ABUNDANCE ANALYSES OF THE FIELD RV TAURI VARIABLES - EP-LYRAE, DY-ORIONIS, AR-PUPPIS, AND R-SAGITTAE

Analyses of the photospheric compositions of the four held RV Tauri st ars, EP Lyr, DY Ori, AR Pup, and R Sge, indicate that to varying degre es they have experienced fractionation processes that have preferentia lly depleted their atmospheres of elements with high condensation temp eratures. The depletion, as indicated by, for instance, [S/Fe], is gre atest for DY Ori, [S/Fe] = 2.5, and least for R Sge, [S/Fe] = 0.9. The initial composition, presumably indicated by the sulfur abundance, wa s nearly solar for AR Pup, R Sge, and DY Ori, while it was about 0.6 d ex less than solar for EP Lyr. This implies that the RV Tauri stars as a group may not be as metal-poor as previously thought-they are inste ad ''metal-depleted.'' The field RV Tauri's are not halo stars, but pr obably belong to the thick disk. This brings to seven the number of ty pe II Cepheids that show such a trend; the other three are IW Car and V1 in omega Cen, RV Tauri stars, and ST Pup, a W Virginis star. The C- 12/C-13 ratios for EP Lyr and DY Ori are 9 +/- 1 and 6 +/- 3, respecti vely, indicating that CN-cycled material has been mixed with their sur face layers. This is consistent with the general consensus that RV Tau stars are in a post-AGB evolutionary stage. There is also evidence th at EP Lyr has a stellar mass companion, but additional observations ar e required to calculate an orbit; hence, EP Lyr could be a link to the group of metal-depleted, high-latitude A-F supergiants, all of which are binaries.