A Study of Cataclysmic Variables from the eFEDS Survey

TL;DR

The study addresses how to robustly measure orbital periods and component masses for CVs detected in X-ray surveys. It uses a crossmatch of eFEDS with SDSS-V DR18 to assemble a CV sample, then derives photometric periods from ZTF/CRTS, confirms orbital periods via radial velocity fits, and constrains masses with Gaia distances and SED fitting. For J0843 and J0935, the orbital periods are $P_{ m{orb}} = 0.34615\,\mathrm{d}$ and $P_{ m{orb}} = 0.1584\,\mathrm{d}$, with mass functions $f(M_1) = 0.38 \pm 0.04\,M_\odot$ and $0.30 \pm 0.01\,M_\odot$. The inferred white dwarf masses are $M_1 \approx 0.93$–$1.21\,M_\odot$ for J0843 and a lower limit $M_1 \ge 0.46\,M_\odot$ for J0935, while the donor masses are $M_2 \approx 0.395\,M_\odot$ and $0.108\,M_\odot$, respectively. These results show the viability of combining X-ray selected CV catalogs with optical spectroscopy and multi-band SED modelling to inform CV evolution and mass-transfer physics.

Abstract

We present 17 cataclysmic variables (CVs) obtained from the crossmatch between the Sloan Digital Sky Survey (SDSS) and eROSITA Final Equatorial Depth Survey (eFEDS), including 8 known CVs before eFEDS and 9 identified from eFEDS. The photometric periods of four CVs are derived from the Zwicky Transient Facility (ZTF) and Catalina Real-Time Transient Survey (CRTS). We focus on two CVs, SDSS J084309.3$-$014858 and SDSS J093555.0+042916, and confirm that their photometric periods correspond to the orbital periods by fitting the radial velocity curves. Furthermore, by the combination of the Gaia distance, the spectral energy distribution, and the variations of $\mathrm{H}\mathrmα$ emission lines, the masses of the white dwarf and the visible star can be well constrained.

Figures (8)

• Figure 1: Spectra and light curves of four CVs. The vertical lines in the left-hand panels indicate the rest wavelengths of the hydrogen Balmer lines (red dashed lines) and the helium I and II lines (blue dashed lines). Light curves with CRTS are shown in grey, ZTF in blue (g-band), and red (r-band) in the right-hand panels.
• Figure 2: The left panel shows the folded light curves of J0935 obtained from various surveys, and the right panel illustrates the folded light curves of J0843. The red and blue dots represent ZTF r-band and g-band data, respectively, while the yellow dots indicate CRTS data. The grey curves depict the three-harmonic model derived from Equation (\ref{['eq1']}). The period of each light curve is denoted in the plot legend with uncertainty for the last digit shown inside the parentheses.
• Figure 3: The left panel: the folded light curves of J0912 obtained from various surveys. The right panel: the Lomb–Scargle periodogram and the phase-folded light curve of J0846 on the period of 0.6566 days. The red and blue dots represent ZTF r-band and g-band data, respectively, while the yellow dots indicate CRTS data.
• Figure 4: SDSS spectra (left panels) and CCF (right panels) for J0935 (upper panels) and J0843 (lower panels). The left panels show the individual spectrum (blue) and a template spectrum (red) used to measure the CCF profile. The dashed lines mark the peaks in the CCF panels.
• Figure 5: The measurement of the $\mathrm{H}\mathrm{\alpha}$ emission line center from one spectrum of J0935. In the left panel, the dashed line represents the reference rest wavelength of $\mathrm{H}\mathrm{\alpha}$ in a vacuum. In the right panel, the blue line shows the spectrum after subtracting the stellar component, while the yellow line represents the best Gaussian fit.