1	IMAPS Interstellar Medium Absorption Profile Spectrograph
2	IMAPS Subsystem Parameters Entrance aperture Multi-grid mechanical collimator with tandem square aperture arrays to provide field restriction Area: 250 cm² Field of view: 1° FWHM Mechanical obscuration: 26% Losses from diffraction and scattering: 16% Primary beam throughput: 62% Optical elements Echelle grating Ruled area 200✕400 mm Groove freq 79 mm^-1 Blaze angle 63.4° Meas. Efficiency @ 1040Å 24% Angles of α = β = 63.4°± 0.15°, ±0.30° and diffraction (4 settings) Off-plane angle: γ = 3.5° Cross-disperser grating Ruled area: 190✕143 mm Groove freq: 171 mm^-1 Blaze angle: 0.5° (8 ½ partitions) Width of each partition 17 mm Theoretical resolution 0.34Å = 11μm at focus of each partition Worst efficiency away from 79% blaze maximum Figure Off-axis paraboloid Focal length 1800 mm Chief ray decenter distance 130 mm Distance from echelle grating 1200 mm Measured efficienty @ 1040Å 25% (incl. coating and blaze efficiencies
3	IMAPS Subsystem Parameters (continued) Detector Photocathode Material KBr Quantum efficiencies 83% @ 950Å 77% @ 1000Å 74% @ 1150Å Permanent Magnet Focus Assembly Field strength 132 gauss Angle between B and E 20° Field uniformity 2 gauss Electrostatic assembly Operating voltage 18.5 kV CCD (RCA type SID-502) Pixel format 320 ✕ 256 Active area 9.6 mm ✕ 7.7mm Charge well dimensions 30μm ✕ 30μm Charge well capacity 8.5 ✕ 10⁵ e^- Amplifier output 1.5μV/e^- Secondary electron yield for 2500 e^- for 18.5 kV Lateral spread of secondary 8 – 12 μm electrons (distance between 1/e points) Output signal characteristics Frame rate 15 Hz Pixel dwell time 0.60 μs Frame transfer time: A→B register 1.78ms rms noise in each pixel 75e^- Dark current: 3000 e^- @20° C ( varies by ~30% over the image format) Image Layout Angles in the sky CCD field of view 18’20” ✕ 14’40” Image scale 115” mm^-1 CCD pixel 3.45” Lowest echelle order 197 Order separation 178 μm Central λ 1150 Å Free spectral range 35.5 mm = 5.5 Å Highest useful echelle order 238 Order separation 122 μm Central λ 950 Å Free spectral range 29.0 mm = 3.7 Å Echelle angle settings Number 4 Overlap of adjacent settings 0.42 mm Sample characteristics Mean dispersion: (λ/1000Å)✕ 0.139Å mm^-1 Sample size along orders 30 μm Sample size ┴ to orders 30 μm Instrumental profile 60 – 90 μm FWHM (Δλ ≥ λ/2.3 ✕ 10⁵) Broad band star images for guidance corrections (sounding rocket flights only) Location 0.78 mm (90”) from short λ edge Brightness ~ 50 events per 1/15 s frame λ range 1250 – 1500 Å
4	IMAPS Detector Windowless, Electron-bombarded Intensified CCD Image Sensor
5	IMAPS Flight History 3 Sounding Rocket Flights: October 1984, April 1985 and September 1988 2 Shuttle-launched ORFEUS-SPAS missions: STS-51 Sept. 12-22, 1993 and STS-80 Nov. 20 – Dec. 4, 1996
6	A Sample IMAPS Image
7	A Sample IMAPS Spectrum Spectrum of B Sco extracted from data recorded on a 5-minute sounding rocket flight in April 1985. (Results published in Jenkins, Lees, van Dishoeck & Wilcots 1989, ApJ, 343, 785.) Resolving power 8/Δ8 ≥ 1.3×10⁵ (2.3 km s^-1)
8	A Study of Interstellar H₂
9	Lyman Series Absorption by D and H
10	Spectral segment of ζ Ori A
11	IMAPS Bibliography Scientific articles: E. B. Jenkins, J. F. Lees, E. F. van Dishoeck, and E. M. Wilcots (1989): "Velocities and Rotational Excitation of Interstellar H₂ toward π Scorpii“ Astrophysical Journal, 343, pp. 785-810. C. L. Joseph and E. B. Jenkins (1991): "UV interstellar lines in the spectrum of π Scorpii recorded at 2 kilometers per second resolution“ Astrophysical Journal, 368, pp. 201-214. F. Bertoldi and E. B. Jenkins (1992): "Dense Clumps of ionized gas near π Scorpii, as revealed by the fine-structure excitation of N II" Astrophysical Journal, 388, pp. 495-512. E. B. Jenkins and A. Peimbert (1997): "Molecular hydrogen in the direction of ζ Ori A" Astrophysical Journal, 477, pp. 265-280. U. J. Sofia and E. B. Jenkins (1998): "Interstellar Medium Absorption Profile Spectrograph Observations of Interstellar Neutral Argon and the Implications for Partially Ionized Gas" Astrophysical Journal, 499, pp. 951-965. E. B. Jenkins, U. J. Sofia, and G. Sonneborn (1998): "Observations of interstellar O VI absorption at 3 km/s resolution" in The Hot Universe, K. Koyama, S. Kitamoto, and M. Itoh, (Kluwer, Dordrecht) 271-272. S. P. Sarlin (1998): “Ultraviolet studies on interstellar molecular hydrogen.” Ph.D. Dissertation, University of Colorado, Boulder. 