arXiv subjects

D. Minniti

Publications and source records attributed to D. Minniti.

At least 19 recordsLinked to original sources

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.

astro-ph.SR↗

arXiv2026

Infrared-excess sources in VVV: candidate debris discs, SED characterization, and variability analysis

Debris disks around main-sequence stars provide important insights into planetary formation and evolution; however, identifying these systems in the Galactic plane, where high interstellar extinction and source crowding are significant, remains challenging. Deep, wide-area surveys such as the VISTA Variables in the Via Lactea (VVV) ESO Public Survey provide multi-epoch infrared observations, enabling systematic searches in these environments. We present a method to construct a refined sample of main-sequence candidates by cross-matching data from Gaia DR3, GLIMPSE, DECaPS, and VIRAC2, to identify infrared excesses through spectral energy distribution (SED) analysis, and to analyse time-series data to detect variability potentially associated with circumstellar material or other astrophysical phenomena. Although infrared excess is commonly associated with debris disks, contributions from unresolved binaries or line-of-sight contamination cannot be excluded. Applying this methodology to the VVV tile d077 using the VIRAC2 catalogue, we analyse an initial sample of 879,556 sources and identify 446 sources flagged by the VO SED Analyser (VOSA) excess-detection algorithm as having infrared excess, of which 171 show candidate periodic variability in the VIRAC2 Ks-band light curves. We further perform SED fitting using theoretical models to derive physical parameters and approximate spectral types for these sources. This work provides a catalogue of infrared-excess candidates in a Galactic field affected by high extinction, along with a reproducible method suitable for future large-scale applications.

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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

Discovery of a low surface brightness galaxy in the Zone of Avoidance using VVVX Deepstack imaging

We report the discovery of VVVX J080705.96-273823.6, the first low-surface-brightness galaxy candidate identified in the Zone of Avoidance by the VISTA Variables in the Via Lactea eXtended Survey (VVVX). The source was detected serendipitously during a visual inspection of the new Deepstack images, reconstructed mosaics generated through an updated reprocessing and stacking procedure that significantly improves the depth and spatial uniformity of the original survey images. First-order morpho-photometric parameters were obtained using SExtractor together with PSF models derived with PSFEx, applied to star-subtracted images to minimize foreground contamination. Structural properties were derived from PSF-convolved modeling of azimuthally averaged surface-brightness profiles in the J, H, and Ks bands using exponential, Sersic, and composite models. The galaxy candidate is clearly detected in all three near-infrared bands. The profiles are consistently described by an exponential disk, with scale lengths of 32-36 arcsec and extinction-corrected central surface brightnesses of 19.82-22.35 mag arcsec^-2. The J band provides the best-constrained profile, while H and Ks show the same behavior with larger uncertainties. The projected proximity to ESO 494-25 and ESO 494-26 suggests a possible physical association. If located at the same distance (11-12 Mpc), the exponential scale length would be about 1.8-2.0 kpc, consistent with nearby LSB disk galaxies, although the lack of a spectroscopic redshift prevents confirmation. This discovery demonstrates that the new VVVX Deepstack products can reveal faint diffuse galaxies at low Galactic latitudes, opening a path toward a more complete census of the obscured nearby Universe.

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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

Faint galaxies in the Zone of Avoidance revealed by JWST/NIRCam

The Zone of Avoidance (ZoA) remains one of the last frontiers in constructing a comprehensive three-dimensional map of the Universe. Galactic extinction, stellar crowding, and confusion noise have historically limited the detection of background galaxies in these regions, with implications for large-scale structure and cosmological measurements. We assess the capability of the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) to detect extragalactic sources in a heavily contaminated region of the Milky Way. We analyzed JWST/NIRCam wide-filter images of NGC 3324 with a customized implementation of SExtractor v2.28. Sources were detected in the F444W band, cross-matched with F090W and F200W, and validated against recent DAOPHOT point spread function (PSF) photometry. A refined sample was obtained through full width at half maximum (FWHM) - signal-to-noise ratio (SNR) criteria and visual inspection. We identified 102 galaxies across the JWST/NIRCam field of view. The magnitude (F444W) distribution is bimodal, with about 10% brighter than m_F444W < 15 mag and about 60% in the range 17 < m_F444W < 19 mag. Typical sizes are FWHM ~6.5 arcsec, from compact to extended systems with isophotal areas up to ~2000 pixels (~7.9 arcsec^2). Morphologies span from compact to spiral and lenticular systems, including a compact group at the eastern edge of the field. We also report the detection of "transnebular galaxies", visible through the most opaque regions of the molecular cloud. These results demonstrate the potential of JWST/NIRCam to probe extragalactic sources through highly obscured Galactic regions, opening new avenues for mapping large-scale structures across the ZoA.

