Binaries: close; Galaxy: stellar content; Stars: early-type; Stars: evolution; Stars: oscillations; White dwarfs; Galaxy:stellar content; Large amplitude; Low-mass; Population synthesis; Radial mode; Star oscillations; Star: evolution; Stars:early type; Stellar astrophysics; Astronomy and Astrophysics; Space and Planetary Science
Abstract :
[en] Context. Blue large-amplitude pulsators (BLAPs) are a recently discovered group of hot stars pulsating in radial modes. Their origin needs to be explained, and several scenarios for their formation have already been proposed. Aims. We investigate whether BLAPs can originate as the product of a merger of two low-mass white dwarfs (WDs) and estimate how many BLAPs can be formed in this evolutionary channel. Methods. We used the Modules for Experiments in Stellar Astrophysics (MESA) code to model the merger of three different double extremely low-mass (DELM) WDs and the subsequent evolution of the merger product. We also performed a population synthesis of Galactic DELM WDs using the COSMIC code. Results. We find that BLAPs can be formed from DELM WDs provided that the total mass of the system ranges between 0.32 and 0.7 M⊙. BLAPs born in this scenario either do not have any thermonuclear fusion at all or show off-centre He burning. The final product evolves to hot subdwarfs and eventually finishes its evolution either as a cooling He WD or a hybrid He/CO WD. The merger products become BLAPs only a few thousand years after coalescence, and it takes them 20-70 thousand years to pass the BLAP region. We found the instability of the fundamental radial mode to be in fair agreement with observations, but we also observed instability of the radial first overtone. The calculated evolutionary rates of period change can be both positive and negative. From the population synthesis, we found that up to a few hundred BLAPs born in this scenario can exist at present in the Galaxy. Conclusions. Given the estimated number of BLAPs formed in the studied DELM WD merger scenario, there is a good chance to observe BLAPs that originated through this scenario. Since strong magnetic fields can be generated during mergers, this scenario could lead to the formation of magnetic BLAPs. This fits well with the discovery of two likely magnetic BLAPs whose pulsations can be explained in terms of the oblique rotator model.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Kolaczek-Szymanski, Piotr ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Pigulski, Andrzej ; University of Wrocław, Faculty of Physics and Astronomy, Astronomical Institute, Wrocław, Poland
Łojko, Piotr ; University of Wrocław, Faculty of Physics and Astronomy, Astronomical Institute, Wrocław, Poland
Language :
English
Title :
Blue large-amplitude pulsators formed from the merger of low-mass white dwarfs
NCN - Narodowe Centrum Nauki ULiège - University of Liège
Funding text :
This research was supported by the University of Li\u00E8ge under the Special Funds for Research, IPD-STEMA Programme.We are grateful to the anonymous referee for carefully reading the manuscript and providing us with many useful comments and suggestions that helped us significantly improve our paper. This work was supported by the National Science Centre, Poland, grant no. 2022/45/B/ST9/03862. This research made use of py-mesa-reader (Wolf & Schwab 2017), PyGYRE (https://pygyre.readthedocs.io/en/stable/), NumPy (Harris et al. 2020), SciPy (Virtanen et al. 2020) and Matplotlib (Hunter 2007). This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (Ochsenbein 1996). The original description of the VizieR service was published in Ochsenbein et al. (2000). This research has made use of NASA's Astrophysics Data System Bibliographic Services.We are grateful to the anonymous referee for carefully reading the manuscript and providing us with many useful comments and suggestions that helped us significantly improve our paper. This work was supported by the National Science Centre, Poland, grant no. 2022/45/B/ST9/03862. This research made use of py_mesa_reader (Wolf & Schwab 2017), PyGYRE ( https://pygyre.readthedocs.io/en/stable/ ), NumPy (Harris et al. 2020), SciPy (Virtanen et al. 2020) and Matplotlib (Hunter 2007). This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (Ochsenbein 1996). The original description of the VizieR service was published in Ochsenbein et al. (2000). This research has made use of NASA\u2019s Astrophysics Data System Bibliographic Services.
