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J. G. Fernández-Trincado

Publications and source records attributed to J. G. Fernández-Trincado.

At least 19 recordsLinked to original sources
arXiv2026

An upper limit on Galactic OB+black hole binaries from SDSS-V

Binaries composed of a luminous OB star and a black hole (BH) are a key evolutionary link between massive stellar binaries and merging compact-object binaries, but only a handful are known and their occurrence fraction remains poorly constrained. We use multi-epoch spectroscopy from the SDSS-V Milky Way Mapper to place a first rigorous empirical upper limit on the fraction of Galactic massive ($\geq 10\,\mathrm{M}_\odot$) OB stars with a close BH companion, $f_\mathrm{BH}$. Radial-velocity (RV) variability alone cannot distinguish BH companions from the far more numerous luminous binaries. We therefore combine the SDSS-V RV variability measurements of 3130 massive OB stars with high-resolution follow-up and literature information to identify luminous companions among the RV-variable subset. Forward-modelling the detectability of OB+BH systems using BH masses and orbital parameters from binary-evolution models, we find $f_\mathrm{BH} \lesssim 3\%$ at 95% credibility. This empirical upper limit approaches, but does not exclude, theoretical predictions for the OB+BH fraction. The constraint is primarily limited by the number of RV-variable systems that can be decisively classified, highlighting the importance of complete, high-quality follow-up for future searches.

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arXiv2026

Unresolved triples in the open cluster NGC 2437 (M 46) confirmed by the KMOS VVVX-GalCen Spectroscopic Survey

Recent optical and near-IR photometric databases like Gaia data release 3 (DR3) and the VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey allow the exploration of candidate unresolved multiple systems (binaries, triples, quadruples, etc.) in nearby clusters, that need spectroscopic confirmation. NGC 2437 (M 46) is a benchmark open cluster with well determined physical parameters. Its relative proximity (D=1.6 kpc) makes this cluster an ideal laboratory to measure the fractions of unresolved multiple systems. We aim here to identify unresolved triple and higher order systems that are reliable members of the open cluster NGC 2437, and provide the spectroscopic confirmation using radial velocities. We confirm that there is a sequence of unresolved binaries in NGC 2437, and report the discovery of a sequence of unresolved triple systems in this cluster. We corroborate membership for 13 binary systems and 8 triple systems using radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. We further select stars with colors consistent with K-dwarfs, in order to have a controlled sample, comparable to the Solar neighborhood. We also find that the fraction of unresolved triples and quadruples is higher than that of the older open cluster Trumpler 19, studied using a similar setup, suggesting that these systems merge to form blue stragglers or get dissolved with time. We report the spectroscopic confirmation of 95% of the selected VVVX targets, thereby securing the presence of a sequence of unresolved triple systems in NGC 2437, located above the sequence of equal-mass binaries. The single stars constitute 60% of the mass of the cluster, while the rest of the mass (40%) is lodged in the unresolved multiple systems.

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arXiv2026

Massive stars in the SDSS-V survey: New O2 stars in the Large Magellanic Cloud

{O2 stars define the hottest end of the normal O-star sequence, but their identification requires blue-optical nitrogen diagnostics absent from many surveys.} {We reassess three luminous Large Magellanic Cloud (LMC) sources with multi-epoch Sloan Digital Sky Survey V (SDSS-V) spectroscopy obtained with the Baryon Oscillation Spectroscopic Survey (BOSS) spectrographs: \wsi, \lh, and \sk.} {We measure visit-resolved radial velocities and H, He, and N equivalent widths (EWs), compare robust combinations with LMC O2 templates at a common effective resolution, and use OSTAR2002 spectral energy distribution (SED) fits and a Gaia colour--magnitude diagram (CMD) as broad-band checks.} {The weighted $\log|{\rm EW}(\niv~\lambda4058)/{\rm EW}(\niii~\lambda4640)|$ values are $0.64\pm0.29$, $0.48\pm0.23$, and $0.34\pm0.44$ for \wsi, \lh, and \sk. The detection of \nv~$λ\lambda4604,4620$ supports the O2~If$^\ast$ and O2~V--III classifications adopted for \wsi\ and \lh, respectively. For \sk, the uncertain \niv/\niii\ ratio and non-detection of \nv\ motivate O2--3~V--III. Weak \hei~$\lambda4471$ may indicate unresolved later-type contamination in \wsi\ and \sk. The radial velocities of \sk\ show suggestive but non-significant variability. OSTAR2002 fits over 45--55~kK and the Gaia CMD place all three sources in the luminous very-early-O regime; \wsi\ shows a strong mid-infrared (MIR) excess, \lh\ is nearly photospheric, and \sk\ shows only a modest $3$--$8\,μ$m excess.} {The BOSS spectra add \wsi\ and \lh\ to the LMC very-early-O population and identify \sk\ as an additional O2--3 source. These cases show how incomplete blue coverage and ambiguous catalogue associations can conceal the hottest massive stars.}

