SDSS 1507+52: A Halo Cataclysmic Variable?11Based on observations obtained at the MDM Observatory, operated by Dartmouth College, Columbia University, Ohio State University, Ohio University, and the University of Michigan.

Abstract

ABSTRACTWe report a photometric and spectroscopic study of the peculiar cataclysmic variable SDSS 1507+52. The star shows very deep eclipses on the 67-minute orbital period, and those eclipses are easily separable into white-dwarf and hot-spot components. This leads to tight constraints on binary parameters, with M1 = 0.83(8) M⊙, M2 = 0.057(8) M⊙, R1 = 0.0097(9) R⊙, R2 = 0.097(4) R⊙, q = 0.069(2), and i = 83.18(13)°. Such numbers suggest possible membership among the WZ Sge stars, a common type of dwarf nova. The spectroscopic behavior (strong and broad H emission, double-peaked and showing a classic rotational disturbance during eclipse) is also typical. But the star’s orbital period is shockingly below the “period minimum” of ∼77 minutes that is characteristic of hydrogen-rich CVs; producing such a strange binary will require some tinkering with the theory of cataclysmic-variable evolution. The proper motion is also remarkably high for a star of its distance, which we estimate from photometry and trigonometric parallax as 230 ± 40 pc. This suggests a transverse velocity of 164 ± 30 km s-1 —uncomfortably high if the star belongs to a Galactic-disk population. These difficulties with understanding its evolution and space velocity can be solved if the star belongs to a Galactic-halo population.