Computer Science
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40035b&link_type=abstract
Spitzer Proposal ID #40035
Computer Science
Scientific paper
It has been known for many years that there is an abundance gradient in the Galaxy. This has been verified by studies of HII regions, young stars and Cepheid variables. While the gradient is well characterised in the solar neighborhood its behavior is more uncertain in the bulge and in the anti-galactic center regions. For instance, results from HII regions indicate that the gradient in the outer part of the Galaxy decreases, but this is not supported from the works on early type stars, and Cepheid results suggest a flattened gradient in the solar vicinity. Planetary Nebulae (PNe) are ideal objects to solve these discrepancies because their abundances can be accurately determined. Certain elements, like sulfur, neon and argon are neither produced nor destroyed in the course of evolution of low- and intermediate-mass stars and therefore represent the composition at the time of star formation. These elements emit many lines in the infrared part of the electromagnetic spectrum and thus, infrared observations are essential to derive their abundances. Infrared observations of PNe have recently been used by Pottasch & Bernard-Salas (2006) to study the Galactic gradient in the solar vicinity using data from the Infrared Space Observatory (ISO). The gradient found reproduces exactly the solar metallicity at 8kpc. The enhanced sensitivity of Spitzer enables one to extend this study to the outer regions of the Galaxy. The study of bulge PNe using the IRS instrument on board Spitzer is the subject of an earlier proposal. With the present proposal we want to study a selection of 24 PNe in the outer part of the Galaxy to fully characterise the gradient in the Galaxy. In addition, we include in this proposal observations of four (extended) PNe. These four PNe have well known distances and will anchor these relations.
Bernard-Salas Jeronimo
Guiles Shannon
Houck James R.
Morris Patrick W.
Pottasch Stuart R.
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