Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt.........5p&link_type=abstract
Ph.D. Thesis Colorado Univ., Boulder.
Astronomy and Astrophysics
Astronomy
26
Astronomical Catalogs, Hertzsprung-Russell Diagram, Magellanic Clouds, Star Clusters, Star Formation, Stellar Evolution, Astronomical Photometry, H Ii Regions, Luminosity, Spectroscopy, Stellar Mass
Scientific paper
UBV photometry for 2400 stars in the OB associations of 30 Doradus in the LMC and new spectroscopic classifications for 54 stars including 23 O stars are presented. The entire catalog (exclusive of the dense core cluster R 136) is photometrically complete to V = B = 18m and U = 17m, although the completeness magnitudes are fainter for regions with less nebular contamination. From these data, I have determined the effective temperatures and bolometric magnitudes of the stars and placed them on the theoretical H-R diagram. Using stellar evolution models, I then bin the stars by mass to obtain the initial mass function (IMF), which is the number distribution as a function of mass. The IMF shows marked curvature, flattening out to lower masses, even for masses above which the photometry is complete. Best estimates of the IMF slope yield values of gamma = -1.3 to -1.5 for M approximately greater than 12 solar mass, where the Salpeter slope is gamma = -1.35. However, there are indications that different regions of 30 Doradus have different IMF slopes, perhaps as the result of sequential star formation effects. Calculations of the Lyman continuum photon luminosity, NLy, lead to the result that approximately 3.2 x 1051 photons s-1 are being produced by the observed stars in 30 Doradus. Less than 60 percent of this luminosity comes from the 150 stars with spectroscopic classifications, implying that there still remain a large number of OB stars yet to be observed spectroscopically. This, along with stellar evolution effects, could explain the IMF curvature and the apparent deficiency of stars in the most massive bins of the IMF. For an ionization-bounded H 2 region, the H alpha luminosity due to the Lyman continuum photons produced by the stars would be LH alpha is approximately equal to 4.5 x 1039 erg s-1. This value agrees with the luminosity determined from the observed H alpha flux, but is a lower limit since the effects of W-R stars and the unresolved cluster of R 136 were not included.
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