Revisiting the extremely long-period cataclysmic variables V479 Andromedae and V1082 Sagitarii
Gagik Tovmassian, Diogo Belloni, Anna F. Pala, Thomas Kupfer, Weitian Yu, Boris T. Gänsicke, Elizabeth O. Waagen, Juan-Luis González-Carballo, Paula Szkody, Domitilla de Martino, Matthias R. Schreiber, Knox S. Long, Alan Bedard, Slawomir Bednarz, Jordi Berenguer, Krzysztof Bernacki, Simone Bolzoni, Carlos Botana-Albá, Christopher Cantrell, Walt Cooney, Charles Cynamon, Pablo De la Fuente Fernández, Sjoerd Dufoer, Esteban Fernández Mañanes, Faustino García-Cuesta, Rafael Gonzalez Farfán, Pierre A. Fleurant, Enrique A. Gómez, Matthew J. Green, Franz-Josef Hambsch, Penko Jordanov, Emmanuel Kardasis, David Lane, Darrell Lee, Isabel J. Lima, Fernando Limón Martínez, Gianpiero Locatelli, Jose-Luis Martin-Velasco, Daniel J. Mendicini, Michel Michaud, Moisés Montero Reyes Ortíz, Mario Morales Aimar, Gordon Myers, Ramon Naves Nogues, Giuseppe Pappa, Andrew Pearce, James Pierce, Adam Popowicz, Claudia V. Rodrigues, Nieves C. Rodríguez, David Quiles Amat, Esteban Reina-Lorenz, José-Luis Salto-González, Jeremy Shears, John Sikora, André Steenkamp, Rod Stubbings, Brad Young, Ivan L. Walton
Published: 2025/8/29
Abstract
The overwhelming majority of CVs have orbital periods shorter than 10 hr. However, a few have much longer periods, and their formation and existence pose challenges for the CV evolution models. These extremely long-period CVs must host nuclearly evolved donor stars, as otherwise, the companion of the white dwarf would be too small to fill its Roche lobe. This makes them natural laboratories for testing binary evolution models and accretion processes with subgiant donors. 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 and V1082 Sgr. We searched for reasonable formation pathways to explain their refined stellar and binary parameters. We used a broad set of new observations, including ultraviolet and infrared spectroscopy, results of circular polarimetry, and improved Gaia distance estimates to determine fundamental parameters to be confronted with numerical simulations. Furthermore, we utilized the MESA code to conduct numerical simulations, employing state-of-the-art prescriptions, such as the CARB model for strong magnetic braking. Both systems have unusual chemical compositions and very low masses for their assigned spectral classes. This most likely indicates that they underwent thermal timescale mass transfer. We found models for both that can reasonably reproduce their properties. We conclude that the donor stars in both V479 And and V1082 Sgr are filling 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.