The radial abundance gradient of oxygen towards the Galactic anti-centre

Recent surveys for planetary nebulae have given the first identifications in Fornax, NGC 6822, M33, IC 10, Leo A, Sextans A, Pegasus, WLM, NGC 404, and M81, and extended the identifications in the SMC, the LMC, and M31. Observations of planetaries have established chemical compositions in old or intermediate age populations in 8 Local Group galaxies. The chemical compositions show that i) the helium abundance is higher in planetary nebulae than in H II regions in the same galaxy, and ii) nitrogen is overabundant relative to H II regions by factors of 4 to 100. Planetary nebulae are not a major source of helium in star-forming galaxies, and are a major source of nitrogen. The planetary in Fornax has a relatively high O abundance, and, together with Fornax's carbon stars, establishes the presence of at least 2 stellar populations. The abundance gradient derived from 3 planetaries in M31 is very shallow, and gives high abundances at ~ 20 kpc. By using planetary nebulae as standard candles, upper and lower distance limits have been set for 10 Local Group candidates, and a new distance estimated for M81.

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Interstellar and Stellar Abundances Across the Galactic Disk

International Astronomical Union Colloquium ◽

10.1017/s0252921100067464 ◽

1977 ◽

Vol 45 ◽

pp. 149-159 ◽

Cited By ~ 1

Author(s):

Manuel Peimbert

Keyword(s):

Chemical Composition ◽

Density Distribution ◽

Chemical Evolution ◽

Galactic Disk ◽

Theoretical Models ◽

Observational Evidence ◽

Stellar Abundances ◽

Abundance Gradient ◽

The Galaxy

Abstract.Observational evidence related to the chemical composition across the disk of the Galaxy is reviewed. The H2density distribution derived for the Galaxy is poorly known, consequently it is still not possible to compare theoretical models of the chemical evolution of the Galaxy with the gaseous density distribution. The H2density distribution is particularly sensitive to the fraction of carbon atoms embedded in CO molecules and to the possible presence of a C/H abundance gradient.

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Chemical evolution of the Galaxy disk in connection with large-scale winds

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027865 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 393-398

Author(s):

Takuji Tsujimoto ◽

Joss Bland-Hawthorn ◽

Kenneth C. Freeman

Keyword(s):

Chemical Evolution ◽

Large Scale ◽

Solar Neighborhood ◽

Elemental Abundance ◽

Abundance Gradient ◽

Chemical Enrichment ◽

Outer Disk ◽

The Galaxy ◽

Galaxy Disk ◽

Set Up

AbstractComparison of elemental abundance features between old and young thin disk stars may reveal the action of ravaging winds from the Galactic bulge, which once enriched the whole disk, and set up the steep abundance gradient in the inner disk (RGC ≲ 10–;12 kpc) and simultaneously the metallicity floor ([Fe/H]~ −0.5) in the outer disk. After the end of a crucial influence by winds, chemical enrichment through accretion of a metal-poor material from the halo onto the disk gradually reduced the metallicity of the inner region, whereas an increase in the metallicity proceeded beyond a solar circle. This results in a flattening of abundance gradient in the inner disk, and our chemical evolution models confirm this mechanism for a flattening, which is in good agreement with the observations. Our scenario also naturally explains an observed break in the metallicity floor of the outer disk by young stars since the limit of self-enrichment in the outer disk is supposed to be [Fe/H]≲ −1 and inevitably incurs a direct influence of the dilution by a low-metal infall whose metallicity is [Fe/H]~ −1. Accordingly, we propose that the enrichment by large-scale winds is a crucial factor for chemical evolution of the disk, and claim to reconsider the models thus far for the disk including the solar neighborhood, in which the metallicity is predicted to monotonously increase with time. Furthermore, we anticipate that a flattening of abundance gradient together with a metal-rich floor in the outer disk are the hallmark of disk galaxies with significant central bulges.

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Spatial Distribution of Metallicity in a Local Part of the Galactic Disk

International Astronomical Union Colloquium ◽

10.1017/s0252921100067580 ◽

1977 ◽

Vol 45 ◽

pp. 207-209

Author(s):

Andrzej Strobel ◽

Janina Strobel

Keyword(s):

Spatial Distribution ◽

Galactic Disk ◽

Galactic Structure ◽

Abundance Gradient ◽

Spiral Arms ◽

Local Part ◽

Systematic Character ◽

Spatial Inhomogeneities

Many recent observations have indicated variations of metallicity within our Galaxy. Apart from a general negative radial abundance gradient indirect evidences suggest the existence of spatial chemical inhomo-geneities in different regions of the galactic disk. Since this problem is of great importance in providing clues to processes of nucleosynthesis and galactic structure and evolution, it seems to be interesting to examine if these spatial inhomogeneities have any systematic character and if they are correlated with position of spiral arms.

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Metallicity Structures of the Milky Way

Symposium - International Astronomical Union ◽

10.1017/s0074180900230040 ◽

1996 ◽

Vol 169 ◽

pp. 427-428

Author(s):

Roland Buser ◽

Jianxiang Rong

Keyword(s):

High Latitude ◽

Preliminary Analysis ◽

Milky Way ◽

Structural Models ◽

Thin Disk ◽

Thick Disk ◽

Abundance Gradient ◽

Galactic Population

The metallicity-sensitive (U – G) colors from the new homogeneous catalog of photographic RGU data in seven high-latitude fields have been used to determine the larger-scale metallicity distributions of the Galactic population components. For the thick disk, preliminary analysis based on our best structural models provides a mean metallicity 〈[M/H]〉 = −0.6 ± 0.3dex and a marginal vertical metallicity gradient ≈ −0.1dex/kpc. The observed color distributions are further consistent with the (old) thin disk having mean abundance 〈[M/H]〉 = −0.3 ± 0.2dex and abundance gradient ∂[M/H]/∂z = −0.6dex/kpc.

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Hydrogen Deficient Planetary Nebulae: Preliminary Results

International Astronomical Union Colloquium ◽

10.1017/s0252921100090953 ◽

1985 ◽

Vol 87 ◽

pp. 359-365 ◽

Cited By ~ 1

Author(s):

S.R. Pottasch ◽

A. Mampaso ◽

A. Manchado ◽

J. Menzies

Keyword(s):

Correction Factor ◽

Heavy Element ◽

Planetary Nebulae ◽

Ionization State ◽

Abundance Gradient ◽

Element Abundances ◽

Preliminary Results ◽

Very High

AbstractNew spectra of A78 and A58 at different positions in the nebulae are presented. An abundance gradient is found in A78, extending quite close to the center. Similarly the nebulous knot near the center of A58 has considerably higher heavy element abundances than the outer regions of this nebula. The ionization state is considerably lower in A58 than A78. In A78 most of the neon is in the form of Ne+3 and Ne+4, indicating that the standard ionization correction factor as used by Jacoby and Ford, is substantially in error. Finally, the very high infrared excesses found in this nebulae are discussed.

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