Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...230l.109c&link_type=abstract
Astrophysical Journal, Part 2 - Letters to the Editor, vol. 230, June 1, 1979, p. L109-L112.
Astronomy and Astrophysics
Astrophysics
15
Cepheid Variables, Helium, Pulsars, Stellar Evolution, Stellar Mass, Astrophysics, Stellar Structure, Stellar Winds
Scientific paper
Linear-nonadiabatic-theory period ratios for models of double-mode Cepheids with their two periods between 1 and 7 days have been computed by assuming differing amounts and depths of surface helium enhancement. Evolution-theory masses and luminosities are found to be consistent with the observed periods. All models give a period ratio of approximately 0.70 as observed for the 11 known variables, contrary to previous theoretical conclusions. The composition structure that best fits the period ratios has the helium mass fraction in the outer 0.001 of the stellar mass (T no more than 250,000 K) as 0.65, similar to a previous model for the triple-mode pulsator AC And. This enrichment can be established by a Cepheid wind and downward inverted-mu-gradient-instability mixing in the lifetime of these low-mass classical Cepheids.
Cox Arthur N.
Hodson Stephen W.
King David S.
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