Kinematics of the Molecular Hydrogen from the Planetary Nebula NGC 2346

We present scanning Fabry-Perot observations of the planetary nebula NGC 2346 at the near-infrared vibrationally excited line H 2 S (1) 1–0 at 2.122 μm. The kinematics matches a model of two ellipsoids with an outflow velocity proportional to the distance of the gas from the central star and moving radially outward. The stronger emission is located in an equatorial torus expanding at 16 km s -1 . It is likely that a shock between 6 and 16 km s -1 , depending on the assumed velocity of the red giant envelope (0 to 10 km s -1 ), excites the molecular gas. Depending on those limiting values for the shock velocity, the density of the preshock gas falls in the range (0.3–1.7) × 10 4 cm -3 , and consequently the mass of the molecular gas in the nebula is estimated to be between 0.34 and 1.85 M ⊙ , much larger than the mass of the ionized gas, and marginally in agreement with the estimate coming from CO observations alone.