Oxygen in Unevolved Metal-Poor Stars from Keck Ultraviolet HIRES Spectra

Boesgaard, Ann Merchant; King, Jeremy R.; Deliyannis, Constantine P.; Vogt, Steven S.

doi:10.1086/300691

Cited by 182 publications

(245 citation statements)

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“…The main observational evidence regarding the evolution of oxygen in the Galaxy comes from the measurement of oxygen abundances in the atmospheres of cool stars. The magnitude and trend of measured oxygen abundance with age or metallicity is not yet well constrained; in particular, the results at low metallicity differ between different studies (e.g., Israelian et al 1998;Boesgaard et al 1999;Nissen et al 2002;Garcia-Perez et al 2006). The use of different spectral diagnostics is most likely the reason for these discrepancies.…”

Section: Introductionmentioning

confidence: 93%

Electron-impact excitation of neutral oxygen

Barklem¹

2006

A&A

105

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Aims. Our goal was to calculate transition rates from ground and excited states in neutral oxygen atoms due to electron collisions for non-LTE modelling of oxygen in late-type stellar atmospheres, thus enabling the reliable interpretation of oxygen lines in stellar spectra. Methods. A 38-state R-matrix calculation in LS -coupling has been performed. Basis orbitals from the literature are adopted, and a large set of configurations are included to obtain good representations of the target wave functions. Rate coefficients are calculated by averaging over a Maxwellian velocity distribution. Results. Estimates for the cross sections and rate coefficients are presented for transitions between the seven lowest LS states of neutral oxygen. The cross sections for excitation from the ground state compare well with existing experimental and recent theoretical results.

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Section: Introductionmentioning

confidence: 93%

Electron-impact excitation of neutral oxygen

Barklem¹

2006

A&A

105

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“…In order to convert from [O/H] to the iron metallicities [Fe/H], we have used the extensive sample of disk stars by Edvardsson et al (1993), from which we derive the relationship The dashed line is the predicted relationship on the basis of the radial gradients of young objects in the galactic disk, at galactocentric distances 4 ≤ R(kpc) ≤ 12, as discussed by Maciel (2002). The figure also includes some representative observational data by Barbuy & Erdelyi-Mendes (1989), asterisks; Boesgaard et al (1999), filled squares; Edvardsson et al (1993), crosses;Israelian et al (1998), solid dots; Spiesman & Wallerstein (1991), open circles; Spite & Spite (1991), plus signs; Takeda et al (2002), empty squares; Mishenina et al (2000), open stars, and Cavallo et al (1997), filled stars, as recomputed by Mishenina et al (2000).…”

Section: The [O/h] × [Fe/h] Relationmentioning

confidence: 99%

An estimate of the time variation of the O/H radial gradient from planetary nebulae

Maciel¹,

Costa²,

Uchida³

2002

A&A

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Abstract. Radial abundance gradients are a common feature of spiral galaxies, and in the case of the Galaxy both the magnitude of the gradients and their variations are among the most important constraints of chemical evolution models. Planetary nebulae (PN) are particularly interesting objects to study the gradients and their variations. Owing to their bright emission spectra, they can be observed even at large galactocentric distances, and the derived abundances are relatively accurate, with uncertainties of about 0.1 to 0.2 dex, particularly for the elements that are not synthesized in their progenitor stars. On the other hand, as the offspring of intermediate mass stars, with main sequence masses in the interval of 1 to 8 solar masses, they are representative of objects with a reasonable age span. In this paper, we present an estimate of the time variation of the O/H radial gradient in a sample containing over 200 nebulae with accurate abundances. Our results are consistent with a flattening of the O/H gradient roughly from −0.11 dex/kpc to −0.06 dex/kpc during the last 9 Gyr, or from −0.08 dex/kpc to −0.06 dex/kpc during the last 5 Gyr.

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“…Attention was sharply focussed on oxygen abundances in metal-poor stars by studies of the OH ultraviolet lines (Israelian et al 1998(Israelian et al , 2001Boesgaard et al 1999). These showed that [O/Fe] …”

Section: [O I] and The Oxygen Problemmentioning

confidence: 99%

“…Six of our stars are in the sample analysed by Boesgaard et al (1999), who presented OH-based results for two different T eff scales. Their atmospheric parameters based on Carney's (1983b) The much discussed subgiant star BD +23 • 3130, which has been added to Fig.…”

Section: [O I] and Oh Linesmentioning

confidence: 99%

“…The problem became strikingly evident with the publication of analyses of the ultraviolet OH lines in dwarfs (Israelian et al 1998;Boesgaard et al 1999). These independent but quite similar analyses showed that [O/Fe] rose linearly with [Fe/H] from zero at [Fe/H] = 0 to about 1.2 at [Fe/H] = −3.0, about the metallicity of the most metal-poor stars studied.…”

Section: Introductionmentioning

confidence: 99%

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