Abundance analyses of field RV Tauri stars. IV. AD Aquilae, DS Aquarii, V360 Cygni, AC Herculis, and V453 Ophiuchi.
GIRIDHAR S., LAMBERT D.L. and GONZALEZ G.
Abstract (from CDS):
Abundance analyses are presented and discussed for five RV Tauri variables. Three stars–DS Aqr, V360 Cyg, and V453 Oph–are RV C stars by spectroscopic classification, i.e., metal lines are weak. They are shown to be metal poor with [Fe/H] from -1.0 to -2.2 with normal relative abundances of other elements. By contrast, AD Aql and AC Her are RV B stars with an odd abundance pattern: elements that condense into grains at a high temperatures are underabundant (i.e., [Fe/H] = -2.1 for AD Aql) but elements with a low condensation temperatures are much less underabundant (i.e., [S/H] = 0.0 and [Zn/H] = -0.1 for AD Aql). This abundance pattern is ascribed to a separation of dust and gas in the upper atmosphere of the star. The present analyses with previously published results are used to investigate the systematics of the dust-gas separation in RV Tauri variables. The process is apparently inoperative in stars with an initial metallicity of about [Fe/H] ≲ -1.0; RV C stars and similar variables in globular clusters are immune to the dust-gas separation. The process achieves more severe effects in RV B than in RV A stars. The strength of the abundance anomalies attributed to dust-gas separation is not correlated with reported infrared excesses. After correction for the effects of the dust-gas separation, there is no strong evidence from the abundances that evolution along the AGB and experience of the third dredge-up preceded the formation of the majority of the RV Tauri variables.