CORE MASS AT THE HELIUM FLASH FROM OBSERVATIONS AND A NEW BOUND ON NEUTRINO ELECTROMAGNETIC PROPERTIES

We use existing measurements of the bolometric magnitudes of the brightest red giants in 26 globular clusters to determine the brightness difference between the tip of the red giant branch (on average found to be ∼0.1 mag brighter than the brightest red giant) and RR Lyrae stars, ΔMRRtip = {(4.19 ± 0.03) + (0.41 ± 0.06)([Fe/H] + 1.3)} mag. The metallicity variation of this result agrees perfectly with theoretical predictions. In conjunction with previous determinations of the number ratio of horizontal-branch versus red giant stars, with statistical parallax determinations of RR Lyrae absolute luminosities, and with theoretical predictions based on the Sweigart and Gross evolutionary sequences, this result yields an allowed range for a hypothetical core mass variation relative to the standard results of δMc = (0.009 ± 0.012) M⊙. If neutrinos had anomalous electromagnetic dipole moments, μv, the increased energy loss near the helium flash would lead to an increased core mass which we find to be δMc = 0.015 M⊙ × μv/10-12μB (Bohr magneton μB = e/2me). Therefore the color-magnitude diagrams of globular clusters imply the most stringent constraints on neutrino electromagnetic properties: μv < 3 × 10-12μB. This bound applies to the diagonal electric and magnetic dipole moments of Dirac neutrinos and to the electric and magnetic transition moments of Majorana neutrinos, while the bound on electric and magnetic transition moments of Dirac neutrinos is μv < 2 × 10-12μB.