J01020100-7122208: an accreted evolved blue straggler that wasn't
  ejected from a supermassive black hole
  J01020100-7122208 is a star whose origin and nature still challenges us. It
was first believed to be a yellow super giant ejected from the Small Magellanic
Cloud, but it was more recently claimed to be a red giant accelerated by the
Milky Way's central black hole. In order to unveil its nature, we analysed
photometric, astrometric and high resolution spectroscopic observations to
estimate the orbit, age, and 16 elemental abundances. Our results show that
this star has a retrograde and highly-eccentric orbit,
$e=0.914_{-0.020}^{+0.016}$. Correspondingly, it likely crossed the Galactic
disk at $550\;\mathrm{pc}$ from the Galactic centre. We obtained a
spectroscopic mass and age of $1.09\pm0.10$ $M_\odot$ and $4.51\pm1.44$ Gyr
respectively. Its chemical composition is similar to the abundance of other
retrograde halo stars. We found that the star is enriched in europium, having
[Eu/Fe] = 0.93 $\pm$ 0.24, and is more metal-poor than reported in the
literature, with [Fe/H] = -1.30 $\pm$ 0.10. This information was used to
conclude that J01020100-7122208 is likely not a star ejected from the central
black of the Milky Way or from the Small Magellanic Cloud. Instead, we propose
that it is simply a halo star which was likely accreted by the Milky Way in the
distant past but its mass and age suggest it is probably an evolved blue
straggler.
