J/A+A/676/A56 Large-scale magnetic field of AD Leo (Bellotti+, 2023)
Monitoring the large-scale magnetic field of AD Leo with SPIRou, ESPaDOnS, and
Narval. Towards a magnetic polarity reversal?
Bellotti S., Morin J., Lehmann L.T., Folsom C.P., Hussain G.A.J., Petit P.,
Donati J-F., Lavail A., Carmona A., Martioli E., Romano Zaire B.,
Alecian E., Moutou C., Fouque P., Alencar S., Artigau E., Boisse I.,
Bouchy F., Cadieux C., Cloutier R., Cook N.J., Delfosse X., Doyon R.,
Hebrard G., Kochukhov O., Wade G.A.
<Astron. Astrophys. 676, A56 (2023)>
=2023A&A...676A..56B 2023A&A...676A..56B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, M-type ; Magnetic fields ; Polarization ; Optical ;
Infrared
Keywords: stars: individual: AD Leo - stars: activity - stars: magnetic field -
techniques: polarimetric
Abstract:
One clear manifestation of dynamo action on the Sun is the 22-yr
magnetic cycle, exhibiting a polarity reversal and a periodic
conversion between poloidal and toroidal fields. For M dwarfs, several
authors claim evidence of activity cycles from photometry and
spectroscopic indices analyses, but no clear polarity reversal has
been identified from spectropolarimetric observations. These stars are
excellent laboratories to investigate dynamo- powered magnetic fields
under different stellar interior conditions, i.e. partly- or
fully-convective. Our aim is to monitor the evolution of the large-
scale field of AD Leo, which has shown hints of a secular evolution
from past dedicated spectropolarimetric campaigns. This is of central
interest to inform distinct dynamo theories, contextualise the
evolution of the solar magnetic field, and explain the variety of
magnetic field geometries observed in the past. We analysed
near-infrared spectropolarimetric observations of the active M dwarf
AD Leo taken with SPIRou between 2019 and 2020 and archival optical
data collected with ESPaDOnS and Narval between 2006 and 2019. We
searched for long-term variability in the longitudinal field, the
width of unpolarised Stokes profiles, the unsigned magnetic flux
derived from Zeeman broadening,and the geometry of the large-scale
magnetic field using both Zeeman-Doppler Imaging and Principal
Component Analysis. We found evidence of a long-term evolution of the
magnetic field, featuring a decrease in axisymmetry (from 99 % to 60%).
This is accompanied by a weakening of the longitudinal field (-300
to -50G) and a correlated increase in unsigned magnetic flux (2.8 to
3.6kG). Likewise, the width of the mean profile computed with
selected near-infrared lines manifests a long-term
evolution corresponding to field strength changes over the full time
series, but does not exhibit modulation with the stellar rotation of
AD Leo in individual epochs. The large-scale magnetic field of AD Leo
manifested first hints of a polarity reversal in late 2020 in the form
of a substantially increased dipole obliquity,while the topology
remained predominantly poloidal and dipolar for 14 yr. This suggests
that low-mass M dwarfs with a dipole dominated magnetic field can
undergo magnetic cycles.
Description:
A total of 77 spectropolarimetric observations in the nearinfrared
were collected with the SpectroPolarimetre InfraRouge (SPIRou) within
the SLS. SPIRou is a stabilised high-resolution near-infrared
spectropolarimeter mounted on the 3.6m CFHT atop Maunakea,
Observations were performed in circular polarisation mode
between February 2019 and June 2020, spanning 482 days in total; the
journal of observations is available in Table D1.
For most of the analyses presented here, we considered all
archival observations collected with ESPaDOnS and Narval, and studied
previously in Morin et al. (2008MNRAS.390..567M 2008MNRAS.390..567M, Cat. J/MNRAS/390/567)
and Lavail et al. (2018MNRAS.479.4836L 2018MNRAS.479.4836L). We also included six new
observations taken in November 2019 (from 2019.87 to 2019.89) with
ESPaDOnS for CFHT programme 19BC06, PI A. Lavail (reported in Table
D2).
The list of measurements is reported in Table D3.
Objects:
---------------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------------
10 19 36.28 +19 52 12.0 AD Leo = 2MASS J10193634+1952122
---------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tabled1.dat 43 71 List of ESPaDOnS 2019 observations for AD Leo
tabled2.dat 43 6 List of ESPaDOnS 2019 observations for AD Leo
tabled3.dat 52 126 List of longitudinal field and magnetic flux
measurements for AD Leo
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See also:
J/MNRAS/390/567 : Magnetic field and velocity of mid M dwarfs (Morin+, 2008)
Byte-by-byte Description of file: tabled1.dat tabled2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "date" Obs.date Date of observation
12- 22 A11 "h:m:s" Obs.time Universal time of observations
24- 29 F6.2 --- Ncyc Cycle number as computed with Eq. 1
31- 35 A5 s Texp Exposure time of polarimetric sequence
37- 39 I3 --- S/N Signal-to-noise ratio of at 1650nm
41- 43 F3.1 --- RMS RMS noise level of Stokes V
(in 1e-4 unpolarised continuum unit)
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Byte-by-byte Description of file: tabled3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.4 d HJD Heliocentric julian date of the observation
(HJD-2450000)
11- 16 F6.1 gauss Bl Longitudinal field
18- 21 F4.1 gauss e_Bl Formal error bar on longitudinal field
23- 28 F6.2 kgauss SBf ? Magnetic flux
30- 35 F6.2 kgauss E_SBf ? Upper error bar on magnetic flux
38- 43 F6.2 kgauss e_SBf ? Lower error bar on magnetic flux
45- 52 A8 --- Inst Instrument
--------------------------------------------------------------------------------
Acknowledgements:
Stefano Bellotti, bellotti(at)strw.leidenuniv.nl
References:
Bellotti et al., The space weather around the exoplanet GJ 436b,
https://ui.adsabs.harvard.edu/abs/2023arXiv230615391B/abstract
(End) Patricia Vannier [CDS] 04-Jul-2023