Other
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........25s&link_type=abstract
PhD Dissertation, University of Western Ontario London, Ontario Canada
Other
B Stars, Hot Stars, Stellar Mass, Star Formation, Early Stars, Star Clusters, Ubv Spectra, Stellar Luminosity, Astronomical Catalogs, A Stars, Temperature Distribution, Main Sequence Stars, O Stars, Error Analysis, Velocity Measurement, Radial Velocity, Scorpius Constellation, Electrophotometers
Scientific paper
The Scorpius-Centaurus OB Association is, at 160 pc, the nearest of all regions where hot, 8-12 solar mass B stars have formed within last 107 years or so. Despite its relative nearness, the stellar content of intermediate mass hot stars, in the 3-7 solar mass range, has never been fully explored. The purpose of this thesis is to identify and count those stars in the lower mass range of the B-type stars that are plausible members of the association and to construct the luminosity function, LF, of Sco-Cen. This is the distribution by luminosity of the numbers of stars that formed during the star formation episode(s) that created the association and is the first step towards determining the initial mass function. To determine the LF, I have greatly extended the catalog of photoelectric photometry in the UBV and beta passbands of potential members in Sco-Cen so that it is essentially complete for the B stars. Most of the possible early A star members have also been observed in the UBV system. I have obtained new radial velocity measurements for some late B stars in three fields within Sco-Cen to gain additional information about their potential membership. The photoelectric data have been used to derive effective temperatures and surface gravities for all the candidate B star members; however, an investigation into the validity of surface gravity calibrations in terms of the beta index reveals systematic errors somewhat larger than the observational uncertainties in the data. Nonetheless, the photometric data were still useful for separating young, near ZAMS association stars from the generally older, more evolved main-sequence field stars. The LF for the association was constructed from the list of plausible members, those stars that could not be rejected as members based on their photometric and kinematic parameters. A power-law of the form N varies as Mvgamma, gamma = 0.24 +/- 0.02 fits the distribution reasonably well for log Mu greater than 2.5 solar mass. There are few, if any, stars less massive than approx. 2.5 solar mass in this OB association. Comparing this with LFs constructed from available data for some other OB associations and with the bright end of the LFs for some young clusters shows that the Sco-Cen LF is essentially identical with the others. This study strengthens the conclusion that the LF of young stellar groups has a nearly universal form. Deriving the IMF itself requires a better handle on the association's star formation history than is possible in the present study.
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