Allison Widhalm Research/Teaching Assistant Entered: 2006 Office: 101 Astronomy Phone: (575)646-4438 Fax: (575)646-1602   E-mail: widhalm (append "@nmsu.edu")
M.S. New Mexico State University, 2008 B.S. University of Southern California, 2005

Research

For four months of the 2005-2006 year, I was an Research Experience for Undergraduates (REU) student researcher at the Cerro-Tololo Inter-American Observatory, in Chile. I worked on longterm monitoring of NGC 2141 as part of the WIYN Open Cluster Study with Dr. Stella Kafka.

I've worked previously with Dr. Donald Hoard (Pomona College) on mining the Two Micron All Sky Survey (2MASS) and Spitzer Space Telescope data for binary systems containing infrared white dwarfs and then finding optical counterparts. The primary goal of the program is to study the group properties of infrared samples of white dwarfs, but we are also finding a serendipitous set of objects with previously unknown, low mass companions. I've observed at Palomar Observatory as part of this project, and also spent a week working with the GoldCam spectrometer on the 2.1-meter telescope at Kitt Peak National Observatory.

I have searched the Sloan Digital Sky Survey (SDSS) for transient and variable objects, including asteroids, variable stars, supernovae, gamma-ray burst afterglows, and quasars, to characterize their properties on various timescales. This work was done in collaboration with Dr. Masao Sako, of Stanford University, and resulted in a SLAC publication on the overall variability of the sky background.

In my sophomore year, I completed an REU project in the molecular physics lab of Dr. Tom Slanger and Dr. Dave Huestis (of SRI International), calculating orbital distributions of molecular spectra. We applied our results to study nightglow in the Earth's upper atmosphere via several forbidden transitions of O₂.

I began my graduate studies in Fall 2006, and am working with Dr. Chris Churchill in the Extragalactic research group. I am currently interested in large-scale optical surveys in the time domain, the phenomenology of gamma-ray burst afterglows, and interstellar materials, to name but a few topics.

My current project involves studying the dynamics of gas within the Milky Way, to better understand its evolution. Key components include a hot corona, built of highly ionized, diffuse layers of gas, tidal streams of material stripped from the Magellanic Cloud satellite galaxies, and high velocity clouds, possible remnants of galactic formation. The combination forms a complex system, covering a wide range of ionization states and densities. How can we observe and study this gas? There are a hundred sight-lines to ultra-luminous deep space quasars distributed across the sky, and their spectra are uniquely suited to illuminate the distribution of gas within the Milky Way halo. As chemical ions within the gas absorb light emitted from the distant quasars, they leave a characteristic pattern of absorption features at key wavelengths within the quasar spectra.

With Dr. Churchill and theorist Dr. Anatoly Klypin, I plan to study the formation and evolution of galaxies like the Milky Way in a CDM universe. We will utilize high-resolution cosmological simulations to resolve structure on sub-kiloparsec scales, critical to determining the formation of galactic disks. The physical processes implemented in the code include radiative cooling, star formation, metal enrichment and thermal feedback due to type II and type Ia supernovae.

We will replicate observational data sets with these theoretical simulations of the Milky Way. We can then trace quasar sight lines through the modeled Milky Way disk in all directions, generating model spectra to compare statistically to quantitative results from the Hubble Space Telescope Quasar Absorption Line (QAL) Key Project (Savage 1993, AJ, 413, 116) and Goddard High Resolution Spectrograph observations (Savage 1997, AJ, 113, 6). We should thus be able to directly compare the covering factors, scale heights, and kinematic, chemical, and ionization conditions of Civ, Nv, and Ovi, and the redistributions of these metals in the halo of the Milky Way to observationally measured quantities. We will also constrain the underlying temperatures, density, and ionization structure of gas in the halo.

I am pleased to acknowledge support from a Consortium for Higher Education HED Fellowship for women in the sciences. This research is supported by a grant from the New Mexico Space Grant Consortium (NMSGC).

Publications

Cool Companions to White Dwarf Stars from the Two Micron All Sky Survey All Sky Data Release,
Hoard, D. W.; Wachter, S.; Sturch, Laura K.; Widhalm, Allison M.; Weiler, Kevin P.; Pretorius, Magaretha L.; Wellhouse, Joseph W.; Gibiansky, Maxsim; Astronomical Journal, 2007

WIYN Open Cluster Study: Long Period Variables in NGC 2141,
A. Widhalm & S. Kafka 2006

A Search for Variable Sources in the Sloan Digital Sky Survey,
A. Widhalm & M. Sako 2004, SLAC-TN-04-072, September 2004

Nightglow Vibrational Distributions in the A³Σ⁺_u and A'³Δ _u States of O₂ Derived from Astronomical Sky Spectra,
T. G. Slanger, P. C. Cosby, D. L. Huestis, & A. M. Widhalm 2004, Annales Geophysicae, 22, 3305

Meetings

January 2008: American Astronomical Society meeting:

• The Evolution of the Gaseous Halo of the Milky Way Galaxy as a Probe for Galaxy Evolution: Comparing Simulations with Observations
  Widhalm, Allison M.; Churchill, C.; Ceverino, D.; Klypin, A.