Seismic modelling of a very young SPB star - KIC 8264293

MC 8264293 is a fast-rotating B-type pulsator observed by Kepler satellite. Its photometric variability is mainly due to pulsations in high-order g modes. Besides, we detected a weak H alpha emission. Thus, the second source of variability is the fluctuation in a disc around the star. The pulsational spectrum of MC 8264293 reveals a frequency grouping and period spacing pattern. Here, we present the thorough seismic analysis of the star based on these features. Taking into account the position of the star in the HR diagram and fitting the 14 frequencies that form the period spacing, we constrain the internal structure of the star. We conclude that the star barely left the zero-age main sequence and the best seismic model has M = 3.54 M-circle dot, V-rot = 248 km s(-1), and Z = 0.0112. We found the upper limit on the mixing at the edge of the convective core, with the overshooting parameter up tofov = 0.03. On the other hand, we were not able to constrain the envelope mixing for the star. To excite the modes in the observed frequency range, we had to modify the opacity data. Our best seismic model with an opacity increase by 100 per cent at the 'nickel' bump log T = 5.46 explains the whole instability. KIC 8264293 is the unique, very young star pulsating in high-order g modes with the Be feature. However, it is not obvious whether the source of this circumstellar matter is the ejection of mass from the underlying star or whether the star has retained its protostellar disc.

Automated summary

In this study, we conducted a thorough seismic analysis of MC 8264293, a fast-rotating B-type pulsator observed by the Kepler satellite. By fitting the period spacing and considering the position of the star in the HR diagram, we constrained the internal structure and physical parameters of the star. We found that the star is very young and has not yet left the zero-age main sequence. The star's photometric variability is mainly due to its pulsations in high-order g modes, as well as the fluctuation in its circumstellar disc.