Modeling Eclipses of the Novalike Variable TT Triangulum

Abstract

ABSTRACTMulticolor (BVRI) light curves of the eclipsing novalike variable TT Tri are presented. The eclipse profiles are analyzed with a parameter‐fitting model that assumes four sources of luminosity: a white dwarf primary star, a main‐sequence secondary star, a flared accretion disk with a rim, and a bright spot at the intersection of the mass‐transfer stream and the disk periphery. Model parameters include the temperatures of the white dwarf, T1, and the secondary star, T2, the radius Rd and temperature Td of the disk periphery, the inner disk radius Rin, the disk power‐law radial brightness temperature exponent α and thickness parameter hr, and a bright spot temperature enhancement factor χs. A grid of model light curves was computed, covering an extensive range of plausible parameter values. The models were then compared with the mean BVRI light curves to determine the optimum values for the fitting parameters and their associated errors. The mass ratio of TT Tri is poorly constrained in our models but must lie roughly in the range 0.3≲q≲0.9 (where q = M2/M1). Models characterized by mass ratios of q = 0.3 (i = 76.°1), q = 0.6 (i = 72.°6), and q = 0.9 (i = 70.°4) were all capable of providing acceptable fits to the data, although the best fits were achieved for mass ratios near the upper end of the permitted range (q = 0.6 and 0.9). The values of the remaining fitting parameters were found to be insensitive to the adopted mass ratio and rim thickness. The accretion disk was found to extend to ∼50%–60% of the distance to the inner Lagrangian point in all models but came closer to reaching the tidal limit (as expected for steady state accretion) in the higher mass ratio models. The same behavior was found for the radial temperature profile of the disk, which increased with mass ratio, becoming more consistent with that expected for steady state accretion in the q = 0.6 and q = 0.9 models. Models with a truncated inner disk (Rin≫R1) generally resulted in a higher white dwarf temperature and a steepening of the disk temperature profile but were not required to achieve a viable steady state disk solution. No evidence was found for a luminous bright spot in the system, which is not surprising given the lack of a pre‐eclipse “hump” in the light curve. A total of 22 eclipse timings were measured for the system, which yielded an ephemeris for the times of mideclipse given by HJD = 2,453,618.953(3) + 0.1396369(4)E. A comparison of the observed brightness and color at mideclipse with the photometric properties of the best‐fitting model suggests that TT Tri lies at a distance of ∼400–500 pc.