J/A+A/684/A106 Chromospheric emissions of 177 M dwarfs (Mignon+, 2024)
Characterisation of stellar activity of M dwarfs.
II. Relationship between Ca, Hα and Na chromospheric emissions.
Meunier N., Mignon L., Kretzschmar M., Delfosse X.
<Astron. Astrophys. 684, A106 (2024)>
=2024A&A...684A.106M 2024A&A...684A.106M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, dwarfs ; Stars, M-type ; Spectroscopy
Keywords: techniques: spectroscopy - stars: activity - stars: chromospheres -
planetary systems
Abstract:
The chromospheric emission estimated in the core of different lines,
such as CaII H & K, Na D1 and D2, and Ha, is not always correlated
between lines. In particular, the CaII H & K and Ha emission time
series are anti-correlated for a few percent of the stars, contrary to
what is observed on the Sun. This puzzling result has been observed
for both solar-type stars and M stars.
Our objective is to characterise these relationships in more detail
using complementary criteria, and based on a large set of spectra
obtained with HARPS for a large sample of M dwarfs. This should allow
to evaluate whether or not additional processes are required to
explain the observations.
We analysed the time average and variability of the Ca, Na, and
Hα emissions for 177 M stars ranging from subspectral types M0
to M8, paying particular attention to their (anti-)correlations on
both short and long timescales as well as slopes between indices. We
also computed synthetic Hα time series based on different
assumptions of plage properties. We compared our findings with
observations in order to evaluate whether or not the main observed
properties could be reproduced.
The statistical properties of our sample, in terms of correlations and
slopes between indices at different timescales, differ from what we
previously obtained for FGK stars: there are fewer stars with a null
correlation, and the correlations we find show a weaker dependence on
timescale. However, there can be a large dispersion from one season to
another for stars with a well identified low or negative correlation.
We also specify the complex relationship between the average activity
levels, with a clear indication of a change in the sign of the slope
from the relation between Ca and Hα (and between Na and
Hα) for the most massive M dwarfs. In addition, we observe a
change in slope in the Na-Ca relation at an intermediate activity
level. At this stage, we are not able to find simple plage properties
that, alone, are sufficient to reproduce the observations. However,
the simulations already allow us to point out that it is not
straightforward to compare the temporal variability correlation and
the integrated indices. Our findings also demonstrate the need for
complex activity patterns to explain some of the observations.
We conclude that the relation between the three indices examined here
exhibits a large diversity in behaviour over the sample studied. More
detailed simulations with complex activity patterns are necessary to
understand these observations. This will teach us about plage
properties for this type of star.
Description:
We studied the relation between three chromospheric indices from a
large sample of M stars in detail; namely CaII H & K, Na D1 and D2,
and Hα, first from their time-averaged values and then in more
detail from the relationship between the corresponding time series.
We considered stars with at least ten nights of observations and a
long enough temporal coverage to be able to implement a study of
long-term variability as in Paper I (Mignon et al.,
2023A&A...675A.168M 2023A&A...675A.168M, Cat. J/A+A/675/A168) (i.e. stars with a temporal
coverage shorter than six times the rotation period are removed),
which led to a sample of 177 stars, which are listed in Table A.1.
We analyse the correlations (defined as the Pearson coefficient),
denoted C, between the time series for the three pairs of indices of
our sample of 177 stars and compare them. The correlations are shown
in Table A.2 for all stars.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 93 177 Main parameters of the stars in our sample and
activity from our analysis
tablea2.dat 106 177 Global correlations and slopes between activity
indicators for the 177 stars in our sample,
with their 1-sigma uncertainty
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See also:
J/A+A/675/A168 : Stellar properties of 177 M dwarfs (Mignon+, 2023)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Name Star name
24- 27 F4.2 mag V-K V-K colour index (1)
29 A1 --- n_V-K [d] d indicates calculate on V-K (1)
31- 34 I4 K Teff Effective temperature (2)
36 A1 --- n_Teff [*] * for estimated Teff value (2)
38- 42 F5.2 [-] [Fe/H] ?=- Metallicity [Fe/H] (3)
44- 46 I3 --- NB Number of nights
48- 53 F6.3 --- logR'HK Chromospheric activity index logR'HK
55- 60 F6.3 --- SCa Average chromospheric activity index SCa
62- 67 F6.3 --- e_SCa rms of SCa
69- 73 F5.3 --- SNa Average chromospheric activity index SNa
75- 79 F5.3 --- e_SNa rms of SNa
81- 85 F5.3 --- SHalpha Average chromospheric activity index SHalpha
87- 91 F5.3 --- e_SHalpha rms of SHalpha
93 A1 --- Season [S] Flag indicating more than four seasons
-------------------------------------------------------------------------------
Note (1): V-K values are from the CDS when available, or derived from
the relationship between G-K versus V-K when V is not available
(indicated by "d" in field "n_V-K"), as in Mignon et al.,
2023A&A...675A.168M 2023A&A...675A.168M, Cat. J/A+A/675/A168.
