In this section, comments are given for new detection of outer structures (if and where they exist) as observed through three interference filters (H $\alpha$ , [NII]6583, and [OIII] 5007). We are interested here with the PN ionized mass estimates. PN distances and electron densities are principal sources of uncertainties. As a matter of fact, our present monochromatic survey shows that most PNe have angular diameters much larger than catalogued so far, which implies to revise values of the PN ionized mass, which is expressed by the formula:

$\begin{displaymath} M_{\rm ion} = \frac{\frac{4}{3} \pi r_{\rm cm}^{3} \times \e... ...\rm H}^{+}) \times 1.4 \times 1.624 \ 10^{-24}}{1.989 ~10^{33}}\end{displaymath}$

where $r_{\rm cm}$ is the linear radius, $\epsilon$ the filling factor and N(H $^{+})\sim N\rm _e$ . In practice, we use distance determinations from CKS92 to determine $r_{\rm cm}$ , and provide estimates of ionized mass as functions of $\epsilon$ $\times$ $N\rm _e$ (the numerical value represented by $\alpha$ is given in Table 2, Col. 11). When possible, we derive electron densities from Zhang (1988, thesis p. 76), but again, the accurate knowledge of distance is crucial here:

$\begin{displaymath} 4.732 \times S_{\rm 6~cm}^{1/2} r_{''}^{-3/2} \epsilon^{-1/2} d_{\rm kpc}^{-1/2}.\end{displaymath}$

**Table 3:** Absolute Fluxes for 22 PNe
$\begin{tabular} {lrrrrr} \hline \hline & & & & & \\ Names & PNG & $F$(H$\alp... ...& 120.~~& 23.3& \\ {\bf SaWe 4} & 014.7$-$11.8& 4.44& & & \\ \hline\end{tabular}$

3.1 A 60 - PN G 025.0 - 11.6

The H $\alpha$ (75'' $\times$ 65'') and [NII]6583 Å (90'' $\times$ 80'') emissions are rather faint as compared to the [OIII]5007 Å (110'' $\times$ 95'') ones (Figs. 1). The latter shows a more evident bipolar structure inside the elliptical shape. The [NII] emission was not reported by spectroscopy (AST91 in Acker93). The global structure is far from homogeneous. At the distance of 1705 pc (CKS92), the [OIII]5007 major axis measures 0.91 pc. Using S(6 cm) = 11 10^-3 Jy and the theoretical relationship (see Pottasch 1984, p. 203) with I(H $\beta$ ), we derive a rather high reddening c(H $\beta$ ) = 1.477, leading to E(B-V) = 1.01. The ionized mass computed with the H $\alpha$ image radius $r_{\rm cm}(37''5)$ provides $M\rm _i$ = 4.35 10^-3 $\epsilon$ $N\rm _e$ . With $N\rm _e$ $\sim$ 95 cm^-3, and assuming $\epsilon$ = 0.3, the ionized mass amounts $\sim$ 0.12 $M_{\odot }$ .. The absolute flux measurements are given in Table 3.

$\begin{figure} \psfig {figure=ds7743f1.eps,height=20cm} \end{figure}$

Figure 1: A 60. a) H $\alpha$ . b) [NII]. c) [OIII]. The bipolar structure of this elliptical planetary nebula is more conspicuous in [OIII]. Such a morphology resembles the bright core of He 2-119 and even the Dumbbell nebula (see below). In general, North is at the top, east towards the left for all figures unless otherwise noted

3.2 A 65 - PN G 017.3 - 21.9

This PN is characterized by a relatively moderate IRAS emission (peak at 100 $\mu$ m) and a rather low expansion velocity ( $v_{\rm [OIII]} = 11$ km s^-1).

We have detected (Figs. 2) more extended structures (overall dimensions 270'' $\times$ 250'') than the 100'' quoted so far (which do correspond to the dimensions of the main and bright rectangular core). As a matter of fact, the nebular core is surrounded by an elliptical diffuse emission, and a faint outer halo, in three emission lines. The rectangular centre consists of two conspicuous lobes, particularly more obvious in [NII] (this emission line was not reported by spectroscopy, see Acker93. Moreover, given such a structure, one can easily miss the [NII] emission, depending on how the slit is placed across the nebula!).

