Cepheid masses from observations and pulsation theory

Abstract

Cepheid masses are calculated using radii measured recently by the Baade-Wesselink and the related Barnes et al. methods. They are compared to masses which use only the well observed fundamental mode period, Pi/sub 0/, and an approximate effective surface temperature, T/sub e/. These latter masses, called theoretical masses, result from the solution for the four unknowns M, R, L, Q/sub 0/ of four equations: evolutionary mass-luminosity (M-L) law for blue looping yellow giants, the period--mean density (Pi/sub 0/-M-R-Q/sub 0/) relation, the variation of the pulsation constant Q/sub 0/ with the unknowns, and the definition equation for T/sub e/. To ensure the proper calibration of these theoretical masses, the effects of a new distance scale and new temperatures on evolutionary theory and pulsation masses are discussed. It is found that pulsation masses using observed Pi/sub 0/, L, and colors (to give the mean T/sub e/) now agree much better with evolutionary and theoretical masses, but the Wesselink and the Barnes et al. radii imply lower average masses for 69 cases. This discrepancy can be alleviated and the agreement of evolution, theoretical, and pulsation masses not destroyed by using recently proposed helium-rich surface layers in theoretical Cepheid models which increase Q/sub 0/more » as well as the bump, beat, and the Wesselink and Barnes et al. radius masses.« less