We present narrow-band optical and near-IR imaging and optical long-slit spectroscopic observations of Hu 1-2 , a Galactic planetary nebula ( PN ) with a pair of [ N ii ] -bright , fast-moving ( > 340 km s ^ { -1 } ) bipolar knots .
Intermediate-dispersion spectra are used to derive physical conditions and abundances across the nebula , and high-dispersion spectra to study the spatio-kinematical structure .
Generally Hu 1-2 has high He/H ( \approx 0.14 ) and N/O ratios ( \approx 0.9 ) , typical of Type I PNe .
On the other hand , its abundances of O , Ne , S , and Ar are low as compared with the average abundances of Galactic bulge and disc PNe .
The position-velocity maps can be generally described as an hour-glass shaped nebula with bipolar expansion , although the morphology and kinematics of the innermost regions can not be satisfactorily explained with a simple , tilted equatorial torus .
The spatio-kinematical study confines the inclination angle of its major axis to be within 10 ^ { \circ } of the plane of sky .
As in the irradiated bow-shocks of IC 4634 and NGC 7009 , there is a clear stratification in the emission peaks of [ O iii ] , H \alpha , and [ N ii ] in the northwest ( NW ) knot of Hu 1-2 .
Fast collimated outflows in PNe exhibit higher excitation than other low-ionization structures .
This is particularly the case for the bipolar knots of Hu1-2 , with He ii emission levels above those of collimated outflows in other Galactic PNe .
The excitation of the knots in Hu 1-2 is consistent with the combined effects of shocks and UV radiation from the central star .
The mechanical energy and luminosity of the knots are similar to those observed in the PNe known to harbor a post-common envelope ( post-CE ) close binary central star .