arXiv subjects

Nicolás Barrera

Publications and source records attributed to Nicolás Barrera.

3 recordsLinked to original sources

arXiv2026

CAPOS: The bulge Cluster APOgee Survey XII. Abundances for 98 PIGS metal-poor Bulge field giants

The inner Milky Way hosts overlapping stellar populations (bar--bulge, inner thin and thick disks, and halo), complicating population assignments along the line of sight. A joint chemical--dynamical approach is required to isolate a clean field bulge sample. Metal-poor bulge stars are valuable as they likely trace the earliest phases of chemical enrichment in the inner Galaxy. We aim to characterize the alpha-element (Si, Mg) and selected Fe-peak abundances of a dynamically defined sample of bulge field stars, and to contrast these trends with the inner-halo tail in the metal-poor regime. We analyze metal-poor candidates from the Pristine Inner Galaxy Survey observed by the bulge Cluster APOGEE Survey. Using APOGEE/ASPCAP abundances (S/N >= 50), we integrate full 6D orbits in a barred Milky Way potential. Bulge membership is defined via orbital confinement using an apocenter cut and the high-density locus in the (E_J, L_z) plane, with uncertainties estimated using Monte Carlo simulations. We identify 98 stars as bulge members. The metallicity distribution spans -2.5 <= [Fe/H] <= -0.4, with a median [Fe/H] = -1.71, offset to higher metallicity than the inner halo (median [Fe/H] = -1.96). The sample follows a high-alpha sequence with slopes d[Si/Fe]/d[Fe/H] = -0.020(+0.012,-0.051) and d[Mg/Fe]/d[Fe/H] = -0.097(+0.062,-0.133). Fe-peak tracers show [Ni/Fe] ~ 0, while [Mn/Fe] declines with [Fe/H] with a mild upturn at higher metallicity. We detect no significant [Si/Fe] gradients with R_apo or Z_max (+0.010(+0.018,0.000) and +0.006(+0.022,-0.011) dex kpc^-1, respectively). Results are insensitive to Omega_p, yielding indistinguishable memberships. The chemo-orbital evidence favors an in situ origin within the inner Galaxy for the metal-poor bulge field, enriched at early times and rearranged by secular bar evolution, with a minor contribution from halo stars at the most metal-poor end.

astro-ph.GA↗

arXiv2025

CAPOS: The bulge Cluster APOGEE Survey VI. Characterizing multiple stellar populations and chemical abundances in the bulge globular cluster NGC 6569

Context. The CAPOS project aims to obtain accurate mean abundances and radial velocities for many elements, and it explores the multiple population (MP) phenomenon in Galactic bulge globular clusters (BGCs). NGC 6569 is one of the CAPOS targets. Aims. This study provides a detailed high-resolution spectroscopic analysis of NGC 6569 to derive precise abundances for elements of different nucleosynthetic origins and to unveil its MPs by focusing on key spectral features. Methods. We analyzed APOGEE-2 near-infrared spectra of 11 giant members with the BACCHUS code, deriving abundances for 12 elements (C, N, O, Mg, Si, Ca, Ti, Fe, Ni, Al, Ce, Nd). Isochrone fitting with Gaia+2MASS photometry was used to estimate atmospheric parameters, cluster distance, and extinction. Results. We obtained [Fe/H] = -0.91 $\pm$ 0.06, consistent with APOGEE pipeline values; the scatter lies within uncertainties. The cluster shows [$α$/Fe] = 0.36 $\pm$ 0.06 dex, similar to other GCs. Al appears homogeneous, while N is strongly enriched ([N/Fe] = 0.68 $\pm$ 0.34) with a spread of 0.90 dex, yielding two populations anticorrelated in C. The n-capture elements Ce and Nd are overabundant compared to the Sun but consistent with GCs of similar metallicity, with $\langle$[Ce/Nd]$\rangle$ = -0.17 $\pm$ 0.12. We also measure RV = -49.75 $\pm$ 3.68 km s$^{-1}$, consistent with previous works, while d$_\odot$ = 12.4 $\pm$ 1.45 kpc and E(B-V) = 0.68 are both higher than literature values. Conclusions. MPs in NGC 6569 are confirmed through a clear C-N anticorrelation. The cluster shows [$α$/Fe] enhancement from Type II SNe and no Mg-Al-Si anticorrelation, suggesting rapid and homogeneous formation. The $\langle$[Ce/Nd]$\rangle$ ratio points to contributions from r-process events such as neutron star mergers, while overall Ce and Nd abundances are reported here for the first time in this cluster.

astro-ph.GA↗

arXiv2025

CAPOS: the bulge Cluster APOgee Survey IX. Spectroscopic Analysis of the Bulge Globular Cluster Terzan 2

We present the first detailed spectroscopic analysis of the heavily extincted bulge globular cluster Terzan 2 (Ter 2) based on high-resolution near-infrared spectra obtained as part of the CAPOS (the bulge Cluster APOgee Survey) project. CAPOS focuses on surveying clusters within the Galactic Bulge, using the APOGEE-2S spectrograph, part of the SDSS-IV survey, a component of the second generation Apache Point Observatory Galactic Evolution Experiment (APOGEE-2). For the spectral analysis, we use the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code which provides line-by-line elemental abundances. We derive abundances for Fe-peak (Fe, Ni), $α$-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z(Al), and the s-process element (Ce) for four members of the cluster. Our analysis yields a mean metallicity of [Fe/H]= $-$0.84 $\pm$ 0.04, with no evidence for an intrinsic variation. We detect a significant abundance variation only in C and N, indicating the presence of multiple populations. Ter 2 exhibits a typical $α$-enrichment, that follows the trend of Galactic GCs. Additionally, our dynamical analysis reveals that Terzan 2 is a bulge globular cluster with a chaotic orbit that is influenced by the Galactic bar but not trapped by it, displaying both prograde and retrograde motions within the inner bulge region. Overall, the chemical patterns observed in Terzan 2 are in good agreement with those of other CAPOS bulge clusters of similar metallicity.

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