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tokens: (NFO, including corrections). The resultant light curves are displayed in Figure 2 . Figure 2. Photometric observations of V506 Oph from the URSA and NFO telescopes, along with the residuals. NFO is displaced vertically for clarity. Enlargements of the minima are shown at the bottom. Our adopted model discussed in Section 5 is overplotted. Table 5 URSA Observations of V506 Oph (This table is available in its entirety in machine-readable form.) Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available. Table 6 NFO Observations of V506 Oph (This table is available in its entirety in machine-readable form.) Only a portion of this table is shown here to demonstrate its form and content. A machine-readable version of the full table is available. 5. Light-curve Analysis The URSA and NFO photometry of V506 Oph was analyzed using version 2013 of the Wilson–Devinney LC program (Wilson Devinney 1971 ; Wilson 1979 , 1990 ) called within a Markov chain Monte Carlo (MCMC) scheme. Our method of solution used the emcee 5 5 http://dfm.io/emcee/current code of Foreman-Mackey et al. ( 2013 ), which is a Python implementation of the affine-invariant MCMC ensemble sampler proposed by Goodman Weare ( 2010 ). We typically used 100 walkers and uniform priors within suitable limits for all fitted quantities. As the system is well detached, we used the LC program in mode 2, along with the option of simple reflection and synchronous rotation of both components (see Section 6 ). The ephemeris and mass ratio of the binary were held fixed at the values in Table 4 , and the primary temperature was set to 6840 K (Section 2 ). The main parameters of the fit were the inclination angle, i ; the temperature of the secondary, T eff,2 ; the surface potentials, Φ 1 and Φ 2 ; a phase shift, Δ φ ; and the out-of-eclipse magnitude difference at phase 0.25, m 0 . We assumed initial measurement errors for the URSA and NFO observations of 0.02 mag, and a scale factor, f (with a log-uniform prior), was included as an additional adjustable parameter, which we solved for self-consistently and simultaneously with the other parameters (see Gregory 2005 ). Convergence of the chains was checked visually, with the additional requirement of a Gelman–Rubin statistic of 1.05 or smaller for each parameter (Gelman Rubin 1992 ). The URSA and NFO data sets were initially analyzed separately. Tests indicated the best results were obtained by solving also for the linear limb-darkening coefficients of each star ( x 1 , x 2 ), as well as the gravity-darkening exponents ( β 1 , β 2 ). More complicated limb-darkening laws did not provide any improvement. The albedos for both components were held fixed at a value of 0.5, commonly adopted for convective stars, as experiments with other values gave poorer results. No significant third light was detected, consistent with the fact that the Gaia /DR2 catalog (Gaia Collaboration et al.