Spectroscopic studies of southern-hemisphere Cepheids: Six objects in Centaurus (V Cen, V737 Cen) and Sagittarius (BB Sgr, W Sgr, X Sgr, Y Sgr)

This paper is the next one in the series of our works aimed at determining the atmospheric parameters and chemical composition of southern-hemisphere Cepheids. We present the results of our study for six bright Cepheids: V Cen, V737 Cen, BB Sgr, W Sgr, X Sgr, and Y Sgr. We have analyzed 14 high-resolution spectra taken with the 1.9-m telescope at the South African Astronomical Observatory. In addition to determining the chemical composition and atmospheric parameters, we point out and discuss several features in the spectra of individual Cepheids. In particular,we have detected emission in the cores of the H beta and H alpha lines forWSgr near its maximum light, while X Sgr shows the splitting of metal absorption lines into individual components without any change of the hydrogen lines. These peculiarities can be explained by different manifestations of shock waves in the Cepheid atmospheres and by the presence of circumstellar envelopes around X Sgr and W Sgr. The chemical composition has been estimated for V737 Cen, BB Sgr, and X Sgr for the first time. On the whole, our abundance estimates for alpha-elements, iron-peak elements, and r- and s-process elements are close to the solar ones for all objects, carbon is underabundant, the oxygen abundance is nearly solar, the "odd" elements, Na and Al, are overabundant (except X Sgr), magnesium is underabundant for V Cen and X Sgr and overabundant for the remaining objects. Such a chemical composition is typical of yellow supergiants after the first dredge-up