J/A+A/662/A41 Magnetic fields in 292 M dwarfs. (Reiners+, 2022)
Magnetism, rotation, and nonthermal emission in cool stars -
Average magnetic field measurements in 292 M dwarfs.
Reiners A., Shulyak D., Kaepylae P.J., Ribas I., Nagel E., Zechmeister M.,
Caballero J.A., Shan Y., Fuhrmeister B., Quirrenbach A., Amado P.J.,
Montes D., Jeffers S.V., Azzaro M., Bejar V.J.S., Chaturvedi P., Henning T.,
Kuerster M., Palle E.
<Astron. Astrophys. 662, A41 (2022)>
=2022A&A...662A..41R 2022A&A...662A..41R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, B-type ; Magnetic fields
Keywords: dynamo - magnetic fields - stars: activity - stars: magnetic field -
stars: rotation
Abstract:
Stellar dynamos generate magnetic fields that are of fundamental
importance to the variability and evolution of Sun-like and low-mass
stars, and for the development of their planetary systems. As a key to
understanding stellar dynamos, empirical relations between stellar
parameters and magnetic fields are required for comparison to ab
initio predictions from dynamo models. We report measurements of
surface-average magnetic fields in 292 M dwarfs from a comparison with
radiative transfer calculations; for 260 of them, this is the first
measurement of this kind. Our data were obtained from more than 15000
high-resolution spectra taken during the CARMENES project. They reveal
a relation between average field strength, , and Rossby number,
Ro, resembling the well-studied rotation-activity relation. Among
the slowly rotating stars, we find that magnetic flux, ΦB, is
proportional to rotation period, P, and among the rapidly rotating
stars that average surface fields do not grow significantly beyond the
level set by the available kinetic energy. Furthermore, we find close
relations between nonthermal coronal X-ray emission, chromospheric
Hα and Ca H&K emission, and magnetic flux. Taken together, these
relations demonstrate empirically that the rotation-activity relation
can be traced back to a dependence of the magnetic dynamo on rotation.
We advocate the picture that the magnetic dynamo generates magnetic
flux on the stellar surface proportional to rotation rate with a
saturation limit set by the available kinetic energy, and we provide
relations for average field strengths and nonthermal emission that are
independent of the choice of the convective turnover time. We also
find that Ca H&K emission saturates at average field strengths of
∼800G while Hα and X-ray emission grow further with stronger
fields in the more rapidly rotating stars. This is in conflict with
the coronal stripping scenario predicting that in the most rapidly
rotating stars coronal plasma would be cooled to chromospheric
temperatures.
Description:
The sample of stars used for our analysis, the number of spectra
co-added for each star, and the approximate S/N around
λ=8700Å are provided in Table B.1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 122 314 Table with stellar parameters and results
from our analysis
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Running Number
5- 15 A11 --- Karmn CARMENCITA Catalogue Number
17- 39 A23 --- Name Name
41- 43 I3 --- NObs ? Number of observations
45- 48 I4 --- S/N ? Signal-to-Noise ratio at 8700Å
50- 53 F4.2 Msun Mass Stellar mass in solar units
55- 58 F4.2 Rsun Rad Stellar radius in solar units
60- 63 I4 K Teff Effective temperature in Kelvin
67- 71 F5.1 d Per ? Rotation Period
73- 78 A6 --- r_Per Reference for Rotation Period (1)
80- 82 I3 d tau Convective overturn time in days
84- 88 F5.2 [Lsun] logLbol Bolometric luminosity relative to solar
in logarithmic units
90- 94 F5.2 [-] logLX/Lbol ? X-ray to bolometric luminosity
in logarithmic units
96-100 F5.2 [-] logLCa/Lbol ? Calcium H&K to bolometric luminosity
in logarithmic units
102-106 F5.2 [-] logLHa/Lbol ? Halpha to bolometric luminosity
in logarithmic units
108 A1 --- l_ Limit flag on
109-112 I4 G Average magnetic field
114-117 I4 G e_ ? Uncertainty of
119-122 F4.1 km/s vsini ? Value of vsini used for fit in km/s
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Note (1): References as follows:
DA19 = Diez Alonso et al., 2019A&A...621A.126D 2019A&A...621A.126D, Cat. J/A+A/621/A126
SM15 = Suarez-Mascareno et al., 2015MNRAS.452.2745S 2015MNRAS.452.2745S
SM17b = Suarez-Mascareno et al., 2017MNRAS.468.4772S 2017MNRAS.468.4772S
SM18 = Suarez-Mascareno et al., 2018A&A...612A..89S 2018A&A...612A..89S
Rev20 = Revilla, PhD
New18 = Newton et al., 2018AJ....156..217N 2018AJ....156..217N. Cat. J/AJ/156/217
New16a = Newton et al., 2016ApJ...821...93N 2016ApJ...821...93N. Cat. J/ApJ/821/93
CC21 = Cortes-Contreras et al. (in prep.)
Kira12 = Kiraga , 2012AcA....62...67K 2012AcA....62...67K, Cat. J/AcA/62/67
Mori08 = Morin et al., 2008MNRAS.390..567M 2008MNRAS.390..567M, Cat. J/MNRAS/390/567
KS07 = Kiraga & Stepien, 2007AcA....57..149K 2007AcA....57..149K
Oel18 = Oelkers et al., 2018AJ....155...39O 2018AJ....155...39O, Cat. J/AJ/155/39
Rae20 = Raetz et al., 2020A&A...637A..22R 2020A&A...637A..22R, Cat. J/A+A/637/A22
Hart11 = Hartman et al., 2011AJ....141..166H 2011AJ....141..166H, Cat. J/AJ/141/166
Wat06 = Watson et al., 2006SASS...25...47W 2006SASS...25...47W, Cat. B/vsx
K20 = Kochukhov et al., 2020A&A...635A.142K 2020A&A...635A.142K
Shu17 = Shulyak et al., 2017NatAs...1..184S 2017NatAs...1..184S
(DA19) = unconfirmed rotation period reported by 2019A&A...621A.126D 2019A&A...621A.126D
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Acknowledgements:
Ansgar Reiners, Ansgar.Reiners(at)phys.uni-goettingen.de
(End) Patricia Vannier [CDS] 22-Apr-2022