Asteroseismology of the double-radial mode $\delta$ Scuti star BP Pegasi

TL;DR

This study analyzes the pulsational frequencies of the $eta$ Cephei star BP Pegasi using photometry and seismic modeling, identifying fundamental and first overtone radial modes and exploring model dependencies on opacity data and stellar parameters.

Contribution

It provides the first detailed seismic analysis of BP Pegasi, identifying radial modes and constraining stellar parameters through Bayesian modeling.

Findings

Only two independent frequencies detected, both radial modes.

Seismic models depend strongly on opacity data and mixing length parameter.

Bayesian analysis constrains stellar parameters and mode identification.

Abstract

Using the ASAS data, we determine the pulsational frequencies of the high-amplitude $\delta$ Sct star BP Pegasi. The analysis revealed only the two known, independent frequencies. On the basis of multicolour Str\"omgren photometry, we independently find that both frequencies can only be associated with radial modes which, according to the frequency ratio, are fundamental and first overtone modes. The models fitting the two frequencies depend strongly on the opacity data. For low values of the mixing length parameter $\alpha_{\rm MLT}\approx 0.5$, only the OPAL seismic models in the post-main sequence phase of evolution are caught within the observed error box. Seismic OP and OPLIB models can only reach the error box if we increase $\alpha_{\rm MLT}$ to at least 2.0. Then, including the non-adiabatic parameter $f$ into our seismic modelling, we constrain various parameters, employing Monte Carlo-based Bayesian analysis.