The following document lists the file abstract/RRUBIN_IRON.abs
from catalogue VI/111.
A plain copy of the file
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The iron abundance is of fundamental interest in astrophysics. Surprisingly little information about Fe abundances is available from gaseous nebulae. HII regions provide a probe of the current mix of elements from which new stars are born. The most abundant ionic species expected in HII regions are Fe++ and Fe+3, with no higher ionization expected. Planetary Nebulae (PNs) provide a means to probe these abundances in material relatively recently ejected by evolved stars. In low to medium ionization PNs, Fe++ and Fe+3 will likely still be the dominant Fe ions but Fe+4 should be present. Many lines even in the IR suffer extinction uncertainties: eg. the [FeIII] 23 um line requires a factor > 2 correction. Much improved atomic data for Fe++ and Fe+3 ions have recently become available or will become available soon as part of the IRON atomic data project. We now include a 17-level atom treatment for Fe++ in our photoionization codes to predict all the line fluxes, including IR lines. Because there are many observable FeIII lines, there is an expanded opportunity to obtain reliable physical parameters - density, temperature, extinction, and its abundance - that is not presented by other heavy element ions, where the collisionally excited lines arise from the lowest 5 or 6 levels only. All the infrared [FeIII] lines, except 23 um, can be done only with ISO. We plan cospatial ISO and ground-based observations. We have selected objects to span a range in extinction and galactocentric distance and where we have complementary line data, including our own KAO data. Even though Fe+3 is likely the MOST abundant Fe species in our objects, quantum mechanically, bright lines are not expected. Recently, we reported the first detection of an FeIV line in an HII region from our HST observations of the Orion Nebula. From expected relative strengths based on atomic data and our observations and model of Orion, the next most promising [FeIV] lines are the set of 6 NIR lines at 2.71-2.86 um. These lines are measurable only with ISO. We propose to measure the NIR FeIII and FeIV lines in the bright PN NGC 7009. By also measuring single FeII and FeV lines, we will test for an Fe depletion gradient within a PN and compare with the Fe abundance in the benchmark Orion Nebula.