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arXiv2026

Unresolved triple systems in the aged open cluster Trumpler 19: Discovery, confirmation, and implications

It is difficult to identify unresolved triple and higher-order systems beyond the solar vicinity. Star clusters yield controlled environments with known physical parameters, providing a way to explore homogeneous stellar samples. Combining modern optical and near-IR surveys, our main goal is to explore the region of the color-magnitude diagrams located above the sequence of equal-mass binaries, which is inhabited by unresolved triple and quadruple systems. Specifically, here we aim to discover and characterize the presence of multiple systems in the aged open star cluster Trumpler 19. We selected cluster members using Gaia astrometry and photometry from the VVVX and DECAPS2 surveys. We made optical and near-IR color-magnitude diagrams to select stars located >0.75 mag above the cluster main sequence, including suitable unresolved triple and quadruple systems. We confirm previous results that there is a sizable sequence of unresolved binaries in Trumpler 19. We also report the discovery of a sequence of unresolved multiple systems in this cluster, and confirm some of these multiple systems via radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. The fraction of multiple stars in this cluster is comparable to that of the solar neighborhood, with the caveat that the local sample probes deeper down the main sequence. The fraction of unresolved triples and quadruples is also three times higher than that of the open cluster M 67, which is of a similar age and chemical composition. The discovery of unresolved triple systems in Trumpler 19 leads to our main conclusion that these systems were able to survive within the cluster for nearly 4 Gyr. In addition, this cluster contains more multiple systems than M 67, which has a similar total present mass. Further investigations are needed to unveil if this is a primordial feature or the result of dynamical evolution.

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arXiv2026

Chemo-dynamical stratification of the Galactic disc using \emph{Gaia}-ESO open clusters

Understanding how the Milky Way disc assembled and evolved requires tracing the coupled evolution of stellar chemistry and orbital structure over time. Open clusters, as coeval stellar populations with well-constrained ages, distances, and chemical properties, provide powerful benchmarks for this purpose. We aim to characterise the age-dependent chemo-dynamical structure of the Galactic disc and to investigate how open clusters populate dynamical phase space as a function of age. We analysed a sample of Galactic open clusters using homogeneous chemical abundances from the Gaia-ESO Survey together with Gaia DR3 phase-space information. Combining cluster ages with orbital parameters and actions, we examined how clusters populate dynamical phase space over the last ~4 Gyr. We find that clusters with similar chemical properties occupy coherent regions of action space, while their orbital structure shows a clear dependence on age. Radial excursions and orbital eccentricities broaden systematically toward older ages, indicating increasingly diverse orbital configurations in the older cluster population. The dispersion in the [Fe/H]-Rg relation also increases with age, consistent with a combination of secular redistribution, survival bias, and dynamically distinct outer-disc populations. In addition, older clusters reach larger vertical amplitudes and vertical actions, revealing a coupled but anisotropic evolution between in-plane and vertical orbital structure. Open clusters provide precise, age-resolved tracers of the chemo-dynamical structure of the Galactic disc. Our results reveal systematic age-dependent variations in the orbital and chemical properties of the cluster population, consistent with the combined effects of secular evolution, orbital redistribution, and environmentally dependent cluster survival over the last few Gyr.

