Volume 643, November 2020
|Number of page(s)||23|
|Section||Stellar structure and evolution|
|Published online||11 November 2020|
Institute for Astro- and Particle Physics, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
2 LESIA, Paris Observatory, PSL University, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, 92195 Meudon, France
3 Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
4 Institute of Astronomy, Russian Academy of Sciences (RAS), Pyatnitskaya 48, 119017 Moscow, Russia
5 Instytut Astronomiczny, Uniwersytet Wroclawski, ul. Kopernika 11, 51-622 Wroclaw, Poland
6 Institut für Kommunikationsnetze und Satellitenkommunikation, Technical University Graz, Inffeldgasse 12, 8010 Graz, Austria
7 Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
8 Département de physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, Québec H3C 3J7, Canada
9 Centre de Recherche en Astrophysique du Québec (CRAQ), Montréal, Québec H3C 3J7, Canada
10 American Association of Variable Star Observers, 49 Bay State Road, Cambridge, MA 02138, USA
11 Silesian University of Technology, Department of Electronics, Electrical Engineering and Microelectronics, Akademicka 15, 44-100 Gliwice, Poland
12 Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston, K7K 7B4 Ontario, Canada
Accepted: 10 September 2020
Context. F-type stars are characterised by several physical processes such as different pulsation mechanisms, rotation, convection, diffusion, and magnetic fields. The rapidly rotating δ Scuti star β Cas can be considered as a benchmark star to study the interaction of several of these effects.
Aims. We investigate the pulsational and magnetic field properties of β Cas. We also determine the star’s apparent fundamental parameters and chemical abundances.
Methods. Based on photometric time series obtained from three different space missions (BRITE-Constellation, SMEI, and TESS), we conduct a frequency analysis and investigate the stability of the pulsation amplitudes over four years of observations. We investigate the presence of a magnetic field and its properties using spectropolarimetric observations taken with the Narval instrument by applying the least-squares deconvolution and Zeeman-Doppler imaging techniques.
Results. The star β Cas shows only three independent p-mode frequencies down to the few ppm-level; its highest amplitude frequency is suggested to be an n = 3, ℓ = 2, m = 0 mode. Its magnetic field structure is quite complex and almost certainly of a dynamo origin. The atmosphere of β Cas is slightly deficient in iron peak elements and slightly overabundant in C, O, and heavier elements.
Conclusions. Atypically for δ Scuti stars, we can only detect three pulsation modes down to exceptionally low noise levels for β Cas. The star is also one of very few δ Scuti pulsators known to date to show a measurable magnetic field and the first δ Scuti star with a dynamo magnetic field. These characteristics make β Cas an interesting target for future studies of dynamo processes in the thin convective envelopes of F-type stars, the transition region between fossil and dynamo fields, and the interaction between pulsations and magnetic field.
Key words: stars: individual: β Cas / stars: variables: δ / stars: atmospheres / stars: magnetic field / stars: abundances
The BRITE data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/643/A110
Based on data collected by the BRITE Constellation satellite mission, designed, built, launched, operated and supported by the Austrian Research Promotion Agency (FFG), the University of Vienna, the Technical University of Graz, the University of Innsbruck, the Canadian Space Agency (CSA), the University of Toronto Institute for Aerospace Studies (UTIAS), the Foundation for Polish Science & Technology (FNiTP MNiSW), and National Science Centre (NCN). Also based on observations obtained at the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique (CNRS) of France.
© ESO 2020
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