CARMENES input catalogue of M dwarfs II. High-resolution imaging with FastCam

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Aims. We search for low-mass companions of M dwarfs and characterize their multiplicity fraction with the purpose of helping in the selection of the most appropriate targets for the CARMENES exoplanet survey. Methods. We obtained high-resolution images in the I band with the lucky imaging instrument FastCam at the 1.5m Telescopio Carlos Sanchez for 490 mid-to late-M dwarfs. For all the detected binaries, we measured angular separations, position angles, and magnitude differences in the I band. We also calculated the masses of each individual component and estimated orbital periods, using the available magnitude and colour relations for M dwarfs and our own M-J-spectral type and mass-M-I relations. To avoid biases in our sample selection, we built a volume-limited sample of M0.0-M5.0 dwarfs that is complete up to 86% within 14 pc. Results. From the 490 observed stars, we detected 80 companions in 76 systems, of which 30 are new discoveries. Another six companion candidates require additional astrometry to confirm physical binding. The multiplicity fraction in our observed sample is 16.7 +/- 2.0%. The bias-corrected multiplicity fraction in our volume-limited sample is 19.5 +/- 2.3% for angular separations of 0.2 to 5.0 arcsec (1.4-65.6 au), with a peak in the distribution of the projected physical separations at 2.5-7.5 au. For M0.0-M3.5V primaries, our search is sensitive to mass ratios higher than 0.3 and there is a higher density of pairs with mass ratios over 0.8 compared to those at lower mass ratios. Binaries with projected physical separations shorter than 50 au also tend to be of equal mass. For 26 of our systems, we estimated orbital periods shorter than 50 a, 10 of which are presented here for the first time. We measured variations in angular separation and position angle that are due to orbital motions in 17 of these systems. The contribution of binaries and multiples with angular separations shorter than 0.2 arcsec, longer than 5.0 arcsec, and of spectroscopic binaries identified from previous searches, although not complete, may increase the multiplicity fraction of M dwarfs in our volume-limited sample to at least 36%.
© ESO, 2016. Artículo firmado por 15 autores. We thank A. Pérez Garrido for the provision and support of the FastCam reduction software and X. Bonfils for the supply of radial velocity measurements from the ESO HARPS GTO Program ID 072.C-0488. M.C.C. thanks L. Peralta de Arriba, V. Pereira and H.M. Tabernero for their assistance and valuable conversations. This article is based on observations made with the Telescopio Carlos Sánchez operated on the island of Tenerife jointly by the Instituto de Astrofísica de Canarias and the Universidad de La Laguna in the Spanish Observatorio del Teide. This research made use of SIMBAD, operated at Centre de Donnees astronomiques de Strasbourg (France), the NASA's Astrophysics Data System, the Washington Double Star catalogue (WDS) maintained at the US Naval Observatory, and the Image Reduction and Analysis Facility (IRAF), distributed by the National Optical Astronomy Observatory and operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. CARMENES is funded by the German Max-Planck-Gesellshaft (MPG), the Spanish Consejo Superior de Investigaciones Científicas (CSIC), the European Union through FEDER/ERF funds, and the members of the CARMENES Consortium (Max-Planck Institut fur Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Konigstuhl, Institut de Ciences de l'Espai, Institut fur Astrophysik Gottingen, Universidad Complutense de Madrid, Thuringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología, and the Centro Astronómico Hispano-Alemán), with additional contributions by the Spanish Ministry of Economy, the state of Niedersachsen, the German Science Foundation (DFG), and by the Junta de Andalucía. Financial support was also provided by the Junta de Andalucía, and the Spanish Ministries of Science and Innovation and of Economy and Competitiveness, under grants 2011-FQM-7363, AP2009-0187, AYA2014-54348-C3-01/02/03-R, AYA2015-69350-C3-2-P, ESP2013-48391-C4-1-R, and ESP2014-57495-C2-2-R.
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