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arXiv2026

Chemical radial gradients for the bulge-bar stellar populations from the APOGEE survey

The Milky Way bulge-bar is composed of multiple populations. Using chemical and kinematical planes, we segregate six populations in a bulge-bar sample observed by the APOGEE survey: two with bar-driven orbits, two with eccentric orbits, and two with low-eccentricity orbits, each composed of low- and high-[Mg/Fe] stars. Our sample spans $-2.0\lesssim$[Fe/H]$\lesssim+0.5$ and Galactocentric distance $R_{Gal}$ $<6$ kpc. We use chemical abundances from APOGEE DR17 for the elements Mg, Si, Ca, Al, K, Mn, Co, Ni, and Fe, and from the BAWLAS catalog for Ce and Nd. We find that the low- and high-[Mg/Fe] stars with low-eccentricity orbits, which exhibit chemical and orbital characteristics similar to those of the low- and high-[$α$/Fe] disks, display slightly negative and positive metallicity gradients, respectively. This result for the low-[Mg/Fe] low-eccentricity stars indicates a break in the global thin disk metallicity gradient. The high eccentricity populations with both low- and high-[Mg/Fe] show approximately flat metallicity gradients. In general, the [X/H] gradients of all elements for all populations follow Fe, except for the neutron-capture elements Ce and Nd. For all elements, the high-[Mg/Fe] bar population shows a much steeper positive [X/H] gradient than the nearly flat gradient for the low-[Mg/Fe] bar stars. The positive [X/H] gradients observed among our high-[Mg/Fe] bar stars probably reflect an age variation along the peanut structure. This interpretation agrees with the N-body simulations. Such steep positive gradients have also been reported in some high-redshift (z$\sim$4--10) galaxies.

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arXiv2026

Abundances in 78 metal-rich bulge spheroid stars from APOGEE

The inner Galaxy is the most complex region of the Milky Way, comprising the bulge, inner thin and thick discs, and inner halo; the formation of the bar transferred gas and stars from the disc inward. Accretion of dwarf galaxies also occurred over the Galaxy's lifetime, merging with the original bulge. In this work, we constrain the metal-rich stars of the earliest spheroidal bulge. To study the oldest bulge stars, distributed in a spheroid, we applied kinematical and dynamical criteria in the metal-rich range [Fe/H] > -0.8. This complements our previous analysis of a symmetric sample with [Fe/H] < -0.8. We derived individual abundances through spectral synthesis for C, N, O, Al, P, S, K, Mn, and Ce using stellar parameters from APOGEE DR17, and compared the results with literature data and chemical-evolution models. The alpha elements Mg, Si, and Ca, and iron-peak elements V, Cr, Co, and Ni follow the expected trends relative to the models. Mn shows secondary behaviour. S and K display significant star-to-star scatter but remain broadly compatible with predictions. Phosphorus and cerium show an excess around [Fe/H] $\sim$ -0.7, more pronounced than in the metal-poor sample, suggesting a distinctive signature of the earliest bulge population. Diagrams of [Mg/Mn] versus [Al/Fe] and [Ni/Fe] versus [(C+N)/O] indicate an in situ origin for most stars. At super-solar metallicities, a subset shows enhanced K and Mn (possibly S) with low [Ce/Fe], hinting at enrichment linked to the nuclear disc and bar, and tracing a chemically distinct population shaped by the innermost Galaxy.