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arXiv2025

The VISCACHA survey XIV. Chemical evolution history of the SMC: The Southern Bridge Clusters

The chemical evolution history of the Small Magellanic Cloud (SMC) is complex and is best understood through a comprehensive analysis of star clusters across its various regions. The VISCACHA survey aims to fully explain the chemical evolution of SMC star clusters by analyzing different sub-regions adopted from an existing framework. The west halo (WH) region, which contains the oldest and most metal-poor stellar populations, exhibits a clear age-metallicity relation (AMR) with minimal dispersion. This region shows a significant dip of ~0.5 dex in metallicity approximately 6 Gyr ago. This was likely caused by a major merger event that subsequently accelerated the star formation rate. Clusters in the Southern Bridge (SB) and Northern Bridge regions of the SMC may have experienced distinct chemical enrichment histories, as suggested by our previous works but with limited data coverage. Furthermore, the AMR of wing/bridge (W/B) shows no sign of enrichment caused by the aforementioned merger event, but exhibits signatures of the recent collisions between the clouds contemporaneous with the epochs of the Magellanic Stream and Bridge formations. In this study, we present an updated AMR for the SB region based on a sample that includes approximately 67% of its known clusters. Contrary to the expectation of a very unique chemical evolution history, these SB clusters show a trend similar to the one of the WH clusters. The chemical evolution models that best fit the AMR trend of the SB clusters show excellent agreement with the major merger model proposed for the WH clusters. Building on this, we suggest a new unified chemical evolution model for both the WH and SB clusters, which can be explained by a major merger at ~6 Gyr followed by episodic chemical enrichment over time.

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arXiv2025

Abundances of P, S, and K in 58 bulge spheroid stars from APOGEE

We have previously studied several elements in 58 selected bulge spheroid stars, based on spectral lines in the H-band. We now derive the abundances of the less-studied elements phosphorus (P; Z=15), sulphur (S; Z=16), and potassium (K; Z=19). The abundances of P, S, and K in 58 bulge spheroid stars are compared both with the results of a previous analysis of the data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), and with a few available studies of these elements. We derive the individual abundances through spectral synthesis, using the stellar physical parameters available for our sample from the DR17 release of the APOGEE project. We provide recommendations for the best lines to be used for the studied elements among those in the H-band. We also compare the present results, together with literature data, with chemical-evolution models. Finally, the neutrino-process was taken into account for the suitable fit to the odd-Z elements P and K. We confirm that the H-band has useful lines for the derivation of the elements P, S, and K in moderately metal-poor stars. The abundances, plotted together with literature results from high-resolution spectroscopy, indicate that: moderately enhanced phosphorus stars are found, reminiscent results obtained for thick disk and halo stars of metallicity [Fe/H]~-1.0. Therefore, for the first time, we identify this effect to occur in the old stars from the bulge spheroid. Sulphur is an alpha-element and behaves as such. Potassium and sulphur both exhibit some star-to-star scatter, but fit within the expectations from chemical evolution models.

astro-ph.SR↗

arXiv2025

The VVV near-IR galaxy catalogue of the southern Galactic disc

The distribution of galaxies in the Zone of Avoidance (ZoA) is incomplete due to the presence of our own Galaxy. Our research focused on the identification and characterisation of galaxies in the ZoA, using the new near-infrared data from the VVVX survey in the regions that cover the southern Galactic disc. We used our previously-established procedure based on photometric and morphological criteria to identify galaxies. The large data volume collected by the VVVX required alternatives to visual inspection, including artificial intelligence techniques, such as classifiers based on neural networks. The VVV NIR galaxy catalogue is presented, covering the southern Galactic disc, significantly extending the vision down to $K^0_s=16$ mag throughout the ZoA. This catalogue provides positions, photometric and morphological parameters for a total of 167,559 galaxies with their probabilities determined by the CNN and XGBoost algorithms based on image and photometric data, respectively. The construction of the catalogue involves the employment of optimal probability criteria. 14% of these galaxies were confirmed by visual inspection or by matching with previous catalogues. The peculiarities exhibited by distinct regions across the Galactic disc, along with the characteristics of the galaxies, are thoroughly examined. The catalogue serves as a valuable resource for extragalactic studies within the ZoA, providing a crucial complement to the forthcoming radio catalogues and future surveys utilizing the Vera C.~Rubin Observatory and the Nancy Grace Roman Space Telescope. We present a deep galaxy map, covering a 1080 sq. deg. region, which reveals that the apparent galaxy density is predominantly influenced by foreground extinction from the Milky Way. However, the presence of intrinsic inhomogeneities, potentially associated with candidate galaxy groups or clusters and filaments, is also discernible.

