Abstract :
[en] Blue large-amplitude pulsators (BLAPs) are a newly discovered group of compact pulsating stars whose origins are yet to be explained. Of the existing evolutionary scenarios that could lead to the formation of BLAPs, there are two positing that BLAPs are the products of the merger of two stars: either a main-sequence star and a helium white dwarf or two low-mass helium white dwarfs. Among over a hundred known BLAPs, three equidistant modes, in terms of frequency, had been found in one, namely, OGLE-BLAP-001. We show that three modes that are similarly equidistant in frequency do exist in yet another BLAP, namely, ZGP-BLAP-08. This perfect separation in frequency is a strong argument for explaining the modes in terms of an oblique pulsator model. This model is supported by the character of the changes of the pulsation amplitude and phase with the rotational phase. Consequently, we hypothesise that these two BLAPs are magnetic, as equidistant modes in terms of the frequency pulsation would be observed in the presence of a magnetic field whose axis of symmetry does not coincide with the rotational axis. A logical consequence of this hypothesis is to postulate that these two BLAPs could have originated in a merger scenario, similarly to what is believed to be behind the origin of magnetic white dwarfs. We also find that period changes in both stars cannot be interpreted by a constant rate of period change. We discuss the possible origins of these changes.
Funding text :
This research was supported by the University of Li ge under the Special Funds for Research, IPD-STEMA Programme. We thank the anonymous referee for useful comments and suggestions. This work was supported by the National Science Centre, Poland, grant no. 2022/45/B/ST9/03862. This work used the SIMBAD and Vizier services operated by Centre des Donn es astronomiques de Strasbourg (France), and bibliographic references from the Astrophysics Data System maintained by SAO/NASA. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www. cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA s Science Mission Directorate. This work used data collected by the Optical Gravitational Lensing Experiment (OGLE) maintained by University of Warsaw, Poland. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for near earth asteroids throughNASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; by products of theNEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grants No. AST-1440341 and AST- 2034437 and a collaboration including current partners Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley, the University of Wisconsin at Milwaukee, University of Warwick, Ruhr University, Cornell University, Northwestern University and Drexel University. Operations are conducted by COO, IPAC, and UW.This research was supported by the University of Li\u00E8ge under the Special Funds for Research, IPD-STEMA Programme.We thank the anonymous referee for useful comments and suggestions. This work was supported by the National Science Centre, Poland, grant no. 2022/45/B/ST9/03862. This work used the SIMBAD and Vizier services operated by Centre des Donn\u00E9es astronomiques de Strasbourg (France), and bibliographic references from the Astrophysics Data System maintained by SAO/NASA. This work has made use of data from the European Space Agency (ESA) mission Gaia ( https://www.cosmos.esa.int/gaia ), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium ). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA\u2019s Science Mission Directorate. This work used data collected by the Optical Gravitational Lensing Experiment (OGLE) maintained by University of Warsaw, Poland. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; by products of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen\u2019s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grants No. AST-1440341 and AST-2034437 and a collaboration including current partners Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley, the University of Wisconsin at Milwaukee, University of Warwick, Ruhr University, Cornell University, Northwestern University and Drexel University. Operations are conducted by COO, IPAC, and UW.
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