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arXiv2025

The VVVX quest for satellites around the Circinus galaxy

The Circinus galaxy is the nearest type-2 Seyfert galaxy, which is at a distance of 4.2 Mpc. Its environment is challenging to explore because it is located at low Galactic latitudes, behind the Galactic disc. The long-term goal is to characterise the Circinus galaxy halo and determine the presence of dwarf satellites using near-infrared data. We selected 1,542 galaxies from the VVV NIRGC within a 2-degree radius around Circinus, representing 2/3 of the virial radius. Structural parameters such as half-light radii and colours were used, and correlations were examined. A neural network was trained with 486 galaxies with known spectroscopic redshifts to estimate photometric redshifts for all galaxies. Potential satellites were defined based on half-light radii compatible with the typical sizes of dwarf satellites, and combined with photometric redshifts. The galaxy properties are reliably characterised down to $K_{s}$ $\sim$ 15.5 mag, which represents about 90% completeness of detections. At the distance of Circinus, this limiting magnitude corresponds to $K_{s}$ absolute magnitude of $-12.6$ mag, which allows us to find dwarf galaxies. There are 20 galaxies with half-light radii larger than 2.45 arcsec, only 8 have photometric redshifts below 0.04. None of these galaxies is close to Circinus, which has a redshift of 0.0015. The ANNz model exhibited a high degree of accuracy in the range $0.001 < z_{phot} < 0.023$. The presence of dwarf satellites could not be confirmed with the available data in the studied region. The apparent lack of satellites may be genuine, possibly related to AGN feedback effects. This work demonstrates the effectiveness of combining near-infrared data and machine learning techniques to estimate photometric redshifts at low Galactic latitudes, providing useful information for future spectroscopic follow-up campaigns.

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arXiv2025

SDSS-V LVM: Detectability of Wolf-Rayet stars and their He II ionizing flux in low-metallicity environments I. The weak-lined, early-type WN3 stars in the SMC

The Small Magellanic Cloud (SMC) is the nearest low-metallicity dwarf galaxy. Its proximity and low reddening has enabled us to detect its Wolf-Rayet (WR) star population with 12 known objects. Quantitative spectroscopy of the stars revealed half of these WR stars to be strong sources of He ii ionizing flux, but the average metallicity of the SMC is below where WR bumps are usually detected in integrated galaxy spectra showing nebular He ii emission. Utilizing the Local Volume Mapper (LVM), we investigate regions around the six SMC WN3h stars, whose winds are thin enough to avoid He recombination and allow photons with > 54 eV to escape. Focusing on He ii 4686 Å, we show that the broad stellar wind component, the strongest optical diagnostic of the WN3h stars, is diluted within 24 pc in the integrated light from LVM, making the WR stars hard to detect in low-metallicity integrated regions. In addition, we compare the He ii ionizing flux from LVM with the values inferred from the stellar atmosphere code PoWR and find that the nebular emission around them only in some cases reflects the high amounts emitted by the stars. We conclude that early-type WN stars with comparably weak winds are viable sources to produce the observed He ii ionizing flux in low-metallicity galaxies. The easy dilution of the stellar signatures can explain the rareness of WR bump detections at 12 + log O/H < 8.0, while at the same time providing major candidates for the observed excess of nebular He ii emission. This constitutes a challenge for population synthesis models across all redshifts as the evolutionary path towards this observed WR population at low metallicity remains enigmatic.

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arXiv2025

Open cluster members in APOGEE DR17 I. Dynamics and star members

Context. Open clusters (OCs) are groups of stars formed from the same cloud of gas and cosmic dust. They play an important role in studies of star formation and evolution and our understanding of galaxy structure and dynamics. Aims. The main objective of this work is to identify stars that belong to OCs using astrometric data from Gaia EDR3 and spectroscopic data from APOGEE DR17. Furthermore, we investigate the metallicity gradients and orbital properties of the OCs in our sample. Methods. By applying the HDBSCAN clustering algorithm to these data, we identified observed stars in our galaxy with similar dynamics, chemical compositions, and ages. The orbits of the OCs were also calculated using the GravPot16 code. Results. We find 1,987 stars that tentatively belong to 49 OCs; 941 of these stars have probabilities above 80 \% of belonging to OCs. Our metallicity gradient presents a two-slope shape for two measures of different Galactic center distances -- the projected Galactocentric distance and the guiding center radius to the Galactic center -- as already reported in previous work. However, when we separate the OCs by age, we observe no significant difference in the metallicity gradient slope beyond a certain distance from the Galactic center. Our results show a shallower gradient for clusters younger than 2 Gyr than those older than 2 Gyr. All our OCs dynamically assemble the disk-like population very well, and they are in prograde orbits, which is typical for disk-like populations. Some OCs resonate with the Galactic bar at the Lagrange points L4 and L5.

