Revisiting the extremely long-period cataclysmic variables V479 Andromedae and V1082 Sagittarii

Context. The overwhelming majority of cataclysmic variables (CVs) have orbital periods shorter than 10 h. However, a few have much longer orbital periods, and their formation and existence pose certain challenges for the CV evolution models. These extremely long-period CVs must host nuclearly evolved donor stars (i.e., subgiants), as the companion of the white dwarf would otherwise be too small to fill its Roche lobe. This makes the extremely long-period CVs natural laboratories for testing binary evolution models and accretion processes with subgiant donors, with applications extending beyond white dwarf binaries. Despite the importance of compact objects accreting from subgiant donors, the process by which they form and evolve remains unclear. Aims. To shed light on the formation and evolution of accreting compact objects with subgiant companions, we investigated two extremely long-period CVs in detail, namely V479 And ( P orb ≃ 14 h) and V1082 Sgr ( P orb ≃ 21 h). We searched for reasonable formation pathways to explain their refined stellar and binary parameters. Methods. We used a broad set of new observations, including ultraviolet and infrared spectroscopy, results of circular polarimetry, and improved Gaia DR3 distance estimates, to determine the fundamental parameters (e.g., effective temperatures, masses, and radii of the donor stars) that would be confronted with numerical simulations. Furthermore, we utilized the MESA code to conduct numerical simulations, employing state-of-the-art prescriptions, such as the Convection And Rotation Boosted (CARB) model for strong magnetic braking. Results. The two systems have an unusual chemical composition and very low masses for their assigned spectral classes. This most likely indicates that they underwent thermal timescale mass transfer. We found models for the two extremely long-period CVs that can reasonably reproduce their properties. CV evolution needs to be convergent (i.e., toward shorter orbital periods), which is only possible if the magnetic braking is sufficiently strong. Conclusions. We conclude that the donor stars in both V479 And and V1082 Sgr are filling their Roche lobes, ruling out previous models in which they are underfilling their Roche lobes. Our findings suggest that orbital angular momentum loss is stronger due to magnetic braking in CVs with subgiant donors compared to those with unevolved donors. In addition, our findings suggest that extremely long-period CVs could significantly contribute to the population of double white dwarf binaries in close orbits (orbital periods ≲1 d).

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Journal
Astronomy and Astrophysics
Published
2025-10-03
DOI
https://doi.org/10.1051/0004-6361/202556385
Citations
1
Primary Topic
Astrophysical Phenomena and Observations
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article
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1.15
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article

Revisiting the extremely long-period cataclysmic variables V479 Andromedae and V1082 Sagittarii

Aude Fleurant, R. G. Farfán, Juan-Luis González-Carballo, Giuseppe Pappa et al.
1 citations
Astronomy and Astrophysics
Astrophysical Phenomena and Observations
1.15
article

Revisiting the extremely long-period cataclysmic variables V479 Andromedae and V1082 Sagittarii

Aude Fleurant, R. G. Farfán, Juan-Luis González-Carballo, Giuseppe Pappa, Rod Stubbings, R. Naves Nogues, Michel Michaud, Jeremy Shears, J. Green, Domitilla de Martino, Adam Popowicz, A. Pearce, J. Lima, Jesús R. Berenguer, Darrell Lee, Paula Szkody, Sjoerd Dufoer, David J. Lane, E. Kardasis, Simone Bolzoni, Gordon Myers, G. Tovmassian, Charles Cynamon, Franz-Josef Hambsch, Alejandro Crespo Gómez, James Sikora, M. R. Schreiber, Krzysztof Bernacki, Mario Morales Aimar, Szczepan Bednarz, Brad de Young, Esteban Fernández Mañanes, Wenfei Yu, Thomas Kupfer, Antoine Bédard, Diogo Belloni, Penko Jordanov, Walt Cooney, Patricio Valdivieso Fernández, C. A. Cantrell, L. Ivan Walton, James C. Pierce, Vanderlei Rodrigues, Fernando Limón Martínez, André Steenkamp, Sinan Long, C. Nieves Rodríguez, M. Ortiz, G. Locatelli, Carlos Botana-Albá, Faustino García-Cuesta, Jose-Luis Martin-Velasco, David Quiles Amat, Esteban Reina-Lorenz, José-Luis Salto-González, F. Anna Pala, J. Daniel Mendicini, T. Boris Gänsicke, O. Elizabeth Waagen
article en
1 citations

