SIMBAD references

We present the results of the detailed spectroscopic investigation of three double-mode Cepheids: EW Sct, VX Pup and BQ Ser. The abundance analysis has shown: (1) Carbon is deficient (the abundance normalized to the iron content with respect to the solar value). (2) This carbon deficiency is accompanied by nitrogen overabundance and normal oxygen content. (3) α - and iron group elements with little exception show solar ratio [M/Fe]. (4) The heavy elements in EW Sct are underabundant. (5) Normal iron abundance for EW Sct ([Fe/H]=-0.08) and metal deficiency for VX Pup ([Fe/H]=-0.39) and BQ Ser ([Fe/H]=-0.36) strongly support the existence of a P₁/P₀-metallicity relation, as first discussed in work of Andrievsky et al. (1993).