The evolutionary history of ultra-compact accreting binaries
Year: 2025
Type: article
Abstract: Context. AM Canum Venaticorum (AM CVn) stars are ultra-compact binary systems composed of a white dwarf primary accreting from a hydrogen-deficient donor. They play a crucial role in astrophysics as potential progenitors of Type Ia supernovae and as laboratories for gravitational wave studies. However, their formation and evolutionary history remain incomplete. Three formation channels have been discussed in the literature: the white dwarf, He-star, and cataclysmic variable channels. Aims. The chemical composition of the accretor atmosphere reflects the material transferred from the donor. In this work we took the first accurate measurements of the fundamental parameters of the accreting white dwarf in ZTF J225237.05−051917.4, including the abundances of key elements such as carbon, nitrogen, and silicon, by analysing ultraviolet spectra obtained with the Hubble Space Telescope (HST). These measurements provide new insight into the evolutionary history of the system and, together with existing optical observations, establish it as a benchmark to develop our pipeline, paving the way for its application to a larger sample of AM CVn systems. Methods. We determined the binary parameters through photometric analysis and constrained the atmospheric parameters of the white dwarf accretor, including its effective temperature, surface gravity, and chemical abundances, by fitting the HST ultraviolet spectrum with synthetic spectral models. We then inferred the system’s formation channel by comparing the results with theoretical evolutionary models. Results. According to our measurements, the accretor’s effective temperature ( T eff ) is 23 300 ± 600 K and the surface gravity (log g ) is 8.4 ± 0.3, which imply an accretor mass ( M WD ) of 0.86 ± 0.16 M ⊙ . We find a high nitrogen-to-carbon abundance ratio by mass of > 153. Conclusions. The accretor is significantly hotter than previous estimates based on simplified blackbody fits to the spectral energy distribution, underscoring the importance of detailed spectral modelling for accurately determining system parameters. Our results show that ultraviolet spectroscopy is well suited to constraining the formation channels of AM CVn systems. Of the three proposed formation channels, the He-star channel can be excluded given the high nitrogen-to-carbon ratio. Our results are consistent with both the white dwarf and cataclysmic variable channels.
Source: Astronomy and Astrophysics
Authors: W. Yu, A. F. Pala, T. Kupfer, B. T. Gänsicke, D. Koester, D. Belloni, T. L. S. Wong, M. R. Schreiber, J. van Roestel, A. J. Brown, E. O. Waagen, J.-L. González-Carballo, S. Bednarz, K. Bernacki, D. De Martino, E. Fernández Mañanes, R. González Farfán, M. J. Green, P. J. Groot, F.-J Hambsch, C. Knigge, J.-L. Martin-Velasco, M. Morales-Aimar, G. Myers, R. Naves Nogues, R. Poggiani, A. Popowicz, G. Ramsay, E. Reina-Lorenz, P. Rodríguez-Gil, J.-L. Salto-González, E. M. Sion, D. Steeghs, P. Szkody, O. Toloza, G. Tovmassian
Institutions: Universität Hamburg, European Southern Observatory, European Southern Observatory, Texas Tech University, University of Warwick, Christian-Albrechts-Universität zu Kiel, Universidade Estadual Paulista (Unesp), Carnegie Institution for Science, Universidad Técnica Federico Santa María, Universidad Técnica Federico Santa María, Institute of Science and Technology Austria, University of Amsterdam, American Association of Variable Star Observers, Silesian University of Technology, Astronomical Observatory of Capodimonte, National Institute for Astrophysics, National Institute of Standards and Technology, Joint Institute for Laboratory Astrophysics, University of Oklahoma, Radboud University Nijmegen, University of Cape Town, South African Astronomical Observatory, Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne, University of Southampton, University of Pisa, Armagh Observatory & Planetarium, Universidad de La Laguna, Instituto de Astrofísica de Canarias, Villanova University, University of Washington, Universidad Nacional Autónoma de México
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Science Foundation, National Aeronautics and Space Administration, European Commission, Deutsche Forschungsgemeinschaft, Fundação de Amparo à Pesquisa do Estado de São Paulo, Ministerio de Ciencia e Innovación, Science and Technology Facilities Council, European Research Council, European Regional Development Fund, Fondo Nacional de Desarrollo Científico, Tecnológico y de Innovación Tecnológica, Agencia Estatal de Investigación
Awards: The Gravitational wave Optical Transient Observer, G1069964796, G1627983296, G1693568110, Warwick Astronomy and Astrophysics Consolidated Grant 2020-2023, G2041577003, G2776820831, Constraining the Evolutionary Pathways for White Dwarfs: Crystallization, Cooling Anomalies, and Mergers, G3470076519, G432818845, G4827947457, The Gravitational wave Optical Transient Observer, G5917133026, Towards a global understanding of how accreting white dwarfs form and evolve, G6972301876, EXC 2121: Quantum Universe, G7434936867, G7649896884, G7867890770, G817261669, G8733234872, G980517918
OpenAlex ID: W4417133247