The Origin of HVS17, an Unbound Main Sequence B Star at 50 kpc

Abstract

We analyze Keck ESI spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km/s in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T_eff and logg with stellar evolution tracks implies that HVS17 is a 3.91 +-0.09 Msun, 153 +-9 Myr old star at a Galactocentric distance of r=48.5 +-4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way's dark matter halo.

6 pages, ApJ accepted

References in corpus (20)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• The Mass Profile of the Galaxy to 80 kpc
• Hypervelocity Stars. I. The Spectroscopic Survey
• A progenitor binary and an ejected mass donor remnant of faint type Ia supernovae
• On type Ia supernovae and the formation of single low-mass white dwarfs
• Hypervelocity Stars: From the Galactic Center to the Halo
• A Successful Targeted Search for Hypervelocity Stars
• Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?
• Hypervelocity Stars III. The Space Density and Ejection History of Main Sequence Stars from the Galactic Center
• Kinematics of hypervelocity stars in the triaxial halo of the Milky Way
• Dynamical and evolutionary constraints on the nature and origin of hypervelocity stars
• Tracing intermediate-mass black holes in the Galactic Centre
• LMC origin of the hyper-velocity star HE 0437-5439. Beyond the supermassive black hole paradigm
• The Nature of the Hyper-Runaway Candidate HIP 60350
• A Galactic Center Origin for HE 0437-5439, the Hypervelocity Star near the Large Magellanic Cloud
• HVS7: a chemically peculiar hyper-velocity star
• 'Slow' and Fast Rotators among Hypervelocity Stars
• HD271791: dynamical versus binary-supernova ejection scenario
• Hypervelocity A & B Stars should be slow rotators
• The Runaway Binary LP 400-22 is Leaving the Galaxy

Cited by in corpus (8)

• MMT Hypervelocity Star Survey III: A Complete Survey of Faint B-type Stars in the Northern Milky Way Halo
• The Peculiar Pulsar Population of the Central Parsec
• Gaia and the Galactic Center Origin of Hypervelocity Stars
• Predicted Space Motions for Hypervelocity and Runaway Stars: Proper Motions and Radial Velocities for the GAIA Era
• Proper Motions and Trajectories for 16 Extreme Runaway and Hypervelocity Stars
• Nearby high-speed stars in Gaia DR2
• Sparkling EUV bright dots observed with Hi-C
• Impact of the Galactic Disk and Large Magellanic Cloud on the Trajectories of Hypervelocity Stars Ejected from the Galactic Center