The Optical Study of the Eclipsing Polar SDSS J002637.06+242915.6

TL;DR

This study analyzes phase-resolved photometry and spectroscopy of the eclipsing polar SDSS J002637.06+242915.6 to map its magnetic and binary geometry. Using Zeeman splitting, emission-line profiles, Doppler tomography, and cyclotron-spectrum modeling, the authors derive $P_{orb}=122.856\pm0.006$ min, $i=78.9\pm1.7^{\circ}$, $q=0.33\pm0.10$, $M_1=0.57\pm0.15\,M_{\odot}$, and $M_2=0.174\pm0.022\,M_{\odot}$, along with a donor radius $R_2=0.206\pm0.009\,R_{\odot}$ and white dwarf radius $R_1=0.013\pm0.002\,R_{\odot}$. The magnetic-field analysis yields a halo field $B_z=15.1\pm1.3$ MG and constrains the accretion-spot cyclotron field to $B_{cyc}\lesssim45$ MG, with a best-fit cyclotron model at $B=34$ MG and $T_e=18$ keV. The Doppler maps indicate distinct formation regions for H$\alpha$ and HeII $\lambda4686$, consistent with ballistic versus magnetic stream components, and a narrow H$\alpha$ component from the irradiated donor hemisphere. Collectively, these results advance the understanding of accretion geometry and magnetic-field structure in polars and enable meaningful comparisons with similar AM Her systems.

Abstract

We have analyzed phase-resolved photometric and spectroscopic observations of the eclipsing polar SDSS J002637.06+242915.6. The light curve has a M-shaped bright phase that was reproduced using a simple model of an accreting magnetic white dwarf. The hydrogen emission lines exhibit a narrow component formed on the irradiated hemispere of the donor. The Doppler tomography revealed differences in the positions of emission regions of hydrogen and HeII $λ$4686 lines. The spectra exhibit a Zeeman absorption triplet of the H$α$ line, formed in the cold halo around the accretion spot at a magnetic field strength of $B = 15.1 \pm 1.3$ MG. The spectra of the bright phase have a red cyclotron continuum, whose orbital variability has been interpreted within a simple model of an accretion spot. The modeling of the cyclotron continuum constrains the white dwarf's magnetic field to $B_{cyc} \lesssim 45$ MG. The analysis of the eclipse light curve and the radial velocities of the irradiated hemisphere yielded estimates for the orbital inclination $77.2^\circ \le i \le 80.6^\circ$, the mass ratio $0.23 \le q \le 0.43$, and the white dwarf mass $0.72 \ge M_1/M_\odot \ge 0.42$.

Figures (9)

• Figure 1: Top panel: long-term light curve of J0026 from ZTF data in $g$ and $r$ bands. Bottom left panel: Lomb-Scargle periodograms constructed from $g$- and $r$-band data. Bottom right panel: phase-folded light curves in $g$ and $r$ bands. Vertical lines mark observation epochs from Szkody24 (blue line), BTA telescope (red), and Zeiss-1000 telescope (black)
• Figure 2: Left panel: phase-folded light curve of J0026 obtained with the Zeiss-1000 telescope (black points with gray error bars). The blue curve shows the model light curve of the accreting white dwarf. The inset illustrates the trapezoidal fit to the eclipse profile. Right panels: accretion model for J0026 as viewed by the observer at phase $\varphi=0$, shown in two different scales. The thin red line indicates the ballistic stream trajectory, while blue lines represent the magnetic trajectory. The accretion spot on the white dwarf is marked by a thick red line, and the magnetic pole position is denoted by a green cross.
• Figure 3: Top panel: averaged spectra of J0026 for the bright phase peaks (blue line) and plateau phase (gray line). Blue and black lines show Savitzky-Golay filtered spectra. The red line represents the fit to the H$\alpha$ line region using a low-order polynomial combined with two Gaussian components. Vertical lines mark the positions of the H$\alpha$ Zeeman triplet components and likely H$\beta$ splitting components. Bottom panel: Zeeman splitting diagrams for H$\alpha$, H$\beta$, and H$\gamma$ lines. Horizontal lines indicate the magnetic field estimate and its uncertainty.
• Figure 4: Top panel: H$\alpha$ trailed spectra (left), sum of fitted Gaussian components (middle), and residual spectrum (right). Radial velocity curves of the narrow (red) and broad (blue) components are overplotted. Bottom panel: HeII $\lambda4686$ trailed spectra (left), fitted Gaussian (middle), and residual spectrum (right).
• Figure 5: Doppler tomograms of J0026 in the H$\alpha$ line (top) and HeII $\lambda$4686 (bottom), shown in standard (left) and inside-out (right) projections. The tomograms are overlaid with the donor star's velocity (closed red curve) and the accretor's Roche lobe velocity. The open red curve marks the ballistic stream trajectory, while green curves correspond to particle velocities along the magnetic trajectory.