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Spectral trends in planetary nebulae: The roles of radiative and shock excitation
We have investigated de-reddened spectral line ratios for some 538planetary nebulae. As a result, it has proved possible to definecomparative variations between differing transitions, evaluate theviability of radiative modeling for the generality of nebulae, andassess the importance of shocks in modifying low- excitation linestrengths. Whilst most transitions are well represented in terms ofradiative excitation, the [OI] lambda 6300 Angstroms line appears to beappreciably too strong in most of the present sample; a deviation whichmay arise through shock interaction between the primary outflow shelland enveloping superwind material. Comparison between shock modeling andline excesses also suggests that an appreciable proportion of [SII]lambda 6716/31 Angstroms emission may arise through shock excitation; aconclusion which, if confirmed, may have serious consequences fornebular density estimations. Some 14 nebulae are identified as likelyshock candidates, whilst it is proposed that the majority of bipolarnebulae may also show spectral deviations associated with shockexcitation. Line excesses for these latter sources are most consistentwith shock velocities V_s ~ 80 => 100 km s(-1) ; values which arealso comparable to observed wind velocities. Finally, sources containingFLIERs (\cite[Balick et al. 1993]{ba93}) are shown to be confined tohighly specific spectral regimes; a result which permits us to identifythree further possible FLIER sources, and propose characteristic lineratio diagnostics for the further discovery of such features.
| The Montreal Blue Galaxy Survey.III.Third List of UV-Bright Candidates
We present and discuss the latest addition of the Montreal Blue Galaxy(MBG) survey. Inspection of 59 Curtis Schmidt plates resulted in theidentification of 135 new UV-bright galaxies with B < 15.5. Thisbrings the total number of MBGs to 469. New results of the V/V_m testshow that our survey is complete to B = 14.7. From our most recentspectroscopic follow-up, we confirm the discovery of one new Seyfert 1galaxy and possibly one new Seyfert 2 galaxy. We confirm also the biasof the MBG survey towards the low-excitation and metal rich StarburstNucleus Galaxies (SBNGs). The spectral characteristics of the MBGs aresimilar to those of the infrared luminous IRAS galaxies. As a commoncharacteristic, they show a mean ratio Log([NII]/Hα ) in excess of0.2 dex as compared to normal disk HII regions. In general, the MBGshave lower far-infrared luminosities (LIR < 10(11)Lsun) and are nearer (z < 0.05) than the luminous IRASgalaxies. The distribution of the morphologies of the MBGs indicates ahigh number of early-type spirals (Sb and earlier). Nearly half of thesegalaxies also possess a bar. In our sample, the fraction of galaxieswith bars depends on the morphology and increases towards the late-typespirals. However, if we consider only isolated galaxies, the late-typespirals show a clear tendency to be barred. Signs of a recentinteraction with neighbor galaxies are obvious only in 24% of ourcandidates. Although this number is only a lower limit, it isnevertheless sufficiently low to suggest that in a majority of massivegalaxies the burst of star formation do not depends solely on dynamicalprocesses.
| Mean galaxy luminosity classifications
To prepare a catalog of weighted means on the classification system ofvan den Bergh, we have combined eight independent lists of luminosityclass estimates, L. Luminosity class values from each set weretransformed to the standard system and weighted according to the errorsderived through a statistical comparison of L differences betweencatalog pairs. Relations were derived for predicting accidental errorsassociated with galaxy diameter and inclination. In addition, we presentformulas for correcting systematic errors associated with diameter andinclination. Finally, we tabulate a high weight subsample of the meanluminosity classes usable as standards. Most values are tabulated in theThird Reference Catalog of Bright Galaxies.
| An extended galaxy redshift survey. I - The catalogue
Redshifts and blue magnitudes are presented for a sample of 264 'field'galaxies virtually complete to a limiting magnitude of 16.80 mag. Thegalaxies were selected by sampling one galaxy in every three in order ofapparent magnitude on each of nine high-latitude UK Schmidt (UKST)fields. The spectral data came from observations with the 1.9-mtelescope at the South African Astronomical Observatory (SAAO), and theresulting radial velocities have a precision of 130 + or - km/s. Thissurvey augments substantially the Durham/AAT redshift survey. Theobservational techniques and reduction procedures are discussed.
| Southern Galaxy Catalogue.
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