Title

A Spectroscopic and Photometric Study of the Metal-Poor, Pulsating, Post-Asymptotic Giant Branch Binary HD 46703

Document Type

Article

Publication Date

10-2008

Abstract

The metal-poor post-asymptotic giant branch (AGB) star HD 46703 is shown to be a single-line spectroscopic binary with a period of 600 days, a high velocity of -94 km s(-1), and an orbital eccentricity of 0.3. Light-curve studies show that it also pulsates with a period of 29 days. High-resolution, high signal-to-noise spectra were used for a new abundance study. The atmospheric model determined is T-eff = 6250 K, log g = 1.0, V-t = 3.0 km s(-1), and a metal abundance of [M/H] = -1.5. A low carbon abundance and a lack of s-process element enhancement indicate that the star has not experienced a third dredge-up on the AGB. The sulfur and zinc abundances are high compared with iron, and the chemical abundances show a clear anti-correlation with condensation temperature. The abundance depletion pattern is similar to that seen in other post-AGB binaries, and, like them, is attributed to the chemical fractionation of refractory elements onto dust stored in a circumbinary disk and the re-accretion of volatiles in the stellar atmosphere. The infrared excess is small but the excess energy distribution is very similar to what can be expected from a disk. HD 46703 joins the growing list of depleted, post-AGB stars which are likely surrounded by a dusty and stable circumbinary disk.