Stellar Properties of Pre – Main Sequence Stars from High Resolution Near – IR Spectra

We present high resolution (R=50,000) spectra at 2.2 µm of 16 young stars in the ρ Ophiuchi dark cloud. Photospheric features are detected in the spectra of 11 of these sources, all Class II young stellar objects. The 5 featureless spectra consist of 2 Class I, 2 Class I.5, & 1 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 12 CO and H 2 CO gas velocities and further confirm the membership of the sources in the ρ Ophiuchi 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 comparing to spectral synthesis models at 2.2 µm. We measure surface gravities in 2 stars from the integrated line flux ratio of the 12 CO line region at 2.3 µm and the Na I line region at 2.2 µm. Although the majority (8/10) of the Class II stars have similar effective temperatures (3530 K ± 100 K), they exhibit a large spread in bolometric luminosities (factor ∼8), as derived from near–IR photometry. In the two stars where we have surface – 2 – gravity measurements from spectroscopy, the photometrically derived luminosi-ties 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 non-photospheric 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 is suggested by photometry at J or K. Most of our sources show a larger amount of continuum excess (F Kex) than stellar flux at 2.2 µm (F K *), substantially higher in many cases (r K ≡ F Kex /F K * = 0.3–4.5). The derived veiling values at K (r K) appear correlated with mid–IR disk luminosity, and with Brackett γ 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 …