SPECTROSCOPY OF MOLECULAR HYDROGEN EMISSION FROM KH 15D

摘要

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 (λ/δλ ～ 1000) reveal the presence of prominent molecular hydrogen emission in five lines near 2 μm. The relative line strengths are consistent with thermal excitation at T ～ 2800 +- 300 K. Observations out of eclipse, at both low and high spectral resolution (λ/δλ ～ 2 x 10~4), show reduced contrast with the stellar continuum. The change in contrast for the strongest 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 approx> 4″ both east and west of the stellar point-spread function (PSF; approx> 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~(-1)) and has significantly greater intensity than the marginally redshifted component (+ 2 km s~(-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.