A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars*

Carlos, M.; Karakas, Amanda I.; Cohen, Judith G.; Meléndez, Jorge

doi:10.3847/1538-4357/aab36c

Cited by 9 publications

(15 citation statements)

References 48 publications

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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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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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“…Roughly half of the light elements such as C, N and F are produced by low-and intermediate-mass stars (∼ 0.8 − 8M depending on metallicity) at their asymptotic giant branch (AGB) phase (Kobayashi et al 2011b, hereafter K11). Isotopes such as 13 C, 17 O, and 25,26 Mg are also enhanced by AGB stars, and thus the isotopic ratios can also be used for galactic archaeology (Carlos et al 2018). The α-elements (O, Mg, Si, S, and Ca) are mostly produced in massive stars before being ejected by core-collapse (Type II, Ib, and Ic) supernovae (SNe II, e.g., Kobayashi et al 2006).…”

Section: Introductionmentioning

confidence: 99%

The role of AGB stars in Galactic and cosmic chemical enrichment

Haynes

Vincenzo

2018

Proc. IAU

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The role of asymptotic giant branch (AGB) stars in chemical enrichment is significant for producing 12,13C, 14N, F, 25,26Mg, 17O and slow neutron-capture process (s-process) elements. The contribution from super-AGB stars is negligible in classical, one-zone chemical evolution models, but the mass ranges can be constrained through the contribution from electron-capture supernovae and possibly hybrid C+O+Ne white dwarfs, if they explode as Type Iax supernovae. In addition to the recent s-process yields of AGB stars, we include various sites for rapid neutron-capture processes (r-processes) in our chemodynamical simulations of a Milky Way type galaxy. We find that neither electron-capture supernovae or neutrino-driven winds are able to adequately produce heavy neutron-capture elements such as Eu in quantities to match observations. Both neutron-star mergers (NSMs) and magneto-rotational supernovae (MRSNe) are able to produce these elements in sufficient quantities. Using the distribution in [Eu/(Fe, α)] – [Fe/H], we predict that NSMs alone are unable to explain the observed Eu abundances, but may be able to together with MRSNe. In order to discuss the role of long-lifetime sources such as NSMs and AGB stars at the early stages of galaxy formation, it is necessary to use a model that can treat inhomogeneous chemical enrichment, such as in our chemodynamical simulations. In our cosmological, chemodynamical simulations, we succeed in reproducing the observed N/O-O/H relations both for global properties of galaxies and for local inter-stellar medium within galaxies, without rotation of stars. We also predict the evolution of CNO abundances of disk galaxies, from which it will be possible to constrain the star formation histories.

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“…Abundâncias químicas detalhadas de estrelas anãs K do halo Galáctico Este capítulo está baseado parcialmente no artigo Carlos et al (2018) desenvolvido durante o doutorado, e em resultados de um novo artigo (Carlos et al 2020, em preparação).…”

Section: Capítulounclassified

“…Para as estrelas G078-026, G128-061, G185-030, G189-045, LHS 3780 e LHS 173, além das abundâncias elementais, também estimamos as razões isotópicas do Mg (Carlos et al, 2018). Como esse estudo de razões isotópicasé anterior ao trabalho de abundâncias ele- G078-026 -1.20±0.02 4288±47 4.7 ( a) 0.24 G128-061 -0.94±0.02 4664±44 5.0 (b) 0.00 G185-030 -1.85±0.01 4524±29 4.5 (b) 0.00 G189-045 -1.33±0.01 4937±187 4.3 ( b) 0.00 LHS 3780 -1.38±0.01 4880±42 4.5 (b) 0.00 LHS 173 -1.49±0.03 4102±46 4.8 (c) 0.77 Como podemos notar na Figura 3.9, a presença dos isótopos 25,26 Mg causa uma assimetria na linha mais forte devidoà presença da molécula de 24 MgH.…”

Section: Amostra E Análiseunclassified

“…A tese de doutorado resultou em quatro artigos como primeira autora, publicados em revistas internacionais arbitradas (Carlos et al, 2016;Carlos et al, 2018;Carlos et al, 2019Carlos et al, , 2020, e outros dois artigos estão sendo preparados como primeira autora, sobre as abundâncias químicas de estrelas anãs K pobres em metais (Capítulo 3) e a nucleossíntese em estrelas de massa intermediária (Capítulo 4). 42,43,44,46,48 Ca/ 40 Ca, 46,47,49,50 Ti/ 48 Ti, 53,54 Cr/ 52 Cr, 54,57,58,60…”

Section: Conclusões E Perspectivasunclassified

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Abundâncias químicas de estrelas anãs G e K e modelos de evolução estelar para [Fe/H]=-1.8 e [Fe/H]=-1.0 com enriquecimento-alpha

Carlos¹

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O estudo de composição química das estrelasé crucial para o entendimento tanto sobre estrutura estelar quanto sobre a história de formação da nossa galáxia.Levando em consideração que o elemento Lié um dos mais importantes traçadores astrofísicos sobre mecanismos de transporte e mistura dentro e abaixo da zona convectiva de estrelas do tipo tardio, concluímos um estudo abrangente sobre depleção de Li em 85 gêmeas solares do campo na vizinhança solar, e mais três gêmeas solares do aglomerado aberto M67. Encontramos uma forte correlação entre depleção de Li e idade estelar, em acordo com modelos não-padrão de evolução estelar. Observamos, também, que o Sol pode ser considerado pobre em Li em comparação a outras gêmeas solares de idades similares (por um fator de ∼ 2σ). Nossos resultados também sugerem que estrelas com os mais baixos conteúdos de Li, para uma dada idade, são acompanhadas de baixos níveis de elementos refratários. Analisamos 8 estrelas anãs K do halo da Galáxia para mais informações sobre a formação dessa componente galáctica, concluindo uma análise química detalhada dos elementos C,

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A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars*

Cited by 9 publications

References 48 publications

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

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

The role of AGB stars in Galactic and cosmic chemical enrichment

Abundâncias químicas de estrelas anãs G e K e modelos de evolução estelar para [Fe/H]=-1.8 e [Fe/H]=-1.0 com enriquecimento-alpha

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A Formation Timescale of the Galactic Halo from Mg Isotopes in Dwarf Stars*

Cited by 9 publications

References 48 publications

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

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

The role of AGB stars in Galactic and cosmic chemical enrichment

Abundâncias químicas de estrelas anãs G e K e modelos de evolução estelar para [Fe/H]=-1.8 e [Fe/H]=-1.0 com enriquecimento-alpha

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

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