The eclipsing novalike cataclysmic variable CRTS SSS100505 J093417-174421

Abstract

Time-resolved optical photometry, complemented by TESS data and long-term survey light curves, reveals that the transient object CRTS SSS100505 J093417-174421 is an eclipsing novalike cataclysmic variable of the VY~Scl subtype, with an orbital period of 0.16329188(8) d. An analysis of the light curves with eclipse mapping techniques and an entropy landscape procedure indicates an orbital inclination of 81.5 degrees and a mass ratio of 0.45. Eclipse maps reveal two diametrically opposed asymmetric arcs of enhanced emission in the intermediate and outer regions of an accretion disk elongated in the direction perpendicular to the line joining both stars, interpreted as tidally-induced spiral shock arms. The accretion disk is 50 per cent larger in the longer wavelength TESS data than in the optical range, in line with the expected radial temperature gradient of an opaque steady-state disk. The combination of a small optical disk radius (of 21 per cent of the orbital separation) and high orbital inclination explains the relatively faint absolute magnitude of $M_g = 7.44$ for a novalike variable.

Figures (4)

• Figure 1: a) Long-term light curve of CRTS 0934. Black and green dots are CRTS and ZTF data, respectively. The red dots represent the nightly average out-of-eclipse magnitude of the OPD observations. The black arrows indicate mid-epochs of the TESS data. b) Time-resolved OPD light curve of 2021, April 12 (starting just before midnight of April 11). c) Sector 35 TESS light curve. The red dots are average flux values (after masking eclipses) within 1 d intervals. The light curves smoothed with a Savitzky-Golay filter (again, eclipses masked) are shown in blue. d) Combined TESS light curve of sectors 8 and 35, folded on the orbital period (small black dots). The red dots represent average values in phase bins of width 0.01.
• Figure 2: Entropy landscape in the ($i,q$) binary parameter plane. The entropy of the eclipse maps are shown as different shades of gray; darker regions have higher entropy. Contour lines indicate the shape of the entropy landscape and a red cross marks the location of highest entropy. White curves show lines of constant $\Delta\phi$ values.
• Figure 3: Left-hand panels: average data (green points with error bars) and best-fit eclipse mapping model (solid line) for the V-band (a) and I-band (b) light curves. Horizontal bars at mid-eclipse show the uneclipsed flux in each case. Vertical dashed lines mark the best-fit $\Delta\phi$ value (indicating the WD ingress/egress phases), and vertical ticks mark the total width of the eclipse, $\Delta\phi_E$. The lower red curve illustrates the eclipse light curve of the asymmetric arcs 1 and 2 (see text). Middle panels: V-band (c) and I-band (d) eclipse maps in a logarithmic grayscale; darker regions are brighter. Regions inside the two solid contour lines are above the 3$\sigma$ and 5$\sigma$ confidence levels, respectively. A cross marks the position of the disk center; dashed lines depict the primary Roche lobe and the gas stream trajectory. Right-hand panels: The asymmetric component of the V-band (e) and I-band (f) eclipse maps in a logarithmic grayscale. Dashed circles mark the estimated disk radii; dotted lines show the edge of the projected shadow of the secondary star at phase zero, while dot-dashed red lines illustrate the expected orientation of tidally-induced spiral arms for constant opening angles of $\theta_s$ = 15$\degr$, 19$\degr$, and 30$\degr$. The location of asymmetric arcs 1 and 2 is indicated.
• Figure 4: a) Dependency on orbital phase of the maximum intensity derived from the asymmetric component of the V-band (black) and I-band (red) eclipse maps. Intensities are plotted on an arbitrary scale; arms 1 and 2 are labeled and horizontal tick marks indicate the phases of maxima of the double-wave orbital modulation. Dotted lines show the uncertainties at the 1$\sigma$ limit. Vertical dashed lines mark the 1-$\sigma$ range of values for the phase of lowest intensity, $\phi_1 (I_\mathrm{min})$ (see text). b) Corresponding radius of maximum intensity in units of $R_\mathrm{L1}$. Horizontal dashed lines mark the circularization radius ($R_\mathrm{circ}= 0.208\,R_\mathrm{L1}$) and the outer disk radius ($R_V= 0.36\,R_\mathrm{L1}$ in the V-band and $R_I= 0.54\,R_\mathrm{L1}$ in the I-band).