CoRoT 102918586: a γ Doradus pulsator in a short-period eccentric eclipsing binary^⋆,⋆⋆

¹ INAF – Osservatorio astronomico di Roma, via Frascati 33, 00040 Monteporzio C., Italy
e-mail: maceroni@oa-roma.inaf.it
² Institut d’Astrophysique et Géophysique, Université de Liège, Allée du 6 Août, 4000 Liège, Belgium
³ ESA Estec, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁵ Department of Physics, University of Zagreb, Bijenička cesta 32, 10000 Zagreb, Croatia
⁶ INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy

Received: 16 November 2012
Accepted: 30 January 2013

Abstract

Pulsating stars in eclipsing binary systems are powerful tools to test stellar models. Binarity enables us to constrain the pulsating component’s physical parameters and this knowledge drastically improves the input physics for asteroseismic studies. The study of stellar oscillations then allows us to improve our understanding of stellar interiors and stellar evolution. The space mission CoRoT discovered several promising objects suitable for these studies. They were photometrically observed with unprecedented accuracy, but needed spectroscopic follow-up. A promising target was the relatively bright eclipsing system CoRoT 102918586, which turned out to be a double-lined spectroscopic binary and also showed clear evidence of γ Dor type pulsations. With the aim of combining the information from binarity and pulsation and fully exploiting the potential of CoRoT photometry we obtained phase resolved high-resolution spectroscopy with the Sandiford spectrograph at the McDonald 2.1m telescope and the FEROS spectrograph at the ESO 2.2 m telescope. Spectroscopy yielded both the radial velocity curves and, after spectra disentangling, the component effective temperatures, metallicity, and line-of-sight projected rotational velocities. The CoRoT light curve was analyzed with an iterative procedure, devised to disentangle eclipses from pulsations. The eclipsing binary light curve analysis, combined with the spectroscopic results, provided an accurate determination of the system parameters, and the comparison with evolutionary models provided strict constraints on the system age. Finally, the residuals obtained after subtraction of the best–fitting eclipsing binary model were analyzed to determine the pulsator properties. We achieved a complete and consistent description of the system. The primary star pulsates with typical γ Dor frequencies and shows a splitting in period that is consistent with high order g-mode pulsations in a star of the corresponding physical parameters. The value of the splitting, in particular, is consistent with pulsations in ℓ = 1 modes.