Magnesium Isotopes in Metal-poor Dwarfs: The Rise of AGB Stars and the Formation Timescale of the Galactic Halo

Meléndez, Jorge; Cohen, Judith G.

doi:10.1086/516735

Cited by 38 publications

(80 citation statements)

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“…Atomic lines were taken from the latest Kurucz line lists 2 and the CN line list described in Meléndez & Barbuy (1999) was adopted. The line list for the 0-1 and 1-2 bands of the C 2 Swan system was constructed in a similar way to the 0-0 band described in Meléndez & Cohen (2007), but with the line positions taken primarily from Tanabashi et al (2007) and complemented with Phillips & Davis (1968) data for the higher excitation lines not included by Tanahashi et al. Relative oscillator strengths for the 0-1 and 1-2 bands were taken from Kokkin et al (2007), normalizing those values to the laboratory oscillator strength of the 0-0 band recommended by Grevesse et al (1991), f 00 = 3.03 × 10 −2 .…”

Section: Discussionmentioning

confidence: 99%

Another forbidden solar oxygen abundance: the [O I] 5577 Å line

Meléndez

Asplund

2008

A&A

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Context. Recent works with improved model atmospheres, line formation, atomic and molecular data, and detailed treatment of blends have resulted in a significant downward revision of the solar oxygen abundance. Conclusions. The oxygen abundance derived here is close to the 3D-based estimates from the two other [O i] lines at 6300 and 6363 Å, the permitted O i lines and vibrational and rotational OH transitions in the infrared. Our study thus supports a low solar oxygen abundance (log O ≈ 8.7), independent of the adopted model atmosphere.

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Section: Discussionmentioning

confidence: 99%

Another forbidden solar oxygen abundance: the [O I] 5577 Å line

Meléndez

Asplund

2008

A&A

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“…As recommended by McWilliam & Lambert (1988) and Gay & Lambert (2000), and also used in the works of Barbuy (1985Barbuy ( , 1987, Yong et al (2003b), Meléndez & Cohen (2007), and Meléndez & Cohen (2009), we adopted three wavelength regions to determine the Mg isotopic abundances ratios, namely 5134.6, 5138.7, and 5140.2 Å.…”

Section: Discussionmentioning

confidence: 99%

“…The isotopic abundances are estimated as described in Meléndez & Cohen (2007), also using the code MOOG and the Kurucz grid of ATLAS9 model atmospheres (Castelli & Kurucz 2004). The line list adopted in this region is the same a that used in the work of Meléndez & Cohen (2007), which includes both molecular and atomic lines.…”

Section: Discussionmentioning

confidence: 99%

“…The line list adopted in this region is the same a that used in the work of Meléndez & Cohen (2007), which includes both molecular and atomic lines. Although the abundance analysis was derived with 1D models, Thygesen et al (2016Thygesen et al ( , 2017 showed that using 3D models in the analysis of Mg isotopes does not have a significant impact, especially for 26 Mg/Mg.…”

Section: Discussionmentioning

confidence: 99%

“…Note that the MgH features are visible only in cool and not too evolved stars (Spinrad & Wood 1965). Regarding the halo population, a limited number of halo stars have been analyzed, with important contributions by Yong et al (2003b) and Meléndez & Cohen (2007). Only seven single metal-poor stars (−2.60<[Fe/H]<−1.35) from the Galactic halo have Mg isotopic measurements in the literature.…”

Section: Introductionmentioning

confidence: 99%

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

Carlos

Karakas

Cohen

et al. 2018

ApJ

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We determine magnesium isotopic abundances of metal-poor dwarf stars from the galactic halo, to shed light on the onset of asymptotic giant branch (AGB) star nucleosynthesis in the galactic halo and constrain the timescale of its formation. We observed a sample of eight new halo K dwarfs in a metallicity range of −1.9<[Fe/H]<−0.9 and 4200 <T eff (K)<4950, using the HIRES spectrograph at the Keck Observatory (R≈10 5 and 200 S/N300). We obtain magnesium isotopic abundances by spectral synthesis on three MgH features and compare our results with galactic chemical evolution models. With the current sample, we almost double the number of metal-poor stars with Mg isotopes determined from the literature. The new data allow us to determine the metallicity when the 26 Mg abundances start to become important, [Fe/H]∼−1.4±0.1. The data with [Fe/H]>−1.4 are somewhat higher (1-3σ) than previous chemical evolution model predictions, indicating perhaps higher yields of the neutron-rich isotopes. Our results using only AGB star enrichment suggest a timescale for formation for the galactic halo of about 0.3 Gyr, but considering also supernova enrichment, the upper limit for the timescale formation is about 1.5 Gyr.

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Evolution of Massive Stars along the Cosmic History

Meynet

Ekström

Georgy

et al. 2009

Reviews in Modern Astronomy

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Massive stars are "cosmic engines" (cf the title of the IAU Symposium 250). They drive the photometric and chemical evolution of galaxies, inject energy and momentum through stellar winds and supernova explosions, they modify in this way the physical state of the interstellar gas and have an impact on star formation. The evolution of massive stars depends sensitively on the metallicity which has an impact on the intensity of the line driven stellar winds and on rotational mixing. We can distinguish four metallicity regimes: 1.- the Pop III regime $0 \le Z < \sim 10^{-10}$; 2.- The low metallicity regime $10^{-10} \le Z < 0.001$; 3.- The near solar metallicity regime $0.001 \le Z < 0.020$; 4.- The high metallicity regime $0.020 \le Z$. In each of these metallicity ranges, some specific physical processes occur. In this review we shall discuss these physical processes and their consequences for nucleosynthesis and the massive star populations in galaxies. We shall mainly focus on the effects of axial rotation and mass loss by line driven winds, although of course other processes like binarity, magnetic fields, transport processes by internal waves may also play important roles.Comment: 32 pages, 13 figures, Reviews in Modern Astronomy", volume 21, proceedings JENAM 2008, Vienn

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Magnesium Isotopes in Metal-poor Dwarfs: The Rise of AGB Stars and the Formation Timescale of the Galactic Halo

Cited by 38 publications

References 38 publications

Another forbidden solar oxygen abundance: the [O I] 5577 Å line

Another forbidden solar oxygen abundance: the [O I] 5577 Å line

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

Evolution of Massive Stars along the Cosmic History

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