Astronomy and Astrophysics, volume 316, 155-163 (1996/12-1)
The chemical composition of the s-Cepheids. III.
KOVTYUKH V.V., ANDRIEVSKY S.M., USENKO I.A. and KLOCHKOVA V.G.
Abstract (from CDS):
The hypothesis about s-Cepheids' first time crossing of the instability strip is checked by spectroscopic testing. On the basis of CCD spectra analysis, we have derived the abundances for seven s-Cepheids. The following results have been obtained: 1) V473 Lyr, IR Cep, UY Mon, BY Cas, V636 Cas have solar iron abundance, while V526 Mon and V924 Cyg show moderate iron deficiency. 2) The absolute carbon deficiency (relatively to the solar (C/H) value) found for all program stars (excepting V636 Cas) and a nitrogen overabundance show that these s-Cepheids are not crossing the instability strip for the first time. 3) Similarly to previously investigated Cepheid V1162 Aql, V636 Cas also demonstrates rather high carbon content. The plausible explanation of this phenomenon is that this star is crossing the instability strip for the first time. 4) Na and Al are overabundant for all program stars where these elements were measured. Sodium overabundance takes place also for two first- time crossing Cepheids. Possibly such an overabundance arises during the main-sequence phase. 5) α-elements show practically solar ratios with respect to Fe. 6) For iron-group elements the (M/Fe) values are close to the solar ones. 7) s-process elements are perhaps slightly enhanced in the program stars. The results of the present paper are discussed together with the results of the recent paper by Andrievsky et al. (1996A&A...305..551A) devoted to s-Cepheids.