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The Recurrent Nova T Pyx: Distance and Remnant Geometry from Light Echoes

The recurrent nova T Pyxidis (T Pyx) is well known for its small binary separation, its unusually high luminosity in quiescence, and the spectacular Hubble Space Telescope (HST) images of its surrounding remnant. In 2011 April, T Pyx erupted for the first time since 1966. Here we describe HST observations in late 2011 of a transient reflection nebula around the erupting white dwarf (WD). Our observations of this light echo in the pre-existing remnant show that it is dominated by a clumpy ring with a radius of about 5", and an inclination of 30 to 40 degrees, with the eastern edge tilted toward the observer. The delay times between the direct optical light from the central source, and the scattering of this light from dust in several clumps with the same foreground distance as the central source, give a distance to T Pyx of 4.8 +- 0.5 kpc. Given past evidence from two-dimensional optical spectra that the remnant contains a shell-like component, it must actually consist of a ring embedded within a quasi-spherical shell. The large distance of 4.8 kpc supports the contention that T Pyx has an extraordinarily high rate of mass transfer in quiescence, and thus that nova explosions themselves can enhance mass loss from a donor star, and reduce the time between eruptions in a close binary.