SDSS 1507+02: A Halo Cataclysmic Variable?

TL;DR

This study investigates SDSS 1507+52, a peculiar cataclysmic variable with an extremely short orbital period and high space velocity, suggesting it may belong to the Galactic halo rather than the disk.

Contribution

The paper provides detailed photometric and spectroscopic analysis of SDSS 1507+52, revealing its unusual properties and proposing its possible halo membership, challenging existing CV evolutionary models.

Findings

Orbital period of 67 minutes below the period minimum for hydrogen-rich CVs.

High proper motion indicating a transverse velocity of 164 km/s.

Binary parameters consistent with a WZ Sge-type dwarf nova.

Abstract

We 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 M_1=0.83(8) solar masses, M_2=0.057(8) solar masses, R_1=0.0097(9) solar radii, R_2=0.097(4) solar radii, q=0.069(2), and i=83.18(13) degrees. 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 approximately 77 min which 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 - 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.