The triple-mode variable AC Andromedae

Details The triple-mode variable AC Andromedae The triple-mode variable AC Andromedae

Jan 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...281..749k&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 281, no. 3, p. 749-755

Astronomy and Astrophysics

Astrophysics

19

Stellar Evolution, Stellar Mass, Stellar Models, Stellar Oscillations, Variable Stars, Metallicity, Stellar Composition, Stellar Luminosity, Stellar Temperature

Scientific paper

We have calculated a large number of linear radial pulsation models to fit the periods of AC And. In the parameter regime representative of RR Lyrae stars no models can be found that match the observed periods for any heavy element abundance Z. There are, however, two groups of higher mass models which yield complete agreement between the observed periods and those of the first three radial modes. The first comprises models with 0.001 less than Z less than 0.002 and masses and luminosities of 1.1 less than M/solar mass less than 1.4, 100 less than L/solar luminosity less than 130 (depending on Z). The second group has higher masses, luminosities and Z, viz. 0.01 less than Z less than 0.02, M/solar mass approximately 2.7, 80 less than L/solar luminosity less than 200. These ranges are sensitive to the assumed uncertainties of the model periods. We give ranges of model parameters as functions of Z and discuss their uncertainties. Present observational constraints and the limited sensitivity of the method of fitting periods do not allow us to sufficiently narrow down the derived parameter ranges. Furthermore, although recent evolution calculations are in fair agreement with both low- and high-mass models, the latter ones are preferred because the theoretical period changes are in better agreement with the observations. Therefore, we suggest that AC And is an evolved high-mass star, with similarities to the delta Scuti type stars, or perhaps a rare oddball. As a side product of our survey, we give accurate fitting formulae for the periods and period ratios.

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