Light‐Element Evolution and Cosmic‐Ray Energetics

Ramaty, R.; Scully, Sean T.; Lingenfelter, R. E.; Kozlovsky, B.

doi:10.1086/308793

Cited by 95 publications

(145 citation statements)

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“…However, the trend of [S/Fe] versus [Fe/H] in the early Galaxy is still debated: Israelian & Rebolo (2001) and Takada-Hidai et al (2002) found [S/Fe] to rise with decreasing [Fe/H], while Ryde & Lambert (2004) and Nissen et al (2004Nissen et al ( , 2007 found [S/Fe] to remain flat. Finally, Caffau et al (2005Caffau et al ( , 2010a, combining their own data with a large sample from the literature covering the multiplets 1, 3, 6, and 8 of S I (see Table 1), suggest a bimodal distribution of [S/Fe] Nakamura et al 2001), or even that they may be responsible for a delayed deposition of the supernova-synthesized products into the interstellar medium (Ramaty et al 2000).…”

Section: Introductionmentioning

confidence: 93%

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Spite

Caffau

Andrievsky

et al. 2011

A&A

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Context. Precise S abundances are important in the study of the early chemical evolution of the Galaxy. In particular the site of the formation remains uncertain because, at low metallicity, the trend of this α-element versus [Fe/H] remains unclear. Moreover, although sulfur is not bound significantly in dust grains in the ISM, it seems to behave differently in DLAs and old metal-poor stars. Aims. We attempt a precise measurement of the S abundance in a sample of extremely metal-poor stars observed with the ESO VLT equipped with UVES, taking into account NLTE and 3D effects. Methods. The NLTE profiles of the lines of multiplet 1 of S I were computed with a version of the program MULTI, including opacity sources from ATLAS9 and based on a new model atom for S. These profiles were fitted to the observed spectra. ratio in EMP stars is solar, as also found in DLAs. We derive an upper limit to the sulfur abundance [S/Fe] < +0.5 for the ultra metal-poor star CS 22949-037. This, along with a previously reported measurement of zinc, argues against the conjecture that the light-element abundance pattern of this star (and by analogy, the hyper iron-poor stars HE 0107-5240 and HE 1327-2326) would be due to dust depletion.

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Section: Introductionmentioning

confidence: 93%

First stars

Spite

Caffau

Andrievsky

et al. 2011

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“…The form of the injection spectrum is motivated by theories of collisionless shock acceleration (e.g. Ellison & Ramaty 1985) and we adopt here the frequently used Fields et al 1994Fields et al , 2001Ramaty et al 1997Ramaty et al , 2000 momentum spectrum of the form…”

Section: Composition Of Gcrmentioning

confidence: 99%

Production and evolution of Li, Be, and B isotopes in the Galaxy

Prantzos

2012

A&A

166

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Context. We reassess the problem of the production and evolution of the light elements Li, Be and B and of their isotopes in the Milky Way in the light of new observational and theoretical developments. Aims. The main novelty is the introduction of a new scheme for the origin of Galactic cosmic rays (GCR), which for the first time enables a self-consistent calculation of their composition during galactic evolution. Methods. The scheme accounts for key features of the present-day GCR source composition, it is based on the wind yields of the Geneva models of rotating, mass-losing stars and it is fully coupled to a detailed galactic chemical evolution code. Results. We find that the adopted GCR source composition accounts naturally for the observations of primary Be and helps understanding why Be follows Fe more closely than O. We find that GCR produce ∼70% of the solar 11 B/ 10 B isotopic ratio; the remaining 30% of 11 B presumably result from ν-nucleosynthesis in massive star explosions. We find that GCR and primordial nucleosynthesis can produce at most ∼30% of solar Li. At least half of the solar Li has to originate in low-mass stellar sources (red giants, asymptotic giant branch stars, or novae), but the required average yields of those sources are found to be much higher than obtained in current models of stellar nucleosynthesis. We also present radial profiles of LiBeB elemental and isotopic abundances in the Milky Way disc. We argue that the shape of those profiles -and the late evolution of LiBeB in general -reveals important features of the production of those light elements through primary and secondary processes.

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“…To summarize, early studies by Israelian & Rebolo (2001) and Takada-Hidai et al (2002) found that the relative sulphur abundance continuously increases in the metallicity range from solar to at least [Fe/H] −2.5, implying a different chemical evolution history from that of other α-elements, which display a (nearly) metallicity-independent enrichment with respect to iron in stars of low ([Fe/H] −1) A&A 559, A115 (2013) metallicity (Cayrel et al 2004;Jonsell et al 2005) 1 . A high rate of sulphur-rich hypernovae (e.g., Nakamura et al 2001) and a time-delayed deposition of iron into the interstellar medium (Ramaty et al 2000) have been proposed as possible explanations for these unexpected results. On the other hand, a number of studies (e.g, Ryde & Lambert 2004;Korn & Ryde 2005;Nissen et al 2007;Spite et al 2011) have found little to no evidence of high ([S/Fe] 0.6) sulphur abundances at any metallicity and instead argued that sulphur is a fairly typical α-element and forms a plateau of [S/Fe] ∼ 0.3 below [Fe/H] ∼ −1, which points to an origin in Type II supernovae (e.g., Kobayashi et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Galactic chemical evolution of sulphur

Matrozis¹,

Ryde²,

Dupree³

2013

A&A

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Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], which is typical for α-elements, while others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. The aim of this study is to contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-local thermodynamic equilibrium (LTE) insensitive spectral diagnostics in disk and halo stars with homogeneously determined stellar parameters. Methods. We derived effective temperatures from photometric colours, surface gravities from stellar isochrones and Bayesian estimation, and metallicities and sulphur abundances from spectrum synthesis. We derived sulphur abundances from the [S ] λ1082 nm line in 39 mostly cool and metal-poor giants using 1D LTE MARCS model atmospheres to model our high-resolution near-infrared spectra obtained with the VLT, NOT, and Gemini South telescopes. Results. We derive homogeneous stellar parameters for 29 of the 39 stars. Our results argue for a chemical evolution of sulphur that is typical for α-elements, contrary to some previous studies that have found high sulphur abundances ([S/Fe] 0.6) for stars with −2.5 < [Fe/H] < −1. Our abundances are systematically higher by about 0.1 dex than those of other studies that arrived at similar conclusions using other sulphur diagnostics. Conclusions. We find the [S ] line to be a valuable diagnostic of sulphur abundances in cool giants down to [Fe/H] −2.3. We argue that a homogeneous determination of stellar parameters is necessary, since the derived abundances are sensitive to them. Our results ([S/Fe]) agree reasonably well with predictions of contemporary models of Galactic chemical evolution. In these models sulphur is predominantly created in massive stars by oxygen burning and is ejected into the interstellar medium during Type II supernovae explosions. Systematic differences with previous studies most likely fall within modelling uncertainties.

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Light‐Element Evolution and Cosmic‐Ray Energetics

Cited by 95 publications

References 71 publications

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Production and evolution of Li, Be, and B isotopes in the Galaxy

Galactic chemical evolution of sulphur

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