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Astron. Astrophys. 336, 263-275 (1998)

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Spectral variability of the binary HR 4049 *, **

Eric J. Bakker *** 1, David L. Lambert 1, Hans van Winckel 2, James K. McCarthy 1, 3, Christoffel Waelkens 2 and Guillermo Gonzalez 1, 4

1 Department of Astronomy and W.J. McDonald Observatory, University of Texas, Austin, TX 78712-1083, USA (ebakker@astro.as.utexas.edu), (dll@astro.as.utexas.edu)
2 Astronomical Institute, Catholic University of Leuven, Celestynenlaan 200, B-3030 Heverlee, Belgium (Hans.VanWinckel@wis.kuleuven.ac.be), (christoffel@ster.kuleuven.ac.be)
3 Department of Astronomy MS 105-24, Caltech, Pasadena, CA 91125, USA (jkm@optkos.caltech.edu)
4 Department of Astronomy, University of Washington, P.O. Box 351580, Seattle, WA 98195-1580, USA (gonzalez@orca.astro.washington.edu)

Received 19 November 1997 / Accepted 20 February 1998

Abstract

The C I, Na I D, and H[FORMULA] lines of the post-AGB binary HR 4049 have been studied. Na I D variability results from a photospheric absorption component ([Na/H]=[FORMULA]) which follows the velocity of the primary and a stationary, non-photospheric component. An emission component is attributed to the circumbinary disc, and an absorption component to mass-loss from the system with a velocity of [FORMULA]  km s-1.

The H[FORMULA] profile varies with the orbital period. The two strong shell type emission peaks are identified as from one single broad emission feature with an absorption centered around -7.5  km s-1. The intensity variations are largely attributed to a differential amount of reddening towards the H[FORMULA] emitting region and the stellar continuum. The radial velocities suggest that the H[FORMULA] emission moves in phase with the primary, but with a slightly lower velocity amplitude. From this we infer that the H[FORMULA] emission comes from outside the orbit of the primary, but still gravitationally bound to the primary. H[FORMULA] also shows a weak emission feature at [FORMULA]  km s-1, which originates from the circumbinary disc and a weak absorption feature at [FORMULA]  km s-1  due to absorption by the circumbinary disc.

We propose two competing models that could account for the observed velocity and intensity variations of the H[FORMULA] profile. Model I: light from the primary reflects on a localized spot near the inner radius of the circumbinary disc which is closest to the primary. Model II: H[FORMULA] emission originates in the outer layers of the extended atmosphere of the primary due to activity. These activities are locked to the position of the primary in its orbit.

We discuss the similarities of variability and shape of the H[FORMULA] emission of HR 4049 with those of early type T-Tauri stars (e.g SU Aur).

Key words: line: formation – line. profiles – AGB and post-AGB stars – close binaries: close – stars: emission line, Be – stars: individual: HR 4049

* Based on observations obtained at the McDonald, ESO, CTIO, and La Palma observatories.
** Tables 3 and 4, Figs. 12 to 17 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html, or from the authors.
*** Current address: TNO-FEL, Electro Optics Group, P.O. Box 96864, 2509 74 The Hague, The Netherlands

Send offprint requests to: Eric J. Bakker

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© European Southern Observatory (ESO) 1998

Online publication: July 7, 1998
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