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.

APOGEE Chemical Anomalies discovered everywhere in the Milky Way: Giant stars with GC-like abundance patterns

2017 ◽  
Vol 13 (S334) ◽  
pp. 285-287 ◽  
Author(s):  
J. G. Fernández-Trincado
Keyword(s):  
Globular Cluster ◽  
Second Generation ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Galactic Bulge ◽  
Giant Stars ◽  
Abundance Patterns ◽  
Chemical Anomalies

AbstractWe report the discovery by APOGEE of five mildly metal-poor ([Fe/H] >−1) anomalous giant stars in the halo/disk/bulge Galaxy with abundances of C, N, and Al that are typically found in globular cluster stars (GCs, see e.g. Carretta et al. 2009a; Mészáros et al. 2015; Pancino et al. 2017; Schiavon et al. 2017a; Tang et al. 2017) and in the inner Galaxy (e.g., Schiavon et al. 2017b; Recio-Blanco et al. 2017) simultaneously with atypical abundances of Mg (Mg-poor: [Mg/Fe] < 0) never before seen in Milky Way (MW) GCs, dwarf galaxies (see Hasselquist et al. 2017) neither in MW field stars. Additionally, four new moderately metal-poor ([Fe/H] <−1) anomalous giant stars (i.e., N-rich, Al-rich and C-poor) with trustly GCs second-generation like chemical patterns were identified within the Galactic bulge, halo and disk field.

Hydrodynamic simulations of second generation star formation in a young globular cluster

2019 ◽  
Vol 14 (S351) ◽  
pp. 269-272
Author(s):  
Francesco Calura
Keyword(s):  
Star Formation ◽  
Globular Cluster ◽  
Second Generation ◽  
Three Dimensional ◽  
Asymptotic Giant Branch ◽  
Central Density ◽  
Agb Stars ◽  
Hydrodynamic Simulations ◽  
Numerical Studies

AbstractI will present results obtained by means of three-dimensional hydrodynamic simulations of the formation of second generation (SG) stars in a young globular cluster (GC). Our setup includes the mass return from Asymptotic Giant branch (AGB) stars, the accretion of pristine gas as well as star formation of SG stars, three ingredients which have never been simultaneously taken into account in previous 3D numerical studies of GC formation. The cluster is set in motion with respect to a distribution of gas and allowed to accrete mass from it. Formation of SG stars occurs out of the gas shed by AGB stars and from the gas accreted during the motion of the cluster. We consider two models characterised by different densities of the external gas. In both cases, we find that a very compact SG subsystem with central density > 105M⊙/pc3 forms in the innermost regions of the cluster.

scholarly journals Jurassic: A chemically anomalous structure in the Galactic halo

2020 ◽  
Vol 644 ◽  
pp. A83
Author(s):  
José G. Fernández-Trincado ◽  
Timothy C. Beers ◽  
Dante Minniti
Keyword(s):  
Globular Clusters ◽  
Galactic Halo ◽  
Chemical Species ◽  
Elemental Abundance ◽  
Evolutionary Stage ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Wide Range ◽  
Evolution Experiment ◽  
C And N

Detailed elemental-abundance patterns of giant stars in the Galactic halo measured by the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have revealed the existence of a unique and significant stellar subpopulation of silicon-enhanced ([Si/Fe] ≳ +0.5) metal-poor stars, spanning a wide range of metallicities (−1.5 ≲ [Fe/H] ≲ −0.8). Stars with over-abundances in [Si/Fe] are of great interest because these have very strong silicon (28Si) spectral features for stars of their metallicity and evolutionary stage, offering clues about rare nucleosynthetic pathways in globular clusters (GCs). Si-rich field stars have been conjectured to have been evaporated from GCs, however, the origin of their abundances remains unclear, and several scenarios have been offered to explain the anomalous abundance ratios. These include the hypothesis that some of them were born from a cloud of gas previously polluted by a progenitor that underwent a specific and peculiar nucleosynthesis event or, alternatively, that they were due to mass transfer from a previous evolved companion. However, those scenarios do not simultaneously explain the wide gamut of chemical species that are found in Si-rich stars. Instead, we show that the present inventory of such unusual stars, as well as their relation to known halo substructures (including the in situ halo, Gaia-Enceladus, the Helmi Stream(s), and Sequoia, among others), is still incomplete. We report the chemical abundances of the iron-peak (Fe), the light- (C and N), the α- (O and Mg), the odd-Z (Na and Al), and the s-process (Ce and Nd) elements of 55 newly identified Si-rich field stars (among more than ∼600 000 APOGEE-2 targets), which exhibit over-abundances of [Si/Fe] as extreme as those observed in some Galactic GCs, and they are relatively well distinguished from other stars in the [Si/Fe]−[Fe/H] plane. This new census confirms the presence of a statistically significant and chemically-anomalous structure in the inner halo: Jurassic. The chemo-dynamical properties of the Jurassic structure is consistent with it being the tidally disrupted remains of GCs, which are easily distinguished by an over-abundance of [Si/Fe] among Milky Way populations or satellites.

