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- Cordoni, G., et al.
(författare)
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Exploring the Galaxy's halo and very metal-weak thick disc with SkyMapper and Gaia DR2
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 503:2, s. 2539-2561
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we combine spectroscopic information from the SkyMapper survey for Extremely Metal-Poor stars and astrometry from Gaia DR2 to investigate the kinematics of a sample of 475 stars with a metallicity range of -6.5 <= [Fe/H] <= -2.05 dex. Exploiting the action map, we identify 16 and 40 stars dynamically consistent with the Gaia Sausage and Gaia Sequoia accretion events, respectively. The most metal poor of these candidates have metallicities of [Fe/H] = - 3.31 and - 3.74, respectively, helping to define the low-metallicity tail of the progenitors involved in the accretion events. We also find, consistent with other studies, that similar to 21 per cent of the sample have orbits that remain confined to within 3 kpc of the Galactic plane, that is, |Z(max)| <= 3 kpc. Of particular interest is a subsample (similar to 11 per cent of the total) of low |Z(max)| stars with low eccentricities and prograde motions. The lowest metallicity of these stars has [Fe/H] = -4.30 and the subsample is best interpreted as the very low-metallicity tail of the metal-weak thick disc population. The low |Z(max)|, low eccentricity stars with retrograde orbits are likely accreted, while the low |Z(max)|, high eccentricity pro- and retrograde stars are plausibly associated with the Gaia Sausage system. We find that a small fraction of our sample (similar to 4 per cent of the total) is likely escaping from the Galaxy, and postulate that these stars have gained energy from gravitational interactions that occur when infalling dwarf galaxies are tidally disrupted.
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| 6. |
- Cordoni, G., et al.
(författare)
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Gaia and Hubble Unveil the Kinematics of Stellar Populations in the Type II Globular Clusters ? Centauri and M22
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 898:2
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Tidskriftsartikel (refereegranskat)abstract
- The origin of multiple stellar populations in globular clusters (GCs) is one of the greatest mysteries of modern stellar astrophysics. N-body simulations suggest that the present-day dynamics of GC stars can constrain the events that occurred at high redshift and led to the formation of multiple populations. Here, we combine multiband photometry from the Hubble Space Telescope (HST) and ground-based facilities with HST and Gaia Data Release 2 proper motions to investigate the spatial distributions and the motions in the plane of the sky of multiple populations in the Type II GCs NGC 5139 (? Centauri) and NGC 6656 (M22). We first analyzed stellar populations with different metallicities. Fe-poor and Fe-rich stars in M22 share similar spatial distributions and rotation patterns and exhibit similar isotropic motions. Similarly, the two main populations with different iron abundance in ? Centauri share similar ellipticities and rotation patterns. When different radial regions are analyzed, we find that the rotation amplitude decreases from the center toward the external regions. Fe-poor and Fe-rich stars of ? Centauri are radially anisotropic in the central region and show similar degrees of anisotropy. We also investigate the stellar populations with different light-element abundances and find that their N-rich stars exhibit higher ellipticity than N-poor stars. In ? Centauri both stellar groups are radially anisotropic. Interestingly, N-rich, Fe-rich stars exhibit different rotation patterns than N-poor stars with similar metallicities. The stellar populations with different nitrogen of M22 exhibit similar rotation patterns and isotropic motions. We discuss these findings in the context of the formation of multiple populations.
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- Carlos, M., et al.
