SIMBAD references

Linear adiabatic models of double-mode or beat Cepheids (DMC) have been constructed for testing the effects of different chemical compositions and corresponding mass-luminosity relations on the period ratios, in order to determine the M-L relations which better represents double-mode Cepheids in Galaxy and LMC. The study has not given a clearcut result, and indicates that generally DMC with low metallicity (Z≲0.016) cannot be used for discriminating reliably between standard and nonstandard relation. The latter gives slightly better results in some cases, but it is confirmed that it is not able to reproduce the galactic second overtone to first overtone pulsator (CO Aur), unless using unrealistic Z values. It is shown that a modified standard relation, with a decreased sensitivity to the metallicity, is able to give a satisfactory representation of all the DMC. Finally, the sensitivity of P₂/P₁ ratio to the T_e of the models is pointed out.