Possible detection of phase changes from the non-transiting planet HD 46375b by CoRoT

摘要

The present work deals with the detection of phase changes in an exoplanetarysystem. HD 46375 is a solar analog known to host a non-transiting Saturn-massexoplanet with a 3.0236 day period. It was observed by the CoRoT satellite for34 days during the fall of 2008. We attempt to identify at optical wavelengths,the changing phases of the planet as it orbits its star. We then try to improvethe star model by means of a seismic analysis of the same light curve and theuse of ground-based spectropolarimetric observations. The data analysis relieson the Fourier spectrum and the folding of the time series. We find evidence ofa sinusoidal signal compatible in terms of both amplitude and phase with lightreflected by the planet. Its relative amplitude is Delta Fp/F* = [13.0, 26.8]ppm, implying an albedo A=[0.16, 0.33] or a dayside visible brightnesstemperature Tb ~ [1880,2030] K by assuming a radius R=1.1 R_Jup and aninclination i=45 deg. Its orbital phase differs from that of theradial-velocity signal by at most 2 sigma_RV. However, the tiny planetarysignal is strongly blended by another signal, which we attribute to a telluricsignal with a 1 day period. We show that this signal is suppressed, but noteliminated, when using the time series for HD 46179 from the same CoRoT run asa reference. This detection of reflected light from a non-transiting planetshould be confirmable with a longer CoRoT observation of the same field. In anycase, it demonstrates that non-transiting planets can be characterized usingultra-precise photometric lightcurves with present-day observations by CoRoTand Kepler. The combined detection of solar-type oscillations on the sametargets (Gaulme et al. 2010a) highlights the overlap between exoplanetaryscience and asteroseismology and shows the high potential of a mission such asPlato.