(författare)
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The chemical compositions of multiple stellar populations in the globular cluster NGC 2808
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 519:2, s. 1695-1712
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Tidskriftsartikel (refereegranskat)abstract
- Pseudo two-colour diagrams or Chromosome maps (ChM) indicate that NGC 2808 host five different stellar populations. The existing ChMs have been derived by the Hubble Space Telescope photometry, and comprise of stars in a small field of view around the cluster centre. To overcome these limitations, we built a ChM with U, B, I photometry from ground-based facilities that disentangle the multiple stellar populations of NGC 2808 over a wider field of view. We used spectra collected by GIRAFFE@VLT in a sample of 70 red giant branch and seven asymptotic giant branch (AGB) stars to infer the abundances of C, N, O, Al, Fe, and Ni, which combined with literature data for other elements (Li, Na, Mg, Si, Ca, Sc, Ti, Cr, and Mn), and together with both the classical and the new ground-based ChMs, provide the most complete chemical characterization of the stellar populations in NGC 2808 available to date. As typical of the multiple population phenomenon in globular clusters, the light elements vary from one stellar population to another; whereas the iron peak elements show negligible variation between the different populations (at a level of less than or similar to 0.10 dex). Our AGB stars are also characterized by the chemical variations associated with the presence of multiple populations, confirming that this phase of stellar evolution is affected by the phenomenon as well. Intriguingly, we detected one extreme O-poor AGB star (consistent with a high He abundance), challenging stellar evolution models that suggest that highly He-enriched stars should avoid the AGB phase and evolve as AGB-manque star.
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- Dondoglio, E., et al.
(författare)
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A deep dive into the Type II globular cluster NGC 1851
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 526:2, s. 2960-2976
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Tidskriftsartikel (refereegranskat)abstract
- About one-fifth of the Galactic globular clusters (GCs), dubbed Type II GCs, host distinct stellar populations with different heavy elements abundances. NGC 1851 is one of the most studied Type II GCs, surrounded by several controversies regarding the spatial distribution of its populations and the presence of star-to-star [Fe/H], C+N+O, and age differences. This paper provides a detailed characterization of its stellar populations through Hubble Space Telescope (HST), ground-based, and Gaia photometry. We identified two distinct populations with different abundances of s-process elements along the red-giant branch (RGB) and the subgiant branch (SGB) and detected two subpopulations among both s-poor (canonical) and s-rich (anomalous) stars. To constrain the chemical composition of these stellar populations, we compared observed and simulated colours of stars with different abundances of He, C, N, and O. It results that the anomalous population has a higher CNO overall abundance compared to the canonical population and that both host stars with different light-element abundances. No significant differences in radial segregation between canonical and anomalous stars are detected, while we find that among their subpopulations, the two most chemical extremes are more centrally concentrated. Anomalous and canonical stars show different 2D spatial distributions outside ∼3 arcmin, with the latter developing an elliptical shape and a stellar overdensity in the north-east direction. We confirm the presence of a stellar halo up to ∼80 arcmin with Gaia photometry, tagging 14 and 5 of its stars as canonical and anomalous, respectively, finding a lack of the latter in the south/south-east field.
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- Jimenez, Antonio M. Jimenez, et al.
(författare)
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An adapted European LeukemiaNet genetic risk stratification for acute myeloid leukemia patients undergoing allogeneic hematopoietic cell transplant. A CIBMTR analysis
- 2021
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Ingår i: Bone Marrow Transplantation. - : Springer Nature. - 0268-3369 .- 1476-5365. ; 56:12, s. 3068-3077
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Tidskriftsartikel (refereegranskat)abstract
- Cytogenetic and molecular abnormalities are known to influence post-transplant outcomes in acute myeloid leukemia (AML) but data assessing the prognostic value of combined genetic models in the HCT setting are limited. We developed an adapted European LeukemiaNet (aELN) risk classification based on available genetic data reported to the Center for International Blood and Marrow Transplant Research, to predict post-transplant outcomes in 2289 adult AML patients transplanted in first remission, between 2013 and 2017. Patients were stratified according to aELN into three groups: favorable (Fav, N = 181), intermediate (IM, N = 1185), and adverse (Adv, N = 923). Univariate analysis demonstrated significant differences in 2-year overall survival (OS) (Fav: 67.7%, IM: 64.9% and Adv: 53.9%; p < 0.001); disease-free survival (DFS) (Fav: 57.8%, IM: 55.5% and Adv: 45.3; p < 0.001) and relapse (Fav: 28%, IM: 27.5% and Adv: 37.5%; p < 0.001). Multivariate analysis (MVA) revealed no differences in outcomes between the Fav and IM groups, thus they were combined. On MVA, patients in the Adv risk group had the highest risk of relapse (HR 1.47 p <= 0.001) and inferior DFS (HR 1.35 p < 0.001) and OS (HR 1.39 p < 0.001), even using myeloablative conditioning or in those without the pre-HCT measurable-residual disease. Novel approaches to mitigate relapse in this high-risk group are urgently needed.