Note (2): Teff values are from the CDS. When missing, the reported value,
indicated by "*" in field "n_Teff", means that we have estimated it
from a Teff versus V-K linear law.
Note (3): The metallicities ([Fe/H]) are from:
Casagrande et al., 2008MNRAS.389..585C 2008MNRAS.389..585C
Neves et al., 2013A&A...551A..36N 2013A&A...551A..36N
Kordopatis et al., 2013AJ....146..134K 2013AJ....146..134K
Gaidos et al., 2014MNRAS.443.2561G 2014MNRAS.443.2561G
Gaspar et al., 2016ApJ...826..171G 2016ApJ...826..171G
Houdebine et al., 2016ApJ...822...97H 2016ApJ...822...97H
Aganze et al., 2016AJ....151...46A 2016AJ....151...46A
Passegger et al., 2018A&A...615A...6P 2018A&A...615A...6P
Maldonado et al., 2019A&A...624A..94M 2019A&A...624A..94M
Hojjatpanah et al., 2019A&A...629A..80H 2019A&A...629A..80H
Kuznetsov et al., 2019ApJ...878..134K 2019ApJ...878..134K
Maldonado et al., 2020A&A...644A..68M 2020A&A...644A..68M
Birky et al., 2020ApJ...892...31B 2020ApJ...892...31B
Steinmetz et al., 2020AJ....160...83S 2020AJ....160...83S
Hojjatpanah et al., 2020A&A...639A..35H 2020A&A...639A..35H
Jonsson et al., 2020AJ....160..120J 2020AJ....160..120J
Sarmento et al., 2021A&A...649A.147S 2021A&A...649A.147S
Buder et al., 2021MNRAS.506..150B 2021MNRAS.506..150B
Marfil et al., 2021A&A...656A.162M 2021A&A...656A.162M
Hubbard-James et al., 2022AJ....164..174H 2022AJ....164..174H
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 22 A22 --- Name Star name
24- 29 F6.3 --- C-Ca-Ha Correlation Ca-Halpha
31- 35 F5.3 --- e_C-Ca-Ha Uncertainty on correlation Ca-Halpha
37- 42 F6.3 --- C-Na-Ca Correlation Na-Ca
44- 48 F5.3 --- e_C-Na-Ca Uncertainty on correlation Na-Ca
50- 55 F6.3 --- C-Na-Ha Correlation Na-Halpha
57- 61 F5.3 --- e_C-Na-Ha Uncertainty on correlation Na-Halpha
63- 69 F7.4 --- sl-Ha-Ca Slope Halpha vs. Ca
71- 76 F6.4 --- e_sl-Ha-Ca Uncertainty on slope Halpha vs. Ca
78- 84 F7.4 --- sl-Na-Ca Slope Na vs. Ca
86- 91 F6.4 --- e_sl-Na-Ca Uncertainty on slope Na vs. Ca
93- 99 F7.4 --- sl-Ha-Na Slope NHalpha vs. Na
101-106 F6.4 --- e_sl-Ha-Na Uncertainty on slope Halpha vs. Na
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Acknowledgements:
Nadege Meunier, nadege.meunier(at)univ-grenoble-alpes.fr
References:
Mignon et al., Paper I 2023A&A...675A.168M 2023A&A...675A.168M, Cat. J/A+A/675/A168
(End) Patricia Vannier [CDS] 17-Jan-2024