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1. Discovery of Two Polars from a Crossmatch of ZTF and the SRG/eFEDS X-Ray Catalog

   https://doi.org/10.3847/1538-4357/acbb6f  

   Rodriguez, Antonio C.; Kulkarni, Shrinivas R.; Prince, Thomas A.; Szkody, Paula; Burdge, Kevin B.; Caiazzo, Ilaria; van Roestel, Jan; Vanderbosch, Zachary P.; El-Badry, Kareem; Bellm, Eric C.; et al (March 2023, The Astrophysical Journal)

   Abstract Magnetic cataclysmic variables (CVs) are luminous Galactic X-ray sources, which have been difficult to find in purely optical surveys due to their lack of outburst behavior. The eROSITA telescope on board the Spektr-RG mission is conducting an all-sky X-ray survey and recently released the public eROSITA Final Equatorial Depth Survey (eFEDS) catalog. We crossmatched the eFEDS catalog with photometry from the Zwicky Transient Facility and discovered two new magnetic CVs. We obtained high-cadence optical photometry and phase-resolved spectroscopy for each magnetic CV candidate and found them both to be polars. Among the newly discovered magnetic CVs is eFEDS J085037.2+044359/ZTFJ0850+0443, an eclipsing polar with orbital period P orb = 1.72 hr and WD mass M WD = 0.81 ± 0.08 M ⊙ . We suggest that eFEDS J085037.2+044359/ZTFJ0850+0443 is a low magnetic field strength polar, with B WD ≲ 10 MG. We also discovered a non-eclipsing polar, eFEDS J092614.1+010558/ZTFJ0926+0105, with orbital period P orb = 1.47 hr and magnetic field strength B WD = 36–42 MG. 

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2. Compact white dwarf binaries in the combined SRG/eROSITA/SDSS eFEDS survey

   https://doi.org/10.1051/0004-6361/202348426  

   Schwope, A; Kurpas, J; Baecke, P; Knauff, K; Stütz, L; Tubín-Arenas, D; Standke, A; Anderson, S F; Bauer, F; Brandt, W N; et al (June 2024, Astronomy & Astrophysics)

   Context.X-ray surveys combined with optical follow-up observations are used to generate complete flux-limited samples of the main X-ray emitting source classes. eROSITA on the Spectrum-Roentgen-Gamma mission provides sufficient sensitivity to build significantly enhanced samples of rare X-ray emitting sources. Aims.We strive to identify and classify compact white dwarf binaries, cataclysmic variables (CVs), and related objects, which were detected in the sky area of eFEDS, the eROSITA Final Equatorial Depths Survey, and they were observed in the plate program of SDSS-V. Methods.Compact white dwarf binaries were selected from spectra obtained in the early SDSS-V plate program. A dedicated set of SDSS plate observations were carried out in the eFEDS field, providing spectroscopic classifications for a significant fraction of the optically bright end (r< 22.5) of the X-ray sample. The identification and subclassification rests on visual inspections of the SDSS spectra, spectral variability, color-magnitude and color-color diagrams involving optical and X-ray fluxes, optical variability, and literature work. Results.Upon visual inspection of SDSS spectra and various auxiliary data products, we have identified 26 accreting compact white dwarf binaries (aCWDBs) in eFEDS, of which 24 are proven X-ray emitters. Among those 26 objects, there are 12 dwarf novae, three WZ Sge-like disk-accreting nonmagnetic CVs with low accretion rates, five likely nonmagnetic high accretion rate nova-like CVs, two magnetic CVs of the polar subcategory, and three double degenerates (AM CVn objects). Period bouncing candidates and magnetic systems are rarer than expected in this sample, but it is too small for a thorough statistical analysis. Fourteen of the systems are new discoveries, of which five are fainter than theGaiamagnitude limit. Thirteen aCWDBs have measured or estimated orbital periods, of which five were presented here. Through a Zeeman analysis, we revise the magnetic field estimate of the polar system J0926+0105, which is likely a low-field polar atB= 16 MG. We quantified the success of X-ray versus optical/UV selection of compact white dwarf binaries which will be relevant for the full SDSS-V survey. We also identified six white dwarf main sequence (WDMS) systems, among them there is one confirmed pre-CV at an orbital period of 17.6 h and another pre-CV candidate. Conclusions.This work presents successful initial work in building large samples of all kinds of accreting and X-ray emitting compact white dwarf binaries that will be continued over the full hemisphere in the years to come. 

