New theoretical instability regions, period-luminosity relations and masses for blue large-amplitude pulsators

Abstract

Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot pulsating stars whose evolutionary status remains uncertain. Their supposed progenitors are either $\simeq 0.3M_{\odot}$ shell H-burning stars or $\simeq 1.0M_{\odot}$ core He-burning stars, both relying on mass loss or a merger event in a (rarely observed) close interacting binary system. With the goal to understand the stellar masses of BLAPs, we therefore carried out a linear non-adiabatic analysis of a grid of models computed using mesa-rsp, with appropriate input stellar parameters $ZXMLT_{\rm eff}$ and convection parameter sets. We discuss the impact of stellar mass, metallicity, helium abundance and convection parameters on the theoretical instability regions of BLAPs. We also derive new theoretical period relations; our theoretical period relations using low stellar masses seem to be in better agreement with the observed period relations. Although only two BLAPS have been observed to be multi-periodic oscillator so far, we analyse theoretical $P_{1O}/P_F$ ratios and compare these values with other classical pulsators. Furthermore, we provide the first asteroseismic mass estimate for the triple-mode pulsator, OGLE-BLAP-030 which seems to be well-constrained in the range of $0.62-0.64 M_{\odot}$ with a high metallicity of $Z=0.07$, albeit with a few sources of uncertainty involved. This would place the BLAP star intermediate to the two proposed mass scenarios so far.