arXiv subjects

Dante Minniti

Publications and source records attributed to Dante Minniti.

At least 109 records · Page 6Linked to original sources

arXiv2020

Homogeneous Analysis of Globular Clusters from the APOGEE Survey with the BACCHUS Code. II. The Southern Clusters and Overview

We investigate the Fe, C, N, O, Mg, Al, Si, K, Ca, Ce and Nd abundances of 2283 red giant stars in 31 globular clusters from high-resolution spectra observed in both the northern and southern hemisphere by the SDSS-IV APOGEE-2 survey. This unprecedented homogeneous dataset, largest to date, allows us to discuss the intrinsic Fe spread, the shape and statistics of Al-Mg and N-C anticorrelations as a function of cluster mass, luminosity, age and metallicity for all 31 clusters. We find that the Fe spread does not depend on these parameters within our uncertainties including cluster metallicity, contradicting earlier observations. We do not confirm the metallicity variations previously observed in M22 and NGC 1851. Some clusters show a bimodal Al distribution, while others exhibit a continuous distribution as has been previously reported in the literature. We confirm more than 2 populations in $ω$ Cen and NGC 6752, and find new ones in M79. We discuss the scatter of Al by implementing a correction to the standard chemical evolution of Al in the Milky Way. After correction, its dependence on cluster mass is increased suggesting that the extent of Al enrichment as a function of mass was suppressed before the correction. We observe a turnover in the Mg-Al anticorrelation at very low Mg in $ω$ Cen, similar to the pattern previously reported in M15 and M92. $ω$ Cen may also have a weak K-Mg anticorrelation, and if confirmed, it would be only the third cluster known to show such a pattern.

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arXiv2020

VVV Survey Microlensing: Catalog of Best and Forsaken Events

We search for microlensing events in the zero-latitude area of the Galactic Bulge using the VVV Survey near-IR data. We have discovered a total sample of $N=630$ events within an area covering $20.68 deg^2$ between the years 2010 and 2015. In this paper we describe the search and present the data for the final sample, including near-IR magnitudes, colors and proper motions, as well as the standard microlensing parameters. We use the near-IR Color-Magnitude and Color-Color Diagram to select $N_{RC}=290$ events with red-clump sources to analyze the extinction properties of the sample in the central region of the Galactic plane. The timescale distribution and its dependence in the longitude axis is presented. The mean timescale decreases as we approach the Galactic minor axis ($b=0$ deg). Finally, we give examples of special microlensing events, such as binaries, short timescale events, and events with strong parallax effect.

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arXiv2020

The Open Cluster Chemical Abundances and Mapping Survey: IV. Abundances for 128 Open Clusters using SDSS/APOGEE DR16

The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to constrain key Galactic dynamical and chemical evolution parameters by the construction of a large, comprehensive, uniform, infrared-based spectroscopic data set of hundreds of open clusters. This fourth contribution from the OCCAM survey presents analysis using SDSS/APOGEE DR16 of a sample of 128 open clusters, 71 of which we designate to be "high quality" based on the appearance of their color-magnitude diagram. We find the APOGEE DR16 derived [Fe/H] abundances to be in good agreement with previous high resolution spectroscopic open cluster abundance studies. Using the high quality sample, we measure Galactic abundance gradients in 16 elements, and find evolution of some of the [X/Fe] gradients as a function of age. We find an overall Galactic [Fe/H] vs R_GC gradient of $-0.068 \pm 0.001$ dex kpc$^{-1}$ over the range of $6 <$ R_GC $< 13.9$ kpc; however, we note that this result is sensitive to the distance catalog used, varying as much as 15%. We formally derive the location a break in the [Fe/H] abundance gradient as a free parameter in the gradient fit for the first time. We also measure significant Galactic gradients in O, Mg, S, Ca, Mn, Cr, Cu, Na, Al, and K, some of which are measured for the first time. Our large sample allows us to explore four well-populated age bins to explore the time evolution of gradients for a large number of elements and comment on possible implications for Galactic chemical evolution and radial migration.

