Showing papers by "Deidre A. Hunter published in 1995"

Gas near the center of 30 Doradus as revealed by Hubble Space Telescope images

Abstract: We present images of a 40 pc region of the 30 Doradus nebula centered about 1 arcminute north of the luminous star cluster R136 in the Large Magellanic Cloud. The region was imaged with the Hubble Space Telescope (HST) Wide Field Camera through H alpha, (S II), and stellar continuum filters. These data allow us to examine this region of star formation and the breakup of the cloud around R136 on a scale of 0.027 pc per pixel. We also present a complementary ground-based echelle spectrum of the H alpha and (N II) emission lines in this region. In the images one sees an extensive filamentary structure surrounding regions that have been hollowed out by R136 and other massive stars in the area. The (S II) image shows a sharper, more filamentary appearance than the H alpha image, and the filaments are offset in (S II) generally away from R136. These characteristics are indicative of ionization fronts that are outlining the neutral material and dust features. We also find fingers of enhanced (S II) emission located about 90 sec to the northwest of R136. The (S II) fingers appear to be readiating generally from a common region, and we suggest that they are composed of material ablated from the high density gas of the ionization fronts and entrained with the flow of the stellar winds from R136. We find that a small knot of emission resolves into two shells of about 0.5 pc diameter, each of which encircles one or two stars. One of the stars has been identified as an early main-sequence O star by Walborn & Blades (1987), and the shell could be a young wind-blown bubble. We also find a parabolic-shaped arc at the head of a long cone that opens up away from R136. The arc is located near a luminous candidate protostar identified by Hyland et al. (1992).

Where Does Star Formation End in NGC1058

Abstract: As part of a large project to study the rate, distribution and history of star formation in the outer parts of galactic disks (Ferguson, PhD thesis), we have obtained very deep Ha and B-band images of the nearby face-on spiral NGC1058. Our images reveal extremely low surface brightness outer spiral arms in the B-band which extend well beyond the Holmberg radius and appear to be aligned with underlying HI spiral arms. These features contrast greatly to the flocculent appearance of the innermost regions of the disk and the complete absence of any well defined-arms in the Ha image. The surface brightness profile derived from the B-band image exhibits a sharp fall off in the inner regions of the disk followed by a much shallower decline beyond ∼ R 25 and consequently a single exponential disk cannot be fit to the entire profile.