scholarly journals The Helium contribution from massive AGBs

2009 ◽  
Vol 5 (S268) ◽  
pp. 147-152
Author(s):  
Paolo Ventura
Keyword(s):  
Interstellar Medium ◽  
Globular Clusters ◽  
Second Generation ◽  
The Self ◽  
Agb Stars ◽  
Two Populations

AbstractThe helium produced by AGB and super-AGB stars is a key quantity to understand whether these objects may have been the main polluters of the interstellar medium within globular clusters, and originate a second generation of stars with a chemistry showing the imprinting of their ejecta. Helium is the most important element for this topic, as any difference in the original helium between the two populations would determine clearly distinguishable features both in the morphology of the Horizontal Branches and in the Main Sequences. We present the helium yields from massive AGB stars, and show that the results are rather robust, being approximately independent of the various uncertainties that affect the description of the evolution of these stars. The implications for the self-enrichment scenario are discussed and commented.

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 Lithium factories in the Galaxy: novae and AGB stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 395-404 ◽  
Author(s):  
Francesca D'Antona ◽  
Paolo Ventura
Keyword(s):  
Globular Clusters ◽  
Second Generation ◽  
State Of The Art ◽  
The State ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Preliminary Results ◽  
The Galaxy

AbstractWe review the state of the art in modelling lithium production, through the Cameron–Fowler mechanism, in two stellar sites: during nova explosions and in the envelopes of massive asymptotic giant branch (AGB) stars. We also show preliminary results concerning the computation of lithium yields from super–AGBs, and suggest that super–AGBs of metallicity close to solar may be the most important galactic lithium producers. Finally, we discuss how lithium abundances may help to understand the modalities of formation of the “second generation” stars in globular clusters.

scholarly journals The pollution of the interstellar medium from AGB stars in Globular Clusters

2012 ◽  
Vol 10 (H16) ◽  
pp. 249-250
Author(s):  
Paolo Ventura ◽  
Roberta Carini
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
The Self ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Initial Value ◽  
Low Metallicity ◽  
Giant Branch Stars ◽  
High Metallicity

AbstractWe discuss the yields from Asymptotic Giant Branch stars, depending on their mass and metallicity. In agreement with previous investigations, we find that the extent of Hot Bottom Burning increases with mass. The yields of models with chemistry typical of high–metallicity Globular Clusters, i.e. Z = 0.008, show only a modest depletion of magnesium, and an oxgen depletion of ~ 0.4 dex. Low–metallicity yields show a much stronger magnesium depletion, and a dramatic drop in the oxygen content, ~ 1.2dex smaller than the initial value. We suggest that the Globular Cluster NGC 2419 is a possible target to the hypothesis of the self–enrichment scenario of Globular Clusters by the winds of Asymptotic Giant Branch stars.

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 Discovery of Infrared Stars in Globular Clusters in the Magellanic Clouds and Their Light Variations

1998 ◽  
Vol 11 (1) ◽  
pp. 395-395
Author(s):  
S. Nishida ◽  
T. Tanabé ◽  
S. Matsumoto ◽  
T. Onaka ◽  
Y. Nakada ◽  
...  
Keyword(s):  
Mass Loss ◽  
Globular Clusters ◽  
Main Sequence ◽  
Near Infrared ◽  
Magellanic Clouds ◽  
Infrared Light ◽  
Agb Stars ◽  
Dust Shells ◽  
Infrared Stars ◽  
Infrared Survey

A systematic near-infrared survey was made for globular clusters in the Magellanic Clouds. Two infrared stars were discovered in NGC419 (SMC) and NGC1783 (LMC). NGC419 and NGC1783 are well-studied rich globular clusters whose turn-off masses and ages are estimated MTO ~ 2.0 Mʘ and т ~1.2 Gyr for NGC419, and MT0 ~ 2.0 Mʘ and т ʘ 0.9 Gyr for NGC1783, respectively. The periods of the infrared light variations were determined to be 540 dfor NGC419IR1 and to be 480 d for NGC1783IR1, respectively. Comparison of the measurements with the period—if magnitude relation for carbon Miras in the LMC by Groenewegen and Whitelock(1996) revealed that the Kmagnitudes of the infrared stars were fainter by about 0.3 — 0.8 magnitude than those predicted by the P — K relation. This deviation can be explained if the infrared stars are surrounded by thick dust shells and are obscured even in the K band. The positions of NGC419IR1and NGC1783IR1 on the P — K diagram suggest that AGB stars with the main sequence masses of about 2 Mʘ start their heavy mass-loss when P ʘ 500 d.

scholarly journals H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia

2019 ◽  
Vol 627 ◽  
pp. A178 ◽  
Author(s):  
J. G. Fernández-Trincado ◽  
O. Zamora ◽  
Diogo Souto ◽  
R. E. Cohen ◽  
F. Dell’Agli ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Second Generation ◽  
Elemental Abundance ◽  
Agb Stars ◽  
Giant Stars ◽  
Abundance Patterns ◽  
Evolution Experiment ◽  
Band Spectra ◽  
Stellar Sources ◽  
Process Element

We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea that NGC 6522 stars are formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary polluters of intra-cluster medium. The peculiar abundance signatures of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.

scholarly journals The peculiar kinematics of the multiple populations in the globular cluster Messier 80 (NGC 6093)

2019 ◽  
Vol 492 (1) ◽  
pp. 966-977 ◽  
Author(s):  
S Kamann ◽  
E Dalessandro ◽  
N Bastian ◽  
J Brinchmann ◽  
M den Brok ◽  
...  
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Evolutionary History ◽  
Hubble Space Telescope ◽  
Light Element ◽  
Nitrogen Enrichment ◽  
Element Abundances ◽  
Angular Momenta ◽  
Uv Photometry ◽  
Two Populations

ABSTRACT We combine MUSE spectroscopy and Hubble Space Telescope ultraviolet (UV) photometry to perform a study of the chemistry and dynamics of the Galactic globular cluster Messier 80 (M80, NGC 6093). Previous studies have revealed three stellar populations that vary not only in their light-element abundances, but also in their radial distributions, with the concentration decreasing with increasing nitrogen enrichment. This remarkable trend, which sets M80 apart from other Galactic globular clusters, points towards a complex formation and evolutionary history. To better understand how M80 formed and evolved, revealing its internal kinematics is key. We find that the most N-enriched population rotates faster than the other two populations at a 2σ confidence level. While our data further suggest that the intermediate population shows the least amount of rotation, this trend is rather marginal (1−2σ). Using axisymmetric Jeans models, we show that these findings can be explained from the radial distributions of the populations if they possess different angular momenta. Our findings suggest that the populations formed with primordial kinematical differences.

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