High-precision Asteroseismology in a Slowly Pulsating B Star: HD 50230

Abstract

The slowly pulsating B star HD 50230, which is in fact a hybrid B-type pulsator, has been observed by CoRoT for at least 137 days. Nearly equidistant period spacing patterns are found among eight modes that are extracted from the oscillation spectrum with more than 500 frequencies. However, it is thought to be most likely accidental by Szewczuk et al. In the present work, we analyze the eight modes in depth with the χ 2 -matching method. Based on the best-fitting model (model MA), we find that they can be well explained as sequences of consecutive dipolar ( l , m ) = (1, 0). The period discrepancies between observations and the best-fitting model are within 100 s except for the outlier, which is up to 300 s. Based on the calculated χ 2 -minimization models, we find that, for pure g-mode oscillations, the buoyancy radius, Λ 0 , can be precisely measured with the χ 2 -matching method between observations and calculations. It represents the “propagation time” of the g-mode from the stellar surface to the center. It is of Λ 0  = 245.78 ± 0.59 μ Hz with a precision of 0.24%. In addition, we also find that HD 50230 is a metal-rich ( Z init = 0.034–0.043) star with a mass of M  = 6.15–6.27  M ⊙ . It is still located in the hydrogen-burning phase with central hydrogen of X C  = 0.298–0.316 (or ); therefore, it has a convective core with a radius of R cc  = 0.525–0.536  R ⊙ (or ). In order to interpret the structure of the observed period spacing pattern well, the convective core overshooting ( f ov = 0.0175–0.0200) and the extra diffusion mixing ( ) should be taken into account in theoretical models.