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Astron. Astrophys. 353, 952-957 (2000)

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High resolution spectroscopy of symbiotic stars *

V. Orbital and stellar parameters for FG Ser (AS 296)

U. Mürset 1, T. Dumm 1, S. Isenegger 1, H. Nussbaumer 1, H. Schild 1, H.M. Schmid 2,3 and W. Schmutz 1,4

1 Institut für Astronomie, ETH-Zentrum, 8092 Zürich, Switzerland
2 Landessternwarte Heidelberg-Königstuhl, 69117 Heidelberg, Germany
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
4 Physikalisch-Meteorologisches Observatorium, 7260 Davos, Switzerland

Received 30 June 1999 / Accepted 23 September 1999


For the eclipsing symbiotic binary FG Ser (AS 296) we have obtained a series of high resolution optical spectra. Combining the measured radial velocity variations for the red giant with published eclipse photometry gives a binary period of 650 days. We derive the radial velocity curve of the red giant, yielding the orbital parameters of the system and a mass function of [FORMULA]  [FORMULA]. We further determine the rotation velocity of the red giant, and assuming corotation derive its photospheric radius. Together with the spectral type surface temperature this yields the position of the red giant in the HR-diagram and a mass estimate of [FORMULA]  [FORMULA]. Combining this value with [FORMULA] results in a mass of [FORMULA]  [FORMULA] for the hot star. With a binary separation of 1.95 AU and a radius of the red giant of [FORMULA] we find that FG Ser is a detached binary with the red giant well inside the Roche lobe.

Key words: stars: binaries: spectroscopic – stars: binaries: symbiotic – stars: fundamental parameters – stars: individual: FG Ser – stars: individual: AS 296

* Based on observations obtained at the European Southern Observatory, La Silla, Chile; the observations were granted for the ESO programs 47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446, 56.E-526

Send offprint requests to: H. Schild (hschild@astro.phys.ethz.ch)

© European Southern Observatory (ESO) 2000

Online publication: January 18, 2000