CAPOS: the bulge Cluster APOgee Survey II. The Intriguing "Sequoia"
  Globular Cluster FSR 1758
  We present results from a study of fifteen red giant members of the
intermediate-metallicity globular cluster (GC) FSR 1758 using high-resolution
near-infrared spectra collected with the Apache Point Observatory Galactic
Evolution Experiment II survey (APOGEE-2), obtained as part of CAPOS (the bulge
Cluster APOgee Survey). Since its very recent discovery as a massive GC in the
bulge region, evoking the name Sequoia, this has been an intriguing object with
a highly debated origin, and initially led to the suggestion of a purported
progenitor dwarf galaxy of the same name. In this work, we use new
spectroscopic and astrometric data to provide additional clues to the nature of
FSR 1758. Our study confirms the GC nature of FSR 1758, and as such we report
for the first time the existence of the characteristic N-C anti-correlation and
Al-N correlation, revealing the existence of the multiple-population
phenomenon, similar to that observed in virtually all GCs. Furthermore, the
presence of a population with strongly enriched aluminium makes it unlikely FSR
1758 is the remnant nucleus of a dwarf galaxy, as Al-enhanced stars are
uncommon in dwarf galaxies. We find that FSR 1758 is slightly more metal rich
than previously reported in the literature, with a mean metallicity [Fe/H]
between $-1.43$ to $-1.36$ (depending on the adopted atmospheric parameters),
and with a scatter within observational error, again pointing to its GC nature.
Overall, the $\alpha$-enrichment ($\gtrsim+0.3$ dex), Fe-peak (Fe, Ni), light-
(C, N), and odd-Z (Al) elements follow the trend of intermediate-metallicity
GCs. ... A new examination of its dynamical properties with the
\texttt{GravPot16} model favors an association with the Gaia-Enceladus-Sausage
accretion event. Thus, paradoxically, the cluster that gave rise to the name of
the Sequoia dwarf galaxy does not appear to belong to this specific merging
event.
