Possible detection of phase changes from the non-transiting planet HD 46375b by CoRoT
Aigrain, S.; Auvergne, M.; Schneider, J.; Donati, J. -F.; Baudin, F.; Michel, E.; Baglin, A.; Catala, C.; Samadi, R.; Mosser, B.; Deeg, H. J.; Appourchaux, T.; Bruntt, H.; Weiss, W. W.; Guillot, T.; Deheuvels, S.; Régulo, C.; Mary, D.; Schmider, F. -X.; Gaulme, P.; Vannier, M.; Bourguignon, S.
France, Austria, Spain, United Kingdom
Abstract
Context. The present work deals with the detection of phase changes in an exoplanetary system. HD 46375 is a solar analog known to host a non-transiting Saturn-mass exoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for 34 days during the fall of 2008.
Aims: We attempt to identify at optical wavelengths, the changing phases of the planet as it orbits its star. We then try to improve the star model by means of a seismic analysis of the same light curve and the use of ground-based spectropolarimetric observations.
Methods: The data analysis relies on the Fourier spectrum and the folding of the time series.
Results: We find evidence of a sinusoidal signal compatible in terms of both amplitude and phase with light reflected by the planet. Its relative amplitude is Δ Fp/Fstar = [13.0, 26.8] ppm, implying an albedo A = [0.16, 0.33] or a dayside visible brightness temperature Tb ≃ [1880, 2030] K by assuming a radius R = 1.1 RJup and an inclination i = 45°. Its orbital phase differs from that of the radial-velocity signal by at most 2 σ_RV. However, the tiny planetary signal is strongly blended by another signal, which we attribute to a telluric signal with a 1 day period. We show that this signal is suppressed, but not eliminated, when using the time series for HD 46179 from the same CoRoT run as a reference.
Conclusions: This detection of reflected light from a non-transiting planet should be confirmable with a longer CoRoT observation of the same field. In any case, it demonstrates that non-transiting planets can be characterized using ultra-precise photometric lightcurves with present-day observations by CoRoT and Kepler. The combined detection of solar-type oscillations on the same targets (Gaulme et al. 2010a) highlights the overlap between exoplanetary science and asteroseismology and shows the high potential of a mission such as Plato.