J/A+A/691/A18 EX Lup ESPaDOnS and SPIRou spectra (Pouilly+, 2024)
Multi-kiloGauss magnetic field driving the magnetospheric accretion process
in EX Lupi.
Pouilly K., Audard M., Kospal A., Lavail A.
<Astron. Astrophys. 691, A18 (2024)>
=2024A&A...691A..18P 2024A&A...691A..18P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, pre-main sequence ; Spectroscopy ; Optical ; Infrared
Keywords: accretion, accretion disks - techniques: polarimetric -
techniques: spectroscopic - stars: magnetic field -
stars: individual: EX Lup - stars: variables: T Tauri - Herbig Ae/Be
Abstract:
EX Lupi is the prototype of EX Lup-type stars, meaning classical T
Tauri stars (cTTSs) showing luminosity bursts and outbursts of 1 to 5
magnitudes lasting for a few months to a few years. These events are
ascribed to an episodic accretion that can occur repeatedly but whose
physical mechanism is still debated.
In this work, we aim to investigate the magnetically-driven accretion
of EX Lup in quiescence, including for the first time a study of the
small and large-scale magnetic field. This allows us to provide a
complete characterisation of the magnetospheric accretion process of
the system.
We use spectropolarimetric times series acquired in 2016 and 2019 with
the Echelle SpectroPolarimetric Device for the Observation of Stars
and in 2019 with the SpectroPolarimetre InfraRouge at the
Canada-France-Hawaii telescope, during a quiescence phase of EX Lup.
We were thus able to perform a variability analysis of the radial
velocity, the emission lines and surface averaged longitudinal
magnetic field along different epochs and wavelength domains. We also
provide a small-scale magnetic field analysis using Zeeman
intensification of photospheric lines and large-scale magnetic
topology reconstruction using Zeeman-Doppler Imaging.
Our study reveals a typical magnetospheric accretion ongoing on
EX Lup, with a main accretion funnel flow connecting the inner disc to
the star in a stable fashion and producing an accretion shock on the
stellar surface close to the pole of the magnetic dipole component. We
also measure one of the strongest fields ever observed on cTTSs. Such
a strong field indicates that the disc is truncated by the magnetic
field close but beyond the corotation radius, where the angular
velocity of the disc equals the angular velocity of the star. Such a
configuration is suitable for a magnetically-induced disc instability
yielding episodic accretion onto the star.
Description:
2016 ESPaDOnS (proposal ID 16AF03, PI J. Bouvier) and 2019 ESPaDOnS
(proposal ID 19AF50, PI A. Carmona) and SPIRou (proposal ID 19AF09 PI
A. Carmona) polarimetric spectra of EX Lup.
Objects:
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RA (2000) DE Designation(s)
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16 03 05.49 -40 18 25.4 EX Lup = HD 325367
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 36 25 List of EX Lup ESPaDOnS and SPIRou reduced
polarimetric spectra
sp/* . 25 Individual spectrum files
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See also:
J/A+A/507/881 : Emission lines in EX Lup optical spectrum (Sipos+, 2009)
J/A+A/641/A33 : EX Lup SPHERE and SINFONI images (Rigliaco+, 2020)
J/MNRAS/526/4885 : EX Lup and TW Hya stable accretion (Sicilia-Aguilar+, 2023)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Inst Instrument (ESPaDOnS or SPIRou)
10- 22 F13.5 d HJD Heliocentric Julain date
24- 36 A13 --- FileName Name of the spectrum file in subdirectory sp
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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2- 10 F9.4 nm lambda Wavelength
12- 22 E11.4 --- I Normalised Stokes I
24- 34 E11.4 --- V ?=- Normalised Stokes V
36- 46 E11.4 --- N1 ?=- Null polarization spectrum value 1 (1)
48- 58 E11.4 --- N2 ?=- Null polarization spectrum value 2 (1)
61- 70 E10.4 --- e_I ?=- Error on normalised Stokes I and V
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Note (1): two check spectra for a null polarisation, allowing to check if a
polarisation signature is real or not
(see Donati et al., 1997MNRAS.291..658D 1997MNRAS.291..658D, Eq. 3).
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Acknowledgements:
Kim Pouilly, Kim.Pouilly(at)unige.ch
(End) Patricia Vannier [CDS] 14-Sep-2024