Astron. Astrophys. Suppl. Ser. 130, 465-476
J.P. Phillips - V. Guzman
Send offprint request: J.P. Phillips
Instituto de Astronomia y Meteorologia,
Av. Vallarta 2602, Col. Arcos Vallarta, C.P. 44130
Guadalajara, Jalisco, Mexico
e-mail: jpp@udgserv.cencar.udg.mx
Received October 27, 1997; accepted January 19, 1998
We have investigated de-reddened spectral line ratios for some 538 planetary
nebulae. As a result, it has proved possible to define comparative
variations between differing transitions, evaluate the viability of
radiative modeling for the generality of nebulae, and assess the importance
of shocks in modifying low- excitation line strengths. Whilst most
transitions are well represented in terms of radiative excitation, the [OI]
Å line appears to be appreciably too strong in most of
the present sample; a deviation which may arise through shock interaction
between the primary outflow shell and enveloping superwind material.
Comparison between shock modeling and line excesses also suggests that an
appreciable proportion of [SII] 
Å emission may arise
through shock excitation; a conclusion which, if confirmed, may have serious
consequences for nebular density estimations. Some 14 nebulae are identified
as likely shock candidates, whilst it is proposed that the majority of
bipolar nebulae may also show spectral deviations associated with shock
excitation. Line excesses for these latter sources are most consistent with
shock velocities 
km s-1; values
which are also comparable to observed wind velocities.
Finally, sources containing FLIERs (Balick et al. 1993) are shown to be confined to highly specific spectral regimes; a result which permits us to identify three further possible FLIER sources, and propose characteristic line ratio diagnostics for the further discovery of such features.
Key words: survey -- ISM: planetary nebulae -- ISM: jets and outflows -- shocks waves
Copyright The European Southern Observatory (ESO)