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- Gavel, Alvin, 1989-, et al.
(författare)
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Atomic diffusion and mixing in old stars VII : Abundances of Mg, Ti, and Fe in M 30
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652, s. A75-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We attempt to constrain the efficiency of additional transport or mixing processes that reduce the effect of atomic diffusion instellar atmospheres.Methods. We apply spectral synthesis methods to spectra observed with the GIRAFFE spectrograph on the VLT to estimate abundances of Mg, Ti, Fe, and Ba in stars in the metal-poor globular cluster M30. To the abundances we fit trends of abundances predicted by stellar evolution models assuming different efficiencies of additional transport or mixing processes. The fitting procedure attempts to take into account the effects of parameter-dependent systematic errors in the derived abundances.Results. We find that the parameter T0, which describes the efficiency of additional transport or mixing processes, can almost certainlybe constrained to the narrow range log10(T0/[K]) between 6.09 and 6.2. This corresponds to decreased abundances for stars at the main sequence turn-off point compared to the red giant branch by 0.2 dex for Mg, 0.1 dex for Fe, and 0.07 dex for Ti. We also find that while our estimates do have non-negligible systematic errors stemming from the continuum placement and the assumedmicroturbulence, our method can take them into account.Conclusions. Our results partly amend the results of an earlier paper in this article series, that tentatively used a value of log10(T0/[K])=6.0 when modelling the Spite plateau of lithium. To more easily distinguish physical effects from systematic errors, we recommend that studies of this kind focus on elements for which the expected surface abundances as functions of effective temperature have a distinct structure and cover a wide range.
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| 2. |
- Nordlander, Thomas, 1985-, et al.
(författare)
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Atomic diffusion and mixing in old stars : VIII. Chemical abundance variations in the globular cluster M4 (NGC 6121)
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 527:4, s. 12120-12139
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Tidskriftsartikel (refereegranskat)abstract
- Variations in chemical abundances with evolutionary phase have been identified among stars in globular and open clusters with a wide range of metallicities. In the metal-poor clusters, these variations compare well with predictions from stellar structure and evolution models considering the internal diffusive motions of atoms and ions, collectively known as atomic diffusion, when moderated by an additional mixing process with a fine-tuned efficiency. We present here an investigation of these effects in the Galactic globular cluster NGC 6121 (M4) ([Fe/H] = −1.13) through a detailed chemical abundance analysis of 86 stars using high-resolution ESO Very Large Telescope (VLT) Fibre Large Array Multi Element Spectrograph (FLAMES) spectroscopy. The stars range from the main-sequence turnoff point (TOP) to the red giant branch (RGB) just above the bump. We identify C-N-O and Mg-Al-Si abundance anticorrelations, and confirm the presence of a bimodal population differing by 1 dex in nitrogen abundance. The composition of the second-generation stars imply pollution from both massive (20–40 M) and asymptotic giant branch stars. We find evolutionary variations in chemical abundances between the TOP and RGB, which are robust to uncertainties in stellar parameters and modelling assumptions. The variations are weak, but match predictions well when employing efficient additional mixing. Without correcting for Galactic production of lithium, we derive an initial lithium abundance 2.63 ± 0.10, which is marginally lower than the predicted primordial big-bang nucleosynthesis value.
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