Chemodynamics of newly identified giants with a globular cluster like abundance patterns in the bulge, disc, and halo of the Milky Way

Abstract

The latest edition of the APOGEE-2/DR14 survey catalogue and the first Payne data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked metal-poor giant stars with anomalously high levels of nitrogen in the chemical space defined by [Fe/H] and [N/Fe]. The APOGEE chemical abundance patterns of such objects revealed that these are chemically distinct from the Milky Way (MW) in most chemical elements. We have found all these objects have a [N/Fe] > ∼ + 0.5, and are thus identified here as nitrogen-rich stars. An orbital analysis of these objects revealed that a handful of them shares the orbital properties of the bar/bulge, and possibly linked to tidal debris of surviving globular clusters trapped into the bar component. 3 of the 31 stars are actually halo interlopers into the bulge area, which suggests that halo contamination is not insignificant when studying N-rich stars found in the inner Galaxy, whereas the rest of the N-rich stars share orbital properties with the halo population. Most of the newly identified population exhibit chemistry similar to the so-called second-generation globular cluster stars (enriched in aluminum, [Al/Fe] > ∼ + 0.5), whereas a handful of them exhibit lower abundances of aluminum, [Al/Fe]< +0.5, which are thought to be chemically associated with the first-generation of stars, as seen in globular clusters, or compatible with origin from a tidally disrupted dwarf galaxy.

Aluminium-enriched metal-poor stars buried in the inner Galaxy

“…The final selected sample amounts to a total of 13 338 stars with high-quality parameters. We search for aluminium-enriched stars by carrying out a semi-independent stellar-abundance analysis of Al I lines using the BACCHUS 4 code (Masseron et al 2016), following the method described by Fernández-Trincado et al (2019b).…”

“…A major advancement in revealing the nature of the low-metallicity stars ([Fe/H] −0.7) in the bulge region was achieved by the discovery of a large population of giant stars with nitrogen over-abundances (N-rich;Schiavon et al 2017;Fernández-Trincado et al 2019b) and low-α stars (see, e.g. Recio-Blanco et al 2017), which mimic the typical chemical patterns only seen in the so-called second-generation 1 GC stars.…”

Jurassic: A chemically anomalous structure in the Galactic halo

“…For each element and each line, the abundance determination proceeds as in Hawkins et al (2016) and Fernández-Trincado et al (2019b): (a) A spectrum synthesis, using the full set of atomic and molecular line lists described in Shetrone et al (2015), (Neodymium: Nd II) (Hasselquist et al 2016) and (Cerium: Ce II) (Cunha et al 2017) (this set of lists is internally labeled as linelist.20170418 based on the date of creation in the format YYYYMMDD). This is used to find the local continuum level via a linear fit; (b) Cosmic and telluric rejections are performed; (c) The local S/N is estimated; (d) A series of flux points contributing to a given absorption line is automatically selected; and (e) Abundances are then derived by comparing the observed spectrum with a set of convolved synthetic spectra characterized by different abundances.…”

“…This is possible because GCs appear to be the only environment responsible for the presence of light-element anti-correlations at all stellar evolutionary phases (e.g., Martell et al 2016;Pancino et al 2017;Bastian & Lardo 2018;Masseron et al 2019;Mészáros et al 2020), unless they are part of a binary system (Bastian & Lardo 2018;Fernández-Trincado et al 2019a), or part of the new kind of recently discovered anomalous Phosphorus-rich field stars (see, e.g., Masseron et al 2020). Thus, a complete census of all those chemically anomalous stars will help develop a better understanding for the assembly of the inner and outer halo, where substantial amount of stellar debris from GCs are thought to currently reside (see, e.g., Martell et al 2016;Fernández-Trincado et al 2019b,c, 2020a.…”

The enigmatic globular cluster UKS 1 obscured by the bulge: H-band discovery of nitrogen-enhanced stars

“…In addition, for the stars selected above, we manually validated their metallicities ([Fe/H]) from the strength of selected iron (Fe I) lines, by adopting the same methodology as described in Fernández-Trincado et al (2019b), i.e. the [Fe/H] ratios have been derived by using the BACCHUS code (Masseron et al 2016), and by performing a LTE analysis with a MARCS grid of spherical models (Gustafsson et al 2008).…”