Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...506..727b&link_type=abstract
The Astrophysical Journal, Volume 506, Issue 2, pp. 727-742.
Astronomy and Astrophysics
Astronomy
17
Ism: H Ii Regions, Infrared: Ism: Lines And Bands, Infrared: Stars, Ism: Individual (Ngc 7538), Open Clusters And Associations: Individual (Ngc 7538), Stars: Formation
Scientific paper
We present images of the cluster of embedded young stars designated NGC 7538 IRS 1, 2, and 3 in the J (1.25 μm), H (1.64 μm), and K (2.16 μm) broad bands; the 1.64 μm line of [Fe II]; the 2.12 μm and 2.25 μm lines of H_2; the 2.17 μm Brackett gamma H-recombination line; and the 3.29 μm ``unidentified'' dust feature. The NGC 7538 IRS 2 compact H II region, as seen in Brackett gamma line emission, possesses a cometary morphology. We find evidence for a shell-like distribution of [Fe II] line emission along the periphery of the compact H II region. This morphology and the observed intensity ratio I([Fe II] 1.64 μm)/I(Brgamma) imply that the [Fe II] line emission emanates from shocked stellar wind material. We observe arcs of H_2 line emission immediately exterior to the [Fe II] line emission shell and suggest that these arcs delineate molecular cloud material shocked via collision with the stellar wind. We observe larger arcs with centers of curvature displaced from each other and IRS 2, in broad-band-continuum, H_2-line, and 3.29 μm feature emission, and suggest that these arcs represent molecular gas (either shocked or UV-excited) and dust swept up during distinct episodes of stellar mass ejection. We submit that the morphological and energetic evidence favors a ``stellar wind bow shock'' interpretation, in which the motion of the central O star with respect to the surrounding molecular cloud, in conjunction with the star's high-velocity stellar wind and episodic mass ejection, gives rise to the observed general cometary morphology and circum-H II region emission.
Ali Babar
Bloomer John D.
Fischer Jacqueline
Forrest William John
Greenhouse Matthew A.
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