Volume 627, July 2019
|Number of page(s)||25|
|Section||Stellar structure and evolution|
|Published online||27 June 2019|
Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria
2 LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
3 Instytut Astronomiczny, Uniwersytet Wroclawski, Kopernika 11, 51-622 Wroclaw, Poland
4 Institut für Kommunikationsnetze und Satellitenkommunikation, Technical University Graz, Inffeldgasse 12, 8010 Graz, Austria
5 Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, CS 34229, 06304 Nice Cedex 4, France
6 Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland
7 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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 Institute of Automatic Control, Silesian University of Technology, Akademicka 16, Gliwice, Poland
11 Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario M5S 3H4, Canada
12 Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Stn Forces, Kingston K7K 7B4 Ontario, Canada
13 Universität Wien, Institut für Astrophysik, Türkenschanzstrasse 17, 1180 Wien, Austria
14 Department of Physics, University of California at Santa Barbara, Santa Barbara, CA 93111, USA
15 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
16 South African Astronomical Observatory, Observatory Rd, Observatory Cape Town, 7700 Cape Town, South Africa
17 Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
18 Department of Astronomy, University of Cape Town, Rondebosch, 7700 Cape Town, South Africa
19 Jet Propulsion Laboratory, California Institute of Technology, M/S 321-100, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
20 Department of Physics & Astronomy, University of Rochester, 500 Wilson Blvd., Rochester, NY 14627, USA
21 Institut de Recherche sur les Exoplanètes, Département de Physique, Université de Montréal, Montréal, QC H3C 3J7, Canada
Accepted: 14 May 2019
Context. Exoplanet properties crucially depend on the parameters of their host stars: more accurate stellar parameters yield more accurate exoplanet characteristics. When the exoplanet host star shows pulsations, asteroseismology can be used for an improved description of the stellar parameters.
Aims. We aim to revisit the pulsational properties of β Pic and identify its pulsation modes from normalized amplitudes in five different passbands. We also investigate the potential presence of a magnetic field.
Methods. We conducted a frequency analysis using three seasons of BRITE-Constellation observations in the two BRITE filters, the about 620-day-long bRing light curve, and the nearly 8-year-long SMEI photometric time series. We calculated normalized amplitudes using all passbands and including previously published values obtained from ASTEP observations. We investigated the magnetic properties of β Pic using spectropolarimetric observations conducted with the HARPSpol instrument. Using 2D rotating models, we fit the normalized amplitudes and frequencies through Monte Carlo Markov chains.
Results. We identify 15 pulsation frequencies in the range from 34 to 55 d−1, where two, F13 at 53.6917 d−1 and F11 at 50.4921 d−1, display clear amplitude variability. We use the normalized amplitudes in up to five passbands to identify the modes as three ℓ = 1, six ℓ = 2, and six ℓ = 3 modes. β Pic is shown to be non-magnetic with an upper limit of the possible undetected dipolar field of 300 Gauss.
Conclusions. Multiple fits to the frequencies and normalized amplitudes are obtained, including one with a near equator-on inclination for β Pic, which corresponds to our expectations based on the orbital inclination of β Pic b and the orientation of the circumstellar disk. This solution leads to a rotation rate of 27% of the Keplerian breakup velocity, a radius of 1.497 ± 0.025 R⊙, and a mass of 1.797 ± 0.035 M⊙. The ∼2% errors in radius and mass do not account for uncertainties in the models and a potentially erroneous mode-identification.
Key words: asteroseismology / stars: individual: β Pictoris / stars: interiors / stars: variables: δ Scuti / stars: magnetic field
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).
Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 094.D-0274A.
Light-curve data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A28
© ESO 2019
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