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

Alessi³

et al. 2022

A&A

Context. The Galactic globular cluster system is incompletely known, especially in the low-latitude regions of the Galactic bulge and disk. We report the physical characterisation of 12 star clusters in the Milky Way, most of which are explored here for the first time. Aims. Our primary aim is determining their main physical parameters, such as reddening, extinction, metallicity, age, total luminosity, mean cluster proper motions (PMs), and distances, in order to reveal the physical nature of these clusters. Methods. We study the clusters using optical and near-infrared (NIR) datasets. In particular, we use the Gaia Early Data Release 3 (EDR3) PMs in order to perform a PM decontamination procedure and build final catalogues with probable members. We match the Gaia EDR3 with the VISTA Variables in the Vía Láctea extended (VVVX) survey and the Two Micron All-Sky survey (2MASS) in the NIR, in order to construct complete NIR and optical colour-magnitude diagrams (CMDs) and investigate the clusters properties. Results. The extinctions are evaluated using existing reddening maps. We find ranges spanning 0.09 ≲ AKs ≲ 0.86 mag and 0.89 ≲ AG ≲ 4.72 mag in the NIR and optical, respectively. Adopting standard intrinsic red clump (RC) magnitudes and extinction values, we first obtain the distance modulus for each cluster and thereafter their heliocentric distances, which range from about 4 to 20 kpc. Therefore, we are able to place these clusters at 3 ≲ RG ≲ 14 kpc from the Galactic centre. The best PARSEC isochrone fit yields a metallicity range of −1.8 < [Fe/H] < +0.3 and an approximate age range of 2 < age < 14 Gyr. Finally, we find that all clusters have low luminosities, with −6.9 < MV < −3.5 mag. Conclusions. Based on our photometric analysis, we find both open clusters (OCs) and globular clusters (GCs) in our sample. In particular, we confirm the OC nature for Kronberger 100, while we classify Patchick 125 as a metal-poor GC, Ferrero 54 as a metal-rich GC, and ESO 92-18 as a possible old OC or young GC. The classification as GC candidates is also suggested for Kronberger 99, Patchick 122, Patchick 126, Riddle 15, FSR 190, and Gaia 2. We also conclude that Kronberger 119 and Kronberger 143 might be either old OCs or young GCs.

Section: Introductionmentioning

confidence: 99%

Unveiling the nature of 12 new low-luminosity Galactic globular cluster candidates

Garro

Alessi³

et al. 2022

A&A

“…Such is the case of VVV CL001 with E(B − V) ∼ 2.2, which was recently re-classified as the most metal-poor GC found so far -with [Fe/H] ∼ −2.45to have survived near the bulge region (Fernández-Trincado et al 2021a), and NGC 6330 (or Tonantzintla 1) a highly reddened, E(B − V) ∼ 1.07 bulge GC, recently identified as the first known case of a relatively high-metallicity GC exhibiting evidence of correlation between its light-and heavy-elements and the presence of the phenomenon of multiple stellar populations (Fernández-Trincado et al 2021b). In addition, UKS 1, a heavily reddened GC, with E(B − V) ∼ 2.62, was recently classified as a fossil relic of the bulge based on its chemodynamics properties (Fernández-Trincado et al 2020).…”

Section: Introductionmentioning

confidence: 99%

APOGEE-2S view of the globular cluster Patchick 125 (Gran 3)

Fernández-Trincado

Garro

et al. 2022

A&A

Self Cite

We present detailed elemental abundances, radial velocity, and orbital elements for Patchick 125, a recently discovered metal-poor globular cluster (GC) in the direction of the Galactic bulge. Near-infrared high-resolution (R ∼ 22 500) spectra of two members were obtained during the second phase of the Apache Point Observatory Galactic Evolution Experiment at Las Campanas Observatory as part of the sixteenth Data Release (DR 16) of the Sloan Digital Sky Survey. We investigated elemental abundances for four chemical species, including α- (Mg, Si), Fe-peak (Fe), and odd-Z (Al) elements. We find a metallicity covering the range from [Fe/H] = −1.69 to −1.72, suggesting that Patchick 125 likely exhibits a mean metallicity ⟨[Fe/H]⟩ ∼ −1.7, which represents a significant increase in metallicity for this cluster compared to previous low-resolution spectroscopic analyses. We also found a mean radial velocity of 95.9 km s−1, which is ∼21.6 km s−1 higher than reported in the literature. The observed stars exhibit an α-enrichment ([Mg/Fe] ≲ 0.20, and [Si/Fe] ≲ +0.30) that follows the typical trend of metal-poor GCs. The aluminum abundance ratios for the present two member stars are enhanced in [Al/Fe] ≳ +0.58, which is a typical enrichment characteristic of the so-called ‘second-generation’ of stars in GCs at similar metallicity. This supports the possible presence of the multiple-population phenomenon in Patchick 125, as well as its genuine GC nature. Further, Patchick 125 shows a low-energy, low-eccentric (< 0.4) and retrograde orbit captured by the inner Galaxy, near the edge of the bulge. We confirm that Patchick 125 is a genuine metal-poor GC, which is currently trapped in the vicinity of the Milky Way bulge.

“…These stars share chemical-abundance patterns that are hypothesised to be associated with the so-called second-generation stars in GCs (see e.g. Schiavon et al 2017a;Fernández-Trincado et al 2019b, 2020bMészáros et al 2020), with only a handful of exceptions, such as the binary hypothesis (see e.g. Fernández-Trincado et al 2019c).…”

Section: Introductionmentioning

confidence: 88%

APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge

Fernández-Trincado

Carigi

et al. 2021

A&A

Self Cite

The central (‘bulge’) region of the Milky Way is teeming with a significant fraction of mildly metal-deficient stars with atmospheres that are strongly enriched in cyanogen (12C14N). Some of these objects, which are also known as nitrogen-enhanced stars, are hypothesised to be relics of the ancient assembly history of the Milky Way. Although the chemical similarity of nitrogen-enhanced stars to the unique chemical patterns observed in globular clusters has been observed, a direct connection between field stars and globular clusters has not yet been proven. In this work, we report on high-resolution, near-infrared spectroscopic observations of the bulge globular cluster NGC 6723, and the serendipitous discovery of a star, 2M18594405−3651518, located outside the cluster (near the tidal radius) but moving on a similar orbit, providing the first clear piece of evidence of a star that was very likely once a cluster member and has recently been ejected. Its nitrogen abundance ratio ([N/Fe] ≳ + 0.94) is well above the typical Galactic field-star levels, and it exhibits noticeable enrichment in the heavy s-process elements (Ce, Nd, and Yb), along with moderate carbon enrichment; all characteristics are known examples in globular clusters. This result suggests that some of the nitrogen-enhanced stars in the bulge likely originated from the tidal disruption of globular clusters.