J/A+A/704/A154 Stellar activity sample of active M dwarfs (Rajpurohit+, 2025)
Exploring stellar activity in a sample of active M dwarfs.
Rajpurohit A.S., Kumar V., Srivastava M.K., Labadie L., Rajpurohit K.,
Fernandez-Trincado J.G
<Astron. Astrophys. 704, A154 (2025)>
=2025A&A...704A.154R 2025A&A...704A.154R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, M-type ; Photometry ; Optical ; Equivalent widths ;
Effective temperatures
Keywords: techniques: spectroscopic - stars: activity - stars: atmospheres -
stars: chromospheres - stars: flare - stars: low-mass
Abstract:
Most M dwarfs present high chromospheric activity that can exceed the
solar magnetic activity. This can substantially influence planetary,
atmospheric, and biological processes, impacting the habitability of
orbiting planets. Therefore, characterizing the magnetic activity of M
dwarfs is very important for understanding the physical mechanisms
responsible for it, which are the primary targets in the search for
exoplanets within the habitable zone.
This study aims to characterize the stellar activity of active M
dwarfs by understanding the relations between magnetic activities,
stellar parameters, and flare properties.
We analyzed TESS photometric data combined with spectroscopic
observations of active M dwarfs. We examined the relationship between
the flare occurrence rate, flare energies, rotation period, filling
factor, and chromospheric activity indicators. Furthermore, the
correlation between flare amplitude and duration and cumulative flare
energy frequency distributions was investigated to probe the
underlying mechanisms driving magnetic activity in flaring M dwarfs.
We find that the flare occurrence rate displays a flat distribution
across spectral types M0-M4 (Teff∼3200K) and declines for later
types. Faster rotators with Prot<1day exhibit a higher flare
occurrence rate and flare activity. M dwarfs with a higher flare
occurrence rate tend to exhibit lower flare amplitudes, indicating
that frequent flares in these M dwarfs are generally less energetic.
Within the mass range of 0.15-0.76M☉, the median of
L{Halpha/Lbol in evenly divided mass bins of ∼0.1M☉ varies
by a factor of ∼2.5, while ΔEW decreases by 92% across the
sample. We derive power-law indexes of the cumulative flare frequency
distribution for M dwarf subgroups, indicating a decreasing trend from
M0 to M5 dwarfs with a value of alpha from 1.68 to 1.95, respectively.
We characterized the stellar activity in M dwarfs through
chromospheric indicators like Hα emission, star-spot coverage,
flare occurrence rates, flare energies, and flare duration. Our
results suggest a stellar activity transition near M4, with stronger
Hα emission linked to higher flare occurrence. Rapid rotators
(Prot<1day) exhibit significantly higher flare occurrence rate,
supporting the idea that strong magnetic dynamos in fast-rotating M
dwarfs sustain frequent flaring activity. Our analysis confirms that
highly active stars dissipate magnetic energy through numerous
low-energy flares rather than fewer high-energy events. We also show
that chromospheric activity and flare activity follow a power-law
relationship.
Description:
In this current study, our sample consists of bright field active
M dwarfs with spectral types ranging from M0 to M8.5, selected from
the catalog of Kumar et al. (2023MNRAS.524.6085K 2023MNRAS.524.6085K).
In this work, we have used TESS short cadence photometric data for the
active M dwarfs in our sample. This high cadence photometric data
enabled us to determine the Prot, FOR, flare energies, and fs of the M
dwarfs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 125 95 Summary of TESS observations of flaring targets
tablea2.dat 125 11 Summary of TESS observations of targets
for non-flaring sources
tableb1.dat 103 106 Stellar properties and derived parameters
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Byte-by-byte Description of file: tablea1.dat tablea2.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Source name
24 A1 --- n_Name [+] Note on Name (1)
26- 34 I9 --- TIC TESS Input Catalog ID
36- 40 F5.2 mag Tmag ? TESS magnitude
42- 46 F5.2 pc Dist ? Distance
48- 79 A32 --- Sectors Observed TESS sectors (comma-separated)
81- 99 A19 --- Years Observing years (comma-separated)
101-114 A14 --- Pipeline Pipeline(s) used (SPOC, TESS-SPOC)
116-125 A10 s Cadence Cadence(s) in seconds (20, 120, 200, 600)
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Note (1): Note as follows:
+ = no Gaia DR3 id (contamination not computed)
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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- 24 A24 --- Name Source identifier
26- 28 F3.1 --- SpType Spectral type
30- 34 F5.1 0.1nm EWHaMed Median Halpha equivalent width
36- 38 F3.1 0.1nm e_EWHaMed Uncertainty on EWHaMed
40- 45 F6.3 [-] log(LHa/Lbol) ? log10 Halpha to bolometric luminosity
ratio
47- 50 I4 K Teff Effective temperature
52- 57 F6.3 d Prot ? Rotation period
59- 62 F4.1 % fspot-pct ? Spot covering fraction
64- 68 F5.3 Msun Mass ? Stellar mass (solar units)
70- 74 F5.3 Rsun Radius ? Stellar radius (solar units)
76- 80 F5.3 % FOR-pct ? Flare occurrence rate
82- 88 F7.3 10-3 Lflare/Lbol ? Flare to bolometric luminosity ratio
90- 96 F7.3 10+25J Eflare ? Mean flare energy (in 1032erg unit)
98-103 F6.4 % Amed-pct ? Median flare amplitude
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Acknowledgements:
Arvind Rajpurohit, arvindr(at)prl.res.in
(End) Patricia Vannier [CDS] 08-Oct-2025