M, L and T Dwarfs

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arXiv.org > astro-ph > astro-ph/0503326

Astrophysics, abstractastro-ph/0503326

G313.3+00.3: A New Planetary Nebula discovered by the Australia Telescope Compact Array and the Spitzer Space Telescope

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arXiv.org > astro-ph > astro-ph/0504086

Astrophysics, abstractastro-ph/0504086

The Vega Debris Disk -- A Surprise from Spitzer

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arXiv.org > astro-ph > astro-ph/0505492

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From ISO to Spitzer: a new view of the AGB-PN transition phase

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arXiv.org > astro-ph > astro-ph/0506407

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Early-time Spitzer observations of the type II-Plateau supernova, 2004dj

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arXiv.org > astro-ph > astro-ph/0506473

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Spitzer detections of new dust components in the outflow of the Red Rectangle

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arXiv.org > astro-ph > astro-ph/0506743

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Spitzer Observations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

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arXiv.org > astro-ph > astro-ph/0506743

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Spitzer Observations of G Dwarfs in the Pleiades: Circumstellar Debris Disks at 100 Myr Age

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arXiv.org > astro-ph > astro-ph/0509199

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Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer/MIPS Survey

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arXiv.org > astro-ph > astro-ph/0509507

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R CrB Candidates in the Small Magellanic Cloud: Observations of Cold, Featureless Dust with the Spitzer Infrared Spectrograph

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arXiv.org > astro-ph > astro-ph/0509695

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ESO-VLT and Spitzer spectroscopy of IRAS05328-6827: a massive young stellar object in the Large Magellanic Cloud

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arXiv.org > astro-ph > astro-ph/0509786

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Spitzer Space Telescope detection of the young supernova remnant 1E 0102.2-7219

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arXiv.org > astro-ph > astro-ph/0510518

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Infrared Supernova Remnants in the Spitzer GLIMPSE Field

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arXiv.org > astro-ph > astro-ph/0510630

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A Spitzer Space Telescope Infrared Survey of Supernova Remnants in the Inner Galaxy

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arXiv.org > astro-ph > astro-ph/0511094

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A Spitzer Search for Infrared Excesses around Massive Young White Dwarfs

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arXiv.org > astro-ph > astro-ph/0511314

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Spitzer/IRAC Photometry of the Eta Chameleontis Association

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