The CARMENES search for exoplanets around M dwarfs: Radial-velocity variations of active stars in visual-channel spectra

L. Tal-Or, M. Zechmeister, A. Reiners, S. V. Jeffers, P. Schöfer, A. Quirrenbach, P. J. Amado, I. Ribas, J. A. Caballero, J. Aceituno, F. F. Bauer, V. J.S. Béjar, S. Czesla, S. Dreizler, B. Fuhrmeister, A. P. Hatzes, E. N. Johnson, M. Kürster, M. Lafarga, D. MontesJ. C. Morales, S. Reffert, S. Sadegi, W. Seifert, D. Shulyak

Research output: Contribution to journalArticlepeer-review

49 Scopus citations


Context. Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from ∼1 cm s-1 to ∼1 km s-1, depending on various stellar and activity parameters. Aims. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra (0.5-1μm), which were taken within the CARMENES RV planet survey during its first 20 months of operation. Methods. During this time, 287 of the CARMENES-sample stars were observed at least five times. From each spectrum we derived a relative RV and a measure of chromospheric Hα emission. In addition, we estimated the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. Results. Despite having a median number of only 11 measurements per star, we show that the RV variations of the stars with RV scatter of >10 m s-1 and a projected rotation velocity v sin i > 2 km s-1 are caused mainly by activity. We name these stars "active RV-loud stars" and find their occurrence to increase with spectral type: from ∼3% for early-type M dwarfs (M0.0-2.5 V) through ∼30% for mid-type M dwarfs (M3.0-5.5 V) to >50% for late-type M dwarfs (M6.0-9.0 V). Their RV-scatter amplitude is found to be correlated mainly with v sin i. For about half of the stars, we also find a linear RV-CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of them we can exclude a linear correlation between RV and Hα emission. Conclusions. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.

Original languageEnglish
Article numberA122
JournalAstronomy and Astrophysics
StatePublished - 1 Jun 2018
Externally publishedYes


  • Stars: activity
  • Stars: late-type
  • Stars: rotation
  • Techniques: radial velocities


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