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arXiv2020

VVV WIN 1733$-$3349: a low extinction window to probe the far side of the Milky Way bulge

Windows of low extinction in the Milky Way (MW) have been used along the past decades for the study of the Galactic structure and the stellar population across the inner bulge and disk. Here we report the analysis of another low extinction near-IR window discovered by the VISTA Variables in the Vía Láctea Survey. VVV WIN 1733$-$3349 is about half a degree in size and is conveniently located right in the MW plane, at Galactic coordinates $(l, b) = (-5.2, -0.3)$. The mean extinction of VVV WIN 1733$-$3349 is $A_{Ks} = 0.61\pm0.08$ mag, which is much smaller than the extinction in the surrounding area. The excess in the star counts is consistent with the reduced extinction, and complemented by studying the distribution of red clump (RC) stars. Thanks to the strategic low-latitude location of VVV WIN 1733$-$3349, we are able to interpret their RC density fluctuations with the expected overdensities due to the presence of the spiral arms beyond the bulge. In addition, we find a clear excess in the number of microlensing events within the window, which corroborates our interpretation that VVV WIN 1733$-$3349 is revealing the far side of the MW bulge.

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arXiv2019

Candidate Hypervelocity Red Clump Stars in the Galactic Bulge Found Using the VVV and Gaia Surveys

We propose a new way to search for hypervelocity stars in the Galactic bulge, by using red clump (RC) giants, that are good distance indicators. The 2nd Gaia Data Release and the near-IR data from the VISTA Variables in the Via Lactea (VVV) Survey led to the selection of a volume limited sample of 34 bulge RC stars. A search in this combined data set leads to the discovery of seven candidate hypervelocity red clump stars in the Milky Way bulge. Based on this search we estimate the total production rate of hypervelocity RC stars from the central supermassive black hole (SMBH) to be $N_{HVRC} = 3.26 \times 10^{-4} $ yr$^{-1}$. This opens up the possibility of finding larger samples of hypervelocity stars in the Galactic bulge using future surveys, closer to their main production site, if they are originated by interactions of binaries with the central SMBH.

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arXiv2019

VVV Survey Microlensing: the Galactic Latitude Dependence

We search for microlensing events in fields along the Galactic minor axis, ranging from the Galactic center to -3.7<b< 3.9 deg., using the VVV survey near-IR photometry. The new search is made across VVV tiles b291, b305, b319, b347, b361 and b375, covering a total area of about 11.5 deg.^2. We find a total of N=238 new microlensing events in this new area, N=74 of which are classified as bulge red clump (RC) giant sources. Combining them with N=122 events that we had previously reported in the Galactic center (VVV tile b333), allows us to study the latitude distribution of the microlensing events reaching the Galactic plane at b=0^0 for the first time. We find a very strong dependence of the number of microlensing events with Galactic latitude, number that increases rapidly towards the Galactic center by one order of magnitude from |b|=2 deg. to b=0 deg. with a much steeper gradient than with Galactic longitude. The microlensing event population shows a flattened distribution (axial ratio b/a \approx 1.5). The final sample shows a shorter mean timescale distribution than the Galactic plane sample for both, the complete population and RC stars.

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arXiv2019

Discovery of a new stellar sub-population residing in the (inner) stellar halo of the Milky Way

We report the discovery of a unique collection of metal-poor giant-stars, that exhibit anomalously high levels of $^{28}$Si, clearly above typical Galactic levels. Our sample spans a narrow range of metallicities, peaking at $-1.07\pm 0.06$, and exhibit abundance ratios of [Si,Al/Fe] that are as extreme as those observed in Galactic globular clusters (GCs), and Mg is slightly less overabundant. In almost all the sources we used, the elemental abundances were re-determined from high-resolution spectra, which were re-analyzed assuming LTE. Thus, we compiled the main element families, namely the light elements (C, N), $α-$elements (O, Mg, Si), iron-peak element (Fe), $\textit{s}-$process elements (Ce, Nd), and the light odd-Z element (Al). We also provide dynamical evidence that most of these stars lie on tight (inner)halo-like and retrograde orbits passing through the bulge. Such kinds of objects have been found in present-day halo GCs, providing the clearest chemical signature of past accretion events in the (inner) stellar halo of the Galaxy, formed possibly as the result of dissolved halo GCs. Their chemical composition is, in general, similar to that of typical GCs population, although several differences exist.

