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

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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 (log R'_HK = -3.7) 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.
© ESO 2015. Artículo firmado por 20 autores. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut fur Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Instituto Nazionale di Astrofisica); and with he Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden; and with the Mercator Telescope, operated on the island of La Palma by the Flemish Community (obtained with the HERMES spectrograph, which is supported by the Fund for Scientific Research of Flanders (FWO), Belgium, the Research Council of K. U. Leuven, Belgium, the Fonds National Recherches Scientific (FNRS), Belgium, the Royal Observatory of Belgium, the Observatoire de Geneve, Switzerland and the Thuringer Landessternwarte Tautenburg, Germany), all operated at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. This work was supported by the Spanish Ministerio de Educación y Ciencia (MEC) under grant AYA2005-02750, Ministerio de Ciencia e Innovación (MICINN) under grant AYA2008-06423-C03-03, AstroMadrid S2009/ESP-1496. M. Hernán Obispo wants to especially thanks to P. Figueira and M. Marmier for their availability to help and for providing us with the CORALIE data used in the activity study and the information requested. M. C. Gálvez Ortiz acknowledges financial support by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006-00070: first Science with the GTC ( She also acknowledges the support of a JAE-Doc CSIC fellowship co-funded with the European Social Fund under the program "Junta para la Ampliación de Estudios". Financial support was also provided by the Spanish Ministerio de Ciencia e Innovación and Ministerio de Economia y Competitividad under AyA2011- 30147-C03-03 grant. M. Tuomi, J.R. Barnes, M. C. Gálvez Ortiz and D.J. Pinfield acknowledge support from RoPACS during this research, a Marie Curie Initial Training Network funded by the European Commissions Seventh Framework Programme. J. S. Jenkins acknowledges funding from CATA (PB06, Conicyt). We want also to thanks Saskia Prins for her help in Mercator observations and HERMES pipeline members (L. Dumortier, Y. Fremat, H. Hensberge, A. Jorissen, S. Van Eck, H. Van Wickel) for their help in the data reduction. M. Hernán Obispo thanks Sito Recuero for his help improving the Fig. 18. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. The authors are grateful to an anonymous referee for valuable comments and suggestions which have helped improve this paper.
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