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arXiv2025

Multi-Wavelength characterization of VVVX open clusters

Context. Large-scale surveys across wavelengths, aided by machine learning, have improved the detection of old open clusters in high-extinction Milky Way regions. Aims. We aim to confirm or reject automatically detected open clusters in poorly studied, contaminated regions, refining samples for Galactic disk formation studies. Methods. Using VVVX, 2MASS, and Gaia DR3, we analyzed nine cluster candidates: BH118, BH144, Schuster-MWSC 1756, Saurer 3, FSR 1521, Saurer 2, Haffner 10-FSR 1231, Juchert 12, and Pismis 3. We examined density maps, proper motion diagrams, and photometry to derive physical parameters. Results. We identified star clusters via overdensities in 2MASS, WISE, and DECaPS, confirmed with VVVX and Gaussian Kernel Density Estimation. Using Gaia proper motions, we refined memberships, building a high-likelihood cluster catalog. We derived extinction ($A_{Ks} = 0.07$-$0.50$), color excess ($E(J-Ks) = 0.16$-$0.60$), distances ($D = 2.06$-$8.64$ kpc), and Galactocentric distances ($R_G = 7.69$-$14.81$ kpc). Ages range from 20 Myr to 5 Gyr, metallicity from [Fe/H] = -0.5 to 0.5. Structural parameters include core radii ($r_c = 0.71'$-$5.21'$) and tidal radii ($r_t = 3.4'$-$12.0'$). Conclusions. We confirm the open cluster nature of nine targets, updating their physical parameters.

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arXiv2024

Examining the brightness variability, accretion disk, and evolutionary stage of the binary OGLE-LMC-ECL-14413

Our study aims to elucidate both short-term and long-term variations in the light curve of the eclipsing system OGLE-LMC-ECL-14413, with a particular focus on the unusual reversals in eclipse depth. We aim to clarify the role of the accretion disk in these fluctuations, especially in long-cycle changes spanning hundreds of days. Additionally, we seek to determine the evolutionary stage of the system and gain insights into the internal structure of its stellar components. We analyzed photometric time series from the Optical Gravitational Lensing Experiment (OGLE) project in the I and V bands, and from the MAssive Compact Halo Objects project in the BM and RM bands, covering a period of 30.85 years. Using light curve data from 27 epochs, we constructed models of the accretion disk. An optimized simplex algorithm was employed to solve the inverse problem, deriving the best-fit parameters for the stars, orbit, and disk. We also utilized the Modules for Experiments in Stellar Astrophysics software to assess the evolutionary stage of the binary system, investigating the progenitors and potential future developments. We found an orbital period of 38.15917(54) d and a long-term cycle of approximately 780 d. Temperature, mass, radius, and surface gravity values were determined for both stars. The photometric orbital cycle and the long-term cycle are consistent with a disk containing variable physical properties, including two shock regions. The disk encircles the more massive star and the system brightness variations align with the long-term cycle at orbital phase 0.25. Our mass transfer rate calculations correspond to these brightness changes. \texttt{MESA} simulations indicate weak magnetic fields in the donor star's subsurface, which are insufficient to influence mass transfer rates significantly.

