2000PASP..112.1467S

Multicolor (BVRI) light curves have been obtained for the newly discovered, 4.21 hr eclipsing dwarf nova RX J0909+1849. The eclipse profiles have been analyzed with a parameter-fitting model to constrain properties of the system. The model assumes four sources of luminosity: the white dwarf primary star and the secondary star (both assumed to radiate as blackbodies) and an accretion disk characterized as a blackbody whose temperature follows a radial power-law distribution: T(r)=T_d(R_d/r)^α, where T_d and R_d are the outer disk temperature and radius, respectively. The model also includes an optically thick bright spot at the intersection of the mass transfer stream and the disk periphery. A matrix of model solutions is computed, which covers an extensive range of plausible parameter values. The solution matrix is then explored to determine the optimum values for the fitting parameters and their associated errors.

The mass ratio of RX J0909+1849 is unknown, thus the orbital inclination is not tightly constrained by the model. Five mass ratios have been considered spanning a range of plausible values, 0.3≤q(=M₂/M₁)≤0.7. Over this range of q, the inclination varies between roughly 74° and 80°. Model parameters include the temperatures of the white dwarf (T₁) and the secondary star (T₂), the radius (R_d) and temperature (T_d) of the disk periphery, the disk power-law temperature exponent (α), and the bright spot temperature (T_s). With the exception of the q=0.3 models, which required a relatively hot white dwarf (80,000 K), the optimum values of the parameters are nearly constant with mass ratio. For a representative mass ratio of q=0.5, values of T₁=26,000±14,000 K, T_s=18,000±7000 K, T_d=3200±600 K, R_d/R_L1=0.54±0.08, α=0.53±0.11, and B-V=0.45±0.07 are found. A value of T₂=3400 K has been adopted for all models based on the spectral type of the secondary star (M3-M4).

The observed color (B-V=0.4±0.2) is consistent with the colors given by the model; thus, it is unlikely that RX J0909+1849 suffers significant interstellar absorption. The observed spectral type of the secondary star suggests an absolute magnitude in the range 10.6<M_V(2)<11.0. After correcting the apparent V magnitude at mideclipse by the fraction of light originating from the secondary star (∼94%), a distance of ∼200-250 pc is derived for the RX J0909+1849 system.