7 research outputs found
bHROS high spectral resolution observations of PN forbidden and recombination line profiles
We have acquired high spectral resolution observations (R=150,000) of the
planetary nebulae NGC 7009 and NGC 6153, using bHROS on Gemini South.
Observations of this type may provide a key to understanding why optical
recombination lines (ORLs) yield systematically higher heavy element abundances
for photoionized nebulae than do the classical forbidden collisionally excited
lines (CELs) emitted by the same ions; NGC 7009 and NGC 6153 have notably high
ORL/CEL abundance discrepancy factors (ADFs) of 5 and 10, respectively. Due to
the opposite temperature dependences of ORLs and CELs, ORLs should be
preferentially emitted by colder plasma. Our bHROS observations of NGC 7009
reveal that the [O III] 4363A CEL has a FWHM linewidth that is 1.5 times larger
than that shown by O II ORLs in the same spectrum, despite the fact that all of
these lines are emitted by the O2+ ion. The bHROS spectra of NGC 6153 also show
that its O II ORLs have significantly narrower linewidths than do the [O III]
4363A and 5007A lines but, in addition, the [O III] 4363A and 5007A lines show
very different velocity profiles, implying the presence of large temperature
variations in the nebula.Comment: 2 pages, 1 figure, for Proceedings of IAU Symposium No. 234,
`Planetary Nebulae in our Galaxy and Beyond