J/A+A/702/A111 Magnetic field measurements of 6 M dwarfs (Cristofari+, 2025)
Rotational modulation and long-term evolution of the small-scale magnetic fields
of M dwarf observed with SPIRou.
Cristofari P.I., Donati J.-F., Bellotti S., Artigau E., Carmona A.,
Moutou C., Delfosse X., Petit P., Finociety B., Dias do Nascimento J.
<Astron. Astrophys. 702, A111 (2025)>
=2025A&A...702A.111C 2025A&A...702A.111C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, M-type ; Magnetic fields
Keywords: techniques: spectroscopic - stars: low-mass - stars: magnetic field
Abstract:
M dwarfs are known to host magnetic fields, impacting exoplanet
studies and playing a key role in stellar and planetary formation and
evolution. Observations revealed the long-term evolution of the
large-scale magnetic field reconstructed with Zeeman-Doppler imaging,
and a diversity of their topologies. These large-scale magnetic fields
only account for a small amount of the unsigned magnetic flux that can
be probed by directly modeling the Zeeman broadening of spectral lines
in unpolarized spectra.
We aim at investigating the long-term behavior of the average
small-scale magnetic field of M dwarfs with time, and assess our
ability to detect rotational modulation from time series of field
measurements derived from unpolarized spectra.
We perform fits of synthetic spectra computed with ZeeTurbo to
near-infrared high-resolution spectra recorded with SPIRou between
2019 and 2024 in the context of the SLS and SPICE large programs. The
analysis is performed on the spectra of 2 partially convective (AD
Leo, DS Leo) and 3 fully convective (PM J18482+0741, CN Leo, Barnard
star) M dwarfs, along with EV Lac whose mass is close to the
fully-convective limit. Our analysis provides measurements of the
average small-scale magnetic field, which are compared to longitudinal
magnetic field and temperature variation measurements (dTemp) obtained
from the same data.
We were able to detect the rotation period in the small-scale magnetic
field series for 4 of the 6 stars in our sample. We find that the
average magnetic field can vary by up to 0.3kG throughout the year
(e.g., CN Leo), or of up to 1kG across rotation phases. The rotation
periods retrieved from longitudinal and small-scale magnetic fields
are found in agreement within error bars. dTemp measurements are found
to anti-correlate with small- scale magnetic field measurements for
three stars (EV Lac, DS Leo and Barnard's star).
The results demonstrate our ability to measure rotation periods from
high-resolution data through small-scale magnetic field measurements,
provided that the inclination of the observed targets is sufficiently
large. We observe long-term fluctuations of the average magnetic field
that could indicate magnetic cycles in the parent dynamo processes.
These long-term variations appear mainly uncorrelated with large-scale
magnetic field variations probed through longitudinal field
measurements. Large variations in the amplitude of the rotationally
modulated signals, in particular, hint towards a change in the
distribution of the surface inhomogeneities accessible to Zeeman
broadening measurements.