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arXiv2019

New Candidate Planetary Nebulae in Galactic Globular Clusters from the VVV Survey

Only four globular cluster planetary nebulae (GCPN) are known so far in the Milky Way. About 50 new globular clusters have been recently discovered towards the Galactic bulge. We present a search for planetary nebulae within 3 arcmin of the new globular clusters, revealing the identification of new candidate GCPN. These possible associations are PN SB 2 with the GC Minni 06, PN G354.9-02.8 with the GC Minni 11, PN G356.8-03.6 with the GC Minni 28, and PN Pe 2-11 with the GC Minni 31. We discard PN H 2-14 located well within the projected tidal radius of the new globular cluster FSR1758 because they have different measured radial velocities. These are interesting objects that need follow-up observations (especially radial velocities) in order to confirm membership, and to measure their physical properties in detail. If confirmed, this would double the total number of Galactic GCPN.

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arXiv2019

VVV-WIT-04: an extragalactic variable source caught by the VVV Survey

We report the discovery of VVV-WIT-04, a near-infrared variable source towards the Galactic disk located ~0.2 arcsec apart from the position of the radio source PMN J1515-5559. The object was found serendipitously in the near-IR data of the ESO public survey VISTA Variables in the Vía Láctea (VVV). Our analysis is based on variability, multicolor, and proper motion data from VVV and VVV eXtended surveys, complemented with archive data at longer wavelengths. We suggest that VVV-WIT-04 has an extragalactic origin as the near-IR counterpart of PMN J1515-5559. The Ks-band light-curve of VVV-WIT-04 is highly variable and consistent with that of an Optically Violent Variable (OVV) quasar. The variability in the near-IR can be interpreted as the redshifted optical variability. Residuals to the proper motion varies with the magnitude suggesting contamination by a blended source. Alternative scenarios, including a transient event such as a nova or supernova, or even a binary microlensing event are not in agreement with the available data.

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arXiv2019

The Tale of the Milky Way Globular Cluster NGC 6362 -- I. The Orbit and its possible extended star debris features as revealed by Gaia DR2

We report the identification of possible extended star debris candidates beyond the cluster tidal radius of NGC 6362 based on the second {\it Gaia} data release ({\it Gaia} DR2). We found 259 objects possibly associated with the cluster lying in the vicinity of the giant branch and 1--2 magnitudes fainter/brighter than the main-sequence turn-off in the cluster color-magnitude diagram and which cover an area on the sky of $\sim$4.1 deg$^{2}$ centered on the cluster. We traced back the orbit of NGC 6362 in a realistic Milky-Way potential, using the \texttt{GravPot16} package, for 3 Gyrs. The orbit shows that the cluster shares similar orbital properties as the inner disk, having peri-/apo-galactic distances, and maximum vertical excursion from the Galactic plane inside the corotation radius (CR), moving inwards from CR radius to visit the inner regions of the Milky Way. The dynamical history of the cluster reveals that it has crossed the Galactic disk several times in its lifetime and has recently undergone a gravitational shock, $\sim 15.9$ Myr ago, suggesting that less than 0.1\% of its mass has been lost during the current disk-shocking event. Based on the cluster's orbit and position in the Galaxy, we conclude that the possible extended star debris candidates are a combined effect of the shocks from the Galactic disk and evaporation from the cluster. Lastly, the evolution of the vertical component of the angular momentum shows that the cluster is strongly affected dynamically by the Galactic bar potential.

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arXiv2019

The VISCACHA survey -- deep and resolved photometry of star clusters in the Magellanic Clouds

The VISCACHA (VIsible Soar photometry of star Clusters in tApii and Coxi HuguA\footnote{LMC and SMC names in the Tupi-Guarani language spoken by native people in Brazil}) Survey is an ongoing project based on deep and spatiallyresolved photometric observations of Magellanic Cloud star clusters, collected using the SOuthern Astrophysical Research (SOAR) telescope together with the SOAR Adaptive Module Imager. So far we have used $>$300h of telescope time to observe $\sim$150 star clusters, mostly with low mass ($M < 10^4 M_{\odot}$) on the outskirts of the LMC and SMC. With this high-quality data set, we homogeneously determine physical properties using deep colour-magnitude diagrams (ages, metallicities, reddening, distances, mass, luminosity and mass functions) and structural parameters (radial density profiles, sizes) for these clusters which are used as a proxy to investigate the interplay between the Magellanic Clouds and their evolution. We present the VISCACHA survey and its initial results, based on our first two papers. The project's long term goals and expected legacy to the community are also addressed.

