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.
Astronomy and Astrophysics
- Pub Date:
- July 2019
- stars: individual: β Pictoris;
- stars: interiors;
- stars: variables: δ Scuti;
- stars: magnetic field;
- Astrophysics - Solar and Stellar Astrophysics
- 26 pages, 19 figures, accepted in Astronomy &