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3. JWST observations of three long-period AM CVn binaries: detection of the donors and hints of magnetically truncated disks

   https://doi.org/10.33232/001c.157856  

   El-Badry, Kareem; Rodriguez, Antonio C; Green, Matthew J; Burdge, Kevin B (January 2026, The Open Journal of Astrophysics)

   We present JWST/NIRSpec high-cadence infrared spectroscopy of three long-period, eclipsing AM CVn binaries, Gaia14aae, SRGeJ0453, and ZTFJ1637. These systems have orbital periods of 50-62 minutes and cool donors that are undetectable in the optical. The data cover a wavelength range of 1.6-5.2 $\mu$ m at resolution $R=1000-2000$ . We obtained 150-200 spectra of each system over two orbits, split between the G235M and G395M gratings. All three systems show strong, double-peaked He I emission lines dominated by an accretion disk. These lines are nearly stationary but contain radial velocity (RV) variable sub-components that trace stream-disk interactions. In Gaia14aae and SRGeJ0453, we detect two Na I doublets in emission whose RVs track the irradiated face of the donor, marking the first direct detection of the donors of long-period AM CVns. No absorption lines from the donors are detected, implying that the IR excesses observed in many long-period AM CVns primarily trace disks, not donors. The He I emission profiles in all systems lack high-velocity wings and show no emission beyond . The morphology of the disk eclipses and Doppler tomograms are best reproduced by models in which the disk is truncated well outside the white dwarf and only material at $r\gtrsim 0.07,R_{\odot }$ contributes to the disk emission. We interpret this as possible evidence of magnetized white dwarf accretors. For plausible mass transfer rates, the truncation radii imply surface magnetic fields of $B=30-100$ kG, consistent with recent constraints based on X-ray periodicity. The absence of cyclotron humps out to 5 $\mu$ m rules out stronger MG-level fields. We make the data from the program publicly available to the community. 

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4. Periodic radio and X-ray emission from an accreting white dwarf binary

   https://doi.org/10.1038/s41550-026-02882-x  

   Rose, Kovi; Pritchard, Joshua; Murphy, Tara; Driessen, L N; Kaplan, D L; Caleb, M; Wang, Ziteng; Zic, A; Andreoni, I; Carney, J; et al (June 2026, Nature Astronomy)

   Abstract Long-period radio transients (LPTs) are coherent bursts of polarized radio emission that repeat periodically on timescales of minutes to hours. Little is known about the physical origins of these systems. Astronomers have proposed magnetars that rotate slowly and white dwarfs that rapidly orbit with a companion star as potential explanations. While several recent examples appear to support the latter hypothesis, the mechanism generating these bright radio pulses remains poorly understood. Here we report our discovery and classification of the LPT ASKAP J174508.9-505149 as an accreting white dwarf binary. This object has an ~1.3 h spectroscopic orbital period and exhibits orbitally modulated X-ray emission and radio bursts. These elliptically polarized radio bursts drift in emission frequency, potentially due to a longer beat period, and turn off for several hours at a time. Some LPTs have been associated with non-interacting white dwarf binaries. We have spectroscopically confirmed this system as an accreting cataclysmic variable, identified through characteristic optical emission lines and an ongoing X-ray outburst. Our results strengthen the link between at least some LPTs and white dwarf binaries. 

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5. A survey for radio emission from white dwarfs in the VLA Sky Survey

   https://doi.org/10.1093/mnras/stae1275  

   Pelisoli, Ingrid; Chomiuk, Laura; Strader, Jay; Marsh, T R; Aydi, Elias; Dage, Kristen C; Kyer, Rebecca; Molina, Isabella; Panurach, Teresa; Urquhart, Ryan; et al (May 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Radio emission has been detected from tens of white dwarfs, in particular in accreting systems. Additionally, radio emission has been predicted as a possible outcome of a planetary system around a white dwarf. We searched for 3 GHz radio continuum emission in 846 000 candidate white dwarfs previously identified in Gaia using the Very Large Array Sky Survey (VLASS) Epoch 1 Quick Look Catalogue. We identified 13 candidate white dwarfs with a counterpart in VLASS within 2 arcsec. Five of those were found not to be white dwarfs in follow-up or archival spectroscopy, whereas seven others were found to be chance alignments with a background source in higher resolution optical or radio images. The remaining source, WDJ204259.71+152108.06, is found to be a white dwarf and M-dwarf binary with an orbital period of 4.1 d and long-term stochastic optical variability, as well as luminous radio and X-ray emission. For this binary, we find no direct evidence of a background contaminant, and a chance alignment probability of only ≈2 per cent. However, other evidence points to the possibility of an unfortunate chance alignment with a background radio and X-ray emitting quasar, including an unusually poor Gaia DR3 astrometric solution for this source. With at most one possible radio emitting white dwarf found, we conclude that strong (≳1–3 mJy) radio emission from white dwarfs in the 3 GHz band is virtually non-existent outside of interacting binaries. 

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