EDP Sciences
Free access
Volume 402, Number 2, May I 2003
Page(s) 745 - 754
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20030299

A&A 402, 745-754 (2003)
DOI: 10.1051/0004-6361:20030299

The radial velocities and physical parameters of ER Vul

R. Duemmler1, 2, C. Doucet1, 3, F. Formanek1, 4, I. Ilyin1 and I. Tuominen1

1  Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
2  Present address: Wilhelm-Leuschner-Str. 16, 60329 Frankfurt/M., Germany
3  Magistère de Physique Fondamentale, Université Paris XI, 91405 Orsay, France
4  Laboratoire d'Optique Physique ESPCI, 10 rue Vauquelin, 75005 Paris, France

(Received 26 July 2002 / Accepted 21 February 2003 )

ER Vul is an eclipsing binary consisting of two solar type stars in a very close orbit with a period of  $0\fd7$. Accordingly, the two stars rotate very fast, leading to a blending of many spectral features at all phases. Therefore, measuring the radial velocity curve without systematic errors is not trivial. Here, we use a two-dimensional cross-correlation method applied to 137 high quality spectra, collected over 3 years, in order to obtain the radial velocity curve and determine the orbital and some physical parameters of the system from it. Primarily, we improve the binary period to $0\fd69809458\pm0\fd00000014$, and find that the two amplitudes are slightly smaller than those measured by others, while the mass ratio is still similar. While at least the primary almost fills its Roche lobe, the system is still detached, i.e. not yet a fully fledged W UMa-system. The behaviour of the $\ion{Ca}{ii}$ IRT line at 8662 Å confirms that the secondary is the more active component, and that the chromospheric emission is not symmetrically distributed over the surfaces of either star.

Key words: stars: individual: ER Vul -- binaries: spectroscopic -- binaries: eclipsing -- stars: late-type -- techniques: radial velocities

Offprint request: I. Ilyin, ilya.ilyin@oulu.fi

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