A Spectroscopic Technique for Measuring Stellar Properties of Pre–Main Sequence Stars

We describe a technique for deriving effective temperatures, surface gravities, rotation velocities, and radial velocities from high resolution near–IR spectra. The technique matches the observed near–IR spectra to spectra synthesized from model atmospheres. Our analysis is geared toward characterizing heavily reddened pre–main sequence stars but the technique also has potential applications in characterizing main sequence and post–main sequence stars when these lie behind thick clouds of interstellar dust. For the pre–main sequence stars, we use the same matching process to measure the amount of excess near–IR emission (which may arise in the protostellar disks) in addition to the other stellar parameters. The information derived from high resolution spectra comes from line shapes and the relative line strengths of closely spaced lines. The values for the stellar parameters we derive are therefore independent of those derived from low resolution spectroscopy and photometry. The new method offers the promise of improved accuracy in placing young stellar objects on evolutionary model tracks. Tests with an artificial noisy spectrum with typical stellar parameters, and signal–to–noise of 50 indicates a 1σ error of 100 K in Teff , 2 km s −1 in v sin i, and 0.13 in continuum veiling for an input veiling of 1. If the line flux ratio between the sum of the Na, Sc, and Si lines at 2.2 μm and the (2–0) CO NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035-1000 Department of Astronomy, 1 University Station C1400, Austin, TX 78712-1083 Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.