A Near‐Infrared Study of NGC 7538 IRS 1, 2, and 3

Abstract

?????We present images of the cluster of embedded young stars designated NGC 7538 IRS 1, 2, and 3 in the J (1.25 ?m), H (1.64 ?m), and K (2.16 ?m) broad bands; the 1.64 ?m line of [Fe II]; the 2.12 ?m and 2.25 ?m lines of H2; the 2.17 ?m Brackett ? H-recombination line; and the 3.29 ?m unidentified dust feature. The NGC 7538 IRS 2 compact H II region, as seen in Brackett ? 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 ?m)/I(Br?) imply that the [Fe II] line emission emanates from shocked stellar wind material. We observe arcs of H2 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, H2-line, and 3.29 ?m 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.