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Published October 2024 | Version Published
Journal Article Open

Searching for new cataclysmic variables in the Chandra Source Catalog

Creators

  • 1. ROR icon Kazan Federal University
  • 2. ROR icon California Institute of Technology
  • 3. ROR icon University of Washington
  • 4. ROR icon Lawrence Berkeley National Laboratory
  • 5. ROR icon University of Amsterdam
  • 6. ROR icon Infrared Processing and Analysis Center

Abstract

Aims. Cataclysmic variables (CVs) are compact binary systems in which a white dwarf accretes matter from a Roche-lobe-filling companion star. For this study we searched for new CVs in the Milky Way in the Chandra Source Catalog v2.0, cross-matched with Gaia Data Release 3 (DR3).

Methods. We identified new CV candidates by combining X-ray and optical data in a color-color diagram called the X-ray main sequence. We used two different cuts in this diagram to compile pure and optically variable samples of CV candidates. We undertook optical spectroscopic follow-up observations with the Keck and Palomar Observatories to confirm the nature of these sources.

Results. We assembled a sample of 25 887 Galactic X-ray sources and found 14 new CV candidates. Seven objects show X-ray and/or optical variability. All sources show X-ray luminosity in the 1029 − 1032 erg s−1 range, and their X-ray spectra can be approximated by a power-law model with photon indices in the Γ ∼ 1 − 3 range or an optically thin thermal emission model in the kT ∼ 1 − 70 keV range. We spectroscopically confirmed four CVs, discovering two new polars, one low accretion rate polar and a WZ Sge-like low accretion rate CV. X-ray and optical properties of the other nine objects suggest that they are also CVs (likely magnetic or dwarf novae), and one other object could be an eclipsing binary, but revealing their true nature requires further observations.

Conclusions. These results show that a joint X-ray and optical analysis can be a powerful tool for finding new CVs in large X-ray and optical catalogs. X-ray observations such as those by Chandra are particularly efficient at discovering magnetic and low accretion rate CVs, which could be missed by purely optical surveys.

Copyright and License

© The Authors 2024. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

This research has made use of data obtained from the Chandra Data Archive and software provided by the Chandra X-ray Center (CXC) in the application packages CIAO. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grants No. AST-1440341 and AST-2034437 and a collaboration including current partners Caltech, IPAC, the Weizmann Institute of Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, IN2P3, University of Warwick, Ruhr University Bochum, Northwestern University and former partners the University of Washington, Los Alamos National Laboratories, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant No. 12540303 (PI: Graham). We are grateful to the staffs of the Palomar and Keck Observatories for their work in helping us carry out our observations. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research made use of matplotlib, a Python library for publication quality graphics (Hunter 2007); NumPy (Harris et al. 2020); Astroquery (Ginsburg et al. 2019); Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018); and the VizieR catalogue access tool, CDS, Strasbourg, France. IG, AS, VD, NT acknowledge support from Kazan Federal University. ACR acknowledges support from the National Science Foundation via an NSF Graduate Research Fellowship. The authors thank the anonymous referee for useful and inspiring suggestions which helped to improve the manuscript.

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2408.00078 (arXiv)

Funding

National Science Foundation
AST-1440341
National Science Foundation
AST-2034437
Heising-Simons Foundation
12540303

Dates

Accepted
2024-07-30
Available
2024-10-22
Published online

Caltech Custom Metadata

Caltech groups
Astronomy Department , Infrared Processing and Analysis Center (IPAC) , Zwicky Transient Facility , Division of Physics, Mathematics and Astronomy (PMA) , Physics Department
Publication Status
Published