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The CARMENES search for exoplanets around M dwarfs Rotational variation in activity indicators of Ross 318, YZ CMi, TYC 3529-1437-1, and EV Lac



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Caballero, J. A. and Cortés Contreras, Miriam and Montes Gutiérrez, David and otros, ... (2022) The CARMENES search for exoplanets around M dwarfs Rotational variation in activity indicators of Ross 318, YZ CMi, TYC 3529-1437-1, and EV Lac. Astronomy & Astrophysics, 663 . ISSN 0004-6361

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Official URL: http://dx.doi.org/10.1051/0004-6361/201936102


Context. The Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Échelle Spectrographs (CARMENES) instrument is searching for periodic radial-velocity (RV) variations of M dwarfs, which are induced by orbiting planets. However, there are other potential sources of such variations, including rotational modulation caused by stellar activity.
Aims. We aim to investigate four M dwarfs (Ross 318, YZ CMi, TYC 3529-1437-1, and EV Lac) with different activity levels and spectral sub-types. Our goal is to compare the periodicities seen in 22 activity indicators and the stellar RVs, and to examine their stability over time.
Methods. For each star, we calculated generalised Lomb-Scargle periodograms of pseudo-equivalent widths of chromospheric lines, indices of photospheric bands, the differential line width as a measure of the width of the average photospheric absorption line, the RV, the chromatic index that describes the wavelength dependence of the RV, and parameters of the cross-correlation function. We also calculated periodograms for subsets of the data and compared our results to TESS photometry.
Results. We find the rotation periods of all four stars to manifest themselves in the RV and photospheric indicators, particularly the TiO 7050 index, whereas the chromospheric lines show clear signals only at lower activity levels. For EV Lac and TYC 3529-1437-1, we find episodes during which indicators vary with the rotation period, and episodes during which they vary with half the rotation period, similarly to photometric light curves.
Conclusions. The changing periodicities reflect the evolution of stellar activity features on the stellar surface. We therefore conclude that our results not only emphasise the importance of carefully analysing indicators complementary to the RV in RV surveys, but they also suggest that it is also useful to search for signals in activity indicators in subsets of the dataset, because an activity signal that is present in the RV may not be visible in the activity indicators all the time, in particular for the most active stars.

Item Type:Article
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© P. Schöfer et al. 2022. Artículo firmado por 25 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. S.V.J. also acknowledges the support of the DFG priority program SPP 1992 “Exploring the Diversity of Extrasolar Planets (JE 701/5-1)”. L.T.-O. also acknowledges support from the Israel Science Foundation (grant no. 848/16). This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Funding for the TESS mission is provided by NASA’s Science Mission directorate.

Uncontrolled Keywords:High-resolution spectroscopy; H-alpha; Stars; Periods; Planet
Subjects:Sciences > Physics > Astrophysics
ID Code:75734
Deposited On:25 Nov 2022 11:33
Last Modified:25 Nov 2022 12:42

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