Bibcode
Shaw, R. A.; Kwitter, Karen B.; Henry, Richard B. C.; Dufour, Reginald J.; Balick, Bruce; Corradi, R. L. M.
Referencia bibliográfica
American Astronomical Society, AAS Meeting #225, #139.03
Advertised on:
1
2015
Número de citas
0
Número de citas referidas
0
Descripción
We obtained HST/STIS long-slit spectra spanning 0.11 to 1.1 μm of
co-spatial regions in 10 Galactic planetary nebulae (Dufour, et al.,
this conference), of which six present substantial changes in ionization
with position. Under the assumption that elemental abundances are
constant within these nebulae (but exterior to the wind of the central
star), these spectra present a unique opportunity to examine the
applicability of common ionization correction factors (ICFs) for
deriving abundances. ICFs are the most common direct method in abundance
analysis for accounting for unobserved or undetected ionization stages
in nebulae, yet most ICF recipes have not been rigorously examined
through modeling nor empirically tested through observation. In this
preliminary study, we focussed on the astrophysically important
abundances of C and N where strong ionic transitions are scarce in
optical band, but plentiful in the satellite UV. We derived physical
diagnostics (extinction, Te, Ne) and ionic
abundances for the species of interest at various positions along the
slit for each PN. We compared the elemental abundances derived from
direct summation of the ionic abundances in the UV and optical to those
derived using only optical emission, but corrected using standard ICFs.
We found that the abundances were usually in good agreement, but there
were significant exceptions. We also found that setting upper limits on
emission from undetected ions was sometimes helpful in constraining the
correction factors. Work is underway to construct photoionization models
of these nebulae (see Miller, et al., this conference) to address the
question of why ICFs are sometimes inaccurate, and to explore other ICF
recipes for those cases.Support for Program number GO-12600 was provided
by NASA through a grant from the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Incorporated, under NASA contract NAS5-26555.