On the oxygen abundance in our Galaxy

Pilyugin, L. S.; Ferrini, F.; Shkvarun, R. V.

doi:10.1051/0004-6361:20030139

Cited by 31 publications

(31 citation statements)

References 40 publications

(83 reference statements)

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“…All the available spectra of Galactic H  regions with measured [OIII]λ4363 lines were compiled by Pilyugin et al (2003), and oxygen abundances in Galactic H  regions were recomputed in the same way, using the T e -method. These data result in oxygen abundance 12+log (O/H) = 8.50 at the solar galactocentric distance although the dispersion in derived abundances is relatively large.…”

Section: Verification Of the Validity Of The T E -Methods At High Metamentioning

confidence: 99%

Abundance determinations in H II regions

Pilyugin

2003

A&A

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Abstract. The discrepancy between the oxygen abundances in high-metallicity H  regions determined through the T e -method (and/or through the corresponding "strong lines -oxygen abundance" calibration) and that determined through the model fitting (and/or through the corresponding "strong lines -oxygen abundance" calibration) is discussed. It is suggested to use the interstellar oxygen abundance in the solar vicinity, derived with very high precision from the high-resolution observations of the weak interstellar OIλ1356 absorption lines towards the stars, as a "Rosetta stone" to verify the validity of the oxygen abundances derived in H  regions with the T e -method at high abundances. The agreement between the value of the oxygen abundance at the solar galactocentric distance traced by the abundances derived in H  regions through the T e -method and that derived from the interstellar absorption lines towards the stars is strong evidence in favor of that i) the two-zone model for T e seems to be a realistic interpretation of the temperature structure within H  regions, and ii) the classic T e -method provides accurate oxygen abundances in H  regions. It has been concluded that the "strong lines -oxygen abundance" calibrations must be based on the H  regions with the oxygen abundances derived with the T e -method but not on the existing grids of the models for H  regions.

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Section: Verification Of the Validity Of The T E -Methods At High Metamentioning

confidence: 99%

Abundance determinations in H II regions

Pilyugin

2003

A&A

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“…Given the estimated distances, it turns out that all stars are within 3 kpc from the the sun. Determinations of abundances through spectroscopic analysis of B stars (Smartt et al 2001;Rolleston et al 2000) reveal the following gradients: −0.07 dex/kpc for C, O and Si, and −0.06 to −0.09 dex/kpc for N. Similarly, Pilyugin et al (2003) derive an Oxygen abundance gradient of −0.05 dex/kpc from studies of HII regions. Taken together, these results indicate that on average we do not expect variation of CNO abundances by more than ±0.25 dex for our sample stars.…”

Section: Abundancesmentioning

confidence: 96%

O stars with weak winds: the Galactic case

Martins

Schaerer

Hillier

et al. 2005

A&A

170

294

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Abstract. We study the stellar and wind properties of a sample of Galactic O dwarfs to track the conditions under which weak winds (i.e. mass loss rates lower than ∼10 −8 M yr −1 ) appear. The sample is composed of low and high luminosity dwarfs including Vz stars and stars known to display qualitatively weak winds. Atmosphere models including non-LTE treatment, spherical expansion and line blanketing are computed with the code CMFGEN (Hillier & Miller 1998, ApJ, 496, 407). Both UV and Hα lines are used to derive wind properties while optical H and He lines give the stellar parameters. We find that the stars of our sample are usually 1 to 4 Myr old. Mass loss rates of all stars are found to be lower than expected from the hydrodynamical predictions of Vink et al. (2001, A&A, 369, 574). For stars with log L L > ∼ 5.2, the reduction is by less than a factor 5 and is mainly due to the inclusion of clumping in the models. For stars with log L L < ∼ 5.2 the reduction can be as high as a factor 100. The inclusion of X-ray emission (possibly due to magnetic mechanisms) in models with low density is crucial to derive accurate mass loss rates from UV lines, while it is found to be unimportant for high density winds. The modified wind momentum -luminosity relation shows a significant change of slope around this transition luminosity. Terminal velocities of low luminosity stars are also found to be low. Both mass loss rates and terminal velocities of low L stars are consistent with a reduced line force parameter α. However, the physical reason for such a reduction is still not clear although the finding of weak winds in Galactic stars excludes the role of a reduced metallicity. There may be a link between an early evolutionary state and a weak wind, but this has to be confirmed by further studies of Vz stars. X-rays, through the change in the ionisation structure they imply, may be at the origin of a reduction of the radiative acceleration, leading to lower mass loss rates. A better understanding of the origin of X-rays is of crucial importance for the study of the physics of weak winds.

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“…Several people have derived O/H gradients from galactic HII regions (see for example Vilchez & Esteban 1996;Afflerbach et al 1997;Deharveng et al 2000;Pilyugin et al 2003, for recent determinations). Generally, the most reliable determinations are those based on measured [OIII] λ4959,5007/4363 lines, so that the electronic temperature can be derived.…”

Section: Hii Regionsmentioning

confidence: 99%

An estimate of the time variation of the abundance gradient from planetary nebulae

Maciel

Lago

Costa

2005

A&A

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Abstract. The temporal behaviour of the radial abundance gradients has important consequences for models of the chemical evolution of the Galaxy. We present a comparison of the time variation of the abundance gradients in the Milky Way disk as determined from a sample of planetary nebulae, open clusters, cepheids and young objects, such as stars in OB associations and HII regions. We conclude that the [Fe/H] gradients as measured in open cluster stars strongly support the time flattening of the abundance gradient as determined from O/H and S/H measurements in planetary nebulae. This conclusion is also supported by the cepheid variables, for which very accurate gradients and ages can be determined, and also by some recent estimates for OB stars and HII regions. It is estimated that the average flattening rate for the last 8 Gyr is in the range 0.005−0.010 dex kpc −1 Gyr −1 .

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On the oxygen abundance in our Galaxy

Cited by 31 publications

References 40 publications

Abundance determinations in H II regions

Abundance determinations in H II regions

O stars with weak winds: the Galactic case

An estimate of the time variation of the abundance gradient from planetary nebulae

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