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

We describe a technique for deriving effective temperatures, surfacegravities, rotation velocities, and radial velocities from high resolutionnear-IR spectra. The technique matches the observed near-IR spectra to spectrasynthesized from model atmospheres. For pre-main sequence stars, we use thesame matching process to also measure the amount of excess near-IR emission.The information derived from high resolution spectra comes from line shapes andthe relative line strengths of closely spaced lines. The values for the stellarparameters we derive are therefore independent of those derived from lowresolution spectroscopy and photometry. The new method offers the promise ofimproved accuracy in placing young stellar objects on evolutionary modeltracks. We discuss the possible systematic effects on our determination of thestellar parameters and evaluate the accuracy of the results derivable from highresolution spectra. The analysis of high resolution near-IR spectra of MKstandards shows that the technique gives very accurate values for the effectivetemperature. The biggest uncertainty in comparing our results with opticalspectral typing of MK standards is in the spectral type to effectivetemperature conversion for the standards themselves. Even including thisuncertainty, the 1 sigma difference between the optical and IR temperatures for3000-5800 K dwarfs is only 140 K. In a companion paper (Doppmann, Jaffe, &White 2003), we present an analysis of heavily extincted young stellar objectsrho Oph.Comment: Accepted for publication in the Astronomical Journal. 37 pages, 9 figure