The analysis of eclipsing binaries containing non-radial pulsators allows: i) to combine two different and independent sources of information on the internal structure and evolutionary status of the components, and ii) to study the effects of tidal f
orces on pulsations. KIC 3858884 is a bright Kepler target whose light curve shows deep eclipses, complex pulsation patterns with pulsation frequencies typical of {delta} Sct, and a highly eccentric orbit. We present the result of the analysis of Kepler photometry and of high resolution phaseresolved spectroscopy. Spectroscopy yielded both the radial velocity curves and, after spectral disentangling, the primary component effective temperature and metallicity, and line-of-sight projected rotational velocities. The Kepler light curve was analyzed with an iterative procedure devised to disentangle eclipses from pulsations which takes into account the visibility of the pulsating star during eclipses. The search for the best set of binary parameters was performed combining the synthetic light curve models with a genetic minimization algorithm, which yielded a robust and accurate determination of the system parameters. The binary components have very similar masses (1.88 and 1.86 Msun) and effective temperatures (6800 and 6600 K), but different radii (3.45 and 3.05 Rsun). The comparison with the theoretical models evidenced a somewhat different evolutionary status of the components and the need of introducing overshooting in the models. The pulsation analysis indicates a hybrid nature of the pulsating (secondary) component, the corresponding high order g-modes might be excited by an intrinsic mechanism or by tidal forces.
Pulsating stars in eclipsing binary systems are powerful tools to test stellar models. Binarity enables to constrain the pulsating component physical parameters, whose knowledge drastically improves the input physics for asteroseismic studies. The st
udy of stellar oscillations allows us, in its turn, to improve our understanding of stellar interiors and evolution. The space mission CoRoT discovered several promising objects suitable for these studies, which have been 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 showed, as well, clear evidence of Gamma Dor type pulsations. We obtained phase resolved high-resolution spectroscopy with the Sandiford spectrograph at the McDonald 2.1m telescope and the FEROS spectrograph at the ESO 2.2m 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. We obtained an accurate determination of the system parameters, and by comparison with evolutionary models 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 quite complete and consistent description of the system. The primary star pulsates with typical {gamma} Dor frequencies and shows a splitting in period which 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.
We present the preliminary results of the study of an interesting target in the first CoRoT exo-planet field (IRa1): CoRoT 102918586. Its light curve presents additional variability on the top of the eclipses, whose pattern suggests multi- frequency
pulsations. The high accuracy CoRoT light curve was analyzed by applying an iterative scheme, devised to disentangle the effect of eclipses from the oscillatory pattern. In addition to the CoRoT photometry we obtained low resolution spectroscopy with the AAOmega multi-fiber facility at the Anglo Australian Observatory, which yielded a spectral classification as F0 V and allowed us to infer a value of the primary star effective temperature. The Fourier analysis of the residuals, after subtraction of the binary light curve, gave 35 clear frequencies. The highest amplitude frequency, of 1.22 c/d, is in the expected range for both gamma Dor and SPB pulsators, but the spectral classification favors the first hypothesis. Apart from a few multiples of the orbital period, most frequencies can be interpreted as rotational splitting of the main frequency (an l = 2 mode) and of its overtones.
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 (e of about 0.3), unus
ual for its short (3.65705d) 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 simultaneous fitting of the light and the radial velocity curves. Individual star spectra were derived by spectrum disentangling. The uncertainties of the fit were derived 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 about 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 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.
