The Runaway Binary LP 400-22 is Leaving the Galaxy

Abstract

We present optical spectroscopy, astrometry, radio, and X-ray observations of the runaway binary LP 400-22. We refine the orbital parameters of the system based on our new radial velocity observations. Our parallax data indicate that LP 400-22 is significantly more distant (3 sigma lower limit of 840 pc) than initially predicted. LP 400-22 has a tangential velocity in excess of 830 km/s; it is unbound to the Galaxy. Our radio and X-ray observations fail to detect a recycled millisecond pulsar companion, indicating that LP 400-22 is a double white dwarf system. This essentially rules out a supernova runaway ejection mechanism. Based on its orbit, a Galactic center origin is also unlikely. However, its orbit intersects the locations of several globular clusters; dynamical interactions between LP 400-22 and other binary stars or a central black hole in a dense cluster could explain the origin of this unusual binary.

MNRAS, in press

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• Precise Atmospheric Parameters for the Shortest Period Binary White Dwarfs: Gravitational Waves, Metals, and Pulsations
• The ELM Survey. VI. Eleven New Double Degenerates
• SDSS J074511.56+194926.5: Discovery of a Metal-Rich and Tidally Distorted Extremely Low Mass White Dwarf
• A high-velocity bulge RR Lyrae variable on a halo-like orbit
• Distant White Dwarfs in the US Naval Observatory Flagstaff Station Parallax Sample
• The Mass Distribution of Companions to Low-Mass White Dwarfs
• The Origin of HVS17, an Unbound Main Sequence B Star at 50 kpc