Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........31c&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF TEXAS AT AUSTIN, 1995.Source: Dissertation Abstracts International, Volume: 57-02, Section: B,
Computer Science
Scientific paper
Using the interstellar and circumstellar dust as a density probe in infrared sources, I have investigated the morphology and internal structure of five galactic star-forming regions: DR 21, G333.6-0.2, Cepheus A, IRAS 05380-0728 and S140. Previous observational work indicates that these sources are sites of massive star formation. Although there is no fully-developed theory for the case of high-mass star formation, we expect that high -mass stars form within the same paradigm as low-mass stars. Via high-angular resolution photometry at far-infrared wave -lengths, I investigated the distribution of the dust associated with the molecular cloud cores from which massive stars have formed. For three of the objects near-infrared polarimetry was also obtained. I participated in the development and construction of a near-infrared camera and adapted a polarimeter to it. In all cases, large values of the near-infrared polarization indicate that scattering is the dominant mechanism for producing the polarization of light. The dust density distributions derived from the modeling of the far-infrared data and near-infrared polarimetry are compared to those predicted by theories for low-mass stars. In the case of Cepheus A, the deduced density distribution is in good agreement with current star formation models. In general however, the density gradients in these high-mass star-forming regions are shallower than those predicted theoretically. A second general trend is found, namely that large inner cavities of dust depletion or very low dust densities in the envelopes of these objects are required in order to reproduce the observations. The observations cannot distinguish between two possible causes for this, namely that indeed, high-mass stars form in molecular cores with relative dust depletion, or that the cavities and the shallow dust density gradients are the result of the interaction of outflows with the parental dust clouds. The latter might be more consistent with some marginal evidence in these objects. No relation is found between the degree of collimation of the outflows associated with these five sources and the steepness of the density gradient of their infalling envelopes. This result suggests that, at least in these five star-forming regions, the outflows are intrinsically collimated (e.g. disks or tori) rather than extrinsically. In addition, for DR 21 and two sources within S140, the data are best interpreted as indirect evidence of the presence of dense and compact dusty structures in the vicinity of these young massive stars, perhaps disks or tori.
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