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Evolution of HII Regions around Massive YSOs

Published online by Cambridge University Press:  21 March 2013

Ian W. Stephens
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
Leslie W. Looney
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
Remy Indebetouw
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
You-Hua Chu
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
Robert A. Gruendl
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
C.-H. Rosie Chen
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
Jonathan P. Seale
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
Jessica Marie Evans
Affiliation:
Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA; email: stephen6@illinois.edu
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Abstract

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We survey HII free-free emission around ∼60 spectroscopically confirmed young stellar objects (YSOs) in the Large Magellanic Cloud using the Australia Telescope Compact Array (ATCA) at 3.3 and 5.5 cm. From each YSOs' infrared spectrum, we: a) quantify how embedded/evolved the YSO is through principle component analysis (PCA) of the silicate absorption (Seale et al. 2009); and b) estimate the mass from SED models (Robitaille et al. 2007). We have four main results: (1) Based on mass estimates from SED models and ATCA detection limits, we find that most massive YSOs are in HII regions regardless of age; (2) Older massive YSOs (as indicated by silicate PCA index) are much more likely to be resolved than younger YSOs, indicating evolving HII regions; (3) Resolved (typically older) sources usually have lower densities. Thus, in our survey we see a transition from ultra-compact HII to HII regions; and (4) We find that accretion about the massive YSO is likely non-spherical, resulting in HII regions in the shape of prolate spheroids.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2013

References

Robitaille, T. P., Whitney, B. A., Indebetouw, R., & Wood, K. 2007, ApJS, 169, 328Google Scholar
Seale, J. P., Looney, L. W., Chu, Y.-H., et al. 2009, ApJ, 699, 150CrossRefGoogle Scholar