Mass-luminosity relation of intermediate-mass stars

Abstract

The mass–luminosity relation (MLR) for intermediate-mass stars is based on data on detached double-lined eclipsing binaries. However, there is a notable difference between the parameters of B0V–G0V components of eclipsing binaries and those of single stars. Single early-type stars are rapid rotators, whereas tidal forces produce synchronous rotation in close binaries and all such pairs are synchronized, so components of close binaries rotate more slowly. As is well known, stellar rotation changes stellar evolution and the global parameters of a star. In this work we collect data on fundamental parameters of stars with masses m > 1.5 m⊙. They are components of binaries with P > 15 d and consequently are not synchronized with the orbital periods and presumably are rapid rotators. These stars are believed to evolve similarly with single stars. Modern data on masses, absolute and bolometric luminosities, radii and temperatures of detached main-sequence double-lined eclipsing binary components (i.e. presumably slow rotators) are also collected. Mass–luminosity, mass–temperature and mass–radius relations of close and wide binaries are presented, as well as their Hertzsprung–Russell diagram. For the mass range 4.5 < m/m⊙ < 5.5 (late B stars) it was found that rapid rotators exhibit slightly higher luminosities and larger radii than predicted by the standard relations, and their main sequence is shifted to the right-hand side with respect to that of the close binary components. The resulting relations for rapidly and slowly rotating A–F and early B stars are not statistically different. As our estimations show, for the given mass range the effect on the initial mass function (IMF) is marginal, but there is no way to estimate the degree to which the effect may be important for higher masses. Available observational data for m > 12 m⊙ are too poor to make definite conclusions. Knowledge of the MLR should come from dynamical mass determinations of visual binaries combined with spatially resolved precise photometry. Then the IMF should be revised for that mass range.