Determining the Physical Properties ofVery-Low-Mass Stars and Brown Dwarfs in theNear-Infrared'

摘要

Accurate measurements of the fundamental physical properties of very-low-mass starsand brown dwarfs are crucial for calibrating evolutionary models. Photometry and low-resolutionspectroscopy effectively average over absorption features that sample different layers in complexcool atmospheres. By studying a large sample of objects bright enough for high-resolution spec-troscopy, we can develop methods for determining physical properties as accurately and efficientlyas possible. As part of the Brown Dwarf Spectroscopic Survey (BDSS; [1, 2]), we are conducting adetailed comparison of observed and synthetic spectra for a sample of young M and L dwarfs andfield M, L, and T dwarfs (~50 objects in total). High-resolution near-infrared spectra from NIR-SPEC on Keck II provide an unequaled combination of resolving power and wavelength coverage.Synthetic spectra were created from PHOENIX atmosphere models calculated exclusively for thisproject with updated line lists and solar abundances. Combined with spectral types from photo-metric studies and low-resolution spectra and surface gravity estimates from age determination, thehigh-resolution spectra enable precise measurements of effective temperature and surface gravity,as well as accurate determination of radial velocity and projected rotational velocity. Our prelimi-nary observation-model comparisons distinguish between wavelength regimes for which the modelsreproduce observed high-resolution spectra and regimes in which model data (line lists, oscillatorstrengths, etc.) are lacking.