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arXiv2019

Discovery of a nitrogen-enhanced mildly metal-poor binary system: Possible evidence for pollution from an extinct AGB Star

We report the serendipitous discovery of a nitrogen-rich, mildly metal-poor ([Fe/H]=-1.08) giant star in a single-lined spectroscopic binary system found in the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) survey, Data Release 14 (DR14). Previous work has assumed that the two percent of halo giants with unusual elemental abundances have been evaporated from globular clusters, but other origins for their abundance signatures, including binary mass transfer, must also be explored. We present the results of an abundance re-analysis of the APOGEE-2 high-resolution near-infrared spectrum of 2M12451043+1217401 with the Brussels Automatic Stellar Parameter (BACCHUS) automated spectral analysis code, and re-derive manually the main element families, namely the light elements (C, N), elements (O, Mg, Si), iron-peak element (Fe), \textit{s}-process element (Ce), and the light odd-Z element (Al). Our analysis confirm the N-rich nature of 2M12451043+1217401, which has a [N/Fe] ratio of $+0.69$, and shows that the abundances of C and Al are slightly discrepant from that of a typical mildly metal-poor RGB star, but exhibit Mg, Si, O and \textit{s}-process abundances (Ce) of typical field stars. We also detect a particularly large variability in its radial velocity over the period of the APOGEE-2 observations, and the most likely orbit fit to the radial velocity data has a period of $730.89\pm106.86$ days, a velocity semi-amplitude of $9.92 \pm 0.14$ km s$^{-1}$, and an eccentricity of $\sim 0.1276 \pm0.1174$, which support the hypothesis of a binary companion, and that has probably been polluted by a now-extinct AGB star.

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arXiv2019

Detailed chemical composition and orbit of the new globular cluster FSR1758: Implications for the accretion of the Sequoia dwarf galaxy onto the Milky Way

We present detailed chemical abundances, radial velocities and orbital parameters for FSR 1758, a recently discovered star cluster in the direction of the Galactic Bulge. High resolution (R~42,000) spectra were obtained using the Magellan/Clay telescope instrumented with MIKE echelle spectrogragh, wavelength range 4900-8700 Å. Cluster membership was determined using Gaia DR2 proper motions and confirmed with our radial velocity measurements. We find metallicity consistent with previous photometric estimates for this cluster, [Fe/H] = -1.58+-0.03 dex, with a small, 0.08 dex, spread. While other studies have suggested this massive object may be the result of a previous accretion event, our results are consistent with Milky Way Halo globular clusters with characteristic Na-O anti-correlations found for the metal-poor cluster members. The mean radial velocity of the cluster, +226.8+-1.6 km/s with a small velocity dispersion, 4.9+-1.2 km/s, is typical for globular clusters. We also confirm a retrograde Galactic orbit that appears to be highly eccentric.

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arXiv2019

Microlensing events in the Galactic bulge

For the first time we detected microlensing events at zero latitude in the Galactic bulge using the VISTA Variables in the Via Lactea Survey (VVV) data. We have discovered a total sample of N = 630 events within an area covering 20.7 sq. deg. Using the near-IR color magnitude diagram we selected N = 291 red clump sources, allowing us to analyse the longitude dependence of microlensing across the central region of the Galactic plane. We thoroughly accounted for the photometric and sampling efficiency. The spatial distribution is homogeneous, with the number of events smoothly increasing toward the Galactic center. We find a slight asymmetry, with a larger number of events toward negative longitudes than positive longitudes, that is possibly related with the inclination of the bar along the line of sight. We also examined the timescale distribution which shows a mean on 17.4 +- 1.0 days for the whole sample, and 20.7 +- 1.0 for the Red Clump subsample.

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arXiv2019

Analysis of the physical nature of 22 New VVV Survey Globular Cluster candidates in the Milky Way Bulge

In order to characterize 22 new globular cluster (GC) candidates in the Galactic bulge, we present their colour-magnitude diagrams (CMDs) and Ks-band luminosity functions (LFs) using the near-infrared VVV database as well as Gaia-DR2 proper motion dataset. CMDs were obtained, on one hand, after properly decontaminating the observed diagrams from background/foreground disc stars and other sources. On the other hand, CMDs were also obtained based upon star selection in proper motion diagrams. Taking into account our deep CMDs and LFs analyses, we find that 17 out of 22 new GC candidates may be real and should therefore be followed-up, while 5 candidates were discarded from the original sample. We also search for RR Lyrae and Mira variable stars in the fields of these new GC candidates. In particular, we confirm that Minni 40 may be a real cluster. If confirmed by further follow-up analysis, it would be the closest GC to the Galactic centre in projected angular distance, located only 0.5 deg away from it. We consider that it is very difficult to confirm the physical reality of these small, poorly-populated bulge GCs so in many cases alternative techniques are needed to corroborate our findings.