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arXiv2024

Abundances of iron-peak elements in 58 bulge spheroid stars from APOGEE

Stars presently identified in the bulge spheroid are probably very old, and their abundances can be interpreted as due to the fast chemical enrichment of the early Galactic bulge. The abundances of the iron-peak elements are important tracers of nucleosynthesis processes, in particular oxygen burning, silicon burning, the weak s-process, and alpha-rich freeze-out. Aims. The aim of this work is to derive the abundances of V, Cr, Mn, Co, Ni, and Cu in 58 bulge spheroid stars and to compare them with the results of a previous analysis of data from APOGEE. We selected the best lines for V, Cr, Mn, Co, Ni, and Cu located within the H-band of the spectrum, identifying the most suitable ones for abundance determination, and discarding severe blends. Using the stellar physical parameters available for our sample from the DR17 release of the APOGEE project, we derived the individual abundances through spectrum synthesis. We then complemented these measurements with similar results from different bulge field and globular cluster stars, in order to define the trends of the individual elements and compare with the results of chemical-evolution models. We verify that the H-band has useful lines for the derivation of the elements V, Cr, Mn, Co, Ni, and Cu in moderately metal-poor stars. The resulting abundances indicate that: V, Cr, and Ni vary in lockstep with Fe; Co tends to vary in lockstep with Fe, but could be showing a slight decrease with decreasing metallicity; and Mn and Cu decrease with decreasing metallicity. These behaviours are well reproduced by chemical-evolution models except for Cu, which appears to drop faster than the models predict for moderate metallicities. Finally, abundance indicators combined with kinematical and dynamical criteria appear to show that our 58 sample stars are likely to have originated in situ.

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arXiv2024

VVVX survey dusts off a new intermediate-age star cluster in the Milky Way disk

Our primary long-term objective is to seek out additional star clusters in the poorly studied regions of the MW. The aim of this pursuit is to finalize the MG's globular and open cluster system census and to gain a comprehensive understanding of both the formation and evolution of these systems and our Galaxy as a whole. We report the discovery of a new star cluster, named Garro~03. We investigated this target using a combination of near-infrared and optical databases. We employed VVVX and 2MASS data in the NIR, and Gaia DR3 and the DECaPS2 datasets in the optical passband. We performed a photometrical analysis in order to derive its main physical parameters. Garro~03 is located at equatorial coordinates RA=14:01:29.3 and Dec=-65:30:57.0. It is not heavily affected by extinction $A_{Ks}=0.25\pm 0.04$ mag. It is located at heliocentric distance of $14.1\pm0.5$ kpc, which places Garro~03 at 10.6 kpc from the Galactic centre and Z=-0.89 kpc below the Galactic plane. We calculated the mean cluster PM of ($μ_α^{\ast},μ_δ) = (-4.57\pm 0.29,\ -1.36\pm 0.27$) mas yr$^{-1}$. We derived an age=3 Gyr and [Fe/H]~$= -0.5\pm 0.2$ by the isochrone-fitting method. The total luminosity was derived in the $K_s$ and V-bands, finding $M_{Ks} = -6.32\pm 1.10$ mag and $M_V =-4.06$ mag. The core and tidal radii were measured constructing the Garro~03 radial density profile and fitting the King model, obtaining $r_c = 3.07\pm 0.98$ pc and $r_t = 19.36\pm 15.96$ pc. We photometrically confirm the cluster nature for Garro~03, located in the Galactic disk. It is a distant, low-luminosity, metal-rich star cluster of intermediate age. We also searched for possible signatures (streams or bridges) between Garro~03 and Garro~01, but we exclude a possible companionship. We need spectroscopic data to classify it as an old open cluster or a young globular cluster, and to understand its origin.

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arXiv2024

The VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey: Completion of the observations and legacy

The ESO public survey VISTA Variables in the Vía Láctea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from $2009-2015$. Upon its conclusion, the complementary VVV eXtended (VVVX) survey has expanded both the temporal as well as spatial coverage of the original VVV area, widening it from $562$ to $1700$ sq. deg., as well as providing additional epochs in $JHK_{\rm s}$ filters from $2016-2023$. With the completion of VVVX observations during the first semester of 2023, we present here the observing strategy, a description of data quality and access, and the legacy of VVVX. VVVX took $\sim 2000$ hours, covering about 4% of the sky in the bulge and southern disk. VVVX covered most of the gaps left between the VVV and the VISTA Hemisphere Survey (VHS) areas and extended the VVV time baseline in the obscured regions affected by high extinction and hence hidden from optical observations. VVVX provides a deep $JHK_{\rm s}$ catalogue of $\gtrsim 1.5\times10^9$ point sources, as well as a $K_{\rm s}$ band catalogue of $\sim 10^7$ variable sources. Within the existing VVV area, we produced a $5D$ map of the surveyed region by combining positions, distances, and proper motions of well-understood distance indicators such as red clump stars, RR Lyrae, and Cepheid variables. In March 2023 we successfully finished the VVVX survey observations that started in 2016, an accomplishment for ESO Paranal Observatory upon 4200 hours of observations for VVV+VVVX. The VVV+VVVX catalogues complement those from the Gaia mission at low Galactic latitudes and provide spectroscopic targets for the forthcoming ESO high-multiplex spectrographs MOONS and 4MOST.

