Evolutionary problems of Cepheids and other giants investigated with new radiative opacities

Journal Article · Mon Mar 01 04:00:00 EST 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154190· OSTI ID:7365128

Carson, T R; Stothers, R

New evolutionary tracks, pulsation constants, and pulsational stability coefficients have been calculated for stellar models applicable to the problems of classical Cepheids, by adopting (a) the standard Cox-Stewart opacities and (b) the new Carson opacities. The theoretical mass-luminosity relation is slightly fainter for the new opacities, but neither this decrease of luminosity nor the somewhat greater duration of the ''blue loop'' during core helium burning can be discriminated on the H-R diagram by the use of present observational data for giant stars in moderately young clusters of the Galaxy and the Magellanic Clouds. The masses of Cepheids inferred from the pulsation constants and from the pulsational period ratios are significantly smaller than the masses inferred from evolutionary theory, for both sets of opacities, but the masses that can be inferred from the secondary bump on the radial-velocity curve are now predicted to agree with the evolutionary masses if the new opacities are used. The new opacities lead to revised pulsational instability results that are in good agreement with observations: thus, convection in the hotter envelopes is much less important than before, so that the phase lag between luminosity and radial velocity at the stellar surface is closer to 90degree; and the blue edge of the theoretical instability strip on the H-R diagram is significantly bluer than before, although it may now have too steep a slope and the problem of the theoretically unlimited red edge remains. Nevertheless, the present improvements are achieved with a normal helium abundance, no mass loss, and a conventional treatment of convection. The predicted transition between second-overtone instability and fundamental-mode instability agrees excellently with the well-observed transition in the Small Magellanic Cloud. Axial rotation is found to increase the effective temperature of the theoretical blue edges by a very slight amount. (AIP)

• Research Organization: Institute for Space Studies, Goddard Space Flight Center, NASA
• OSTI ID: 7365128
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 204:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CEPHEIDS
ENERGY TRANSFER
GIANT STARS
HEAT TRANSFER
INSTABILITY
LUMINOSITY
MASS
MATHEMATICAL MODELS
MOTION
OPACITY
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PULSATIONS
RADIAL VELOCITY
RADIANT HEAT TRANSFER
ROTATION
STAR CLUSTERS
STAR EVOLUTION
STAR MODELS
STARS
VARIABLE STARS
VELOCITY