Theoretical periods and masses of double-mode dwarf Cepheids

Details Theoretical periods and masses of double-mode dwarf Cepheids Theoretical periods and masses of double-mode dwarf Cepheids

Mar 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...228..870c&link_type=abstract

Astrophysical Journal, Part 1, vol. 228, Mar. 15, 1979, p. 870-874.

Astronomy and Astrophysics

Astrophysics

30

Cepheid Variables, Dwarf Stars, Periodic Variations, Stellar Mass, Abundance, Helium, Opacity, Radii, Stellar Evolution, Stellar Models

Scientific paper

With newly calculated opacities for Population I and II stellar compositions, models with radial fundamental mode periods between 0.05 and 0.22 day have been constructed. These models have been used to study the first-overtone to fundamental period ratios to compare with dwarf Cepheids (AI Vel stars). Contrary to previous results, the observed period ratios match the theoretical ones for masses between 1.1 and 2.2 solar masses, and these variables, with effective temperatures between 7000 and 8000 K, all seem to be in the post-main-sequence evolution stage. For the shortest-known-period dwarf Cepheid, SX Phe, it appears that only Population II compositions with Z = 0.001 can produce the observed very large period ratio of 0.778 at a mass of 1.1 solar masses. The periods for these models have been used to determine the pulsation constant as a function of mass, radius, luminosity, and effective temperature. With observed periods and at least approximate surface effective temperatures, the period-mean density and mass-luminosity relations based on the evolution tracks of Mengel and Sweigart (1978) for various compositions give theoretical masses also between 1.1 and 2.2 solar masses. The dwarf Cepheids are apparently only large-amplitude Delta Scuti variables, possibly with more helium in their surface ionization zones, which gives them their larger light-variation amplitude.

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