THE ASTROPHYSICAL JOURNAL, 479:427-440, 1997 April 10

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

      GUILLERMO GONZALEZ[1], DAVID L. LAMBERT[2], AND SUNETRA GIRIDHAR [3]


                                   ABSTRACT

        Analyses of the photospheric compositions of the four field RV
     Tauri stars, EP Lyr, DY Ori, AR Pup, and R Sge, indicate that to
     varying degrees they have experienced fractionation processes that
     have preferentially depleted their atmospheres of elements with high
     condensation temperatures.  The depletion, as indicated by, for
     instance, [S/Fe], is greatest 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, was nearly solar for AR Pup, R Sge, and DY Ori,
     while it was about 0.6 dex 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 instead ``metal-depleted.'' The field RV
     Tauri's are not halo stars, but probably belong to the thick
     disk. This brings to seven the number of type 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 12C/13C ratios for EP Lyr and DY Ori are 9 +/- 1 and 6 +/- 3,
     respectively, indicating that CN-cycled material has been mixed with
     their surface layers. This is consistent with the general consensus
     that RV Tau stars are in a post-AGB evolutionary stage. There is also
     evidence that EP Lyr has a stellar mass companion, but additional
     observations are 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.

     Subject headings: stars: abundances -- stars: AGB and post-AGB -- 
                       stars: variables: other (RV Tauri)

     1 Department of Astronomy, University of Texas, Austin, TX 78712;
     gonzalez@crown.as.utexas.edu.

     2 Department of Astronomy, University of Texas, Austin, TX 78712;
     dll@astro.as.utexas.edu; and Visiting Observer, Cerro Tololo
     InterAmerican Observatory, which is operated by the Association of
     Universities for Research in Astronomy, Inc. under contract with the
     US National Science Foundation.

     3 Indian Institute of Astrophysics, Bangalore, 560 034 India;
     giridhar@iiap.ernet.in.