Pulsations and metallicity of the pre-main sequence eclipsing spectroscopic binary RS Cha

¹ Observatoire de Paris, LESIA, 5 place Jules Janssen, 92195 Meudon Principal Cedex, France e-mail: evelyne.alecian@obspm.fr
² Observatoire de Paris, GEPI, 5 place Jules Janssen, 92195 Meudon Principal Cedex, France
³ South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape, South Africa

Received: 26 August 2004

Abstract

We present new spectroscopic observations of the pre-main sequence eclipsing spectroscopic binary RS Cha. A sample of 174 spectra were obtained with the GIRAFFE spectrograph at the SAAO at 32 000 resolution. The radial velocity curves derived from these spectra were combined with previous observations spanning a period of about 30 years to correct the ephemeris of the system, and the result indicates that the orbital period is not constant.
Residuals of the binary radial velocity curve for both components with amplitudes up to a few km s^-1 and periods on the order of 1 h are clearly seen in our data, which we interpret as the signatures of delta-Scuti type pulsations.
We revisited the masses of both components and determined the surface metallicity Z of both components of the RS Cha system by fitting synthetic spectra to observed spectra in a set of selected spectral regions. The synthetic spectra are calculated with the SYNTH code using stellar atmosphere models computed with the Kurucz ATLAS 9 code, along with a list of lines obtained from the VALD database. A selection of the best spectra and the most relevant spectral regions allowed us to determine . We also derived new values of :  km s^-1 and  km s^-1 for the primary and the secondary star, respectively. Finally, we observationally confirm that the RS Cha system is a synchronized and circularized system.