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

摘要

Accurate photometric CoRoT space observations of a secondary seismologicaltarget, HD 174884, led to the discovery that this star is an astrophysicallyimportant double-lined eclipsing spectroscopic binary in an eccentric orbit (eof about 0.3), unusual for its short (3.65705d) orbital period. The higheccentricity, coupled with the orientation of the binary orbit in space,explains the very unusual observed light curve with strongly unequal primaryand secondary eclipses having the depth ratio of 1-to-100 in the CoRoT 'seismo'passband. Without the high accuracy of the CoRoT photometry, the secondaryeclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-upprogram provided 45 high dispersion spectra. The analysis of the CoRoT lightcurve was performed with an adapted version of PHOEBE that supports CoRoTpassbands. The final solution was obtained by simultaneous fitting of the lightand the radial velocity curves. Individual star spectra were derived byspectrum disentangling. The uncertainties of the fit were derived by bootstrapresampling and the solution uniqueness was tested by heuristic scanning. Theresults provide a consistent picture of the system composed of two late Bstars. The Fourier analysis of the light curve fit residuals yields twocomponents, with orbital frequency multiples and an amplitude of about 0.1mmag, which are tentatively interpreted as tidally induced pulsations. Anextensive comparison with theoretical models is carried out by means of theLevenberg-Marquardt minimization technique and the discrepancy between modelsand the derived parameters is discussed. The best fitting models yield a youngsystem age of 125 million years which is consistent with the eccentric orbitand synchronous component rotation at periastron.