Other
Scientific paper
Nov 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aas...198.9402s&link_type=abstract
American Astronomical Society, 198th AAS Meeting, #94.02; Bulletin of the American Astronomical Society, Vol. 33, p.1181
Other
Scientific paper
Unresolved binaries exhibit a large luminosity spread at any given set of the uvby color indices b-y and δ c1, which are sensitive to temperature and surface gravity, respectively. The deviation of luminosity from the normal value expected for a single star with the same δ c1 and b-y can be characterized by the difference Δ Mc0 = Mc0 - MV, where MV is the actual absolute magnitude in V, and Mc0 is the absolute magnitude predicted for a single star with the same values of δ c1 and b-y. We find that underluminous binaries, Δ Mc0 < 0, have low velocity dispersions typical for young stars. Underluminosity is apparently due to fast rotation of the primary, which makes Mc0 brighter, on average, than MV. For the population of overluminous binaries, Δ Mc0 > 0, the velocity dispersion is much higher, indicating older age. This is consistent with slow rotation of old stars. It appears that in the absence of rotation, other mechanisms impacting Δ Mc0 become statistically noticeable, the net effect being the overluminosity. The latter must be associated, in particular, with the light contribution from the unresolved companion. However, this effect only cannot explain Δ Mc0 > 0.75, which suggests the presence of additional factors making a binary overluminous. Higher stellar velocity dispersion at larger values of Δ Mc0 is consistent with the binary's primary getting in many cases increasingly overluminous as it ages, which implies that its surface gravity gets higher with respect to that of a normal single star at the same temperature and luminosity. This effect may be indicative of a non-standard stellar evolution caused by the interaction of the primary with a close companion
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