Physics
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40536d&link_type=abstract
Spitzer Proposal ID #40536
Physics
Scientific paper
We propose to obtain IRS spectral maps of 3 spatially extended planetary nebulae (PNe) in order to test the currently popular proposal that there are inclusions of cold, hydrogen-deficient material within the normal, hot, ionized gas. The presence of such cold (T < 1000 K) inclusions was suggested in order to account for the anomalous strength of the optical recombination lines (ORLs) of heavy elements such as O, C, N, and Ne in a number of PNe, as well as the discrepant electron temperature values that are found when different diagnostics are applied to a given nebula. If such cold, metal-rich (by factors of 10 - 100) material is really present, this represents a major change in our picture of PNe ( and also many H II regions which exhibit similar behavior), which we can no longer think of as possessing a single chemical composition. Since infrared emission lines from low energy states are emitted by the cold material nearly as efficiently as from warmer gas, infrared spectroscopy is the ideal way to test this picture, independently of the recombination line observations themselves. We will use the SH setup on the IRS, which enables us to simultaneously map emission lines from 3 ions of Ne: [Ne II], [Ne III], and [Ne V], thereby circumventing the potential problem of ionization balance variations with position. We have chosen targets which are already known to display large anomalies in the optical recombination lines of neon (specifically, Ne II, which traces triply-ionized Ne) as well as in O, C, and N, and will obtain new, complementary ground-based spectral maps of the ORLs for direct comparison with the Spitzer maps. Whether or not we are able to spatially localize the cold, line-emitting material, we expect the Spitzer data to provide novel and fundamental constraints and insights on the physical state and chemical constituents of the nebular gas.
Dinerstein Harriet
Sellgren Kris
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