Magnetic blue large-amplitude pulsators (BLAPs)

With the discovery of blue large-amplitude pulsators (BLAPs), one of the most important questions to be resolved was to answer the question in which evolutionary channel(s) these radially pulsating stars can be formed. Situated on the H-R diagram between hot subdwarfs and the main sequence, they cannot be products of the evolution of single stars. Therefore, virtually all the scenarios that have been proposed to explain their origin, assumed binarity at some stage of their evolution. Among the scenarios that have emerged are those that assume that some BLAPs may have formed as the result of the merger of two low-mass white dwarfs or a white dwarf and a main-sequence star. The merger scenario may result in the formation of a magnetic field in the product of the merger, as is for example, postulated for magnetic white dwarfs. Pulsations in a star with a strong mognetic field can manifest in the way we know from rapidly oscillating Ap stars, that is, in the form of equidistant frequencies in the frequency spectrum, explained by the oblique pulsator model. We have shown that the three equidistant modes discovered in the first BLAP, OGLE-BLAP-001, can be explained in this way. Using all existing photometric data, including TESS observations, we found another BLAP with a similar frequency spectrum. Thus, at least these two stars seem to be good candidates for magnetic BLAPs, presumably the products of an evolution via merger. In our talk, we will summarize their properties and the current state of our work on magnetic BLAPs.