scholarly journals Why the globular cluster NGC 6752 contains no sodium-rich second-generation AGB stars

2013 ◽  
Vol 557 ◽  
pp. L17 ◽  
Author(s):  
Corinne Charbonnel ◽  
William Chantereau ◽  
Thibaut Decressin ◽  
Georges Meynet ◽  
Daniel Schaerer
Keyword(s):  
Globular Cluster ◽  
Second Generation ◽  
Agb Stars

scholarly journals The Oldest Stars as Tracers of Heavy Element Formation at Early Epochs

2001 ◽  
Vol 204 ◽  
pp. 333-334 ◽  
Author(s):  
James W. Truran
Keyword(s):  
Star Formation ◽  
Theoretical Models ◽  
Elemental Abundance ◽  
Agb Stars ◽  
Lower Mass ◽  
Set Constraints ◽  
Abundance Patterns ◽  
History Of ◽  
R Process ◽  
Process Elements

Elemental abundance patterns in very metal-poor halo field stars and globular cluster stars play a crucial role both in guiding theoretical models of nucleosynthesis and in providing constraints upon the early star formation and concomitant nucleosynthesis history of our Galaxy. The abundance patterns characterizing the oldest and most metal deficient stars ([Fe/H] ≤ −3) are entirely consistent with their being products of metal-poor massive stars of lifetimes τ ≤ 108years. This includes both the elevated abundances of thealpha-elements (O, Mg, Si, S, Ca, and Ti) relative to iron-peak elements and the dominance of r-process elements over s-process elements. The nucleosynthetic contributions of lower mass AGB stars of longer lifetimes (τ ≈ 109years) begin to appear at metallicities [Fe/H] ≈ −2.5, while clear evidence for iron-peak nuclei produced in supernovae Ia (τ ≥ 1-2x109years?) does not appear until metallicities approaching [Fe/H] ~ −1. Similar trends are also suggested by abundances determined for gas clouds at high redshifts. We review the manner in which a knowledge of the abundances of the stellar and gas components of early populations, as a function of [Fe/H], time, and/or redshift, can be used to set constraints on their star formation and nucleosynthesis histories.

scholarly journals Galactic or extragalactic chemical tagging for NGC 3201?

2018 ◽  
Vol 614 ◽  
pp. A146 ◽  
Author(s):  
B. Dias ◽  
I. Araya ◽  
J. P. Nogueira-Cavalcante ◽  
L. Saker ◽  
A. Shokry
Keyword(s):  
High Resolution ◽  
Globular Cluster ◽  
High Resolution Spectroscopy ◽  
Low Resolution ◽  
Element Abundances ◽  
Giant Stars ◽  
Mass Size ◽  
Red Giant ◽  
Process Element ◽  
Size Relation

Context. The origin of the globular cluster (GC) NGC 3201 is under debate. Its retrograde orbit points to an extragalactic origin, but no further chemical evidence supports this idea. Light-element chemical abundances are useful to tag GCs and can be used to shed light on this discussion. Aims. Recently it was shown that the CN and CH indices are useful to identify GCs that are anomalous to those typically found in the Milky Way. A possible origin of anomalous clusters is the merger of two GCs and/or the nucleus of a dwarf galaxy. We aim to derive CN and CH band strengths for red giant stars in NGC3201 and compare these with photometric indices and high-resolution spectroscopy and discuss in the context of GC chemical tagging. Methods. We measure molecular band indices of S(3839) and G4300 for CN and CH, respectively from low-resolution spectra of red giant stars. Gravity and temperature effects are removed. Photometric indices are used to indicate further chemical information on C+N+O or s-process element abundances that are not derived from low-resolution spectra. Results. We found three groups in the CN–CH distribution. A main sequence (S1), a secondary less-populated sequence (S2), and a group of peculiar (pec) CN-weak and CH-weak stars, one of which was previously known. The three groups seem to have different C+N+O and/or s-process element abundances, to be confirmed by high-resolution spectroscopy. These are typical characteristics of anomalous GCs. The CN distribution of NGC 3201 is quadrimodal, which is more common in anomalous clusters. However, NGC 3201 does not belong to the trend of anomalous GCs in the mass-size relation. Conclusions. The globular cluster NGC 3201 shows signs that it can be chemically tagged as anomalous: it has an unusual CN–CH relation, indications that pec-S1-S2 is an increasing sequence of C+N+O or s-process element abundances, and a multi-modal CN distribution that seems to correlate with s-process element abundances. The non-anomalous characteristics are that it has a debatable Fe-spread and it does not follow the trend of mass size of all anomalous clusters. Three scenarios are postulated here: (i) if the sequence pec-S1-S2 has increasing C+N+O and s-process element abundances, NGC 3201 would be the first anomalous GC outside of the mass-size relation; (ii) if the abundances are almost constant, NGC 3201 would be the first non-anomalous GC with multiple CN–CH anti-correlation groups; or (iii) it would be the first anomalous GC without variations in C+N+O and s-process element abundances. In all cases, the definition of anomalous clusters and the scenario in which they have an extragalactic origin must be revised.

