scholarly journals Mass-loss along the red giant branch in 46 globular clusters and their multiple populations

2020 ◽  
Vol 498 (4) ◽  
pp. 5745-5771
Author(s):  
M Tailo ◽  
A P Milone ◽  
E P Lagioia ◽  
F D’Antona ◽  
A F Marino ◽  
...  
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
First Generation ◽  
Hubble Space Telescope ◽  
Population Synthesis ◽  
Data Set ◽  
Complex Interactions ◽  
The Difference ◽  
Red Giant ◽  
First Time

ABSTRACT The location of Galactic globular clusters’ (GC) stars on the horizontal branch (HB) should mainly depend on GC metallicity, the ‘first parameter’, but it is actually the result of complex interactions between the red giant branch (RGB) mass-loss, the coexistence of multiple stellar populations with different helium content, and the presence of a ‘second parameter’ that produces dramatic differences in HB morphology of GCs of similar metallicity and ages (like the pair M3–M13). In this work, we combine the entire data set from the Hubble Space Telescope Treasury survey and stellar evolutionary models, to analyse the HBs of 46 GCs. For the first time in a large sample of GCs, we generate population synthesis models, where the helium abundances for the first and the ‘extreme’ second generations are constrained using independent measurements based on RGB stars. The main results are as follows: (1) The mass-loss of first-generation stars is tightly correlated to cluster metallicity. (2) The location of helium enriched stars on the HB is reproduced only by adopting a higher RGB mass-loss than for the first generation. The difference in mass-loss correlates with helium enhancement and cluster mass. (3) A model of ‘pre-main sequence disc early loss’, previously developed by the authors, explains such a mass-loss increase and is consistent with the findings of multiple-population formation models predicting that populations more enhanced in helium tend to form with higher stellar densities and concentrations. (4) Helium-enhancement and mass-loss both contribute to the second parameter.

scholarly journals Correlation between mass segregation and structural concentration in relaxed stellar clusters

2019 ◽  
Vol 485 (4) ◽  
pp. 5752-5760 ◽  
Author(s):  
Ruggero de Vita ◽  
Michele Trenti ◽  
Morgan MacLeod
Keyword(s):  
Globular Clusters ◽  
Initial Conditions ◽  
Hubble Space Telescope ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Best Fitting ◽  
Low Mass ◽  
The Difference ◽  
Mass Segregation ◽  
First Time

Abstract The level of mass segregation in the core of globular clusters has been previously proposed as a potential indicator of the dynamical constituents of the system, such as presence of a significant population of stellar-mass black holes (BHs), or even a central intermediate-mass black hole (IMBH). However, its measurement is limited to clusters with high-quality Hubble Space Telescope data. Thanks to a set of state-of-the-art direct N-body simulations with up to 200k particles inclusive of stellar evolution, primordial binaries, and varying BH/neutron stars, we highlight for the first time the existence of a clear and tight linear relation between the degree of mass segregation and the cluster structural concentration index. The latter is defined as the ratio of the radii containing 5 per cent and 50 per cent of the integrated light (R5/R50), making it robustly measurable without the need to individually resolve low-mass stars. Our simulations indicate that given R5/R50, the mass segregation Δm (defined as the difference in main-sequence median mass between centre and half-light radius) is expressed as Δm/M⊙ = −1.166R5/R50 + 0.3246, with a root-mean-square error of 0.0148. In addition, we can explain its physical origin and the values of the fitted parameters through basic analytical modelling. Such correlation is remarkably robust against a variety of initial conditions (including presence of primordial binaries and IMBHs) and cluster ages, with a slight dependence in best-fitting parameters on the prescriptions used to measure the quantities involved. Therefore, this study highlights the potential to develop a new observational tool to gain insight on the dynamical status of globular clusters and on its dark remnants.

scholarly journals A chromosome map to unveil stellar populations with different magnesium abundances. The case of ω Centauri

2020 ◽  
Vol 497 (3) ◽  
pp. 3846-3859
Author(s):  
A P Milone ◽  
A F Marino ◽  
A Renzini ◽  
C Li ◽  
S Jang ◽  
...  
Keyword(s):  
Globular Clusters ◽  
First Generation ◽  
Hubble Space Telescope ◽  
Stellar Populations ◽  
Stellar Content ◽  
Chemical Abundances ◽  
Chromosome Map ◽  
First Time ◽  
Host Stars

