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Session 106 - HII Regions and Ultracompact HII Regions.
Display session, Thursday, January 16
Metropolitan Ballroom,

[106.06] Direct Observations of the Ionizing Star of the UC HII Region G29.96-0.02: A Strong Constraint on the Stellar Birth Line for Massive Stars

A. M. Watson (NMSU), A. L. Coil (Princeton U.), D. S. Shepherd (Caltech), P. Hofner (NAIC), E. B. Churchwell (U. Wisconsin - Madison)

We have observed the ultracompact HII region G29.96-0.02 in the near infrared J, H, and K bands and in the Br\gamma line. By comparison with radio observations, we are able to determine that the extinction to the nebula is A_K \approx 2.3. We identify the ionizing star and determine its intrinsic K magnitude. The star does not have an infrared excess and so appears to be no longer accreting. The K magnitude and the bolometric luminosity allow us to place limits on the location of the ionizing star in the HR diagram. These limits exclude stars on the ZAMS and stars within 10^6yr of the ZAMS. Since the age of the UC HII region is estimated to be only about 10^5yr, we suggest that this is direct evidence that the stellar birth line for massive stars must be significantly redder than the ZAMS.

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Program listing for Thursday