The accretion disk and white dwarf in the short-period dwarf novae TY piscium and V436 Centauri during quiescence

The short-period dwarf novae TY Psc and V436 Cen are SU UMa systems with ve ry similar orbital periods, similar recurrence times for normal outbursts ( similar to 23 days) and superoutbursts (similar to 340 days), and nearly id entical outburst amplitudes. We have carried out high-gravity model atmosph ere and accretion disk synthetic spectra from the grid of Wade & Hubeny. Th e best-fit stellar model spectrum, from spectral slope and line fitting, is a white dwarf photosphere having T-eff = 25,000 K, log g = 8, and essentia lly solar chemical abundances, while the best-fit optically thick accretion disk model, from spectral slope fitting, has M-wd = 0.55 M-., (M) over dot = 10(-9.5) M-. yr-1, and an inclination i = 18 degrees. The implied accret ion rate is almost certainly too large for dwarf nova quiescence. The predi cted fluxes using parameters from the photosphere and disk spectral slope f itting models reveal enormous differences compared with the observed lumino sity using a reasonable distance estimate. For TY Psc, the predicted accret ion disk luminosity is similar to 100 times too luminous, while the stellar luminosity is too luminous by a factor of similar to 10. For V436 Cen, the best-fit high-gravity model photosphere, from spectral slope fitting, yiel ds T-eff = 24,000 K, log g = 8, and essentially solar abundance, while the best-fit accretion disk models, from spectral slope fitting, yield M-wd = 0 .8 M., M = 10(-10) M-. yr(-1), and i = 75 degrees. The presence of broad ab sorption troughs at unusual wavelength positions suggests the presence of a n absorption curtain (upper disk atmosphere) in V436 Cen. The temperatures we have for TY Psc and V436 Cen are higher than normal for the accreting wh ite dwarfs in dwarf novae below the period gap. This could indicate that th e systems were not in the deepest level of quiescence when they were observ ed.