ABSTRACT Historically, photometry has been largely used to identify stellar populations [multiple populations (MPs)] in globular clusters (GCs) by using diagrams that are based on colours and magnitudes that are mostly sensitive to stars with different metallicities or different abundances of helium, carbon, nitrogen, and oxygen. In particular, the pseudo-two-colour diagram called chromosome map (ChM), allowed the identification and the characterization of MPs in about 70 GCs by using appropriate filters of the Hubble Space Telescope (HST) that are sensitive to the stellar content of He, C, N, O, and Fe. We use here high precision HST photometry from F275W, F280N, F343N, F373N, and F814W images of ω Centauri to investigate its MPs. We introduce a new ChM whose abscissa and ordinate are mostly sensitive to stellar populations with different magnesium and nitrogen, respectively, in monometallic GCs. This ChM is effective in disentangling the MPs based on their Mg chemical abundances, allowing us to explore, for the first time, possible relations between the production of these elemental species for large samples of stars in GCs. By comparing the colours of the distinct stellar populations with the colours obtained from appropriate synthetic spectra we provide ‘photometric-like’ estimates of the chemical composition of each population. Our results show that, in addition to first-generation (1G) stars, the metal-poor population of ω Cen hosts four groups of second-generation stars with different [N/Fe], namely, 2GA–D. 2GA stars share nearly the same [Mg/Fe] as the 1G, whereas 2GB, 2GC, and 2GD are Mg depleted by ∼0.15, ∼0.25, and ∼0.45 dex, respectively. We provide evidence that the metal-intermediate populations host stars with depleted [Mg/Fe].

scholarly journals Mass-loss law for red giant stars in simple population globular clusters

2021 ◽  
Vol 503 (1) ◽  
pp. 694-703
Author(s):  
M Tailo ◽  
A P Milone ◽  
E P Lagioia ◽  
F D’Antona ◽  
S Jang ◽  
...  
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
Multiple Populations ◽  
Mass Losses ◽  
Red Giant ◽  
Stellar Masses

ABSTRACT The amount of mass lost by stars during the red-giant branch (RGB) phase is one of the main parameters to understand and correctly model the late stages of stellar evolution. Nevertheless, a fully comprehensive knowledge of the RGB mass-loss is still missing. Galactic Globular Clusters (GCs) are ideal targets to derive empirical formulations of mass-loss, but the presence of multiple populations with different chemical compositions has been a major challenge to constrain stellar masses and RGB mass-losses. Recent work has disentangled the distinct stellar populations along the RGB and the horizontal branch (HB) of 46 GCs, thus providing the possibility to estimate the RGB mass-loss of each stellar population. The mass-losses inferred for the stellar populations with pristine chemical composition (called first-generation or 1G stars) tightly correlate with cluster metallicity. This finding allows us to derive an empirical RGB mass-loss law for 1G stars. In this paper, we investigate seven GCs with no evidence of multiple populations and derive the RGB mass-loss by means of high-precision Hubble-Space Telescope photometry and accurate synthetic photometry. We find a cluster-to-cluster variation in the mass-loss ranging from ∼0.1 to ∼0.3 M⊙. The RGB mass-loss of simple-population GCs correlates with the metallicity of the host cluster. The discovery that simple-population GCs and 1G stars of multiple population GCs follow similar mass-loss versus metallicity relations suggests that the resulting mass-loss law is a standard outcome of stellar evolution.

Reassessing the Generational Disparity in Immigrant Offending: A Within-family Comparison of Involvement in Crime

2019 ◽  
Vol 56 (6) ◽  
pp. 851-887 ◽  
Author(s):  
Bianca E. Bersani ◽  
Adam W. Pittman
Keyword(s):  
First Generation ◽  
Second Generation ◽  
Well Being ◽  
Foreign Born ◽  
Data Set ◽  
The Difference ◽  
Successive Generations ◽  
Offending Patterns ◽  
High Degree ◽  
Parent Child

