AAS 205th Meeting, 9-13 January 2005
Session 105 Triggered Star Formation and the Orion Protostellar Population
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[105.02] HST WFPC2 Imaging of the G353.2+0.9 HII region in NGC~6357

K. R. Healy, J. J. Hester, P. A. Scowen, K. D. Snider (Arizona State University)

We present HST WFPC2 images of the H~II region G353.2+0.9 in NGC~6357. This H~II region is excited by a rich stellar cluster, Pismis 24, which contains half a dozen late O stars and two of the hottest and most luminous stars in the Galaxy, Pis 24-1 (O3.5If*) and Pis 24-17 (O3.5III(f*)). The combined ionizing flux of these stars has formed an intense photoionized photoevaporative flow from the dense molecular cloud that lies only 1 parsec to the north. Just south of the photoevaporative interface is a region of extreme [O~III] brightness. From a comparison of the F502N image to the F656N image, we find evidence that this [O~III] emission arises from an interaction between the photoevaporative flow from the molecular cloud and the winds from the cluster O stars. The new WFPC2 images show that the previously known elephant trunk terminates in a sharp point that is tipped by a young star. We have also identified several EGGs in silhouette against the nebular emission like those seen in M16. In addition, we have identified an EGG bright in H\alpha and [S~II] that lies less than 0.5 pc from the brightest O stars. Comparing the optical images with 2MASS data shows that G353.2+0.9 contains a very high concentration of stars with infrared excesses.

This work is supported by STScI General Observer Program GO-09091.

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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.