An HST parallax of the distant cataclysmic variable V1223 Sgr, its system parameters, and accretion rate

Using the Hubble space Telescope Fine Guidance Sensor. we have measured the trigonometric parallax of the bright cataclysmic variable 1223 Sgr. The absolute parallax is pi(abs) = 1.96 +/- 0.18 mas, making V 1223 Sur the most distant CV with a well-determined trigonometric parallax. This distance, a Lutz-Kelker correction, and the previously measured extinction yield an absolute visual high-state magnitude M(V) = 4.0 +/- 0.2. We outline a model, which is consistent with the observed spin-down of the white dwarf and provides for much Of the UV/optical emission by reverberation of X-rays. From previous X-ray and UV/optical data, we derive an accretion luminosity L(acc) = (2.6 +/- 0.8) x 10(34) erg s(-1), a white dwarf mass M(1) = 0.93 +/- 0.12 M(circle dot) and an accretion rate M = (1.4 +/- 0.3) x 10(17) g s(-1).