Publication: The CARMENES search for exoplanets around M dwarfs A Neptune-mass planet traversing the habitable zone around HD 180617
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2018-10-17
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EDP Sciences S A
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Abstract
Despite their activity, low-mass stars are of particular importance for the search of exoplanets by the means of Doppler spectroscopy, as planets with lower masses become detectable. We report on the discovery of a planetary companion around HD 180617, a bright (J = 5.58 mag), low-mass (M = 0.45 M-circle dot) star of spectral type M2.5 V. The star, located at a distance of 5.9 pc, is the primary of the high proper motion binary system containing vB 10, a star with one of the lowest masses known in most of the twentieth century. Our analysis is based on new radial velocity (RV) measurements made at red-optical wavelengths provided by the high-precision spectrograph CARMENES, which was designed to carry out a survey for Earth-like planets around M dwarfs. The available CARMENES data are augmented by archival Doppler measurements from HIRES and HARPS. Altogether, the RVs span more than 16 yr. The modeling of the RV variations, with a semi-amplitude of K = 2.85(-0.25)(+0.16)m s(-1), yields a Neptune-like planet with a minimum mass of 12.2(1.4)(+1.0) M-circle plus on a 105.90(-0.10)(+0.09) d circumprimary orbit, which is partly located in the host star's habitable zone. The analysis of time series of common activity indicators does not show any dependence on the detected RV signal. The discovery of HD 180617 b not only adds information to a currently hardly filled region of the mass-period diagram of exoplanets around M dwarfs, but the investigated system becomes the third known binary consisting of M dwarfs and hosting an exoplanet in an S-type configuration. Its proximity makes it an attractive candidate for future studies.
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Ā© ESO 2018. ArtĆculo firmado por 40 autores. CARMENES is an instrument for the Centro AstronĆ³mico Hispano-AlemĆ”n de Calar Alto (CAHA, AlmerĆa, Spain). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones CientĆficas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut fĆ¼r Astronomie, Instituto de AstrofĆsica de AndalucĆa, Landessternwarte Kƶnigstuhl, Institut de CiĆØncies de lāEspai, Insitut fĆ¼r Astrophysik Gƶttingen, Universidad Complutense de Madrid, ThĆ¼ringer Landessternwarte Tautenburg, Instituto de AstrofĆsica de Canarias, Hamburger Sternwarte, Centro de AstrobiologĆa and Centro AstronĆ³mico Hispano-AlemĆ”n), with additional contributions by the Spanish Ministry of Science through projects AYA2016-79425-C3-1/2/3-P, ESP2016-80435-C2-1-R, and AYA2015- 69350-C3-2-P, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 āBlue Planets around Red Starsā, the Klaus Tschira Stiftung, the states of Baden-WĆ¼rttemberg and Niedersachsen, and by the Junta de AndalucĆa. Based on data from the CARMENES data archive at CAB (INTA-CSIC). N. A. D. acknowledges support from FONDECYT #3180063. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme(s) 072.C-0488(E), 183.C-0437(A), 191.C-0873(A), 191.C0873(B), 191.C-0873(D), 191.C-0873(E), 191.C-0873(F). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We made use of the corner.py package (Foreman-Mackey 2016). We thank the anonymous referee for useful comments that improved the paper.