Discovery of two new polars evolved past the period bounce
: Cunningham, Tim; Caiazzo, Ilaria; Sienkiewicz, Gracjan; Wheatley, Peter J.; Gänsicke, Boris T.; El-Badry, Kareem; Arcodia, Riccardo; Charbonneau, David; Connor, Liam; De, Kishalay; Hakala, Pasi; Kenyon, Scott J.; Maheshwari, Sumit Kumar; Rodriguez, Antonio C.; van Roestel, Jan; Tremblay, Pier-Emmanuel
Publisher: OXFORD UNIV PRESS
: OXFORD
: 2025
: Monthly Notices of the Royal Astronomical Society
: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
: MON NOT R ASTRON SOC
: 540
: 1
: 633
: 649
: 17
: 0035-8711
: 1365-2966
DOI: https://doi.org/10.1093/mnras/staf561
: https://academic.oup.com/mnras/article/540/1/633/8112867
: https://research.utu.fi/converis/portal/detail/Publication/498695817
We report the discovery of two new magnetic cataclysmic variables with brown dwarf companions and long orbital periods (Porb = 95 +/- 1 and 104 +/- 2 min). This discovery increases the sample of candidate magnetic period bouncers with confirmed sub-stellar donors from four to six. We also find their X-ray luminosity from archival XMM-Newton observations to be in the range L-X approximate to 1028-1029 ergs-1 in the 0.25-10 keV band. This low luminosity is comparable with the other candidates, and at least an order of magnitude lower than the X-ray luminosities typically measured in cataclysmic variables. The X-ray fluxes imply mass transfer rates that are much lower than predicted by evolutionary models, even if some of the discrepancy is due to the accretion energy being emitted in other bands, such as via cyclotron emission at infrared wavelengths. Although it is possible that some or all of these systems formed directly as binaries containing a brown dwarf, it is likely that the donor used to be a low-mass star and that the systems followed the evolutionary track for cataclysmic variables, evolving past the period bounce. The donor in long period systems is expected to be a low-mass, cold brown dwarf. This hypothesis is supported by near-infrared photometric observations that constrain the donors in the two systems to be brown dwarfs cooler than approximate to 1100 K (spectral types T5 or later), most likely losing mass via Roche Lobe overflow or winds. The serendipitous discovery of two magnetic period bouncers in the small footprint of the XMM-Newton catalogue implies a large space density of these type of systems, possibly compatible with the prediction of 40-70 per cent of magnetic cataclysmic variables to be period bouncers.
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Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51527.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Support for this work was provided by NASA through Chandra Award Number GO4-25014X issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. IC was also supported by NASA through grants from the Space Telescope Science Institute, under NASA contracts NASA.22K1813, NAS5-26555, and NAS5-03127. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101020057). This research was supported in part by grant NSF PHY-1748958 to the Kavli Institute for Theoretical Physics (KITP). PJW acknowledges support from the UK Science and Technology Facilities Council (STFC) through consolidated grants ST/T000406/1 and ST/X001121/1. RA was supported by NASA through the NASA Hubble Fellowship grant #HST-HF2-51499.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.
