Astro/Professional 
Astro/Professional I'm a postdoctoral researcher in astrophysics at Princeton University in Princeton, NJ.
I received my PhD in astronomy at Columbia University in New York City.
I majored in math as an undergraduate at Amherst College in Amherst, MA.
I grew up in Brookline, MA, and attended Brookline High School and before that the Edward Devotion School -- not a Catholic school, despite the name.
I became intersted in astronomy because of my interest in astrobiology -- the search for life in space. Since we are likeliest to find extraterrestrial life (if indeed we find it) on a planet, I became interested in planetary science, both within and outside of our Solar System. Below is a selection of the research projects on which I have worked in recent years.
I have revisited the habitability of terrestrial planets around sun-like stars.
(1) By using a 1-dimensional energy balance climate model, based on the one presented in a paper by Williams & Kasting (1997), I have considered regional habitability, the fact that portions of a planet may be habitable while other parts are not, and portions of a planet may be habitable for parts of the year and not during other parts.
(2) By varying planetary dynamical conditions to be different from those on Earth, I have started to explore how regional habitability depends on star-planet distance for planets that are very different from the Earth.
Results of initial investigations are presented in "Habitable Climates" and "Habitable Climates: The Influence of Obliquity", both collaborations with Kristen Menou and Caleb Scharf.
There is good reason to believe that hot Jupiters are tidally locked to their stars, with one side in permanent day and the other side in permanent night -- but this prediction has not been observationally tested. Instead, a planet could be trapped in a Cassini state, with obliquity nearly 90 degrees (Winn & Holman 2005).
If a hot Jupiter transits along the line of sight between Earth and its parent star, its transit spectrum bears the Doppler signature of its atmospheric motion with respect to its star. I developed a detailed model of the time-dependent transit spectrum of a transiting gas giant planet, in order to test whether such a signature would be legible against the noise imposed by star-light and by systematics. I found that a planet that is rotating at the tidally locked rate would have a transit spectrum whose absorption features (arising from the planet's atmosphere) would be Doppler-shifted during ingress and egress by ~100 cm/s relative to where they would be for a non-rotating planet, and these shifts might be discernable (for nearby systems) by accumulating the signal over many transits.
In collaboration with Zoltan Haiman and Scott Gaudi I analyzed the feasibility of performing this analysis: "On Constraining a Transiting Exoplanet's Rotation Rate with Its Transit Spectrum".
In October of 2006, an otherwise unremarkable A0 star at a distance of ~1 kpc (GSC 3656-1328) brightened achromatically by a factor of nearly 40 over the span of several days and then decayed in an apparently symmetrical way.
I reported both the preliminary results of a world-wide amateur effort to monitor the event, and Swift X-ray observations that failed to detect the star: "VAR CAS 2006, A Nearby Microlens?".
The light curve was well-fit by a gravitational microlensing model, and is difficult to explain in any other way. This, therefore, was almost certainly the closest gravitational microlensing event ever observed. Scott Gaudi and Joe Patterson took the lead on the paper, to which I contributed, that presents the full multi-wavelength light curves and analysis of the event: "Discovery of a Very Bright, Nearby Gravitational Microlensing Event".
A large fraction of the baryonic matter in the local universe might be hiding in the intragroup medium of galaxy groups. The Canadian Network for Observational Cosmology (CNOC2) performed a deep redshift survey, identifying likely galaxy groups at intermediate redshift -- 0.1 < z < 0.6 -- (Carlberg et al. 2001). Since there was a statistical gravitational lensing signal associated with the putative groups, there is good reason to think that these are real, gravitationally bound objects, not chance alignments of galaxies (Hoekstra et al. 2001).
With Frits Paerels and Caleb Scharf, I analyzed 100 ksec of XMM-Newton observations of one of the CNOC2 fields. I found no association between the X-ray photons received and the locations of the groups, even though it is likely that, if the groups are representative of a population with same luminosity distribution as groups at redshift ~0, several of them would have been visible in the X-ray observation. The detailed analysis is described in our paper: "A Possible Dearth of Hot Gas in Galaxy Groups at Intermediate Redshift".
If a giant planet in the source plane of a gravitational microlensing event crosses the fold-caustic of a foreground binary lens, the planet-star brightness ratio might be greatly enhanced. In a favorable situation, this could allow for a crude optical spectrum of the planet, yielding information about the planet's composition. By modeling observations of such a scenario, I found that if a planet's caustic-crossing were monitored by large telescopes equipped with filters tuned specifically to molecular absorption bands of, for example, methane, it would be possible to determine whether there are significant quantities of that molecule in the planet's atmosphere. For instance, a Jupiter could be distinguished from a methane-free Jupiter. Details are in the paper I wrote in collaboration with Michel Zamojski, Zoltan Haiman, Alan Gersch, and Jen Donovan: "Can We Probe the Atmospheric Composition of an Extrasolar Planet from Its Reflection Spectrum in a High-Magnification Microlensing Event?".
1. I obtained and analyzed a Swift X-ray observation of the recent outburst from Comet Holmes (2007). This observation showed no evidence of X-rays from the event.
2. I have considered in detail the feasibility of detecting redshifted X-ray absorption features from a filament of warm-hot intergalactic medium (WHIM). There have been no unambiguous detections of such filaments yet (Rasmussen et al. 2007). With collaborators, I have found that it is unlikely that realisitcally long observations, with existing X-ray observatories, will allow for a solid detection of X-ray-absorbing WHIM, neither by monitoring nearby, brightly flaring QSOs, nor more distant QSOs.