A near-infrared study of NGC 7538 IRS 1, 2, and 3

We present images of the cluster of embedded young stars designated NGC 753 8 IRS 1, 2, and 3 in the J (1.25 mu m), H (1.64 mu m), and K (2.16 mu m) br oad bands; the 1.64 mu m line of [Fe II]; the 2.12 mu m and 2.25 mu m lines of H-2; the 2.17 mu m Brackett gamma H-recombination line; and the 3.29 mu m "unidentifed" dust feature. The NGC 7538 IRS 2 compact H II region, as s een in Brackett gamma line emission, possesses a cometary morphology. We fi nd evidence for a shell-like distribution of [Fe II] line emission along th e periphery of the compact H II region. This morphology and the observed in tensity ratio [Fe II] 1.64 mu m)I(Br gamma) imply that the [Fe II] line emi ssion emanates from shocked stellar wind material. We observe arcs of H, li ne emission immediately exterior to the [Fe II] line emission shell and sug gest that these arcs delineate molecular cloud material shocked via collisi on with the stellar wind. We observe larger area with centers of curvature displaced from each other and IRS 2, in broad-band-continuum, H-2-line, and 3.29 mu m feature emission, and suggest that these arcs represent molecula r gas (either shocked or UV-excited) and dust swept up during distinct epis odes of stellar mass ejection. We submit that the morphological and energet ic evidence favors a "stellar wind bow shock" interpretation, in which the motion of the central O star with respect to the surrounding molecular clou d, in conjunction with the star's high-velocity stellar wind and episodic m ass ejection, gives rise to the observed general cometary morphology and ci rcum-H II region emission.