Analysis of combined radial velocities and activity of BD+20 1790: evidence supporting the existence of a planetary companion^⋆,⋆⋆

¹ Dpto. de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040, Madrid, Spain
e-mail: mhernanobispo@fis.ucm.es
² Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Hertfordshire AL10 9AB, UK
³ University of Turku, Tuorla Observatory, Deparment of Physics and Astronomy, Väisäläntie 20, 21500 Piikkiö, Finland
⁴ Centro de Astrobiología (CSIC-INTA), Ctra. Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁵ Main Astronomical Observatory of National Academy of Sciences of Ukraine, Zabolotnogo str., 27, 03680 Kiev, Ukraine
⁶ Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁷ Department of Physics & Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132, USA
⁸ Departmento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago, Casilla 36-D, Chile
⁹ Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 31400 Toulouse, France
¹⁰ CNRS, Institut de Recherche en Astrophysique et Planétologie, 14 Avenue Edouard Belin, 31400 Toulouse, France
¹¹ Universität Göttingen, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹² Computational Engineering and Science Research Centre, University of Southern Queensland, 4350 Toowoomba, Australia
¹³ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
¹⁴ Institut de Ciénces de l’Espai (IEEC-CSIC), Facultad de Ciéncies, Campus UAB, 08193 Bellaterra, Spain
¹⁵ Department of Electrical Engineering and Center of Astro-Engineering UC, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹⁶ Institute of Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D BUS 2401, 3001 Leuven, Belgium
¹⁷ Terskol Branch of Institute of Astronomy RAS, Kabardino-Balkaria Republic, 361605 Terskol, Russia

Received: 23 February 2012
Accepted: 12 January 2015

Abstract

Context. In a previous paper we reported a planetary companion to the young and very active K5Ve star BD+20 1790. We found that this star has a high level of stellar activity () that manifests in a plethora of phenomena (starspots, prominences, plages, large flares). Based on a careful study of these activity features and a deep discussion and analysis of the effects of the stellar activity on the radial velocity measurements, we demonstrated that the presence of a planet provided the best explanation for the radial velocity variations and all the peculiarities of this star. The orbital solution resulted in a close-in massive planet with a period of 7.78 days. However, a paper by Figueira et al. (2010, A&A, 513, L8) questioned the evidence for the planetary companion.

Aims. This paper aims to more rigorously assess the nature of the radial velocity measurements with an expanded data set and new methods of analysis.

Methods. We have employed Bayesian methods to simultaneously analyse the radial velocity and activity measurements based on a combined data set that includes new and previously published observations.

Results. We conclude that the Bayesian analysis and the new activity study support the presence of a planetary companion to BD+20 1790. A new orbital solution is presented, after removing the two main contributions of stellar jitter, one that varies with the photometric period (2.8 days) and another that varies with the synodic period of the star-planet system (4.36 days). We present a new method to determine these jitter components, considering them as second and third signals in the system. A discussion on possible star-planet interaction is included, based on the Bayesian analysis of the activity indices, which indicates that they modulate with the synodic period. We propose two different sources for flare events in this system: one related to the geometry of the system and the relative movement of the star and planet, and a second one purely stochastic source that is related to the evolution of stellar surface active regions. Also, we observe for the first time the magnetic field of the star, from spectropolarimetric data.