Abundance Analyses of Field RV Tauri Stars. V. DS Aquarii, UY Arae, TW Camelopardalis, BT Librae, U Monocerotis, TT Ophiuchi, R Scuti, and RV Tauri

Abundance analyses are presented and discussed for eight RV Tauri variables. The RVB star UY Ara shows the abundance anomalies seen in other RVB stars, namely, elements that condense into grains at high temperature are underabundant, but elements of low condensation temperature are much less underabundant. This pattern is ascribed to a separation of dust from gas with accretion of gas but not dust by the atmosphere. Abundances for two RVC stars with earlier results for other RVC stars show that these intrinsically metal-poor stars do not show effects of dust-gas separation. Analyses of five RVA stars show that these cooler stars are very largely unaffected by dust-gas separation. It is proposed that the deeper convective envelope of cooler stars dilutes anomalies resulting from dust-gas separation. Possible sites for dust formation and dust-gas separation—the dusty wind off the RV Tauri variable or a dusty circumbinary disk—are reviewed and observational tests suggested.