The Runaway White Dwarf LP400-22 Has a Companion
arXiv:0903.1843 · doi:10.1088/0004-637X/695/1/L92
Abstract
We report the detection of a radial velocity companion to the extremely low mass white dwarf LP400-22. The radial velocity of the white dwarf shows variations with a semi-amplitude of 119 km/s and a 0.98776 day period, which implies a companion mass of M > 0.37 Msun. The optical photometry rules out a main sequence companion. Thus the invisible companion is another white dwarf or a neutron star. Using proper motion measurements and the radial velocity of the binary system, we find that it has an unusual Galactic orbit. LP400-22 is moving away from the Galactic center with a velocity of 396 km/s, which is very difficult to explain by supernova runaway ejection mechanisms. Dynamical interactions with a massive black hole like that in the Galactic center can in principle explain its peculiar velocity, if the progenitor was a triple star system comprised of a close binary and a distant tertiary companion. Until better proper motions become available, we consider LP400-22 to be most likely a halo star with a very unusual orbit.
ApJ Letters, in press
References in corpus (10)
- The RAVE Survey: Constraining the Local Galactic Escape Speed
- White Dwarf Mass Distribution in the SDSS
- On type Ia supernovae and the formation of single low-mass white dwarfs
- Hypervelocity Stars: From the Galactic Center to the Halo
- The masses of PSR J1911-5958A and its white dwarf companion
- The Future is Now: the Formation of Single Low Mass White Dwarfs in the Solar Neighborhood
- Dynamical and evolutionary constraints on the nature and origin of hypervelocity stars
- The Discovery of a Companion to the Lowest Mass White Dwarf
- LP 400-22, A very low-mass and high-velocity white dwarf
- Timing of millisecond pulsars in NGC 6752 - II. Proper motions of the pulsars in the cluster outskirts