High Velocity Stars in SDSS/APOGEE DR17

TL;DR

This study identifies and analyzes 23 high-velocity stars in the SDSS/APOGEE DR17 dataset, examining their kinematics, chemical properties, and potential to be unbound, with one notable CEMP star highlighted.

Contribution

The paper presents a new sample of high-velocity stars from APOGEE DR17, combining Gaia eDR3 data, and assesses their kinematics, chemical properties, and potential to be unbound, including the discovery of a CEMP star.

Findings

Three stars could be unbound depending on the Galactic potential.

All stars are consistent with halo star kinematics.

Identified a high velocity CEMP star at 482 km/s.

Abstract

We report 23 stars having Galactocentric velocities larger than $450~\mathrm{km\,s}^{-1}$ in the final data release of the APOGEE survey. This sample was generated using space velocities derived by complementing the high quality radial velocities from the APOGEE project in Sloan Digital Sky Survey's Data Release 17 (DR17) with distances and proper motions from Gaia early Data Release 3 (eDR3). We analyze the observed kinematics and derived dynamics of these stars, considering different potential models for the Galaxy. We find that three stars could be unbound depending on the adopted potential, but in general all of the stars show typical kinematics of halo stars. The APOGEE DR17 spectroscopic results and Gaia eDR3 photometry are used to assess the stellar parameters and chemical properties of the stars. All of the stars belong to the red giant branch, and, in general, they follow the abundance pattern of typical halo stars. There are a few exceptions that would deserve further analysis through high-resolution spectroscopy. In particular, we identify a high velocity Carbon-Enhanced Metal-Poor (CEMP) star, with Galactocentric velocity of 482 km\,s$^{-1}$. We do not confirm any hypervelocity star in the sample, but this result is very sensitive to the adopted distances, and less sensitive to the Galactic potential.