scholarly journals Helium-rich stars in globular clusters: constraints for self-enrichment by massive stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 135-140 ◽  
Author(s):  
Thibaut Decressin ◽  
G. Meynet ◽  
C. Charbonnel
Keyword(s):  
Globular Clusters ◽  
Massive Stars ◽  
Stellar Populations ◽  
The Self ◽  
Heavy Elements ◽  
Light Elements ◽  
Intracluster Gas ◽  
Fast Rotating

AbstractGlobular clusters exhibit peculiar chemical patterns where Fe and heavy elements are constant inside a given cluster while light elements (Li to Al) show strong star-to-star variations. This pattern can be explained by self-pollution of the intracluster gas by the slow winds of fast rotating massive stars. Besides, several main sequences have been observed in several globular clusters which can be understood only with different stellar populations with distinct He content. Here we explore how these He abundances can constrain the self-enrichment in globular clusters.

scholarly journals Spectroscopic studies of stellar populations in globular clusters and field stars: Implications for globular cluster and Milky Way halo formation

2019 ◽  
Vol 14 (S351) ◽  
pp. 241-250
Author(s):  
Raffaele Gratton
Keyword(s):  
Globular Clusters ◽  
Second Generation ◽  
Massive Stars ◽  
Stellar Populations ◽  
Spectroscopic Studies ◽  
Chemical Compositions ◽  
Agb Stars ◽  
Intermediate Mass ◽  
Massive Clusters ◽  
Fast Rotating

AbstractWe review spectroscopic results concerning multiple stellar populations in globular clusters. The cluster initial mass is the most important parameter determining the fraction of second generation stars. The threshold for the onset of the multiple population phenomenon is 1–3×105 M⊙. Nucleosynthesis is influenced by metallicity: Na/O and Mg/Al anti-correlations are more extended in metal-poor than in metal-rich clusters. Massive clusters are more complex systems than the smaller ones, with several populations characterized by different chemical compositions. The high Li abundance observed in the intermediate second generation stars strongly favours intermediate mass AGB stars as polluters for this class of stars; however, it is well possible that the polluters of extreme second generation stars, that often do not have measurable Li, may be fast rotating massive stars or super-massive stars. The mass budget factor should be a function of the cluster mass, and needs to be large only in massive clusters.

scholarly journals Non-standard s-process in massive rotating stars

2018 ◽  
Vol 618 ◽  
pp. A133 ◽  
Author(s):  
Arthur Choplin ◽  
Raphael Hirschi ◽  
Georges Meynet ◽  
Sylvia Ekström ◽  
Cristina Chiappini ◽  
...  
Keyword(s):  
Critical Velocity ◽  
Rotation Rate ◽  
Reaction Rate ◽  
Massive Stars ◽  
Strong Impact ◽  
Light Elements ◽  
Rotating Stars ◽  
Stellar Models ◽  
Fast Rotating

Context. Recent studies show that rotation significantly affects the s-process in massive stars. Aims. We provide tables of yields for non-rotating and rotating massive stars between 10 and 150 M⊙ at Z = 10−3 ([Fe/H] = −1.8). Tables for different mass cuts are provided. The complete s-process is followed during the whole evolution with a network of 737 isotopes, from hydrogen to polonium. Methods. A grid of stellar models with initial masses of 10, 15, 20, 25, 40, 60, 85, 120, and 150 M⊙ and with an initial rotation rate of both 0% or 40% of the critical velocity was computed. Three extra models were computed in order to investigate the effect of faster rotation (70% of the critical velocity) and of a lower 17O(α, γ) reaction rate. Results. At the considered metallicity, rotation has a strong impact on the production of s-elements for initial masses between 20 and 60 M⊙. In this range, the first s-process peak is boosted by 2−3 dex if rotation is included. Above 60 M⊙, s-element yields of rotating and non-rotating models are similar. Increasing the initial rotation from 40% to 70% of the critical velocity enhances the production of 40 ≲ Z ≲ 60 elements by ∼0.5−1 dex. Adopting a reasonably lower 17O(α, γ) rate in the fast-rotating model (70% of the critical velocity) boosts again the yields of s-elements with 55 ≲ Z ≲ 82 by about 1 dex. In particular, a modest amount of Pb is produced. Together with s-elements, some light elements (particularly fluorine) are strongly overproduced in rotating models.

