Multi-instrumental view of magnetic fields and activity of ϵ Eridani with SPIRou, NARVAL, and TESS

• Published in: Astronomy & Astrophysics
• Main Authors: Petit, P., Folsom, C. P., Donati, J.-F., Yu, L., Do Nascimento, J.-D., Jeffers, S. V., Marsden, S. C., Morin, J., Vidotto, A. A.
• Other Authors: Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Université Fédérale Toulouse Midi-Pyrénées-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Royal Military College of Canada, Universidade Federal do Rio Grande do Norte Natal (UFRN), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University Cambridge -Smithsonian Institution, Max-Planck-Institut für Sonnensystemforschung (MPS), Max-Planck-Gesellschaft, University of Southern Queensland (USQ), Laboratoire Univers et Particules de Montpellier (LUPM), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Trinity College Dublin
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: stars: activity; stars: solar-type; stars: magnetic field; stars: rotation; [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]; narval
• Online Access: https://hal.archives-ouvertes.fr/hal-03197552; https://hal.archives-ouvertes.fr/hal-03197552/document; https://hal.archives-ouvertes.fr/hal-03197552/file/aa40027-20.pdf; https://doi.org/10.1051/0004-6361/202040027

International audience Aims. We report on observations of the active K2 dwarf ϵ Eridani based on contemporaneous SPIRou, NARVAL and TESS data obtained over two months in late 2018, when the activity of the star was reported to be in a non-cyclic phase.Methods. Near-infrared (NIR) spectropolarimetry was obtained using SPIRou over four nights in late September, while visible spectropolarimetry was collected with NARVAL over 20 nights, spread between 18 September and 07 November. We first recovered the fundamental parameters of the target from both visible and NIR spectral fitting. The large-scale magnetic field was investigated from polarimetric data. From unpolarized spectra, we estimated the total magnetic flux through Zeeman broadening of magnetically sensitive NIR lines and the chromospheric emission using the CaII H&K lines. The photometric monitoring, secured with TESS between 19 October and 15 November, is modelled with pseudo-periodic Gaussian process regression.Results. Fundamental parameters of ϵ Eridani derived from visible and NIR wavelengths provide us with consistent results, which also agree with published values. We report a progressive increase of macroturbulence towards larger NIR wavelengths. Zeeman broadening of individual lines highlights an unsigned surface magnetic field Bmono = 1.90 ± 0.13 kG, with a filling factor f = 12.5 ± 1.7% (unsigned magnetic flux Bf = 237 ± 36 G). The large-scale magnetic field geometry, chromospheric emission and broadband photometry display clear signs of non-rotational evolution over the course of data collection. Characteristic decay times deduced from the light curve and longitudinal field fall in the range 30–40 days, while the characteristic timescale of surface differential rotation, as derived through the evolution of the magnetic geometry, is equal to 57 ± 5 days. The large-scale magnetic field exhibits a combination of properties not observed previously for ϵ Eridani, with a surface field among the weakest previously reported, but this field is also ...