The Nature of the Hyper-Runaway Candidate HIP 60350

TL;DR

This study investigates the origin of the hyper-velocity star HIP 60350 through spectroscopic and kinematic analysis, exploring whether it was ejected by a supernova or dynamical interactions, and finds it may be unbound from the Galaxy.

Contribution

It provides a detailed chemical and kinematic analysis of HIP 60350, offering insights into its ejection scenario and potential to escape the Galaxy.

Findings

HIP 60350 has a high velocity of 530 km/s, possibly unbound from the Galaxy.

Chemical abundances suggest a slightly supersolar metallicity.

The star's orbit is consistent with an origin in the Galactic disk.

Abstract

Young, massive stars in the Galactic halo are widely supposed to be the result of an ejection event from the Galactic disk forcing some stars to leave their place of birth as so-called runaway stars. Here, we present a detailed spectroscopic and kinematic analysis of the runaway B-star HIP 60350 to determine which runaway scenario - a supernova explosion disrupting a binary system or dynamical interaction in star clusters - may be responsible for HIP 60350's peculiar orbit. Based on a non-local thermodynamic equilibrium approach, a high-resolution optical echelle spectrum was examined to revise spectroscopic quantities and for the first time to perform a differential chemical abundance analysis with respect to the B-type star 18 Peg. The results together with proper motions from the Hipparcos Catalog further allowed the three-dimensional kinematics of the star to be studied numerically. The abundances derived for HIP 60350 are consistent with a slightly supersolar metallicity agreeing with the kinematically predicted place of birth ca. 6 kpc away from the Galactic center. However, they do not exclude the possibility of an alpha-enhanced abundance pattern expected in the case of the supernova scenario. Its outstanding high Galactic rest frame velocity of 530 plus-minus 35 km/s is a consequence of ejection in the direction of Galactic rotation and slightly exceeds the local Galactic escape velocity in a standard Galactic potential. Hence HIP 60350 may be unbound to the Galaxy.