Query : 2001A&A...372..601A

2001A&A...372..601A - Astronomy and Astrophysics, volume 372, 601-615 (2001/6-3)

On OH line formation and oxygen abundances in metal-poor stars.


Abstract (from CDS):

The formation of the UV OH spectral lines has been investigated for a range of stellar parameters in the light of 3D hydrodynamical model atmospheres. The low atmospheric temperatures encountered at low metallicities compared with the radiative equilibrium values enforced in classical 1D hydrostatic model atmospheres have a profound impact on the OH line strengths. As a consequence, the derived O abundances using 3D models are found to be systematically lower by more than 0.6dex at [Fe/H]=-3.0 compared with previous 1D analyses, casting doubts on the recent claims for a monotonic increase in [O/Fe] towards lower metallicities. In fact, taken at face value the resulting 3D LTE trend is in rough agreement with the conventional [O/Fe] plateau. Caution must, however, be exercised in view of the remaining assumptions in the 3D calculations. We have verified that the stellar parameters remain essentially unchanged with 3D model atmospheres provided that the infrared flux method (ΔTeff≲20K), Hipparcos parallaxes (Δlogg≲0.05) and FeII lines (Δ[Fe/H]≲0.1dex) are utilised, leaving the 3D O abundances from OH lines largely intact (Δ[O/H]≲0.05dex). Greater concern stems from possible departures from LTE in both the line formation and the molecular equilibrium, which, if present, would increase the derived O abundances again. Non-LTE line formation calculations with 1D model atmospheres suggest no significant steepening of the [O/Fe] trend even if the abundance corrections amount to about 0.2dex for all investigated stellar parameters. We note, however, that the 3D case may not necessarily be as metallicity-independent. The apparent lack of laboratory or theoretical rate coefficients at the relevant temperatures for the involved molecular reactions unfortunately prevents a quantitative discussion on the possible effects of non-equilibrium chemistry.

Abstract Copyright:

Journal keyword(s): convection - line: formation - stars: abundances - stars: atmospheres - stars: population II - galaxy: evolution

Simbad objects: 4

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Number of rows : 4
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
1 BD+37 1458 Pe* 06 16 01.5222885381 +37 43 18.754343426 9.41 9.52 8.92 8.34 7.91 G0 138 0
2 Wolf 1492 Pe* 13 40 02.4921849768 -00 02 18.750053436 11.601 11.832 11.451 11.184 10.892 sdF0: 282 0
3 HD 140283 Pe* 15 43 03.0971190219 -10 56 00.595693188 7.508 7.711 7.212 6.63 8.21 F9VkA5mA1 925 0
4 BD+23 3130 Pe* 17 32 41.6247211304 +23 44 11.625460773     8.9 8.6   G0III 133 0

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