Description:
Small-scale and large-scale magnetic field measurements, along with
relative temperature variation estimates for EV Lac, DS Leo, CN Leo,
AD Leo, Barnard's star and PM J18482+0741.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 102 6 Atmospheric parameters and small-scale magnetic field
tablea7.dat 92 188 and dTemp Measurements obtained each night
for DS Leo
tablea8.dat 92 178 and dTemp Measurements obtained each night
for EV Lac
tablea9.dat 92 77 and dTemp Measurements obtained each night
for AD Leo
tablea10.dat 92 166 and dTemp Measurements obtained each night
for CN Leo
tablea11.dat 92 106 and dTemp Measurements obtained each night
for PMJ 18482+074
tablea12.dat 92 399 and dTemp Measurements obtained each night
for Barnard's star
tablea13.dat 24 185 Bl measurements obtained each night for DS Leo
tablea14.dat 24 174 Bl measurements obtained each night for EV Lac
tablea15.dat 24 67 Bl measurements obtained each night for AD Leo
tablea16.dat 24 155 Bl measurements obtained each night for CN Leo
tablea17.dat 24 98 Bl measurements obtained each night for PMJ 18482+0741
tablea18.dat 24 390 Bl measurements obtained each night for Barnard's star
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Star Star name
16- 19 I4 K Teff Effective temperature
21- 22 I2 K e_Teff Effective temperature error
24- 27 F4.2 [cm/s2] logg Surface gravity
29- 32 F4.2 [cm/s2] e_logg Surface gravity error
34- 38 F5.2 [-] [M/H] Metallicity
40- 43 F4.2 [-] e_[M/H] Metallicity error
44 A1 --- n_[M/H] [c] Notre on [M/H] (1)
46 A1 --- l_vsini Limit flag on vsini
47- 49 F3.1 km/s vsini Projected rotational velocity (2)
50 A1 --- n_vsini [d] Note on vsini (1)
52- 53 I2 deg Incl ?=- Inclination (3)
55- 56 I2 deg e_Incl ?=- Inclination error
58- 61 F4.2 km/s ksiRT Micro-turbulent velocity (4)
63- 66 F4.2 km/s e_ksiRT Micro-turbulent velocity error
68- 71 F4.2 kG Surface magnetic field
73- 76 F4.2 kG e_ Surface magnetic field error
78- 89 A12 --- FileName1 Name of the table with and dTemp
measurements
91-102 A12 --- FileName2 Name of the table with Bl measurements
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Note (1): Notes as follows:
c = For Barnard's star, we additionally fit for the [alpha/Fe] parameter
(see Cristofari et al., 2022MNRAS.516.3802C 2022MNRAS.516.3802C),
yielding [alpha/Fe]=0.09±0.10dex.
d = Maximum vsini assuming an inclination of 90° .
Note (2): Projected rotational velocities (vsini) for our analyses were taken
from Morin et al. (2008MNRAS.390..567M 2008MNRAS.390..567M, Cat. J/MNRAS/490/567) for AD Leo and
Reiners et al. (2018A&A...612A..49R 2018A&A...612A..49R, Cat. J/A+A/612/A59) for PM J18482+0741.
For CN Leo, EV Lac, and DS Leo, vsini estimates were taken from Cristofari
et al. (2023MNRAS.522.1342C 2023MNRAS.522.1342C), who revised some values based on rotation periods
and radii. Inclinations were derived from vsini, Prot and radii.
Note (3): Inclinations computed assuming a 1.0km/s uncertainty on vsini.
Note (4): In the present analysis, we fixed vsini and fit ksiRT. Consequently,
broadening arising from non-physical or unidentified sources may lead to
larger ksiRT estimates.
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Byte-by-byte Description of file: tablea[789].dat tablea1[012].dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 --- MJD Modified Julian Date
12- 15 F4.2 kG Surface magnetic field
17- 20 F4.2 kG e_ Uncertainty on surface magnetic field
22- 25 F4.1 --- f0 0kG component filling factor
27- 30 F4.1 --- e_f0 Uncertainty on f0
32- 35 F4.1 --- f2 2kG component filling factor
37- 40 F4.1 --- e_f2 Uncertainty on f2
42- 45 F4.1 --- f4 4kG component filling factor
47- 50 F4.1 --- e_f4 Uncertainty on f4
52- 55 F4.1 --- f6 6kG component filling factor
57- 60 F4.1 --- e_f6 Uncertainty on f6
62- 65 F4.1 --- f8 8kG component filling factor
67- 70 F4.1 --- e_f8 Uncertainty on f8
72- 75 F4.1 --- f10 10kG component filling factor
77- 80 F4.1 --- e_f10 Uncertainty on f10
82- 87 F6.2 K dTemp ?=- Temperature variation estimates
89- 92 F4.2 K e_dTemp ?=- Uncertainty on dTemp
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Byte-by-byte Description of file: tablea1[345678].dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d MJD Modified Julian Date
12- 18 F7.2 G Bl Longitudinal magnetic field
20- 24 F5.2 G e_Bl Uncertainty on longitudinal magnetic field
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Acknowledgements:
Paul Cristofari, cristofari(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 23-Sep-2025