  System parameters are re-determined: $M_1=0.86\pm0.18M\odot$,
$M_2=0.103\pm0.022M\odot$, $A=1.508\pm 0.100\times 10^{10}$cm, and
$i=69\pm3^{\circ}$. The secondary component is a semi-degenerate helium star
loosing mass at a rate $\dot M=4.93\pm 1.65\times10^{-9}M\odot/yr$. The
accretion disk is sufficiently hot to avoid thermal instability. The orbital
light curve recovered from observations made in 1962 shows minimum shifted to
phase $\phi=0.50$, corresponding to $O-C=0.0060$d. Together with mimima
observed in 1992-99 this implies that the orbital period is increasing at a
rate $dP/dt\approx 8.5 \times 10^{-13}$ consistent with predictions involving
the emission of gravitational waves.
