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Stothers, R., 1972: Red supergiants and neutrino emission. II. Astrophys. J., 175, 717-730.
The variation with stellar mass of the ratio of the numbers of blue and red supergiants is investigated. Statistical data for supergiants in young open clusters and subgroups of associations are collected to supplement a more restricted list in Paper I. Improved methods are used to identify hydrogen-burning supergiants, as well as faint supergiant remnants of binary mass exchange, and to arrange the bright evolved supergiants in order. of their masses. Neither of these two operations requires knowledge of stellar distances or luminosities. Relevant published work on stellar evolution, rotation, mass loss, and duplicity is used to predict upper and lower limits on the blue-to-red ratio. I t is concluded that (1) the observed paucity of very massive red supergiants (and of carbon stars) confirms and extends the trend observed in Paper I, and thereby supports the idea of neutrino-induced acceleration of the carbonburning and later phases of evolution; (2) the h and χPersei association shows the same dependence of the blue-to-red ratio on stellar mass as do other clusters and associations; and (3) a moderate decrease of the blue-to-red ratio is observed with increasing galactocentric distance in the Galaxy (as in M33) and seems to be due to a relative scarcity of extremely young stars in distant galactic regions.
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