Tal-Or, L.; Zechmeister, M.; Reiners, A.; Jeffers, S. V.; Schöfer, P.; Quirrenbach, A.; Amado, P. J.; Ribas, I.; Caballero, J. A.; Aceituno, J.; Bauer, F. F.; Béjar, V. J. S.; Czesla, S.; Dreizler, S.; Fuhrmeister, B.; Hatzes, A. P.; Johnson, E. N.; Kürster, M.; Lafarga, M.; Montes, D.; Morales, J. C.; Reffert, S.; Sadegi, S.; Seifert, W.; Shulyak, D.
Bibliographical reference
Astronomy and Astrophysics, Volume 614, id.A122, 17 pp.
Description
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.
The data presented in Figs. 5 and A.1 are only available in electronic
form at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr (
http://130.79.128.5) or via
http://cdsarc.u-strasbg.fr/viz-
bin/qcat?J/A+A/614/A122
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