Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pasp..104.1107p&link_type=abstract
Publications of the Astronomical Society of the Pacific, v.104, p.1107
Astronomy and Astrophysics
Astronomy
2
Scientific paper
I present 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 stasr. The entire catalog (exclusive of the dense core cluster R136) 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 functions (IMF), which is the number distribution as a function of stellar 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> 12 solar mass, where the Salpeter slope is Gamma=-1.35. However, there are indications that different regions of 30 Dor have different IMF slopes, perhaps the result of sequential star-formation effects. Calculations of the Lyman-continuum photon luminosity N_Ly lead to the result that 3.2 X 10^51 photons s^-1 are being produced by the observed stars in 30 Dor. This is equivalent to the ionzation luminosity of 440 O7 V stasr or 77 O5 V stasr. Less than 60% 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 II region, the H-alpha luminosity due to the Lyman-continuum photons produced by the stars would be L_H-alpha 4.5 X 10^39 erg s^-1. This value agrees with the luminosity determined from the observed H-alpha flux, but it is a lower limit since the effects of Wolf-Rayet stars and the unresolved cluster of R136 have not been included. (SECTION: Dissertation Abstracts)
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