Searching for Cataclysmic Variable Stars in Unidentified X-Ray Sources

Abstract

We carry out a photometric search for new cataclysmic variable stars (CVs), with the goal of identification for candidates of AR Scorpii-type binary systems. We select GAIA sources that are likely associated with unidentified X-ray sources, and analyze the light curves taken by the Zwicky Transient Facility, Transiting Exoplanet Survey Satellite, and Lulin One-meter Telescope in Taiwan. We investigate eight sources as candidates for CVs, among which six sources are new identifications. Another two sources have been recognized as CVs in previous studies, but no detailed investigations have been done. We identify two eclipsing systems that are associated with an unidentified XMM-Newton or Swift source, and one promising candidate for polar associated with an unidentified ASKA source. Two polar candidates may locate in the so-called period gap of a CV, and the other six candidates have an orbital period shorter than that of the period gap. Although we do not identify a promising candidate for AR Scorpii-type binary systems, our study suggests that CV systems that have X-ray emission and do not show frequent outbursts may have been missed in previous surveys.

Identification of 1RXS J165424.6-433758 as a Polar Cataclysmic Variable

“…The low-state photometry allows us to analyze the secondary star, determining that it is likely of late spectral type. Highspeed photometry carried out over multiple nights yields an orbital period of ∼2.87 hr, in agreement with Takata et al (2022). Our optical spectroscopy reveals numerous lines of hydrogen and helium, demonstrating an inverse Balmer decrement.…”

“…Our optical spectroscopy reveals numerous lines of hydrogen and helium, demonstrating an inverse Balmer decrement. In particular, our spectroscopic observations point toward the classification of the source as a typical polar at a Gaia distance of ∼460 pc, solidifying its previous classification (Takata et al 2022).…”

“…We note that an independent analysis of data from TESS was carried out by Takata et al (2022; their source G596) who find a period of 0.12 days (2.88 hr). Our observations are in agreement with their result.…”

“…The source was later observed with Swift (Reynolds et al 2013) as part of a shallow Galactic plane survey. Takata et al (2022) analyzed a sample of unclassified X-ray sources with Gaia counterparts, including J1654 (G596 in that paper). Using a combination of Swift, NuSTAR, and the Transiting Exoplanet Survey Satellite (TESS), they classify J1654 as a candidate polar.…”

A Systematic Search for Short-period Close White Dwarf Binary Candidates Based on Gaia EDR3 Catalog and Zwicky Transient Facility Data

“…We also apply a signal-to-noise ratio (S/N) threshold of 5 on the parallax measurements (parallax_over_error > 5). The filter conditions for the threshold of parallax_over_error > 5 are often adopted for searches with Gaia data, for example, the search for ELM-WD candidates (Pelisoli & Vos 2019), the search for pulsating white dwarfs (Guidry et al 2021), the search for evolved CVs (El-Badry et al 2021b), and the search for AR Scorpii-type binary systems (Takata et al 2022). Since the motivation of this work is to obtain reliable candidate GW sources, we conclude that precise measurement of parallaxes is very important so that the estimation of GW S/N can be trustworthy.…”