A Bright Molecular Core in a Crab Nebula Filament
  In a sub-arcsec near-infrared survey of the Crab Nebula using the new Spartan
Infrared Camera, we have found several knots with high surface brightness in
the H_2 2.12 micron line and a very large H_2 2.12 micron to Br-gamma ratio.
The brightest of these knots has an intensity ratio I(H_2 2.12
micron)/I(Br-gamma) = 18+/-9, which we show sets a lower limit on the ratio of
masses in the molecular and recombination (i.e. ionized) zones M_mol / M_rec
>/- 0.9, and a total molecular mass within this single knot M_mol >/- 5E-5
M_sun. We argue that the knot discussed here probably is able to emit so
strongly in the 2.12 micron line because its physical conditions are better
tuned for such emission than is the case in other filaments. It is unclear
whether this knot has an unusually large M_mol / M_rec ratio, or if many other
Crab filaments also have similar amounts of molecular gas which is not emitting
because the physical conditions are not so well tuned.
