Near-infrared spectrophotometry of HH 7-11

被引:20
作者
Everett, ME
机构
[1] Department of Astronomy, Ohio State University, Columbus, OH 43210-1106
关键词
infrared; ISM; lines and bands; individual; (HH; 7-11); jets and outflows; shock waves; stars; formation;
D O I
10.1086/303792
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Near-infrared emission-line imaging and long-slit spectroscopy of H-2 and [Fe II] emission lines in the 1.25-2.25 mu m wavelength range at multiple positions toward the Herbig-Haro objects HH 7-11 and a nearby H-2 emission-line source, ASR 57, are presented. The relative line strengths are used to examine the processes responsible for exciting H-2 emission in these objects. All of the H-2 emission-line ratios are consistent with collisional excitation in these objects, and no evidence is seen for noncollisional excitation mechanisms. Nonetheless, the H-2 level populations in HH 7-11 are inconsistent with LTE predictions and show underpopulations relative to a Boltzmann distribution in accordance with the different critical densities of each level. The level populations are consistent with either a purely molecular gas or gas containing a mixture of H and H-2, provided that the gas has a range of temperatures and relatively law density. The slit positions toward HH 7-11 sample a wide range of H-2 surface brightness and relative brightness of [Fe II] versus H-2 emission lines. The H-2 emission from HH 7 is assumed to originate in a bow shock with decreasing shock velocity from the bow shock apex to the wings. Spectra are taken across HH 7 using a series of slit positions in order to observe any changes in the spectra with velocity. The slit positions are chosen to include a wide range in shock conditions among the spectra; however, the H-2 line ratios are similar at all of the observed positions, a result interpreted as evidence that the emission originates behind J-shocks.
引用
收藏
页码:246 / 260
页数:15
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