Red Supergiants and Neutrino Emission

Data on the supergiants in all early-type clusters and associations of the Galaxy and Magellanic Clouds which contain known red-supergiant members have been collected and analyzed in the light of current theory. No major differences seem to exist between the Galaxy and the Magellanic Clouds in this study. The composite bolometric H-R diagram for the "M associations" shows (1) many blue supergiants (09.5-A5) mostly in the range BO-B3 with Mbol -6 to -10; (2) a roughly equal number of red supergiants (MO-M4.5) mostly in the range MO-M2, but the brightest being latest in spectral type, with Mbol `~` -5 to -8 and no correlation with luminosity class; and (3) a thin scatter of yellow super- giants (F, G, and K). Dating of the clusters from the luminosities of their blue supergiants indicates decreasing and increas- ing numbers of blue and red supergiants, respectively, with age. Luminosity functions show that the blue/red ratio is >5 at high masses (15-60 ~1~) and `-4 at lower masses (10-15 9Jt~). While a one-to- one correspondence exists between luminosity and mass for the core helium-burning blue supergiants, it is lacking for the red supergiants because of a "funneling effect" (in analogy with the K giants). The red supergiants are shown theoretically to be in two basically different evolutionary phases: (1) helium core contraction and early core helium burning and (2) carbon core contraction and later phases The first case explains the blue/red ratio at low masses. The second case refers to high masses and depends on the existence of the hypothetical photoneutrino process; the predicted blue/red ratio is <17 and <1.7 with and without the neutrino process, respectively. On the basis of the large blue/red ratio among the most massive supergiants and the independent theoretical and observational evidence that early core helium burning occurs in the red-supergiant region, it is concluded that some effect must take massive stars rapidly through, or away from, the red-super- giant region after core helium burning. Mixing and mass loss are shown to be inadequate mechanisms. If photoneutrino losses are permitted to occur, the stars do evolve rapidly as red supergiants, as required by the observations. One might accept this as supporting evidence for the existence of a direct electron- neutrino weak interaction in nature