Spectroscopy of Molecular Hydrogen Emission from Kh 15d

We report infrared spectroscopy of the unusual eclipsing pre–main-sequence object KH 15D, obtained using NIRSPEC on Keck II. During eclipse, observations using low spectral resolution ( ) reveal the presence l/dl ∼ 1000 of prominent molecular hydrogen emission in five lines near 2 mm. The relative line strengths are consistent with thermal excitation at K. Observations out of eclipse, at both low and high spectral resolution T ∼ 2800 300 ( ), show reduced contrast with the stellar continuum. The change in contrast for the strongest 4 l/dl ∼ 2 # 10 line, 1–0 S(1), is consistent with an approximately constant emission line superposed on a variable stellar continuum. Emission in the 1–0 S(1) line is observed to extend by 4 both east and west of the stellar pointspread function (PSF; 3000 AU). Observed at high spectral resolution, the velocity and the intensity structure of the 1–0 S(1) profile are both asymmetric. East of the stellar PSF (by 1 .1–2 .3) the emission is blueshifted ( 63 km s ) and has significantly greater intensity than the marginally redshifted component ( 2 km s , 1 1 approximately consistent with zero) that dominates west of the stellar PSF. The spatial extent of the emission and the excitation temperature suggest shock excitation of ambient gas by a bipolar outflow from the star and/ or the disk. However, it is difficult to account for the observed radial velocity unless the outflow axis is inclined significantly to the plane of the sky. Subject headings: planetary systems: formation — planetary systems: protoplanetary disks — stars: pre–main-sequence