astro-ph.GA↗

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

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.

astro-ph.SR↗

arXiv2024

The young exoplanetary system TOI-4562: Confirming the presence of a third body in the system

Young planetary systems represent an opportunity to investigate the early stages of (exo)planetary formation because the gravitational interactions have not yet significantly changed the initial configuration of the system. TOI-4562 b is a highly eccentric temperate Jupiter analogue orbiting a young F7V-type star of $<700$ Myr in age with an orbital period of $P_{orb} \sim 225$ days and an eccentricity of $e=0.76$, and is one of the largest known exoplanets to have formed in situ. We observed a new transit of TOI-4562 b using the 0.6-m Zeiss telescope at the Pico dos Dias Observatory (OPD/LNA) in Minas Gerais, Brazil, and combine our data with Transiting Exoplanet Survey Satellite (TESS) and archive data, with the aim being to improve the ephemerides of this interesting system. The $O-C$ diagram for the new ephemeris is consistent with the presence of a giant planet in an outer orbit around TOI-4562. TOI-4562 c is a planet with a mass of $M=5.77 M_{Jup}$, an orbital period of $P_{orb}= 3990$ days, and a semi-major axis of $a = 5.219$ AU. We report the discovery of TOI-4562 c, the exoplanet with the longest orbital period discovered to date via the transit timing variation (TTV) method. The TOI-4562 system is in the process of violent evolution with intense dynamical changes - judging by its young age and high eccentricity - and is therefore a prime target for studies of formation and evolution of planetary systems.

astro-ph.EP↗

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

Extremely metal-poor stars in the Fornax and Carina dwarf spheroidal galaxies

We present our analysis of VLT/UVES and X-shooter observations of six very metal-poor stars, including four stars at [Fe/H]$\approx$$-3$ in the Fornax and Carina dwarf spheroidal (dSph) galaxies. To date, this metallicity range in these two galaxies has not yet been investigated fully, or at all in some cases. The chemical abundances of 25 elements are presented, based on 1D and local thermodynamic equilibrium (LTE) model atmospheres. We discuss the different elemental groups, and find that $α$- and iron-peak elements in these two systems are generally in good agreement with the Milky Way halo at the same metallicity. Our analysis reveals that none of the six stars we studied exhibits carbon enhancement, which is noteworthy given the prevalence of carbon-enhanced metal-poor stars without s-process enhancement (CEMP-no) in the Galaxy at similarly low metallicities. Our compilation of literature data shows that the fraction of CEMP-no stars in dSph galaxies is significantly lower than in the Milky Way, and than in ultra-faint dwarf galaxies. Furthermore, we report the discovery of the lowest metallicity, [Fe/H]=$-2.92$, r-process rich (r-I) star in a dSph galaxy. This star, fnx_06_019, has $\rm[Eu/Fe]=+0.8$, and also shows enhancement of La, Nd, and Dy, $\rm[X/Fe]>+0.5$. Our new data in Carina and Fornax help populate the extremely low metallicity range in dSph galaxies, and add to the evidence of a low fraction of CEMP-no stars in these systems.

astro-ph.GA↗

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.

astro-ph.GA↗

arXiv2024

High-precision astrometry with VVV -- II. A near-infrared extension of Gaia into the Galactic plane

Aims. We use near-infrared, ground-based data from the VISTA Variables in the Via Lactea (VVV) survey to indirectly extend the astrometry provided by the Gaia catalog to objects in heavily-extincted regions towards the Galactic bulge and plane that are beyond Gaia's reach. Methods. We make use of the state-of-the-art techniques developed for high-precision astrometry and photometry with the Hubble Space Telescope to process the VVV data. We employ empirical, spatially-variable, effective point-spread functions and local transformations to mitigate the effects of systematic errors, like residual geometric distortion and image motion, and to improve measurements in crowded fields and for faint stars. We also anchor our astrometry to the absolute reference frame of the Gaia Data Release 3. Results. We measure between 20 and 60 times more sources than Gaia in the region surrounding the Galactic center, obtaining an single-exposure precision of about 12 mas and a proper-motion precision of better than 1 mas yr$^{-1}$ for bright, unsaturated sources. Our astrometry provides an extension of Gaia into the Galactic center. We publicly release the astro-photometric catalogs of the two VVV fields considered in this work, which contain a total of $\sim$ 3.5 million sources. Our catalogs cover $\sim$ 3 sq. degrees, about 0.5% of the entire VVV survey area.

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