4,174 research outputs found
Planetary nebulae in the inner Milky Way: new abundances
The study of planetary nebulae in the inner-disk and bulge gives important
information on the chemical abundances of elements such as He, N, O, Ar, Ne,
and on the evolution of these abundances, which is associated with the
evolution of intermediate-mass stars and the chemical evolution of the Galaxy.
We present accurate abundances of the elements He, N, S, O, Ar, and Ne for a
sample of 54 planetary nebulae located towards the bulge of the Galaxy, for
which 33 have the abundances derived for the first time. The abundances are
derived based on observations in the optical domain made at the National
Laboratory for Astrophysics (LNA, Brazil). The data show a good agreement with
other results in the literature, in the sense that the distribution of the
abundances is similar to those works.Comment: Accepted for publication in RevMexAA (29 pages, 15 figures, 7 tables,
uses rmaa.cls
An estimate of the time variation of the O/H radial gradient from planetary nebulae
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.Comment: 9 pages, 7 encapsulated postscript figures, LaTeX, uses Astronomy and
Astrophysics macro aa.cls, graphicx package, to be published in Astronomy and
Astrophysics (2002), Also available at: http://www.astro.iag.usp.br/~macie
Planetary nebulae in the inner Milky Way
New abundances of planetary nebulae located towards the bulge of the Galaxy
are derived based on observations made at LNA (Brazil). We present accurate
abundances of the elements He, N, S, O, Ar, and Ne for 56 PNe located towards
the galactic bulge. The data shows a good agreement with other results in the
literature, in the sense that the distribution of the abundances is similar to
those works. From the statistical analysis performed, we can suggest a
bulge-disk interface at 2.2 kpc for the intermediate mass population, marking
therefore the outer border of the bulge and inner border of the disk.Comment: 2 pages, 1 figure, uses iaus.cls, in press, IAU Symp. 265, Chemical
abundances in the Universe: Connecting the first Stars to Planets, Ed. K.
Cunha, M. Spite, B. Barbu
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