Our simulations were performed with Our research was kindly supported by evolved sdB stars, core or envelope He-burning surviving companions of Ia-type supernovae products of MS+WD mergers products of a merger of two ELM WDs BLAPs BLAPs formed from the merger of extremely low-mass white dwarfs Piotr A. Kołaczek-Szymański *, Andrzej Pigulski , and Piotr Łojko 1,2, 1 1 A „digestible” poster Instytut Astronomiczny, Wydział Fizyki i Astronomii, Uniwersytet Wrocławski, Kopernika 11, 51-622 Wrocław, Poland 1 STAR Institute, Université de Liège, Quartier Agora, Allée du 6 Août 19c, Bât. B5c, 4000, Liège, Belgium 2 ... just follow the steps below to grasp its content Acknowledgements. PKS was supported by the University of Liège under the Special Funds for Research, IPD-STEMA Programme. PKS, AP, and PŁ appreciate the financial support from the Polish National Science Center grant no. 2022/45/B/ST9/03862. *e-mail:
[email protected] Blue Large-Amplitude Pulsators (BLAPs) are hot evolved stars with masses below or around that of the Sun. They pulsate radially with periods between 3 and 75 min and Vband amplitudes up to 0.5 mag, which is why they are named. In the H-R diagram, BLAPs are located between the main-sequence B-type stars and hot subdwarfs. Although they are usually faint (V>15 mag), their variability can be studied with the TESS data. BLAPs are extremely rare – only over 100 have been found in the Galaxy so far, after inspecting millions of stars. Their rarity suggests that they form through an unusual evolutionary scenario(s). BLAPs cannot form as a result of single-star evolution – they are products of interacting binary systems. Here are possible scenarios of their origin. pre-He white dwarfs, envelope H-burning Rapid accretion-phase (orange) and post-merger (red) MESA evolutionary tracks of BLAPs with three different masses, denoted as models “A”, “B”, and “C”. Seismic properties of our three BLAP models from the previous plot. Clockwise from top left: period of fundamental mode; its normalized growth rate; normalized growth rate of first-overtone; first-overtone-to-fundamental-mode period ratio. Predicted merger rate of Galactic binary HeWDs (black) and those that have a chance of becoming a BLAP (orange). The vertical line highlights the current age of the Universe. If you are interested in details, feel free to read our recent paper: Kołaczek-Szymański, Pigulski, and Łojko (2024), A&A, 691, A103 Worth remembering... BLAPs can be descendants of the mergers of binary (extremely) low-mass WDs. There should be currently up to a few hundreds of them in the Galaxy. Our seismic analysis shows that in such BLAPs both fundamental and first-overtone radial modes can be excited. We expect BLAPs formed from the mergers to exhibit large-scale, strong magnetic fields, making them behave as oblique pulsators. Questions to be answered... ...and the methods used Despite some loose suggestions, the hypothesis that BLAPs originate from merging binary ELM WDs has not been tested yet. We decided to address this question, along with two others: 1. What are the seismic properties of BLAPs formed in such a way? 2. How many of them might exist in our Galaxy today? The merger and the evolution of its product were simulated with MESA in the “slow merger” regime. Seismic properties were examined with GYRE. COSMIC served as the rapid binary population synthesis code.
