Discovery of two new polars evolved past the period bounce

ABSTRACT We report the discovery of two new magnetic cataclysmic variables with brown dwarf companions and long orbital periods ($P_{\rm orb}$ = $95\pm 1$ and $104\pm 2$ 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 $L_{\rm X}$ $\approx$ $10^{28}$–$10^{29}$ $\mathrm{erg\, s^{-1}}$ 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 $\approx$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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Publication Details

Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-04-12
DOI
https://doi.org/10.1093/mnras/staf561
Citations
3
Primary Topic
Geological Studies and Exploration
Type
article
Field-Weighted Citation Impact
7.04

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article

Discovery of two new polars evolved past the period bounce

Tim Cunningham, Scott J. Kenyon, Antonio C. Rodriguez, Liam Connor et al.
3 citations
Monthly Notices of the Royal Astronomical Society
Geological Studies and Exploration
7.04
article

Discovery of two new polars evolved past the period bounce

Tim Cunningham, Scott J. Kenyon, Antonio C. Rodriguez, Liam Connor, Pasi Hakala, Ilaria Caiazzo, Kareem J. El-Badry, R. Arcodia, David Charbonneau, Pier-Emmanuel Tremblay, P. J. Wheatley, Jan van Roestel, Boris T. Gänsicke, Kishalay De, Sumit Kumar Maheshwari, Gracjan Sienkiewicz
article en
3 citations

Abstract

ABSTRACT We report the discovery of two new magnetic cataclysmic variables with brown dwarf companions and long orbital periods ($P_{\rm orb}$ = $95\pm 1$ and $104\pm 2$ 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 $L_{\rm X}$ $\approx$ $10^{28}$–$10^{29}$ $\mathrm{erg\, s^{-1}}$ 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 $\approx$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.

Monthly Notices of the Royal Astronomical SocietyVol. 540(1)
California Institute of Technology (US), University of Turku (FI), Institute of Science and Technology Austria (AT), Universität Hamburg (DE), Turku Centre for Computer Science (FI), University of Warwick (GB), Kavli Institute for Particle Astrophysics and Cosmology (US), Center for Astrophysics Harvard & Smithsonian (US), Astronomical Institute of the Slovak Academy of Sciences (SK), University of Amsterdam (NL)
National Science Foundation, Smithsonian Institution, National Aeronautics and Space Administration, Gordon and Betty Moore Foundation, Johns Hopkins University, Space Telescope Science Institute, European Space Agency, European Commission, Queen's University Belfast, Durham University, Queen's University, National Central University, Eötvös Loránd Tudományegyetem, Max-Planck-Institut für Astronomie, Smithsonian Astrophysical Observatory, Science Mission Directorate, Science and Technology Facilities Council, Kavli Institute for Theoretical Physics, University of California, Santa Barbara, Planetary Science Division, Los Alamos National Laboratory
Openalex Percentile: Top 4%
Geological Studies and Exploration
7.04
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