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| EPoS Contribution |
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A survey of Massive Star Formation in the LMC
Leslie Looney University of Illinois, Urbana, USA | |
| We present the results of our survey of 277 young massive protostars in the LMC, an excellent laboratory for understanding massive star formation. Many of the problems of Galactic observations are mitigated in the LMC given its high level of star formation activity, low foreground extinction, and known distance. By using Spitzer spectroscopic observations (5-38 micron), which show a variety of spectral features including absorption from silicates and ices and emission lines from PAHs and ionized atoms, we classify the sources into groups based on a principal component analysis. These groups are consistent with a rough evolutionary sequence. The majority of sources are dominated by PAH emission and/or fine structure lines, suggesting that massive YSOs spend a significant portion of their formation time radiating in the UV. In addition, we detect the CO2 ice feature at 15.2 micron for 41 objects. Although ice absorption features are mostly common among the youngest, most embedded sources, we still detect ice in the spectra of more evolved sources, suggesting that compact HII regions and photodissociation regions form very early in YSO evolution before the star can significantly warm or dissipate its circumstellar envelope. We show that the ices in the circumstellar envelopes are warmed/thermally processed and chemically different from ices observed towards quiescent, cold clouds, as well as different from low-mass protostars. In fact, the amount of processed ice is proportional to luminosity. Finally, we use ATCA observations of HCN and HCO+ toward the star forming region N44 to probe the compact dense gas toward 6 of our sources. All of the massive YSOs are associated with dense clumps of gas with sizes of 2-5 pc. The dense clumps represent the remnants of the prestellar molecular cores from which the stars formed. We see a difference in the gas distribution between the less evolved sources and the more evolved sources - older YSOs tend to be offset from the molecular clump peaks. Furthermore, clumps of the less-evolved sources tend to be more spherical in shape. These differences are likely indicators that massive YSOs disperse the dense gas soon after their most embedded phase. | |
| Collaborators: J.P. Seale, University of Illinois, USA |
Key publication
Suggested Session: Massive Stars |