Abstract

Context. The overwhelming majority of cataclysmic variables (CVs) have orbital periods shorter than 10 h. However, a few have much longer orbital periods, and their formation and existence pose certain challenges for the CV evolution models. These extremely long-period CVs must host nuclearly evolved donor stars (i.e., subgiants), as the companion of the white dwarf would otherwise be too small to fill its Roche lobe. This makes the extremely long-period CVs natural laboratories for testing binary evolution models and accretion processes with subgiant donors, with applications extending beyond white dwarf binaries. Despite the importance of compact objects accreting from subgiant donors, the process by which they form and evolve remains unclear. Aims. To shed light on the formation and evolution of accreting compact objects with subgiant companions, we investigated two extremely long-period CVs in detail, namely V479 And ( P orb ≃ 14 h) and V1082 Sgr ( P orb ≃ 21 h). We searched for reasonable formation pathways to explain their refined stellar and binary parameters. Methods. We used a broad set of new observations, including ultraviolet and infrared spectroscopy, results of circular polarimetry, and improved Gaia DR3 distance estimates, to determine the fundamental parameters (e.g., effective temperatures, masses, and radii of the donor stars) that would be confronted with numerical simulations. Furthermore, we utilized the MESA code to conduct numerical simulations, employing state-of-the-art prescriptions, such as the Convection And Rotation Boosted (CARB) model for strong magnetic braking. Results. The two systems have an unusual chemical composition and very low masses for their assigned spectral classes. This most likely indicates that they underwent thermal timescale mass transfer. We found models for the two extremely long-period CVs that can reasonably reproduce their properties. CV evolution needs to be convergent (i.e., toward shorter orbital periods), which is only possible if the magnetic braking is sufficiently strong. Conclusions. We conclude that the donor stars in both V479 And and V1082 Sgr are filling their Roche lobes, ruling out previous models in which they are underfilling their Roche lobes. Our findings suggest that orbital angular momentum loss is stronger due to magnetic braking in CVs with subgiant donors compared to those with unevolved donors. In addition, our findings suggest that extremely long-period CVs could significantly contribute to the population of double white dwarf binaries in close orbits (orbital periods ≲1 d).

Astronomy and AstrophysicsVol. 703
Western Carolina University (US), Silesian University of Technology (PL), Texas Tech University (US), Space Telescope Science Institute (US), Universität Hamburg (DE), American Association of Variable Star Observers (US), University of Washington (US), Universidad Iberoamericana (MX), British Astronomical Association (GB), Kitt Peak National Observatory (US), Astronomical Observatory of Capodimonte (IT), Austrian Federal Railways (AT), University of Warwick (GB), TMT Observatory (US), Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne (DE), Hong Kong Observatory (CN), National Observatory (BR), Geotechnical Observations (United Kingdom) (GB), Instituto de Astrofísica de Canarias (ES), Astronomical Institute of the Slovak Academy of Sciences (SK), Abbey Ridge Observatory (CA), Observatori de l'Ebre (ES), Institute of Astronomy and Space Physics (AR), Eureka Scientific (US), International Dark Sky Association (US), Stichting tot Steun VCVGZ (NL), Federico Santa María Technical University (CL), Instituto Nacional de Pesquisas Espaciais (BR), University of Oklahoma (US), Universidade Estadual Paulista (Unesp) (BR), Union astronomique internationale (FR), Universidad Nacional Autónoma de México (MX)
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Astrophysical Phenomena and Observations
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