HE 0437–5439: An Unbound Hypervelocity Main-Sequence B-Type Star

By H. Edelmann, R. Napiwotzki, U. Heber, N. Christlieb, D. Reimers. 2005

147 citations recorded by the source corpus.

We report the discovery of a 16th magnitude star, HE 0437-5439, with a heliocentric radial velocity of +723 ± 3 km s-1. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT and UVES shows that HE 0437-5439 is a main-sequence B-type star with Teff = 20,350 K, log g = 3.77, a solar (within a factor of a few) helium abundance and metal content, and rotating at v sin i = 54 km s-1. Using appropriate evolutionary tracks, we derive a mass of 8 M☉ and a corresponding distance of 61 kpc. Its Galactic rest-frame velocity is at least 563 km s-1, 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 hypervelocity stars can be formed by the tidal disruption of a binary through interaction with the supermassive black hole at the Galactic center (GC). HE 0437-5439 needs about 100 Myr to travel from the GC to its present position, much longer than its main-sequence lifetime of 25 Myr. This can only be reconciled if HE 0437-5439 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; 18 kpc) than to the GC, it can reach its position from the center of the LMC. The proper motion predicted in this case is about 2 mas yr-1 (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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/7934cde27a33f87f2a99a3e50b9ae24d1b5aef8e

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In Astronomy and Astrophysics

1. H. Perets
2. Clovis Hopman
3. T. Alexander
4. Zhanwen Han
5. P. Madau
6. Lucas Schiefelbein
7. F. Haardt
8. A. Irrgang

Citations in the corpus

• Milky Way mass models for orbit calculations (2012, background): “There are several pros and cons of whether the object originated in the LMC as proposed by the discoverers of the star (Edelmann et al. 2005) or from the GC, which is the suspected place of origin of all hypervelocity stars (Brown et al. 2005).”
• Massive Perturber-driven Interactions between Stars and a Massive Black Hole (2006, background): “04 pc of the GC (Eisenhauer et al. 2005), and at the same time can account for the observed HVSs well on their way out of the Galaxy (Brown et al. 2005; Edelmann et al. 2005; Hirsch et al. 2005; Brown et al. 2006a,b; Bromley et al. 2006).”
• Interaction of Massive Black Hole Binaries with Their Stellar Environment. I. Ejection of Hypervelocity Stars (2006, background): “This and five more HVSs, recently discovered by Hirsch et al. (2005) and Brown et al. (2006a, 2006b), are all consistent with a Galactic center origin, while an ejection from the LMC is more plausible for the seventh HVS currently known (Edelmann et al. 2005).”
• The Progenitors of Type Ia Supernovae (2012, background): “Edelmann et al. (2005) suggested that the star could have originated in the Large Magellanic Cloud, since it is much closer to this galaxy (∼18 kpc) than to the GC (see also Przybilla et al., 2008).”