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arXiv2019

KMT-2018-BLG-1292: A Super-Jovian Microlens Planet in the Galactic Plane

We report the discovery of KMT-2018-BLG-1292Lb, a super-Jovian $M_{\rm planet} = 4.5\pm 1.3\,M_J$ planet orbiting an F or G dwarf $M_{\rm host} = 1.5\pm 0.4\,M_\odot$, which lies physically within ${\cal O}(10\,\pc)$ of the Galactic plane. The source star is a heavily extincted $A_I\sim 5.2$ luminous giant that has the lowest Galactic latitude, $b=-0.28^\circ$, of any planetary microlensing event. The relatively blue blended light is almost certainly either the host or its binary companion, with the first explanation being substantially more likely. This blend dominates the light at $I$ band and completely dominates at $R$ and $V$ bands. Hence, the lens system can be probed by follow-up observations immediately, i.e., long before the lens system and the source separate due to their relative proper motion. The system is well characterized despite the low cadence $Γ=0.15$--$0.20\,{\rm hr^{-1}}$ of observations and short viewing windows near the end of the bulge season. This suggests that optical microlensing planet searches can be extended to the Galactic plane at relatively modest cost.

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arXiv2019

The Relationship Between Globular Cluster Mass, Metallicity, and Light Element Abundance Variations

We investigate aluminum abundance variations in the stellar populations of globular clusters using both literature measurements of sodium and aluminum and APOGEE measurements of nitrogen and aluminum abundances. For the latter, we show that the Payne is the most suitable of the five available abundance pipelines for our purposes. Our combined sample of 42 globular clusters spans approximately 2 dex in [Fe/H] and 1.5 dex in $\log{M_{GC}/M_{\odot}}$. We find no fewer than five globular clusters with significant internal variations in nitrogen and/or sodium with little-to-no corresponding variation in aluminum, and that the minimum present-day cluster mass for aluminum enrichment in metal-rich systems is $\log{M_{GC}/M_{\odot}} \approx 4.50 + 2.17(\rm{[Fe/H]}+1.30)$. We demonstrate that the slopes of the [Al/Fe] vs [Na/Fe] and [Al/Fe] vs [N/Fe] relations for stars without field-like abundances are approximately log-linearly dependent on both the metallicity and the stellar mass of the globular clusters. In contrast, the relationship between [Na/Fe] and [N/Fe] shows no evidence of such dependencies. This suggests that there were (at least) two classes of non-supernovae chemical polluters that were common in the early universe, and that their relative contributions within globular clusters somehow scaled with the metallicity and mass of globular clusters. The first of these classes is predominantly responsible for the CNO and NeNa abundance variations, and likewise the second for the MgAl abundance variations. 47 Tuc and M4 are particularly striking examples of this dichotomy. As an auxiliary finding, we argue that abundance variations among Terzan 5 stars are consistent with it being a normal globular cluster.

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arXiv2019

The asymptotic evolution of the stellar merger V1309 Sco: a Blue Straggler in the making?

Stellar mergers are estimated to be common events in the Galaxy. The best studied stellar merger case to date is V1309 Sco (= Nova Scorpii 2008) which was originally misclassified as a Nova event. Later identified as the merger of the components of a cool overcontact binary system with 1.52 Msun and 0.16 Msun, V1309 Sco showed an initial period of P = 1.4 days before the merger. Post-outburst evolution demonstrated that V1309 Sco was unlike the typical Classical Novae and Symbiotic Recurrent Novae with significant dust production around it, and indicated that the system may become a post-AGB (or pre-PN) soon. Here we present a study of V1309 Sco about ten years after the outburst, based on near-IR variability and colour data from the ESO surveys VISTA Variables in the Vía Láctea (VVV) and VVV eXtended (VVVX). We find that reasonable equilibrium in this stellar merger is being reached and that the star has settled into a nearly constant magnitude. A dramatic change in its near-IR colours from (J-Ks) = 1.40 in 2010 to (J-Ks) = 0.42 in 2015 and a possible low amplitude periodic signal with P = 0.49 days in the post-outburst data are consistent with a "blue straggler" star, predicted to be formed from a stellar merger.

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