Near-Infrared Spectrophotometry of HH 7-11

Details Near-Infrared Spectrophotometry of HH 7-11 Near-Infrared Spectrophotometry of HH 7-11

Mar 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997apj...478..246e&link_type=abstract

Astrophysical Journal v.478, p.246

Astronomy and Astrophysics

Astronomy

22

Infrared: Ism: Lines And Bands, Ism: Individual Alphanumeric: Hh 7-11, Ism: Jets And Outflows, Shock Waves, Stars: Formation

Scientific paper

Near-infrared emission-line imaging and long-slit spectroscopy of H2 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 H2 emission-line source, ASR 57, are presented. The relative line strengths are used to examine the processes responsible for exciting H2 emission in these objects. All of the H2 emission-line ratios are consistent with collisional excitation in these objects, and no evidence is seen for noncollisional excitation mechanisms. Nonetheless, the H2 level populations in HH 7--11 are inconsistent with LTE predictions and show under-populations 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 H2, provided that the gas has a range of temperatures and relatively low density. The slit positions toward HH 7--11 sample a wide range of H2 surface brightness and relative brightness of [Fe II] versus H2 emission lines. The H2 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 H2 line ratios are similar at all of the observed positions, a result interpreted as evidence that the emission originates behind J-shocks.

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