HIGH-DISPERSION SPECTROSCOPY OF IC 351--A CASE STUDY OF A HIGH-EXCITATION PLANETARY NEBULA

In 1988 and 1991 we made high-dispersion spectroscopic observations of IC 351 = PK 159-15 degrees 1, a compact high-excitation planetary nebula. The H-alpha and [O III] lines obtained in 1988 are decomposed into two components. The resultant expansion velocities (the difference between these components), VDelta rho, are 25.3 ± 5.8 km s-1 and 25.1 ± 8.0 km s-1 for H-alpha (P.A. = -21.4) and [O III] (P.A. = +30.8). We found the expansion velocity, 2Vexp, from H-alpha(P.A. = -21.4), [O III] (P.A. = +30.8) and He II (P.A. = +60.1) lines, of 45.1 km s-1, 38.7 km s-1, and 33.3 km s-1, respectively. Moreover, for the H-alpha line we detected an additional faint component at the velocity of -120 km s-1. Although the intensity of this apparently blueshifted component of H-alpha is estimated as two and a half times the expected intensity of the coincident helium line, He II lambda-6560 (Pickering 6), it might be due to the helium line itself.