Stellar Properties of Pre-Main-Sequence Stars from High-Resolution Near-Infrared Spectra

Abstract

We present high-resolution (R = 50,000) spectra at 2.2 ?m of 16 young stars in the ??Ophiuchi dark cloud. Photospheric features are detected in the spectra of 11 of these sources, all Class II young stellar objects. The five featureless spectra consist of two Class I, two Class I.5, and one Class II. One star, GSS 29, is identified as a spectroscopic binary based on radial velocity variations. The radial velocities for the remaining sample are consistent with 12CO and H2CO gas velocities and further confirm the membership of the sources in the ??Oph cluster. For the 10 spectroscopically single Class II sources, we measure effective temperatures, continuum veiling, and v sin i rotation from the shapes and strengths of atomic photospheric lines by comparison with spectral synthesis models at 2.2 ?m. We measure surface gravities in two stars from the integrated line flux ratio of the 12CO line region at 2.3 ?m and the Na I line region at 2.2 ?m. Although the majority (8/10) of the Class II stars have similar effective temperatures (3530 ? 100 K), they exhibit a large spread in bolometric luminosities (a factor of ~8), as derived from near-IR photometry. In the two stars for which we have surface gravity measurements from spectroscopy, the photometrically derived luminosities are systematically higher than the spectroscopic luminosities. The spread in the photometrically derived luminosities in our other sources suggests either a large spread in stellar ages or nonphotospheric emission in the J band since anomalous and significant veiling at J has been observed in other T Tauri stars. Our spectroscopic luminosities result in older ages on the Hertzsprung-Russell diagram than are suggested by photometry at J or K. Most of our sources show a larger amount of continuum excess (FK ex) than stellar flux at 2.2 ?m (FK*), substantially higher in many cases (rK ? FK ex/FK* = 0.3?4.5). The derived veiling values at K (rK) appear correlated with mid-IR disk luminosity and with Brackett ? equivalent width, corrected for veiling. The derived v sin i rotation is substantial (12?39 km s-1), but systematically less than the rotation measured in Class I.5 (flat) and Class I sources from other studies in Ophiuchus. In four stars (Class I and I.5 sources), the absence of any photospheric lines is likely due to large continuum excess and/or rapid rotation if the stars have late-type photospheres.