Discovery of two new hypervelocity stars from the LAMOST spectroscopic surveys

Abstract

We report the discovery of two new unbound hypervelocity stars (HVSs) from the LAMOST spectroscopic surveys. They are respectively a B2V type star of ~ 7 M${}_{\odot }$ with a Galactic rest-frame radial velocity of 502 km/s at a Galactocentric radius of ~ 21 kpc and a B7V type star of ~ 4 M${}_{\odot }$ with a Galactic rest-frame radial velocity of 408 km/s at a Galactocentric radius of ~ 30 kpc. The origins of the two HVSs are not clear given their currently poorly measured proper motions. However, the future data releases of Gaia should provide proper motion measurements accurate enough to solve this problem. The ongoing LAMOST spectroscopic surveys are expected to yield more HVSs to form a statistical sample, providing vital constraint on understanding the nature of HVSs and their ejection mechanisms.

5 pages, 3 figures, 1 table, accepted for publication in ApJL

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• Hypervelocity Stars in the Gaia era. Revisiting the most extreme stars from the MMT survey
• Constraints on the Galactic Centre environment from Gaia hypervelocity stars
• Discovery of A candidate Hypervelocity star originated from the Sagittarius Dwarf Spheroidal galaxy
• On the origins of extreme velocity stars as revealed by large-scale Galactic surveys
• Constraints on the Galactic Centre environment from \textit{Gaia} hypervelocity stars III: Insights on a possible companion to Sgr A*
• Comparing hypervelocity star populations from the Large Magellanic Cloud and the Milky Way
• Flying far and fast: the distribution of distant hypervelocity star candidates from Gaia DR2 data
• Blue extreme disk-runaway stars with Gaia EDR3
• The influence of the secular perturbation of an intermediate-mass companion: II. Ejection of hypervelocity stars from the Galactic Center
• Probing the shape of the Milky Way dark matter halo with hypervelocity stars: a new method
• Probing modified Newtonian dynamics with hypervelocity stars
• Three New Late-type Hypervelocity Star Candidates from Gaia DR2 with Refined Selection Criteria