HE 0437-5439: An Unbound Hypervelocity Main-Sequence B-Type Star
- 16 November 2005
- journal article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 634 (2), L181-L184
- https://doi.org/10.1086/498940
Abstract
We report the discovery of a 16th magnitude star, HE0437-5439, with a heliocentric radial velocity of +723+-3km/s. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT and the UVES spectrograph shows that HE0437-5439 is a main sequence B-type star with Teff=20350K, log g=3.77, solar within a factor of a few helium abundance and metal content, rotating at v sin i=54km/s. Using appropriate evolutionary tracks we derive a mass of 8 Msun and a corresponding distance of 61 kpc. Its galactic rest frame velocity is at least 563km/s, almost twice the local Galactic escape velocity, indicating that the star is unbound to the Galaxy. Numerical kinematical experiments are carried out to constrain its place of birth. It has been suggested that such hyper-velocity stars can be formed by the tidal disruption of a binary through interaction with the super-massive black hole at the Galactic center (GC). HE0437-5439 needs about 100Myrs to travel from the GC to its presentposition, much longer than its main sequence lifetime of 25Myrs. This can only be reconciled if HE0437-5439 is a blue straggler star. In this case, the predicted proper motion is so small that it can only be measured by future space missions. Since the star is much closer to the Large Magellanic Cloud (LMC, 18kpc) than to the GC, it can reach its position from the center of the LMC. The proper motion predicted in this case is about 2mas/y (relative to the LMC), large enough to be measurable with conventional techniques from the ground. The LMC origin could also be tested by a high-precision abundance analysis.Comment: 13 pages, 4 figures. Astrophysical Journal Letters, accepteKeywords
This publication has 13 references indexed in Scilit:
- Discovery of an Unbound Hypervelocity Star in the Milky Way HaloThe Astrophysical Journal, 2005
- Hot subdwarfs from the ESO Supernova Ia Progenitor SurveyAstronomy & Astrophysics, 2005
- Chemical Abundances and Rotation Velocities of Blue Horizontal‐Branch Stars in Six Globular ClustersThe Astrophysical Journal Supplement Series, 2003
- Early type stars at high galactic latitudesAstronomy & Astrophysics, 2001
- The SuperCOSMOS Sky Survey - III. AstrometryMonthly Notices of the Royal Astronomical Society, 2001
- Final Results from theHubble Space TelescopeKey Project to Measure the Hubble ConstantThe Astrophysical Journal, 2001
- The stellar content of the Hamburg/ESO surveyAstronomy & Astrophysics, 2001
- A Comparative Study of the Mass Distribution of Extreme‐Ultraviolet–selected White DwarfsThe Astrophysical Journal, 1999
- Orbits of galactic globular clustersAstronomische Nachrichten, 1992
- Hyper-velocity and tidal stars from binaries disrupted by a massive Galactic black holeNature, 1988