scholarly journals The Concept of Old Stellar Populations

1983 ◽  
Vol 6 ◽  
pp. 95-100
Author(s):  
Gösta Lyngå
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Age Groups ◽  
Stellar Populations ◽  
Heavy Elements ◽  
The Galaxy ◽  
Star Formation In Galaxies ◽  
Solar Abundances ◽  
Central Bulge ◽  
Stellar Envelopes

Almost 25 years ago Walter Baade told the Vatican conference about the meaning of stellar populations:“We also understand now why the two stellar populations, either singly or combined, are such conspicuous features in most galaxies. They are age groups which represent two significant phases of the star formation in galaxies.”There appeared a straight-forward picture with an old, metal-poor halo containing stars in elongated galactic orbits and a younger disk population, where the stars have near solar abundances and near circular orbits. The central bulge of the galaxy was considered part of the older system.New observations have made the picture more complex and also more controversial, indicating that it still might not be fully understood. Stars in the bulge of our spiral galaxy have been shown to have rather high contents of heavy elements. The gas and perhaps also the stars of the disk show a metal content that is decreasing outwards in the disk. The abundances in globular clusters differ widely between individual clusters and even between individual stars of the same cluster. It has become clear that one must discuss separately the different heavy elements; that some abundances may be considered primordial and thus characteristic of the evolution of the stellar population, whereas other abundance differences may be caused by mixing into the stellar envelopes.

scholarly journals Dynamical implications of multiple stellar populations

2006 ◽  
Vol 2 (14) ◽  
pp. 436-437
Author(s):  
Alison I. Sills ◽  
Jonathan M. Downing
Keyword(s):  
Star Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Stellar Populations ◽  
The Self ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Early Generation ◽  
Single Burst

AbstractWe investigate some implications of having two star formation episodes in globular clusters, rather than the traditional single-burst approximation. Evidence for more than one stellar generation is accumulating in observations of abundances of elements lighter than iron in globular cluster stars, and is thought to imply some self-enrichment of the globular cluster gas. In particular, we explore models based on the assumption that the self-enrichment comes from an early generation of asymptotic giant branch (AGB) stars.

scholarly journals The quite complex “Simple Stellar Populations” of globular clusters

2009 ◽  
Vol 5 (S268) ◽  
pp. 119-128
Author(s):  
Angela Bragaglia
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Populations ◽  
Observational Evidence ◽  
Formation Mechanisms ◽  
Light Elements ◽  
Complex Objects ◽  
Growing Body ◽  
Iron Abundance ◽  
The Many

AbstractThere is compelling observational evidence that globular clusters (GCs) are quite complex objects. A growing body of photometric results indicate that the evolutionary sequences are not simply isochrones in the observational plane -as believed until a few years ago- from the main sequence, to the subgiant, giant, and horizontal branches. The strongest indication of complexity comes however from the chemistry, from internal dispersion in iron abundance in a few cases, and in light elements (C, N, O, Na, Mg, Al, etc.) in all GCs. This universality means that the complexity is intrinsic to the GCs and is most probably related to their formation mechanisms. The extent of the variations in light elements abundances is dependent on the GC mass, but mass is not the only modulating factor; metallicity, age, and possibly orbit can play a role. Finally, one of the many consequences of this new way of looking at GCs is that their stars may show different He contents.

scholarly journals Fast rotating massive stars and the origin of the abundance patterns in galactic globular clusters

2007 ◽  
Vol 464 (3) ◽  
pp. 1029-1044 ◽  
Author(s):  
T. Decressin ◽  
G. Meynet ◽  
C. Charbonnel ◽  
N. Prantzos ◽  
S. Ekström
Keyword(s):  
Globular Clusters ◽  
Massive Stars ◽  
Abundance Patterns ◽  
Galactic Globular Clusters ◽  
Fast Rotating

scholarly journals Chemical abundances of multiple stellar populations in massive globular clusters

2015 ◽  
Vol 12 (S316) ◽  
pp. 267-274 ◽  
Author(s):  
Anna F. Marino
Keyword(s):  
Neutron Capture ◽  
Globular Clusters ◽  
Milky Way ◽  
Stellar Populations ◽  
Slow Neutron ◽  
Light Elements ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Origin And Evolution

AbstractMultiple stellar populations in the Milky Way globular clusters manifest themselves with a large variety. Although chemical abundance variations in light elements, including He, are ubiquitous, the amount of these variations is different in different globulars. Stellar populations with distinct Fe, C+N+O and slow-neutron capture elements have been now detected in some globular clusters, whose number will likely increase. All these chemical features correspond to specific photometric patterns. I review the chemical+photometric features of the multiple stellar populations in globular clusters and discuss how the interpretation of data is being more and more challenging. Very excitingly, the origin and evolution of globular clusters is being a complex puzzle to compose.

