Volume 405, Number 1, July I 2003
|Page(s)||271 - 283|
|Section||Stellar structure and evolution|
|Published online||16 June 2003|
IRAS 08544–4431: A new post-AGB star in a binary system surrounded by a dusty disc*
Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
2 School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, Scotland KY16 9SS, UK
3 European Southern Observatory, Casilla 19001, Santiago 19, Chile
4 Onsala Space Observatory, 43992 Onsala, Sweden
5 South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
Corresponding author: T. Maas, Thomas.Maas@ster.kuleuven.ac.be
Accepted: 15 April 2003
We present an analysis of our extensive data-set on IRAS 08544–4431. It is the first object we discuss of our newly defined sample of stars, selected for their position in the “RV Tauri” box in the IRAS –, – two-color diagram. Moreover, our selection criteria included an observed excess in the L-band, indicative of a dusty disc. The SED of IRAS 08544–4431 shows a broad IR excess starting already at H. Our optical photometric data reveal some evidence for deep and shallow minima in the light curve and a pulsation time-scale of around 100 days with a small amplitude ( peak-to-peak = 0.17 mag). Our CORALIE radial velocity measurements show that IRAS 08544–4431 is a binary system with a period of days and a mass function of 0.02 . Moreover, IRAS 08544–4431 is detected in both the CO (2–1) and (1–0) mm-wave emission lines. The triangular shape of the weak CO profile confirms that part of the circumstellar material is not freely expanding but resides probably in a dusty circumbinary disc. Our chemical abundance analysis of a high resolution spectrum of high S/N reveals that a depletion process has modified the photospheric abundances to a moderate extent (). All these findings confirm that the F-type IRAS 08544–4431 is another good example of a binary Post-AGB star surrounded by a dusty disc. The Hα P-Cygni profile shows ongoing mass-loss with a very high outflow velocity, the origin of which is not understood. The strength and velocity of the Hα-absorption are modulated with the orbital motion; the maxima of both quantities (~400 , 5 Å respectively) occur at superior conjunction.
Key words: stars: abundances / stars: AGB and post-AGB / stars: evolution / stars: individual: IRAS 08544–4431 / stars: individual: RV Tauri / stars: binaries: spectroscopic
© ESO, 2003
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