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

摘要

Accurate photometric CoRoT space observations of a secondary seismological target, HD 174884, led to the discovery that this staris an astrophysically important double-lined eclipsing spectroscopic binary in an eccentric orbit (e – 0.3), unusual for its short3~d.65705 orbital period. The high eccentricity, coupled with the orientation of binary orbit in space, explains the very unusualobserved 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. Aspectroscopic follow-up program provided 45 high dispersion spectra. The analysis of the CoRoT light curve was performed with anadapted version of PHOEBE that supports CoRoT passbands. The final solution was obtained by a simultaneous fitting of the light andthe radial velocity curves. Individual star spectra were obtained by spectrum disentangling. The uncertainties of the fit were achievedby bootstrap resampling and the solution uniqueness was tested by heuristic scanning. The results provide a consistent picture ofthe system composed of two late B stars. The Fourier analysis of the light curve fit residuals yields two components, with orbitalfrequency multiples and an amplitude of –0.1 mmag, which are tentatively interpreted as tidally induced pulsations. An extensivecomparison with theoretical models is carried out by means of the Levenberg-Marquardt minimization technique, and the discrepancybetween the models and the derived parameters is discussed. The best fitting models yield a young system age of 125 million yearswhich is consistent with the eccentric orbit and synchronous component rotation at periastron.