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| 19. |
- Marino, A. F., et al.
(författare)
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A JWST Project on 47 Tucanae : NIRSpec Spectroscopy of Multiple Populations among M Dwarfs
- 2024
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 969:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the first spectroscopic estimates of the chemical abundance of M dwarf stars in a globular cluster (GC), namely 47 Tucanae. By exploiting NIRSpec on board the James Webb Space Telescope, we gathered low-resolution spectra for 28 stars with masses in the range ∼0.4-0.5 M⊙. The spectra are strongly affected by the H2O water vapor bands, which can be used as indicators of oxygen abundance. The spectral analysis reveals that the target stars feature a different O abundance, with a difference of ∼0.40 dex between the first and the most polluted second population. The observed range is similar to that observed among red giant stars. This result reinforces previous findings based on the analysis of photometric diagrams, including the "chromosome maps," providing a first, and more direct, evidence of light element variations in the M dwarfs' mass regime. The observation that the multiple populations, with their variations in light elements, exhibit the same patterns from the lower main sequence all the way to the red giant branch further strengthens the notion that multiple stellar populations in GCs formed in a series of bursts of star formation.
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| 20. |
- Marino, A. F., et al.
(författare)
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A JWST Project on 47 Tucanae. Overview, Photometry, and Early Spectroscopic Results of M Dwarfs and Observations of Brown Dwarfs
- 2024
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 965:2
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Tidskriftsartikel (refereegranskat)abstract
- James Webb Space Telescope (JWST) observations have been demonstrated to be efficient in detecting multiple stellar populations in globular clusters (GCs) in the low-mass regime of M dwarfs. We present an overview, and first results, of different projects that can be explored by using the JWST observations gathered under program GO2560 for 47 Tucanae, the first program entirely devoted to the investigation of multiple populations in very-low-mass stars, which includes spectroscopic data for the faintest GC stars for which spectra are available. Our color-magnitude diagram (CMD) shows some substructures for ultracool stars, including gaps and breaks in slope. In particular, we observe both a gap and a minimum in the F322W2 luminosity function less than 1 mag apart, and discuss which it could be associated with the H-burning limit. We detect stars fainter than this minimum, very likely brown dwarfs. We corroborate the ubiquity of the multiple populations across different masses, from ∼ 0.1 M⊙ up to red giants (∼ 0.8 M⊙). The oxygen range inferred for the M dwarfs, both from the CMD and from the spectra of two M dwarfs associated with different populations, is similar to that observed for giants. We have not detected any difference between the fractions of stars in distinct populations across stellar masses greater than or ∼ 0.1 M⊙. This work demonstrates the JWST's capability in uncovering multiple populations within M dwarfs and illustrates the possibility to analyze very-low-mass stars in GCs approaching the H-burning limit and the brown-dwarf sequence.
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| 21. |
- Marino, A. F., et al.
(författare)
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Iron and s-elements abundance variations in NGC 5286 : comparison with 'anomalous' globular clusters and Milky Way satellites
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:1, s. 815-845
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster (GC) NGC 5286. We have determined abundances of representative light proton-capture, a, Fe-peak and neutron-capture element groups, and combined them with photometry of multiple sequences observed along the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal distribution in s-process element abundance ratios, with two main groups, the s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the s-rich stars having higher Fe, e.g. <[Fe/H]>(s-rich) - <[Fe/H]>(s-poor) similar to 0.2 dex; and (iii) the presence of O-Na-Al (anti) correlations in both stellar groups. We have defined a new photometric index, c(BVI) = (B - V) -(V - I), to maximize the separation in the colour-magnitude diagram between the two stellar groups with different Fe and s-element content, and this index is not significantly affected by variations in light elements (such as the O-Na anticorrelation). The variations in the overall metallicity present in NGC 5286 add this object to the class of anomalous GCs. Furthermore, the chemical abundance pattern of NGC 5286 resembles that observed in some of the anomalous GCs, e.g. M 22, NGC 1851, M 2, and the more extreme omega Centauri, that also show internal variations in s-elements, and in light elements within stars with different Fe and s-elements content. In view of the common variations in s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class of objects. The similarities in chemical abundance ratios between these objects strongly suggest similar formation and evolution histories, possibly associated with an origin in tidally disrupted dwarf satellites.
