J/A+A/708/A207 Relative magnetic fields of 3 M dwarfs (Cristofari+, 2026)
A fast method for deriving relative small-scale magnetic field variations from
high-resolution spectroscopy.
Cristofari P.I., Saar S.H., Vidotto A.A., Bellotti S.
<Astron. Astrophys. 708, A207 (2026)>
=2026A&A...708A.207C 2026A&A...708A.207C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, M-type ; Magnetic fields ; Optical
Keywords: techniques: spectroscopic - stars: low-mass -stars: magnetic field
Abstract:
Setting observational constraints on stellar magnetic fields is
essential for both stellar and planetary physics. They play a key role
in the formation and evolution of stars and planets, and they are
responsible for spurious signals in radial velocity curves that impact
the detection and characterization of exoplanets. Recent observations
have revealed the diversity and evolution of large-scale magnetic
fields in low-mass stars. However, these large-scale fields only
account for a small fraction of the observed unsigned magnetic flux.
The other crucial stellar magnetism information originates from
(spatially) small-scale magnetic fields, which account for most of the
surface magnetic flux and exhibit a clear temporal evolution on
timescales of many years.
With this work, we aim to develop new fast techniques to extract
small-scale magnetic field estimates from time series of observed
high-resolution spectra. One objective is to develop tools that will
enable the community to take full advantage of the upcoming monitoring
surveys carried out with various high-resolution spectrometers. Our
ultimate goal is to study the temporal evolution of small-scale
magnetic fields and offer insights into the magnetic properties of
low-mass stars and their magnetic cycles.
We implemented a process to capture relative pixel variations caused
by changes in magnetic field strengths, relying on synthetic spectra
computed with ZeeTurbo. This approach provides extremely fast and
reliable estimates of relative magnetic field strength variations from
series of high-resolution spectra, mitigating the impact of
systematics between models and observations. We assessed the
performance of the proposed method through its application to
simulated data and publicly available observed spectra recorded with
SPIRou, Narval, and ESPaDOnS. In addition, we implemented a
model-driven process to derive relative temperature variations and we
explored the influence magnetic fields have on these measurements.
Our results are in excellent agreement with the magnetic field
estimates previously obtained from spectra recorded with SPIRou. This
method provides robust constraints on the structure of the magnetic
field variations and proves to be relatively insensitive to small
changes in the assumed atmospheric parameters and broadening. We find
that magnetic field variations have the potential of introducing
biases in relative temperature estimates. This is particularly
relevant in the case of the Narval/ESPaDOnS spectral domains, which
contain a large number of magnetically sensitive transitions and where
contrast is more important. Our application to archival data provides
new constraints on the evolution of small-scale magnetic fields and
underscores the potential of the proposed method for analyzing data in
the context of large observation programs.
By reducing the problem to a set of linear equations, our method
offers extremely fast results, making it viable for integration in
future pipelines developed for large spectroscopic surveys. These
estimates will provide much needed information to correct radial
velocity curves and constrain dynamo processes.
Description:
The tables contain the relative small-scale magnetic field
measurements and relative temperature variations derived with the
methods described in the paper.
For each table, the first column contains the modified Julian date
(MJD), the second column contains the relative surface magnetic field
estimates, and the third column contains the uncertainties associated
with the surface magnetic fields estimates. The fourth and fifth
columns contain the relative temperature variations and uncertainties
on the relative temperature variations, respectively.
Objects:
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RA (2000) DE Designation(s)
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22 46 49.73 +44 20 02.3 EV Lac = BD+43 4305
11 02 38.34 +21 58 01.7 DS Leo = HIP 53985
17 57 48.49 +04 41 36.1 Barnard's star = BD+04 3561a
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 33 177 δB and δT measurements obtained for
EV Lac from spectra recorded with SPIRou
tablea2.dat 33 173 δB and δT measurements obtained for
DS Leo from spectra recorded with SPIRou
tablea3.dat 33 419 δB and δT measurements obtained for
Barnard's star from spectra recorded with SPIRou
tablea4.dat 33 67 δB and δT measurements obtained for
EV Lac from spectra recorded with Narval/ESPaDOnS
tablea5.dat 33 61 δB and δT measurements obtained for
DS Leo from spectra recorded with Narval/ESPaDOnS
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Byte-by-byte Description of file: tablea?.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d MJD Modified Julian Date
12- 16 F5.2 kG Relative surface magnetic field estimate
18- 21 F4.2 kG e_ Uncertainty on relative surface magnetic field
23- 28 F6.2 K dTemp Relative temperature variation estimate
30- 33 F4.2 K e_dTemp Uncertainty on relative temperature variation
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Acknowledgements:
Paul Cristofari, cristofari(at)strw.leidenuniv.nl
(End) Patricia Vannier [CDS] 03-Mar-2026