HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT^*,**

¹ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio C. (RM), Italy e-mail: maceroni@oa-roma.inaf.it
² Institut d'Astrophysique et Géophysique Université de Liège, Allée du 6 Aôut, 4000 Liège, Belgium
³ Observatoire de Paris, LESIA, UMR 8109, 92195 Meudon, France
⁴ Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
⁵ Villanova University, Dept. Astron. Astrophys., 800 E Lancaster Ave., Villanova, PA 19085, USA
⁶ University of Ljubljana, Dept. of Physics, Jadranska 19, 1000 Ljubljana, Slovenia
⁷ Instituut for Sterrenkunde, K.U. Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
⁸ Astronomical Institute of Wrocław University, ul. Kopernika 11, 51-622 Wrocław, Poland
⁹ Institut d'Astrophysique Spatiale, Campus d'Orsay, 91405 Orsay, France
¹⁰ Dept. of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, The Netherlands

Received: 16 September 2009
Accepted: 17 October 2009

Abstract

Accurate photometric CoRoT space observations of a secondary seismological target, HD 174884, led to the discovery that this star is an astrophysically important double-lined eclipsing spectroscopic binary in an eccentric orbit (), unusual for its short 365705 orbital period. The high eccentricity, coupled with the orientation of the binary orbit in space, explains the very unusual observed light curve with strongly unequal primary and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT “seismo” passband. Without the high accuracy of the CoRoT photometry, the secondary eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up program provided 45 high dispersion spectra. The analysis of the CoRoT light curve was performed with an adapted version of PHOEBE that supports CoRoT passbands. The final solution was obtained by a simultaneous fitting of the light and the radial velocity curves. Individual star spectra were obtained by spectrum disentangling. The uncertainties of the fit were achieved by bootstrap resampling and the solution uniqueness was tested by heuristic scanning. The results provide a consistent picture of the system composed of two late B stars. The Fourier analysis of the light curve fit residuals yields two components, with orbital frequency multiples and an amplitude of ~0.1 mmag, which are tentatively interpreted as tidally induced pulsations. An extensive comparison with theoretical models is carried out by means of the Levenberg-Marquardt minimization technique, and the discrepancy between the models and the derived parameters is discussed. The best fitting models yield a young system age of 125 million years which is consistent with the eccentric orbit and synchronous component rotation at periastron.