Comet Coma Studies
My work with comet Hale-Bopp, in
particular the its over-abundance
of oxygen [O I] 6300 A emission has led to a long-term interest
in cometary coma physics.
Bob Glinksi did some work on the collisional chemistry of oxygen,
water, and OH in dense cometary comas and found a plausible
mechanism for the formation of excessive [O I] emission. Glinski's
work suggested that there still may be a need to tweak the
photochemical branching ratios of OH. In order to check this, I did
some work with observations of comet
Hyakutake, which suggested that for comets with more modest
production rates than Hale-Bopp, the OH branching ratio problem went
away. In other words, Glinksi was on the right track, but his model
could use some improvement. In the Hyakutake work, I went on to
examine why [O I] observations by other groups may have been yielding
artificially high water production rates and came up with a plausible
mechanism. I have since discovered an error in my calculations which
suggests that the other water production rates were closer to being
correct than the paper suggests. This ends up highlighting the need for
more comprehensive comet coma models, like the one Glinksi et
al. used, in order to fully interpret [O I] data.
I have continued to collect high-quality wide-field observations of
coma emissions with the
GALEX satellite and ground-based observatories. The GALEX data have
enabled measurement
of CS and OH emission in comet 9P/Tempel 1 during Deep Impact and
a measurement of the
ionization lifetime of carbon. I hope to continue the work by
measuring the lifetime of CO and quantitatively tracing the
contribution of carbon-bearing molecules to the comae of the comets studied by
GALEX.
Jeffrey P. Morgenthaler
2010-11-18