Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt........11s&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF WISCONSIN - MADISON, 1996.Source: Dissertation Abstracts International, Volume: 57-06, Sectio
Astronomy and Astrophysics
Astronomy
Scientific paper
Bipolar molecular outflows are a basic component of the star formation process although it has not been well established how outflows from massive stars differ from those from low-mass stars. This thesis presents results from a project to identify bipolar outflows from massive young stellar objects (YSOs) and determine how they compare with low-mass YSOs. In phase I of the project, 122 massive star formation regions were surveyed in ^ {12}CO(J=1-0) using the National Radio Astronomy Observatory (NRAO) 12 m telescope. Fully 90% of the survey sources are associated with high velocity (HV) gas in the beam. If the HV gas is due to bipolar outflows, then these results indicate that molecular outflows are a common property of newly formed massive stars; similar to that found for low-mass YSOs. In phase II of this project, 12 massive star formation regions with high velocity 12CO(J=1-0) line wings were mapped at low spatial resolution with the 12 m telescope. Seven of the regions have bipolar outflows with masses between 16 and 72 M_odot and kinetic energies between 1045 and 1046 ergs. We predict the stellar luminosities of the YSO sources range from 10^2 to 10^4 L_odot which corresponds to B type stars; the precursors of Herbig Be stars. In phase III of this project, we made high spatial resolution observations of the most massive outflow studied in phase II, G75.78 NE, located in the ON2-N cloud core. Observations were made with the BIMA mm-wave interferometer of the line emission from 12CO(J=1 -0), SiO(v=0, J=2-1), H13CO ^+(J=1-0) and SO_2(8 _{3,5}-9_{2,8 }) and of the continuum emission at 86 and 111 GHz. The 12CO BIMA data were combined with observations from the 12 m telescope to recover extended emission in the final images. We find evidence for at least four separate molecular outflows from YSOs within a diameter of 1.5 parsecs. The dominant outflow has 58 M_odot of molecular material in the HV flow with a total kinetic energy of 5times1046 ergs. The predicted bolometric luminosity of this YSO source is 5.0times103 L _odot which corresponds to an early-B type star.
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