The fastest unbound star in our Galaxy ejected by a thermonuclear supernova

Creators: Geier, S.; Fürst, F.; Ziegerer, E.; Kupfer, T.; Heber, U.; Irrgang, A.; Wang, B.; Liu, Z.; Han, Z.; Sesar, B.; Levitan, D.; Kotak, R.; Magnier, E. A.; Smith, K.; Burgett, W.; Chambers, K.; Flewelling, H.; Kaiser, N.; Wainscoat, R.; Waters, C.

Abstract

Hypervelocity stars (HVSs) travel with velocities so high that they exceed the escape velocity of the Galaxy. Several acceleration mechanisms have been discussed. Only one HVS (US 708, HVS 2) is a compact helium star. Here we present a spectroscopic and kinematic analysis of US 708. Traveling with a velocity of ~1200 kilometers per second, it is the fastest unbound star in our Galaxy. In reconstructing its trajectory, the Galactic center becomes very unlikely as an origin, which is hardly consistent with the most favored ejection mechanism for the other HVSs. Furthermore, we detected that US 708 is a fast rotator. According to our binary evolution model, it was spun-up by tidal interaction in a close binary and is likely to be the ejected donor remnant of a thermonuclear supernova.

Additional Information

© 2015 American Association for the Advancement of Science. Received for publication 22 July 2014. Accepted for publication 29 January 2015. We thank H. Hirsch for providing us with the Low Resolution Imaging Spectrometer spectra. This work is based on observations obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The W. M. Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We wish to recognize the important cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work is also based on observations at the Palomar Observatory. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions from the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes (the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching), The Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network, the National Central University of Taiwan, the Space Telescope Science Institute, the NASA under grant no. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the NSF under grant no. AST-1238877, the University of Maryland, and Eotvos Lorand University (ELTE). Z.H. is supported by the Natural Science Foundation of China (grant nos. 11390374 and 11033008). E.Z. and A.I. are supported by the Deutsche Forschungsgemeinschaft through grant HE1356/45-2. T.K. acknowledges support from the Netherlands Research School for Astronomy (NOVA). A.I. acknowledges support from a research scholarship by the Elite Network of Bavaria. R.K. acknowledges support from Science and Technologies Council UK grant no. ST/L000709/1, Queen's University Belfast's contribution to the PanSTARRS1 science consortium. K.S. acknowledges support from European Union FP7 Programme ERC grant no. 291222. F.F. acknowledges NASA contract no. NNG08FD60C for the NuSTAR mission. The data observed with the SDSS and Keck telescope are published via the SDSS and Keck data archive; the PS1 data and catalog are available upon request.

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