A seismic and gravitationally bound double star observed by Kepler

Implication for the presence of a convective core^⋆

¹ Univ. Paris-Sud, Institut d’Astrophysique Spatiale, UMR 8617, CNRS, Bâtiment 121, 91405 Orsay Cedex, France
² Tata Institute of Fundamental Research, Homi Bhabha Road, 400005 Mumbai, India
³ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁴ Observatoire de Paris, GEPI, CNRS UMR 8111, 5 place Jules Janssen, 92195 Meudon, France
⁵ Institut de Physique de Rennes, Université de Rennes 1, CNRS UMR 6251, 35042 Rennes, France
⁶ Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK
⁷ Institute of Physics of the Earth, B. Gruzinskaya 10, 123810 Moscow, Russia
⁸ School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁹ Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
¹⁰ Department of Astronomy, New Mexico State University, PO Box 30001, MSC 4500, Las Cruces, NM 88003-8001, USA
¹¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
¹² Universidad de La Laguna, Departamento de Astrofísica, 38206 La Laguna, Tenerife, Spain
¹³ Department of Physics, Southern Connecticut State University, New Haven, CT 06515, USA
¹⁴ NASA Ames Research Center, Moffett Field, CA 94035, USA
¹⁵ National Optical Astronomy Observatory, 950 N. Cherry Ave, Tucson, AZ 85719, USA
¹⁶ NASA Exoplanet Science Institute, California Institute of Technology, 770 South Wilson Avenue, Mail Code 100-22, Pasadena, CA 91125, USA
¹⁷ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁸ University of Padova, Dipartimento di Fisica e Astronomia “Galileo Galilei”, via Marzolo, 8, 35131 Padova, Italy
¹⁹ Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot – IRFU/SAp, Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France
²⁰ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany

Received: 27 May 2015
Accepted: 24 July 2015

Abstract

Context. Solar-like oscillations have been observed by Kepler and CoRoT in many solar-type stars, thereby providing a way to probe stars using asteroseismology.

Aims. The derivation of stellar parameters has usually been done with single stars. The aim of the paper is to derive the stellar parameters of a double-star system (HIP 93511), for which an interferometric orbit has been observed along with asteroseismic measurements.

Methods. We used a time series of nearly two years of data for the double star to detect the two oscillation-mode envelopes that appear in the power spectrum. Using a new scaling relation based on luminosity, we derived the radius and mass of each star. We derived the age of each star using two proxies: one based upon the large frequency separation and a new one based upon the small frequency separation. Using stellar modelling, the mode frequencies allowed us to derive the radius, the mass, and the age of each component. In addition, speckle interferometry performed since 2006 has enabled us to recover the orbit of the system and the total mass of the system.

Results. From the determination of the orbit, the total mass of the system is 2.34_-0.33^+0.45 M_⊙. The total seismic mass using scaling relations is 2.47 ± 0.07 M_⊙. The seismic age derived using the new proxy based upon the small frequency separation is 3.5 ± 0.3 Gyr. Based on stellar modelling, the mean common age of the system is 2.7–3.9 Gyr. The mean total seismic mass of the system is 2.34–2.53 M_⊙  consistent with what we determined independently with the orbit. The stellar models provide the mean radius, mass, and age of the stars as R_A = 1.82−1.87R_⊙, M_A = 1.25−1.39 M_⊙, Age_A = 2.6–3.5 Gyr; R_B = 1.22−1.25 R_⊙, M_B = 1.08−1.14 M_⊙, Age_B = 3.35–4.21 Gyr. The models provide two sets of values for Star A: [1.25–1.27] M_⊙ and [1.34–1.39] M_⊙. We detect a convective core in Star A, while Star B does not have any. For the metallicity of the binary system of Z ≈ 0.02, we set the limit between stars having a convective core in the range [1.14–1.25] M_⊙.