Searching for merger debris in the Galactic halo: Chemodynamical evidence based on local blue HB stars

Abstract

We report on the discovery of a group of local A-type blue horizontal-branch (HBA) stars moving in a prograde, comet-like orbit with very similar kinematics and abundances. This serendipitously discovered group contains 5 or 6 local HBA stars venturing very close to the Galactic centre; their [Fe/H] is around -1.7, and they seem to present minimum scatter in at least Mg, Si, Ti, Fe, Al, and Cr abundances. This ``Cometary Orbit Group'' (COG) was found while we were testing a new method to detect the debris associated with the merger of smaller, specific protogalactic entities into our galaxy. The method is primarily intended to identify field HBA stars with similar kinematics and detailed, multi-species abundance patterns as seen among members of a surviving remnant (e.g., omega Centauri). Quite possibly, the COG is the remnant, on a highly decayed orbit, of a merging event that took place in the relatively remote past (i.e., at least one revolution ago).

arXiv comment4 pages and 2 EPS figures, accepted for publication in Astronomy and Astrophysics Letters

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• Phase-Space Distributions of Chemical Abundances in Milky Way-type Galaxy Halos
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• Formation of Multiple Populations in Globular Clusters: Another Possible Scenario
• Discovery of a Metal-Poor Field Giant with a Globular Cluster Second-Generation Abundance Pattern
• On the Origin of Bimodal Horizontal-Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441
• Kinematic Structure in the Galactic Halo at the North Galactic Pole: RR Lyrae and BHB Stars show different kinematics
• Dynamical Orbital classification of selected N-rich stars with \textit{Gaia} DR2 astrometry
• An Updated Census of RR~Lyrae Stars in the Globular Cluster $\omega$~Centauri (NGC\,5139)
• The Kapteyn moving group is not tidal debris from $\omega$ Centauri
• Near-IR period-luminosity relations for pulsating stars in $\omega$ Centauri (NGC 5139)
• The Globular Cluster NGC 6402 (M14). II. Variable Stars
• Does the Oosterhoff Dichotomy Exist in The Andromeda Galaxy? I. The case of G11