HD 46375: seismic and spectropolarimetric analysis of a young Sun hosting a Saturn-like planet^⋆

¹ Institut d’Astrophysique Spatiale, UMR 8617, Université Paris Sud, 91405 Orsay Cedex, France
e-mail: Patrick.Gaulme@ias.u-psud.fr
² LESIA, UMR 8109, Observatoire de Paris, 92195 Meudon Cedex, France
³ University of Vienna, Inst. of Astronomy, Türkenschanzstr. 17, AT 1180 Vienna, Austria
⁴ Laboratoire d’Astrophysique de Marseille, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁵ LATT, UMR 5572, CNRS and University P. Sabatier, 14 Av. E. Belin, 31400 Toulouse, France
⁶ Laboratoire Fizeau, Université de Nice, CNRS-Observatoire de la Côte d’Azur, 06108 Nice Cedex 2, France
⁷ Laboratoire Cassiopée, Université de Nice, CNRS-Observatoire de la Côte d’Azur, 06304 Nice Cedex 4, France

Received: 27 January 2010
Accepted: 27 July 2010

Abstract

Context. HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star. Stellar light reflected by the planet was tentatively identified in the 34-day CoRoT run acquired in October − November 2008.

Aims. We constrain the properties of the magnetic field of HD 46375 based on spectropolarimetric observations with the NARVAL spectrograph at the Pic du Midi observatory. In addition, we use a high-resolution NARVAL flux spectrum to contrain the atmospheric parameters. With these constraints, we perform an asteroseismic analysis and modelling of HD 46375 using the frequencies extracted from the CoRoT light curve.

Methods. We used Zeeman Doppler imaging to reconstruct the magnetic map of the stellar surface. In the spectroscopic analysis we fitted isolated lines using 1D LTE atmosphere models. This analysis was used to constrain the effective temperature, surface gravity, and chemical composition of the star. To extract information about the p-mode oscillations, we used a technique based on the envelope autocorrelation function (EACF).

Results. From the Zeeman Doppler imaging observations, we observe a magnetic field of  ≈5 Gauss. From the spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with high metallicity  [Fe/H]  =  +0.39. Owing to the relative faintness of the star (m_hip = 8.05), the signal-to-noise ratio is too low to identify individual modes. However, we measure the p-mode excess power and large separation Δν₀ = 153.0 ± 0.7μHz.

Conclusions. We are able do constrain the fundamental parameters of the star thanks to spectrometric and seismic analyses. We conclude that HD 46375 is similar to a young version of α Cen B. This work is of special interest because of its combination of exoplanetary science and asteroseismology, which are the subjects of the current Kepler mission and the proposed Plato mission.