The Impact of Accurate Distances on UV Spectroscopy of White Dwarfs and Cataclysmic Variables

J‐MAPS and Gaia are two asterometry missions to be launched in 2012. The positions of stars brighter than 15 magnitude will be measured to accuracies of better than one milli‐arcsecond and 25 micro‐arcseconds, respectively. Accurate distances (⁠$<few$ percent) will constrain the luminosity and hence, effective temperature, radius and mass of isolated white dwarfs. With a sufficiently large sample, evolutionary models can be tested. For cataclysmic variables (CVs), evolutionary models can also be tested, particularly for dwarf novae in quiescence where the white dwarf is detected. By measuring the $Teff$ of the white dwarf, the long‐term accretion rate of the binary can be estimated and compared with the expected accretion rate of magnetic braking for CVs above the period gap $(>3 hr)$ and gravitational braking for those below the gap $(<2 hr).$ For nova‐like systems, whose luminosity is dominated by the accretion disk and affected by interstellar extinction and reddening, accurate distances can help constrain the temperature profile of the disk.