Magnesium isotopes: a tool to understand self-enrichment in globular clusters

Ventura, P.; D’Antona, F.; Imbriani, G.; Criscienzo, M. Di; Dell’Agli, F.; Tailo, M.

doi:10.1093/mnras/sty635

Cited by 17 publications

(16 citation statements)

References 85 publications

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“…As a result the P2 fraction may be unusually high in NGC 6402, especially when compared against the NGC 2808 P2 component that constitutes only 25 per cent of the Carretta (2015) sample. Shetrone 1996;Yong et al 2003;Sneden et al 2004;Da Costa et al 2013;Ventura et al 2018). Although the P2 gas could have been burned at higher temperatures and then diluted with "pristine" P1 composition material, no single dilution model fits through the P1, P2, and E populations shown in Fig.…”

Section: Population Ratiosmentioning

confidence: 99%

“…The first generation stars are characterized as having light element compositions that mirror those of similar metallicity halo field stars (e.g., Sneden et al 2004) while the second generation groups tend to have lower C, O, and Mg abundances and higher He, N, Na, and Al abundances. Aside from a general consensus that second generation stars likely formed from gas that was processed at temperatures exceeding 40−80 MK (e.g., Langer et al 1993;Prantzos et al 2007;Denissenkov et al 2015;Ventura et al 2018), little agreement exists regarding the origins of the (anti-)correlated light element variations. Various enrichment sites have been proposed, including intermediate mass asymptotic giant branch (AGB) stars (e.g., Ventura & D'Antona 2009;Karakas et al 2014), fast rotating massive stars (e.g., Decressin et al 2007;Krause et al 2013), interacting massive binary stars (de Mink et al 2009;Bastian et al 2013), Wolf-Rayet stars (Smith 2006), white dwarf novae (Maccarone & Zurek 2012), black hole accretion disks (Breen 2018), and supermassive stars (Denissenkov & Hartwick 2014).…”

Section: Introductionmentioning

confidence: 99%

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

Johnson

Caldwell

Rich

et al. 2019

Monthly Notices of the Royal Astronomical Society

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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 cluster members 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 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 ( < ∼ 5−10 Myr) phase, which results in first generation and "extreme" composition stars, and a delayed phase ( > ∼ 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.

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Section: Population Ratiosmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Johnson

Caldwell

Rich

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Gay & Lambert 2000;Yong et al 2003;Meléndez & Cohen 2009;Agafonova et al 2011). Comparisons between GCE models and observations have been used for example to constrain star formation rates on cosmological timescales (Vangioni & Olive 2019), to determine the onset of the contribution of AGB stars to GCE (Fenner et al 2003;Meléndez & Cohen 2007), to establish the timescale for the formation of the Galactic halo (Carlos et al 2018), or to understand self-enrichment in globular clusters (Ventura et al 2018). All three stable magnesium isotopes can be formed in both massive and intermediate-mass stars, however massive stars are not able to produce the heavier isotopes 25,26 Mg in significant amounts (see Timmes et al 1995;Alibés et al 2001), as opposed to low-metallicity AGB stars (Karakas & Lattanzio 2003).…”

Section: Preliminary Exploration Of the Implications On Galactic Chemical Evolutionmentioning

confidence: 99%

Nucleosynthetic yields of Z = 10⁻⁵ intermediate-mass stars

Gil‐Pons

Doherty

Gutiérrez

et al. 2020

A&A

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Context. Observed abundances of extremely metal-poor stars in the Galactic halo hold clues for understanding the ancient universe. Interpreting these clues requires theoretical stellar models in a wide range of masses in the low-metallicity regime. The existing literature is relatively rich with extremely metal-poor massive and low-mass stellar models. However, relatively little information is available on the evolution of intermediate-mass stars of Z ≲ 10−5, and the impact of the uncertain input physics on the evolution and nucleosynthesis has not yet been systematically analysed. Aims. We aim to provide the nucleosynthetic yields of intermediate-mass Z = 10−5 stars between 3 and 7.5 M⊙, and quantify the effects of the uncertain wind rates. We expect these yields could eventually be used to assess the contribution to the chemical inventory of the early universe, and to help interpret abundances of selected C-enhanced extremely metal-poor (CEMP) stars. Methods. We compute and analyse the evolution of surface abundances and nucleosynthetic yields of Z = 10−5 intermediate-mass stars from their main sequence up to the late stages of their thermally pulsing (Super) AGB phase, with different prescriptions for stellar winds. We use the postprocessing code MONSOON to compute the nucleosynthesis based on the evolution structure obtained with the Monash-Mount Stromlo stellar evolution code MONSTAR. By comparing our models and others from the literature, we explore evolutionary and nucleosynthetic trends with wind prescriptions and with initial metallicity (in the very low-Z regime). We also compare our nucleosynthetic yields to observations of CEMP-s stars belonging to the Galactic halo. Results. The yields of intermediate-mass extremely metal-poor stars reflect the effects of very deep or corrosive second dredge-up (for the most massive models), superimposed with the combined signatures of hot-bottom burning and third dredge-up. Specifically, we confirm the reported trend that models with initial metallicity Zini ≲ 10−3 give positive yields of 12C, 15N, 16O, and 26Mg. The 20Ne, 21Ne, and 24Mg yields, which were reported to be negative at Zini ≳ 10−4, become positive for Z = 10−5. The results using two different prescriptions for mass-loss rates differ widely in terms of the duration of the thermally pulsing (Super) AGB phase, overall efficiency of the third dredge-up episode, and nucleosynthetic yields. We find that the most efficient of the standard wind rates frequently used in the literature seems to favour agreement between our yield results and observational data. Regardless of the wind prescription, all our models become N-enhanced EMP stars.

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“…• understanding the role played by intermediate-mass stars in the self-enrichment scenario of globular clusters. [25][26][27][28][29][30] 2.2 A recent use of our AGB models: interpretation of the extreme He-rich population of NGC2808 Recently, we focused on the chemical composition of stars belonging to the extreme He-rich population of NGC2808 populated by stars with the most extreme abundance of Mg, Al, Na, O, and Si. We checked whether the most recent measures are consistent with the AGB yields of stars of 6.5 -8M .…”

Section: Our Projectmentioning

confidence: 99%