Other
Scientific paper
Aug 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt........10g&link_type=abstract
Thesis (PhD). THE UNIVERSITY OF ROCHESTER, Source DAI-B 61/02, p. 891, Aug 2000, 191 pages.
Other
2
Scientific paper
We have undertaken a complete near-infrared study of three massive star forming regions to better understand how clusters of pre-main sequence stars and young stars of various ages interact with each other and with their environment. In our study, we attempt to determine the age of each region. The primary mode of interaction for the youngest cluster of massive objects (<<10 5 yr) appears to be via jets; jets from the environs of these forming stars encounter dense molecular material and create observable shock- excited gas. Massive stars in more evolved clusters (~105-10 6 yr) interact through photoionization of the gas. The expansion of those HII regions provides additional interaction. Further star formation is stimulated in their wake. In our youngest region Cep A East, which contains a small core cluster of pre-main sequence objects, we analyze emission shock-excited by jets emanating from young stellar objects to determine which cluster members are responsible for the excitation of the region. A crucial element of this analysis is the mapping of local extinction throughout the region, utilizing several distinct methods. Association with a more evolved stellar cluster is expected; however, the cluster members are most likely obscured by high levels of extinction. S88B, our oldest region, consists of a small cluster of already formed massive young stars, identified by radio continuum emission from their HII regions; at least one massive protostar; and a more evolved cluster of main sequence, giant and supergiant stars. We analyze hydrogen recombination line emission to map the extinction to the HII regions and we will argue that the HII region we have studied in the infrared is not a separate entity but is rather a diffuse extension of one of the compact radio HII regions. Our J-, H-, and K-band study of the more evolved stellar population enables us to identify potential young stellar objects and to estimate the age of the cluster through comparison with main sequence, giant, and supergiant infrared colors and evolutionary isochrones. The S235A/B region appears as two HII regions powered by massive stars or pre-main sequence stars, identified by infrared hydrogen recombination line emission, and at least one massive young stellar object, in addition to a more evolved cluster of stars. We will argue that one HII region is photoionized, and the other is caused by a circumstellar wind. Again, analysis of the evolved cluster allows us to estimate the age of the cluster and identify potential pre-main sequence stars.
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