J/A+A/700/A227 AU Mic SPIRou RV, Bl, Bs and DetlaT (Donati+, 2025)
Six-year SPIRou monitoring of the young planet-host AU Mic.
Donati J.-F., Cristofari P.I., Moutou C., L'Heureux A., Cook N.J.,
Artigau E., Alencar S.H.P., Gaidos E., Vidotto A., Petit P., Carmona A.,
Ray T., the SPIRou science team
<Astron. Astrophys. 700, A227 (2025)>
=2025A&A...700A.227D 2025A&A...700A.227D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Stars, M-type ;
Radial velocities ; Magnetic fields
Keywords: techniques: polarimetric - stars: formation - stars: imaging -
stars: magnetic fields - planetary systems - stars: individual: AU Mic
Abstract:
In this paper we revisit our spectropolarimetric and velocimetric
analysis of the young M dwarf AU Mic based on data collected with
SPIRou at the Canada-France-Hawaii telescope, over a monitoring period
of 2041 d from 2019 to 2024. The longitudinal magnetic field, the
small-scale magnetic field, and the differential temperature of AU
Mic, derived from the unpolarized and circularly-polarized spectra,
were clearly modulated with the stellar rotation period, with a
pattern that evolved over time. The magnetic modeling with
Zeeman-Doppler imaging provides a consistent description of the global
field of AU Mic that agrees not only with the Least-Squares
Deconvolved profiles of the circularly-polarized and unpolarized
spectral lines, but also with the small-scale field measurements
derived from the broadening of spectral lines, for each of the 11
subsets of the full data. We find that the large-scale field was
mostly poloidal, with a dominant dipole component slightly tilted to
the rotation axis which decreased from 1.4 to 1.1kG before increasing
at the end of the campaign. The average small-scale field followed a
similar trend, decreasing from 2.8 to 2.6kG then rising. The
long-term magnetic evolution we report for AU Mic suggests that, if
cyclic, the cycle period is significantly longer than 6yr. From
velocimetric data, we derived improved mass estimates for the two
transiting planets, respectively equal to
Mb=6.3+2.5-1.8M{earth} and Mc=11.6+3.3-2.7M{earth},
yielding very contrasting densities of 0.32+0.13-0.10 and
2.9+1.1-0.8g/cm3, and a new 90% confidence upper limit of
4.9M{earth} for candidate planet d (period 12.7d) suspected to
induce the transit-timing variations of b and c. We also confirm our
claim regarding candidate planet e orbiting with a period of
33.11±0.06d, albeit with a smaller mass of
Me=21.1^+5.46-4.3M{earth}.
Description:
During this monitoring program, we recorded 161 new spectra of AU Mic
with SPIRou: 18 in late 2022, 76 in 2023 and 67 in 2024.
SPIRou records spectra covering the entire 0.95-2.50um (YJHK)
wavelength range in a single exposure, at a resolving power of 70000.
We analyzed an extended data set of 382 unpolarized and
circularly-polarized spectra of AU Mic collected with SPIRou over a
total timespan of 2041d from early 2019 to late 2024.
Objects:
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RA (2000) DE Designation(s)
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20 45 09.53 -31 20 27.2 AU Mic = TOI-2221
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 49 382 Observation log of Libre ESpRIT spectra,
AU Mic longitudinal magnetic field data
tablea2.dat 52 344 Observation log of APERO spectra,
AU Mic RV, Bs ans dT data
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See also:
J/A+A/654/A159 : CHEOPS photometry of Au Mic b transits in 2020 (Szabo+, 2021)
J/AJ/162/137 : Minerva-Australis radial velocity of AU Mic (Addison+, 2021)
J/AJ/164/110 : HST/COS far-UV spectra of AU Mic flares (Feinstein+, 2022)
J/A+A/659/L7 : AU Mic b and c transits with CHEOPS (Szabo+, 2022)
J/A+A/682/A170 : AU Mic dynamic spectra of 42 radio observations (Bloot+, 2024)
J/A+A/689/A132 : AU Mic radial velocity curves (Mallorquin+, 2024)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 12 F12.7 d BJD Barycentric Julian date (BJD-2459000)
14- 16 I3 --- c Cycle number
18- 22 F5.3 --- phi Phase
24- 28 F5.1 s Texp Exposure time
30- 32 I3 --- SN Signal-to-noise ratio
34- 37 F4.2 10-4 sigmaV rms noise level of Stokes V
39- 44 F6.1 G Bl Longitudinal magnetic field
46- 49 F4.1 G e_Bl Longitudinal magnetic field error
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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- 11 F11.6 d BJD Barycentric Julian date (BJD-2459000)
13- 15 I3 --- c Cycle number
17- 21 F5.3 --- phi Phase
23- 28 F6.1 m/s RV Radial velocity
30- 32 F3.1 m/s e_RV Radial velocity error
34- 37 F4.2 kG Bs ? Surface magnetic field
39- 42 F4.2 kG e_Bs ? Surface magnetic field error
44- 48 F5.1 K dT Differential temperature
50- 52 F3.1 K e_dT Differential temperature error
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Acknowledgements:
Jean-Francois Donati, jean-francois.donati(at)irap.omp.eu
(End) Patricia Vannier [CDS] 21-Jul-2025