High-velocity CP2 stars in the Galactic halo

Abstract

Context. The second subclass of chemically peculiar stars, the CP2 stars, are early-type stars exhibiting anomalous abundances with variable line strengths possibly also accompanied by photometric variability that typically belong to the Galactic disk. However, a small fraction of these objects were recently found to be located far from the Galactic plane and are thought to belong to the Galactic halo, which is unexpected for this class of objects. Aims. Our study investigates the halo membership of the proposed halo CP2 star candidates based on their velocities and Galactic orbits, to determine their points of origin. In addition, we searched for further halo CP2 star candidates using an as-yet-unpublished sample of CP stars. Methods. Our analysis relied on the astrometry from the early third \textit{Gaia} data release and radial velocities based on the spectroscopy from LAMOST and SDSS, which was also employed in spectral classification. The light variability of the confirmed CP2 stars in our sample was analyzed using data from the ZTF and ATLAS surveys. Results. After filtering our initial sample using kinematic and spectroscopic criteria, we identified six CP2 stars with kinematical properties consistent with a halo membership. The orbits of these stars are in agreement with an origin in the Galactic disk where they were probably ejected through dynamical interactions or in the binary supernova scenario, making them the first runaway CP2 stars known.

13 pages, 11 figures, accepted for publication in A&A

References in corpus (11)

• The Gaia mission
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• galpy: A Python Library for Galactic Dynamics
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Stellar labels for hot stars from low-resolution spectra - I. the HotPayne method and results for 330,000 stars from LAMOST DR6
• Characterizing and correcting the proper motion bias of the bright Gaia EDR3 sources
• New Photometrically Variable Magnetic Chemically Peculiar Stars in the ASAS-3 Archive
• New and improved rotational periods of magnetic CP stars from ASAS-3, KELT and MASCARA data
• Global properties of the light curves of magnetic, chemically peculiar stars as a testbed for the existence of dipole-like symmetry in surface structures
• HD 240121 - an ACV variable showing anti-phase variations of the B and V light curves
• New magnetic chemically peculiar stars and candidates in the ATLAS First Catalog of Variable Stars

Cited by in corpus (1)

• Eta-Earth Revisited II: Deriving a Maximum Number of Earth-like Habitats in the Galactic Disk