The CARMENES search for exoplanets around M dwarfs Activity indicators at visible and near-infrared wavelengths



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Cortés Contreras, Miriam and Montes Gutiérrez, David (2019) The CARMENES search for exoplanets around M dwarfs Activity indicators at visible and near-infrared wavelengths. Astronomy and astrophysics, 623 . ISSN 1432-0746

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Context. The Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs (CARMENES) survey is searching for Earth-like planets orbiting M dwarfs using the radial velocity method. Studying the stellar activity of the target stars is important to avoid false planet detections and to improve our understanding of the atmospheres of late-type stars.
Aims. In this work we present measurements of activity indicators at visible and near-infrared wavelengths for 331 M dwarfs observed with CARMENES. Our aim is to identify the activity indicators that are most sensitive and easiest to measure, and the correlations among these indicators. We also wish to characterise their variability. Methods. Using a spectral subtraction technique, we measured pseudo-equivalent widths of the He ı D_(3), Hα, He ı λ10833 Å, and Paβ lines, the Na ı D doublet, and the Ca ıı infrared triplet, which have a chromospheric component in active M dwarfs. In addition, we measured an index of the strength of two TiO and two VO bands, which are formed in the photosphere. We also searched for periodicities in these activity indicators for all sample stars using generalised Lomb-Scargle periodograms.
Results. We find that the most slowly rotating stars of each spectral subtype have the strongest Hα absorption. Hα is correlated most strongly with He ı D_(3), whereas Na ı D and the Ca ıı infrared triplet are also correlated with Hα. He ı λ10833 Å and Paβ show no clear correlations with the other indicators. The TiO bands show an activity effect that does not appear in the VO bands. We find that the relative variations of Hα and He ı D_(3) are smaller for stars with higher activity levels, while this anti-correlation is weaker for Na ı D and the Ca ıı infrared triplet, and is absent for He ı λ10833 Å and Paβ. Periodic variation with the rotation period most commonly appears in the TiO bands, Hα, and in the Ca ıı infrared triplet.

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© ESO 2019. Artículo firmado por 24 autores. CARMENES is an instrument for the Centro Astronómico Hispano-Alemán de Calar Alto (CAHA, Almería, Spain). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Científicas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, and the members of the CARMENES Consortium (Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Andalucía, Landessternwarte Königstuhl, Institut de Ciències de l’Espai, Institut für Astrophysik Göttingen, Universidad Complutense de Madrid, Thüringer Landessternwarte Tautenburg, Instituto de Astrofísica de Canarias, Hamburger Sternwarte, Centro de Astrobiología and Centro Astronómico Hispano-Alemán), with additional contributions by the Spanish Ministry of Science, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía.

Uncontrolled Keywords:Star spectroscopic survey; H-Alpha emission; Proper motion stars; Digital sky survey; Low-mass stars; Ca-II triplet; Chromospheric activity; Cool stars; Rotational braking; Spectral sequence
Subjects:Sciences > Physics > Astrophysics
ID Code:55247
Deposited On:28 May 2019 11:11
Last Modified:28 May 2019 11:11

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