Near-IR Spectroscopy and the Photospheres of Embedded YSOs

Abstract

We present a study of weak near-IR absorption lines in 44 low luminosity YSOs. Using a spectral resolution of ~ 1000 most Class II sources show CO overtone absorption bands of varying strength in the K window, whether they have optical counterparts or not. Class I sources tend to show featureless 2 μm continua even though a S/N > 100 was achieved. High resolution (R=17000) echelle spectra were also obtained for a sub-sample of YSOs. Most show an unresolved ¹²CO(2–0) bandhead, which when combined with inferred CO excitation temperatures and optical depths clearly points to a photospheric rather than a disk origin for the bands. They also show that embedded Class Its are not rapidly rotating.