Objective:This study reassesses the generational disparity in immigrant offending. Patterns and predictors of offending are compared using traditional peer-based models and an alternative within-family (parent–child dyad) model.Method:The National Longitudinal Survey of Youth (1979; NLSY79) and NLSY-Child and Young Adult (NLSY_CYA) data are merged to create an intergenerational data set to compare generational disparities in immigrant offending across peers and within families. Differences in self-reported offending (prevalence and variety) by immigrant generation are assessed using a combination of descriptive analyses (χ2and analysis of variance) and regression models.Results:While NLSY_CYA children generally are at a greater risk of offending compared with the NLSY79 mothers, the difference in offending is greatest between first-generation mom and second-generation child dyads. Disparities in offending are driven in large part by exceedingly low levels of offending among first-generation immigrants.Conclusion:Although the factors driving an increase in offending between parent–child generations are not unique to immigrants, they are amplified in immigrant families. Whereas the second generation is remarkably similar to their U.S.-born counterparts in terms of their involvement in crime, suggesting a high degree of swift integration, the greater involvement in crime among the children of immigrants compared to their foreign-born mothers suggests a decline in well-being across successive generations.

scholarly journals Light element discontinuities suggest an early termination of star formation in the globular cluster NGC 6402 (M14)

2019 ◽  
Vol 485 (3) ◽  
pp. 4311-4329 ◽  
Author(s):  
Christian I Johnson ◽  
Nelson Caldwell ◽  
R Michael Rich ◽  
Mario Mateo ◽  
John I Bailey
Keyword(s):  
Globular Clusters ◽  
First Generation ◽  
Light Element ◽  
Chemical Abundances ◽  
Intermediate Composition ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
Red Giant ◽  
Composition Properties ◽  
Delayed Phase

ABSTRACT NGC 6402 is among the most massive globular clusters in the Galaxy, but little is known about its detailed chemical composition. Therefore, we obtained radial velocities and/or chemical abundances of 11 elements for 41 red giant branch stars using high resolution spectra obtained with the Magellan-M2FS instrument. We find NGC 6402 to be only moderately metal-poor with 〈[Fe/H]〉 = −1.13 dex (σ = 0.05 dex) and to have a mean heliocentric radial velocity of −61.1 km s−1 (σ = 8.5 km s−1). In general, NGC 6402 exhibits mean composition properties that are similar to other inner Galaxy clusters, such as [α/Fe] ∼+0.3 dex, [Cr,Ni/Fe] ∼ 0.0 dex, and 〈[La/Eu]〉 = −0.08 dex. Similarly, we find large star-to-star abundance variations for O, Na, Mg, Al, and Si that are indicative of gas that experienced high temperature proton-capture burning. Interestingly, we not only detect three distinct populations but also find large gaps in the [O/Fe], [Na/Fe], and [Al/Fe] distributions that may provide the first direct evidence of delayed formation for intermediate composition stars. A qualitative enrichment model is discussed where clusters form stars through an early ($\lesssim$5–10 Myr) phase, which results in first generation and ‘extreme’ composition stars, and a delayed phase ($\gtrsim$40 Myr), which results in the dilution of processed and pristine gas and the formation of intermediate composition stars. For NGC 6402, the missing intermediate composition stars suggest the delayed phase terminated prematurely, and as a result the cluster may uniquely preserve details of the chemical enrichment process.

scholarly journals Synthetic spectroscopic indices for identifying multiple stellar populations in globular clusters

2020 ◽  
Vol 493 (2) ◽  
pp. 2195-2206
Author(s):  
Emanuele Bertone ◽  
Miguel Chávez ◽  
J César Mendoza
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Populations ◽  
Stellar Model ◽  
Chemical Compositions ◽  
Horizontal Branch ◽  
Atmospheric Parameters ◽  
Data Set ◽  
Spectral Diagnostics ◽  
Red Giant

ABSTRACT We present an investigation of synthetic spectroscopic indices that can plausibly help in identifying the presence of multiple stellar populations in globular clusters. The study is based on a new grid of stellar model atmospheres and high-resolution (R  = 500 000) synthetic spectra, that consider chemical partitions that have been singled out in Galactic globular clusters. The data base is composed of 3472 model atmospheres and theoretical spectra calculated with the collection of Fortran codes DFSYNTHE, ATLAS9 and SYNTHE, developed by Robert L. Kurucz. They cover a range of effective temperature from 4300 to 7000 K, surface gravity from 2.0 to 5.0 dex and four different chemical compositions. A set of 19 spectroscopic indices were calculated from a degraded version (R  = 2500) of the theoretical spectra data set. The set includes five indices previously used in the context of globular clusters analyses and 14 indices that we have newly defined by maximizing the capability of differentiating the chemical compositions. We explored the effects of atmospheric parameters on the index values and identified the optimal spectral diagnostics that allow to trace the signatures of objects of different stellar populations, located in the main sequence, the red giant branch and the horizontal branch. We found a suitable set of indices, that mostly involve molecular bands (in particular NH, but also CH and CN), that are very promising for spectroscopically identifying multiple stellar populations in globular clusters.