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arXiv2024

Over 200 globular clusters in the Milky Way and still none with super-Solar metallicity

Many globular clusters (GCs) in the Milky Way (MW) have been studied in recent years, especially in hidden regions such as those of the Galactic bulge. Our main goal is to understand what we can learn if we include these new objects into the MWGC system that we know today. We catalogue 37 recently discovered GCs. We use different distributions for investigating the MWGC system: metallicity distribution (MD), luminosity function (LF), and age distribution. We first treat separately the new GCs sample from the known and well-characterised GCs. We merge these two samples, upgrading the MWGC system. We performed a comparison between our clusters sample and field star (FS) population. We find a double peaked distribution for the LF, which shows an elongated faint end tail. Considering the "merged" sample, the LF and the MDs display a bimodality trend. We construct the MD for the FS sample, and comparing this with that one of the GCs, we learn that a high percentage of FS show [Fe/H]$>0$, whereas we do not detect any GCs in the same metallicity range. In order to understand this inconsistency, we construct the age-metallicity diagram for both samples, noting that the old and metal-poor population (age$\geq8$ Gyr and [Fe/H]$\leq -1.0$) is represented by GCs, while the young and metal-rich population (age$<8$ Gyr and [Fe/H]$>-1.0$) corresponds to FS. From the analysis of the GC LF and MD, we can conclude that many GCs, probably those very faint, have survived strong dynamical processes, typical of the Bulge regions. We cannot exclude the possibility that some of them have been accreted during past merging events, especially the metal-poor component, whereas the metal-rich population may be related to the formation of the bulge and/or disk. Finally, the difference that we notice between the GC and FS samples should be sought in the evolutionary difference between these two stellar populations.

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arXiv2024

Abundances in eight bulge stars from the optical and near-infrared

Context: The abundances of the $α$-elements are key for understanding the early chemical enrichment of the Galactic bulge. The elements of interest present lines in different wavelength regions, and some of them show lines only in part of the spectra. In the present work, the CNO trio, the alpha-elements Mg, Si, Ca, and Ti, and odd-Z Na and Al are examined as measured from optical and H-band lines. Aims: The aim of this work is to carry out a detailed comparison of stellar parameters and abundances derived in the optical and near-infrared (H-band). We also inspect the best available lines for a list of bulge stars previously analyzed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) team in the H-band and by our group in the optical. This work is mainly of interest to spectroscopists. Methods: In the present work, we compared the stellar parameters and abundance results derived from APOGEE H-band spectra with optical analyses based on Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope (VLT/UVES) data for eight bulge stars. Results:We point out the most suitable wavelength region for each of the studied elements, and highlight difficulties in the derivation of stellar parameters both in the optical and H-band. The near-infrared will allow observations of a large number of stars in the near future given new instruments soon to be available. The identification of spectral lines in this spectral region and the investigation of their reliability are ongoing efforts worldwide. New instruments will also allow simultaneous observation of H-band and optical.

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arXiv2024

A perspective on the Milky Way Bulge-Bar as seen from the neutron-capture elements Cerium and Neodymium with APOGEE

This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of $\sim$2000 stars in the Galactic Bulge/bar spatially contained within $|X_{Gal}|<$5 kpc, $|Y_{Gal}|<$3.5 kpc, and $|Z_{Gal}|<$1 kpc, and spanning metallicities between $-$2.0$\lesssim$[Fe/H]$\lesssim$+0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our Bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd]$<$0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of Bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the Bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magneto-rotational supernovae.

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