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| 22. |
- Milone, A. P., et al.
(författare)
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Multiple stellar populations in globular clusters with JWST : an NIRCam view of 47 Tucanae
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 522:2, s. 2429-2447
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Tidskriftsartikel (refereegranskat)abstract
- We use images collected with the near-infrared camera (NIRCam) onboard the JWST and with the Hubble Space Telescope ( HST ) to investigate multiple populations at the bottom of the main sequence (MS) of 47 Tucanae. The m(F115W) versus m(F 115 W )- m(F322W2) colour-magnitude diagram (CMD) from NIRCam sho ws that, belo w the knee, the MS stars span a wide colour range, where the majority of M-dwarfs exhibit blue colours, and a tail of stars are distributed towards the red. A similar pattern is observed from the m(F160W) versus m(F 110 W) - m(F160W) CMD from HST , and multiple populations of M-dwarfs are also visible in the optical mF606W versus m(F606W -) m(F814W) CMD. The NIRCam CMD shows a narrow sequence of faint MS stars with masses smaller than 0 . 1 M-?. We introduce a chromosome map of M-dwarfs that reveals an extended first population and three main groups of second-population stars. By combining isochrones and synthetic spectra with appropriate chemical composition, we simulate colours and magnitudes of different stellar populations in the NIRCam filters (at metallicities [Fe/H] = -1.5 and [Fe/H] = -0.75) and identify the photometric bands that provide the most efficient diagrams to investigate the multiple populations in globular clusters. Models are compared with the observed CMDs of 47 Tucanae to constrain M-dwarfs' chemical composition. Our analysis suggests that the oxygen range needed to reproduce the colours of first-and second-population M-dwarfs is similar to that inferred from spectroscopy of red giants, constraining the proposal that the chemical variations are due to mass transfer phenomena in proto-clusters.
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| 23. |
- Milone, A. P., et al.
(författare)
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The ACS survey of Galactic globular clusters XII. Photometric binaries along the main sequence
- 2012
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 540
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Tidskriftsartikel (refereegranskat)abstract
- Context. The fraction of binary stars is an important ingredient to interpret globular cluster dynamical evolution and their stellar population. Aims. We investigate the properties of main-sequence binaries measured in a uniform photometric sample of 59 Galactic globular clusters that were observed by HST WFC/ACS as a part of the Globular Cluster Treasury project. Methods. We measured the fraction of binaries and the distribution of mass-ratio as a function of radial location within the cluster, from the central core to beyond the half-mass radius. We studied the radial distribution of binary stars, and the distribution of stellar mass ratios. We investigated monovariate relations between the fraction of binaries and the main parameters of their host clusters. Results. We found that in nearly all the clusters, the total fraction of binaries is significantly smaller than the fraction of binaries in the field, with a few exceptions only. Binary stars are significantly more centrally concentrated than single MS stars in most of the clusters studied in this paper. The distribution of the mass ratio is generally flat (for mass-ratio parameter q > 0.5). We found a significant anti-correlation between the binary fraction in a cluster and its absolute luminosity (mass). Some, less significant correlation with the collisional parameter, the central stellar density, and the central velocity dispersion are present. There is no statistically significant relation between the binary fraction and other cluster parameters. We confirm the correlation between the binary fraction and the fraction of blue stragglers in the cluster.
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