scholarly journals Leveraging HST with MUSE – I. Sodium abundance variations within the 2-Gyr-old cluster NGC 1978

2020 ◽  
Vol 498 (3) ◽  
pp. 4472-4480
Author(s):  
S Saracino ◽  
S Kamann ◽  
C Usher ◽  
N Bastian ◽  
S Martocchia ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Large Magellanic Cloud ◽  
Host Galaxy ◽  
Very Large Telescope ◽  
Nearby Galaxies ◽  
Red Giant ◽  
Sodium Abundance ◽  
Massive Clusters ◽  
Cluster Age

ABSTRACT Nearly all of the well-studied ancient globular clusters (GCs), in the Milky Way and in nearby galaxies, show star-to-star variations in specific elements (e.g. He, C, N, O, Na, and Al), known as ‘multiple populations’ (MPs). However, MPs are not restricted to ancient clusters, with massive clusters down to ∼2 Gyr showing signs of chemical variations. This suggests that young and old clusters share the same formation mechanism but most of the work to date on younger clusters has focused on N variations. Initial studies even suggested that younger clusters may not host spreads in other elements beyond N (e.g. Na), calling into question whether these abundance variations share the same origin as in the older GCs. In this work, we combine Hubble Space Telescope (HST) photometry with Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy of a large sample of red giant branch (RGB) stars (338) in the Large Magellanic Cloud cluster NGC 1978, the youngest globular to date with reported MPs in the form of N spreads. By combining the spectra of individual RGB stars into N-normal and N-enhanced samples, based on the ‘chromosome map’ derived from HST, we search for mean abundance variations. Based on the NaD line, we find a Na difference of Δ[Na/Fe] = 0.07 ± 0.01 between the populations. While this difference is smaller than typically found in ancient GCs (which may suggest a correlation with age), this result further confirms that the MP phenomenon is the same, regardless of cluster age and host galaxy. As such, these young clusters offer some of the strictest tests for theories on the origin of MPs.

scholarly journals Is Mass Loss Along the Red Giant Branch of Globular Clusters Sharply Peaked? The Case of M3

2008 ◽  
Vol 673 (2) ◽  
pp. 847-853 ◽  
Author(s):  
Vittoria Caloi ◽  
Francesca D’Antona
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Red Giant

scholarly journals New population synthesis approach: The golden path to constrain stellar and galactic physics

2019 ◽  
Vol 15 (S357) ◽  
pp. 184-187
Author(s):  
Nadège Lagarde ◽  
Céline Reylé
Keyword(s):  
White Dwarfs ◽  
European Space Agency ◽  
Chemical Properties ◽  
Population Synthesis ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Red Giant ◽  
Stellar Masses ◽  
First Time ◽  
Synthesis Approach

AbstractThe cornerstone mission of the European Space Agency, Gaia, has revealed properties of 260 000 white dwarfs in the Galaxy, allowing us for the first time to constrain the evolution of white dwarfs with a large sample. Complementary surveys (CoRoT, Kepler, K2, APOGEE and Gaia-ESO), will revolutionize our understanding of the formation and history of our Galaxy, providing accurate stellar masses, radii, ages, distances, and chemical properties for very large samples of stars across different Galactic stellar populations. To exploit the potential of the combination of spectroscopic, seismic and astrometric observations, the population synthesis approach is a very crucial and efficient tool. We develop the Besançon Galaxy model (BGM, Lagarde et al.2017) for which stellar evolution predictions are included, providing the global asteroseismic properties and the surface chemical abundances along the evolution of low- and intermediate-mass stars. For the first time, the BGM can explore the effects of an extra-mixing occurring in red-giant stars Lagarde et al.2019, changing their stellar properties. The next step is to model a consistent treatment of giant stars and their remnants (e.g., white dwarfs). This kind of improvement would help us to constrain stellar and Galactic evolutions.

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