scholarly journals Empirical estimates of the Na–O anti-correlation in 95 Galactic globular clusters

2019 ◽  
Vol 624 ◽  
pp. A24 ◽  
Author(s):  
Eugenio Carretta
Keyword(s):  
Globular Clusters ◽  
Structural Parameters ◽  
Stellar Populations ◽  
Red Giants ◽  
Light Elements ◽  
Empirical Estimates ◽  
Bivariate Correlation ◽  
Identity Line ◽  
Consistent Picture ◽  
Galactic Globular Clusters

Large star-to-star abundance variations are direct evidence of multiple stellar populations in Galactic globular clusters (GCs). The main and most widespread chemical signature is the anti-correlation of the stellar Na and O abundances. The interquartile range (IQR) of the [O/Na] ratio is well suited to quantifying the extent of the anti-correlation and to probe its links to global cluster parameters. However, since it is quite time consuming to obtain precise abundances from spectroscopy for large samples of stars in GCs, here we show empirical calibrations of IQR[O/Na] based on the O, Na abundances homogeneously derived from more than 2000 red giants in 22 GCs in our FLAMES survey. We find a statistically robust bivariate correlation of IQR as a function of the total luminosity (a proxy for mass) and cluster concentration c. Calibrated and observed values lie along the identity line when a term accounting for the horizontal branch (HB) morphology is added to the calibration, from which we obtained empirical values for 95 GCs. Spreads in proton-capture elements O and Na are found for all GCs in the luminosity range from MV = −3.76 to MV = −9.98. This calibration reproduces in a self-consistent picture the link of abundance variations in light elements with the He enhancements and its effect on the stellar distribution on the HB. We show that the spreads in light elements seem already to be dependent on the initial GC masses. The dependence of IQR on structural parameters stems from the well known correlation between c and MV, which is likely to be of primordial origin. Empirical estimates can be used to extend our investigation of multiple stellar populations to GCs in external galaxies, up to M 31, where even integrated light spectroscopy may currently provide only a hint of such a phenomenon.

Scattering-angle dependence of signal/background ratio of inner-shell electron excitation loss in EELS

1983 ◽  
Vol 41 ◽  
pp. 390-391
Author(s):  
T. Oikawa ◽  
M. Inoue ◽  
T. Honda ◽  
Y. Kokubo
Keyword(s):  
Energy Loss ◽  
Electron Excitation ◽  
Heavy Elements ◽  
Background Intensity ◽  
Light Elements ◽  
Energy Analyzer ◽  
High Background ◽  
Scattering Angle ◽  
Angle Dependence ◽  
Shell Electron

EELS allows us to make analysis of light elements such as hydrogen to heavy elements of microareas on the specimen. In energy loss spectra, however, elemental signals ride on a high background; therefore, the signal/background (S/B) ratio is very low in EELS. A technique which collects the center beam axial-symmetrically in the scattering angle is generally used to obtain high total intensity. However, the technique collects high background intensity together with elemental signals; therefore, the technique does not improve the S/B ratio. This report presents the experimental results of the S/B ratio measured as a function of the scattering angle and shows the possibility of the S/B ratio being improved in the high scattering angle range.Energy loss spectra have been measured using a JEM-200CX TEM with an energy analyzer ASEA3 at 200 kV.Fig.l shows a typical K-shell electron excitation edge riding on background in an energy loss spectrum.

Kinematical evolution of Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 524-527
Author(s):  
Maria A. Tiongco ◽  
Enrico Vesperini ◽  
Anna Lisa Varri
Keyword(s):  
Angular Momentum ◽  
Structural Properties ◽  
Globular Clusters ◽  
Velocity Dispersion ◽  
Three Dimensional ◽  
Stellar Populations ◽  
Velocity Space ◽  
Fundamental Understanding

AbstractWe present several results of the study of the evolution of globular clusters’ internal kinematics, as driven by two-body relaxation and the interplay between internal angular momentum and the external Galactic tidal field. Via a large suite of N-body simulations, we explored the three-dimensional velocity space of tidally perturbed clusters, by characterizing their degree of velocity dispersion anisotropy and their rotational properties. These studies have shown that a cluster’s kinematical properties contain distinct imprints of the cluster’s initial structural properties, dynamical history, and tidal environment. Building on this fundamental understanding, we then studied the dynamics of multiple stellar populations in globular clusters, with attention to the largely unexplored role of angular momentum.

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