E m i l y    L.    R i c e

The goal of my thesis project is to better understand the physical properties of brown dwarf atmospheres and the deficiencies in atmosphere models by comparing observed and synthetic high-resolution, near-infrared spectra.

The observed spectra are obtained with NIRSPEC, the high-resolution, near-infrared echelle spectrometer on the Keck II telescope on Mauna Kea, Hawai'i as part of the Brown Dwarf Spectroscopic Survey.   The target sample covers a range of spectral types (corresponding to effective temperature) and age (corresponding to surface gravity), in order to explore a range of input parameters for the model atmospheres. These observations are part of the BDSS Atmospheres Project, to which I have contributed observations of young low-mass stars and brown dwarfs from near-by star-forming regions and moving groups.

The synthetic spectra are calculated from temperature-pressure structures created using the PHOENIX model atmosphere code in collaboration with Travis Barman.   Both the structures and the spectra are calculated specifically for this project in order to achieve higher resolution in effective temperature, surface gravity, and wavelength than are publicly available.

The robust statistical comparison of these two datasets is key to achieving the goals of this project.   I am currently focusing my efforts on implementing and testing least-squares minimization code and Monte Carlo modeling to determine the best-fit model parameters and uncertainties for a subset of the observational sample.

For my Master's thesis I characterized a young stellar association in the Aquila star-forming region.   Using high-resolution near-infrared spectra obtained primarily by Lisa Prato with NIRSPEC on Keck II, I measured spectral type, radial velocity variability, absolute radial velocity, and projected rotational velocity for seven Hα-emitting objects, around and including AS 353, the exciting source of Herbig-Haro object HH 32.

Results from this project have been published in the Astrophysical Journal (Rice et al. 2006) and the forthcoming Handbook of Star Forming Regions.   Follow-up work to identify additional young stars in this star-forming region, to fully characterize the multiplicity of known objects, and to understand the unusual emission-line source HBC 684.

I am collaborating with my classmate Quinn Konopacky, who is measuring dynamical masses of very-low-mass stars and brown dwarfs using astrometric monitoring made possible with Laser Guide Star Adaptive Optics. Quinn is using NIRSPEC with LGSAO to obtain spatially resolved high-resolution K-band spectra of binaries in her sample in order to measure relative radial velocities and determine individual masses (relative astrometric measurements only provide total mass of the binary systems). My contribution to the project is to use these resolved spectra and synthetic spectra from PHOENIX model atmospheres to obtain high-precision measurements of effective temperature for these objects, which enables meaningful comparison of the dynamical masses to masses predicted by evolutionary models.