Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
2 : 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
Corresponding author: I. Ilyin, email@example.com
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 . 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 , 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 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
Based on observations made with the SOFIN échelle spectrograph at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto Astrofisica de Canarias; and the coudé spectrograph at the 2 m-RCC-telescope of the National Astronomical Observatory at Rozhen, Bulgaria.
© ESO, 2003