186 p. E. B. Jenkins, T. M. Tripp, P. R. Wozniak, U. J. Sofia, and G. Sonneborn (1999): "Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. I. Observations toward δ Orionis by the Interstellar Medium Absorption Profile Spectrograph" Astrophysical Journal, 520, pp. 182-195. G. Sonneborn, E. B. Jenkins, T. Tripp, P. Wozniak, R. Ferlet, A. Vidal- Madjar, and U. J. Sofia (2000): "Spatial variations in the atomic D/H ratio in the ISM" in The Light elements and their Evolution, L. da Silva, M. Spite, and R. de Medeiros, (Astr. Soc. Pacific, San Francisco) 242-243. E. B. Jenkins, P. R. Wozniak, U. J. Sofia, G. Sonneborn, and T. M. Tripp (2000): "The Properties of Molecular Hydrogen toward the Orion Belt Stars from Observations by the Interstellar Medium Absorption Profile Spectrograph“ Astrophysical Journal, 538, pp. 275-288. G. Sonneborn, T. M. Tripp, R. Ferlet, E. B. Jenkins, U. J. Sofia, A. Vidal-Madjar, and P. R. Wozniak (2000): "Spatial Variability in the Ratio of Interstellar Atomic Deuterium to Hydrogen. II. Observations toward γ² Velorum and ζ Puppis by the Interstellar Medium Absorption Profile Spectrograph" Astrophysical Journal, 545, pp. 277-289. E. B. Jenkins, C. Gry, and O. Dupin (2000): "Electron densities, temperatures and ionization rates in two interstellar clouds in front of β Canis Majoris, as revealed by UV absorption lines observed with IMAPS“ Astronomy and Astrophysics, 354, pp. 253-260. C. Gry and E. B. Jenkins (2001): "Local clouds: Ionization, temperatures, electron densities and interfaces, from GHRS and IMAPS spectra of ε Canis Majoris" Astronomy and Astrophysics, 367, pp. 617-628. D. E. Welty, E. B. Jenkins, J. C. Raymond, C. Mallouris, and D. G. York (2002): "Intermediate- and high-velocity ionized gas toward ζ Orionis“ Astrophysical Journal, 579, pp. 304-326.
12	IMAPS Bibliography (continued) Technical or Instrumental articles: E. B. Jenkins, C. L. Joseph, D. Long, P. M. Zucchino, G. R. Carruthers, M. Bottema, and W. A. Delamere (1988): "IMAPS: a high-resolution, echelle spectrograph to record far-ultraviolet spectra of stars from sounding rockets“ in Ultraviolet Technology II R. E. Huffman, (The International Society for Optical Engineering, Bellingham) 213-229. E. B. Jenkins, C. L. Joseph, M. A. Reale, P. Zucchino, and T. B. Williams (1990): "Use of a high-density digital tape drive to improve complex spectroscopic data acquisition" Spectroscopy, 5, pp. 37-40. M. Reale (1990): “Serial transmission of digitized video over an RF link using the Advanced Micro Devices TAXI chipset” in Advanced Devices Article Reprints, 33‑. E. B. Jenkins, M. A. Reale, P. M. Zucchino, and U. J. Sofia (1996): "High resolution spectroscopy in the far uv: Observations of the interstellar medium by IMAPS on ORFEUS-SPAS" Astrophysics and Space Science, 239, pp. 315-360. E. B. Jenkins (1993): "The IMAPS instrument: A new horizon for recording the real shapes of interstellar absorption lines in the far UV" in UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas, E. H. Silver and S. M. Kahn, (Cambridge U. Press, Cambridge) 254-269. E. B. Jenkins (1995): "IMAPS Observations of Interstellar Absorption Lines between 950 and 1150 A at 2 km/s Resolution" in Laboratory and Astronomical High Resolution Spectra, A. J. Sauval, R. Blomme, and N. Grevesse, (Astronomical Society of the Pacific, San Francisco) 453-458. E. B. Jenkins, M. A. Reale, and P. M. Zucchino (1999): “Development of a photon‑counting capability for the electron‑bombarded far‑UV image sensor” in Ultraviolet and X‑Ray Detection, Spectroscopy, and Polarimetry III, S. Fineschi, B. E. Woodgate, and R. A. Kimble, (SPIE (Intl. Soc. for Optical Eng.), Bellingham) 226‑233. Analysis Methodology inspired by IMAPS results: E. B. Jenkins (1996): "A procedure for correcting the apparent optical depths of moderately saturated interstellar absorption lines" Astrophysical Journal, 471, pp. 292-301