New distant planetary nebulae

摘要: Discovering New Planetary Nebulae In the procedures developed at era, as 216 adjacent fields, exploiting, Astronomical Observatory of Padua, for X and Y movements, carriage The number known galactic Planeteach Palomar print is automatically diof PDS machine, after a proper ary (PN) present above gitized, by means fixed CCD camalignment on some reference stars. 1600. Even so, they are thought to be only 10% l PN in Galaxy, rest being hidden due heavy absorption. fact, concentrated solar neighbourhood distances which usually smaller than 3 4 kpc statistical parameters such kinematics, luminosity functions, chemical abundance, etc. have been derived this local sample extrapolated whole Galaxy population. Therefore, it appears important extend observations larger distances. It not surprise that improving instrumentation allows find new even regions sky previously carefully searched. search we performing, however, does require last-generation instruments, but involves comparative analysis plates taken, cases, more 20 years ago. starting point was realization that, differential absorption, all distant, normalstars tend fainter red (6000-7000A) near infrared ' (7500-8500A) prints Near Infrared Photographic Survey Galactic Plane (PNIPS). Only emission-like objects can appear brighter red. Following idea, Sabbadin (1986) able identify misclassified existing catalogues. A quick look suggested comparison very effective also identification hitherto unknown PN. particular, well suited faint, compact were missed other types searches. first attempts systematic work direction made clear order diminish candidate (excluding plate faults, variable stars, etc), simultaneous examination blue Sky (POSS) useful. efficient four different images same region (B, R POSS; R, IR PNIPS), allowing slightly field centres, scales quality, required devoted system result considerable experimentation. Figure 1 : Ha + [NII] image = 07"55"'2OS, 6 -35'58' (ESO filter # 694, RCA 15, 20-min. exposure). North top, east right.