Mass transfer and the period decrease in RXJ0806.3+1527

We examine the nature of RXJ0806.3+1527 and show that it is possible to reconcile the observed period decrease and X-ray luminosity with the transfer of mass between two white dwarfs provided that: either the system is (i) still in the early and short-lived (less than ~100yr) stages of mass transfer due to atmospheric Roche-lobe overflow, or (ii) in a standard, long-term, quasi-stationary mass-transfer phase that is significantly (~90%) non-conservative and the conversion of accretion energy to X-rays is quite inefficient. In either of the two cases and for a wide range of physical parameters, we find that orbital angular momentum is lost from the system at a rate that is a factor of a few (less than ~4) higher than the rate associated with the emission of gravitational waves. Although the physical origin of this extra angular momentum loss is not clear at present, it should be taken into account in the consideration of RXJ0806.3+1527 as a verification Galactic source for LISA.