scholarly journals Globular cluster contributions to Galactic halo assembly

2012 ◽  
Vol 10 (H16) ◽  
pp. 286-287
Author(s):  
Sarah L. Martell
Keyword(s):  
Star Formation ◽  
Globular Cluster ◽  
Second Generation ◽  
Galactic Halo ◽  
Cluster Formation ◽  
Light Element ◽  
Element Abundances ◽  
Giant Stars ◽  
Red Giant

AbstractI discuss a search for red giant stars in the Galactic halo with light-element abundances similar to second-generation globular cluster stars, and discuss the implications of such a population for globular cluster formation models and the balance between in situ star formation and accretion for the assembly of the Galactic halo.

scholarly journals Core Collapse Supernova Models and Nucleosynthesis

2013 ◽  
Vol 9 (S296) ◽  
pp. 27-36
Author(s):  
Ken'ichi Nomoto
Keyword(s):  
Big Bang ◽  
Elemental Abundance ◽  
Core Collapse ◽  
Solar Abundance ◽  
First Stars ◽  
Abundance Pattern ◽  
Core Collapse Supernova ◽  
Abundance Patterns ◽  
Supernova Explosions ◽  
The Big Bang

AbstractAfter the Big Bang, production of heavy elements in the early Universe takes place in the first stars and their supernova explosions. The nature of the first supernovae, however, has not been well understood. The signature of nucleosynthesis yields of the first supernovae can be seen in the elemental abundance patterns observed in extremely metal-poor stars. Interestingly, those abundance patterns show some peculiarities relative to the solar abundance pattern, which should provide important clues to understanding the nature of early generations of supernovae. We review the recent results of the nucleosynthesis yields of massive stars. We examine how those yields are affected by some hydrodynamical effects during the supernova explosions, namely, explosion energies from those of hypernovae to faint supernovae, mixing and fallback of processed materials, asphericity, etc. Those parameters in the supernova nucleosynthesis models are constrained from observational data of supernovae and metal-poor stars.

Metallicity, pulsation and mass loss in globular cluster low-mass AGB stars

2009 ◽  
Author(s):  
Iain McDonald ◽  
Jacco Th. van Loon ◽  
Martha L. Boyer ◽  
Eric Stempels
Keyword(s):  
Mass Loss ◽  
Globular Cluster ◽  
Agb Stars ◽  
Low Mass

scholarly journals Are Galactic globular cluster AGB stars rich or poor in Sodium? Sodium abundance of AGB and RGB stars in NGC 2808

2015 ◽  
Vol 12 (S316) ◽  
pp. 361-362
Author(s):  
Yue Wang ◽  
Francesca Primas ◽  
Corinne Charbonnel ◽  
Mathieu Van der Swaelmen ◽  
William Chantereau ◽  
...  
Keyword(s):  
Spectroscopic Study ◽  
Globular Cluster ◽  
Main Sequence ◽  
Significant Fraction ◽  
Agb Stars ◽  
2Nd Generation ◽  
Red Giant ◽  
Sodium Abundance

AbstractA spectroscopic study comparing the [Na/Fe] distributions of RGB and AGB stars in the Galactic globular cluster (GC) NGC 6752 found that there was no Na-rich, 2nd-generation star along the early-AGB of this cluster. This came as a surprise since in this GC, as well as other Galactic GCs studied so far, 1st- and 2nd-generation stars have usually been found from the main sequence turnoff up to the red giant branch. To investigate whether the failure of a significant fraction of stars to ascend the AGB also happens to other GCs, we studied a sample of AGB and RGB stars in NGC 2808 observed at the ESO/VLT with FLAMES. Contrary to NGC 6752, we find that the AGB and RGB stars we studied in NGC 2808 have comparable [Na/Fe] dispersions.

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