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

Abstract

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. For pre-main sequence stars, we use the same matching process to also measure the amount of excess near-IR emission. 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. We discuss the possible systematic effects on our determination of the stellar parameters and evaluate the accuracy of the results derivable from high resolution spectra. The analysis of high resolution near-IR spectra of MK standards shows that the technique gives very accurate values for the effective temperature. The biggest uncertainty in comparing our results with optical spectral typing of MK standards is in the spectral type to effective temperature conversion for the standards themselves. Even including this uncertainty, the 1 sigma difference between the optical and IR temperatures for 3000-5800 K dwarfs is only 140 K. In a companion paper (Doppmann, Jaffe, & White 2003), we present an analysis of heavily extincted young stellar objects rho Oph.