Origin of a massive hyper-runaway subgiant star LAMOST-HVS1: implication from Gaia and follow-up spectroscopy.
HATTORI K., VALLURI M., CASTRO N., ROEDERER I.U., MAHLER G. and KHULLAR G.
Abstract (from CDS):
We report that LAMOST-HVS1 is a massive hyper-runaway subgiant star with a mass of 8.3 M☉ and super-solar metallicity, which was ejected from the inner stellar disk of the Milky Way ∼33 Myr ago with the intrinsic ejection velocity of 568–17+19kms–1 (corrected for the streaming motion of the disk), based on the proper motion data from Gaia Data Release 2 (DR2) and high-resolution spectroscopy. The extremely large ejection velocity indicates that this star was not ejected by the supernova explosion of a binary companion. Rather, it was probably ejected by a three- or four-body dynamical interaction with more massive objects in a high-density environment. Such a high-density environment may be attained at the core region of a young massive cluster (YMC) with mass of >=104 M☉. The ejection agent that took part in the ejection of LAMOST-HVS1 may be an intermediate mass black hole (>=100 M☉), a very massive star (>=100 M☉), or multiple ordinary massive stars (>=30 M☉). Based on the flight time and the ejection location of LAMOST-HVS1, we argue that its ejection agent or its natal star cluster is currently located near the Norma spiral arm. The natal star cluster of LAMOST-HVS1 may be an undiscovered YMC near the Norma spiral arm.