RE 0044 + 09: A new K dwarf rapid rotator with a white dwarf companion?

We report the discovery of a new K dwarf rapid rotator with a potential white dwarf companion. The white dwarf accounts for over 90% of the observed extreme ultraviolet flux detected from this system. Analysis of ROSAT Wide Field Camera and IUE data both suggest a white dwarf temperature of ∼28,700 K. Optical photometry and the IUE LWP spectrum (with the white dwarf contribution removed) imply that the late-type star has a spectral type of K1-3 V, and a distance of 55 ± 5 pc. Using this distance, the observed IUE SWP flux, and the best-fit temperature results in a white dwarf radius of 0.0088 R⊙. The estimated white dwarf mass is then ∼0.91 M⊙; somewhat over-massive compared to field white dwarfs. Optical photometry of the K star reveals a "spot" modulation period of ∼10 hr (now observed over 3 yr). However, radial velocity observations have revealed no significant variations. Spectroscopic observations place a low limit on the lithium abundance, but do show rapid rotation with a ν sin i of 90 ± 10 km s-1. The K star was detected as a radio source at 3.6 cm (on two occasions) and 6 cm by the Very Large Array. The most likely evolutionary scenario is that the K star and hot white dwarf form either a wide binary or common proper motion pair with an age of 0.1-0.2 Gyr - consistent with the evolutionary timescale of the white dwarf and the rapid rotation of the K star. However, from the proper motion of the K. star, this system does not seem to be associated with any of the known young stellar groups.