The H $\alpha$ overall dimensions measure 270'' $\times$ 250'' (in Table 2 we give the inner area dimensions), while the [NII] dimensions are slightly smaller with 250'' $\times$ 210'' and [OIII] with 240'' $\times$ 220'' or 1.93 $\times$ 1.77 pc (at 1655 pc, CKS92, 1'' = 8.02 10^-3 pc). The ionized mass of the inner (r = 70'') bright area amounts 2.60 10^-2 $\times$ $\epsilon$ $N\rm _e$ . Assuming $N\rm _e$ = 100 cm^-3 and $\epsilon$ = 0.3, we obtain $M\rm _i$ = 0.78 $M_{\odot }$ . For the overall nebula (r = 100'') which would concern a less dense medium, we get 7.55 10^-2 $\times$ $\epsilon$ $N\rm _e$ . If $N\rm _e$ = 50 cm^-3, the overall ionized mass would be larger than 1 $M_{\odot }$ . The outer halo in [OIII] suggests two large rings intersecting southwards. The comparison with the theoretical H $\beta$ flux provides c(H $\beta$ ) = 0.241 and E(B-V) = 0.165.

$\begin{figure} \psfig {figure=ds7743f2.eps,height=20cm} \end{figure}$

Figure 2: A 65. a) H $\alpha$ . b) [NII]. c) [OIII]. The elongated core is surrounded by a spectacular outer ring (double in [OIII]). The [NII] core is composed with two 60'' $\times$ 60'' blobs superimposed on a faint diffuse emission. The faint outer filament is still seen NE. Given such a structure, it is not surprising to "miss'' the N⁺⁺ lines, depending where the slit is placed! The [OIII] image displays almost the same structure as in H $\alpha$ , but the outer filament shows up with a double ring much stronger

3.3 A 66 - PN G 019.8 - 23.7

This "old'' planetary nebula was reported in Abell 1955 and 1966 and given a circular type with a 267'' diameter (CaKa71). Our observations show the spectacular extension spreading over the 6'5 field of view, definitely larger than quoted. The H $\alpha$ image (Figs. 3) shows a NE filamentary structure attached to the main annulus, along with circular rings surrounding the central area. Radial structures escape outwards. These features are less obvious in the [NII]6583 Å, no longer seen in [OIII]5007 Å which displays strong bipolar E-W emission. Moreover, the [NII] dimensions appear much larger than that in H $\alpha$ . At 567 pc, 1'' = 2.749 10^-3 pc, the overall diameter (320'') of this nearby planetary nebula measures $\sim$ 0.90 pc. The ionized mass of the inner spheroidal nebula (260'') amounts 6.67 10^-3 $\times$ $\epsilon$ $N\rm _e$ , or 0.12 $M_{\odot }$ , assuming $\epsilon$ = 0.3 and $N\rm _e$ = 60 cm^-3, whereas the overall planetary would have 12.44 10^-3 $\times$ $\epsilon$ $N\rm _e$ . and assuming $\epsilon$ = 0.3, the ionized mass amounts $\sim\!0.12$ $M_{\odot }$ . The ratio inner/outer ionized mass is roughly 0.70, since we suspect the total dimensions of this PN would be even larger than our field of view. The [OIII]5007 image displays a spheroidal structure crossed by a dusty patch close to the centre. The previous NE "tail'' seen in H $\alpha$ and [NII] is no longer visible, probably too faint. The radio flux S(6 cm) = 58 mJy leads to I(H $\alpha$ ) = 45.4 10^-13 erg cm^-2s^-1.

$\begin{figure} \psfig {figure=ds7743f3.eps,height=20cm} \end{figure}$

Figure 3: A 66. a) H $\alpha$ . b) [NII]. c) [OIII]. This planetary nebula resembles the "Owl Nebula''. The H $\alpha$ diameter measures 320''. The N filament displays a string of eastward condensations. The overall dimensions should be even larger than the actual field of view offered by the CCD (northward extension). The outer [NII]6583 emission is much more conspicuous than that seen in H $\alpha$ which also displays helical strings (NW-SE) around the broken circular annulus. The outer emission detected in the two previous emission lines is no longer seen in the (smaller due to higher ionization potential) [OIII] image which shows a patchy line across the bright centre separated in two blobs. The two cavities seen in H $\alpha$ and [NII] no longer exist here

3.4 A 70 - PNG 038.1 - 25.4

The H $\alpha$ image (Figs. 4) showing a prominent central star, displays condensations along the elliptical ring. A faint eastward emission is visible on the H $\alpha$ and [NII] images. The overall diameter measures 50''. The [OIII] is rather circular and $\sim\!15\%$ smaller than the previous emission lines. The ionized mass with r = 25'' amounts 3.40 10^-3 $\times$ $\epsilon$ $\times$ $N\rm _e$ . Assuming $\epsilon$ = 0.3, we compute $N\rm _e$ = 150 cm^-3, and find $M\rm _i$ = 0.16 $M_{\odot }$ .

$\begin{figure} \psfig {figure=ds7743f4.eps,height=20cm} \end{figure}$

Figure 4: A 70. a) H $\alpha$ . b) [NII]. c) [OIII]. A faint NE emission is detected for this nearly circular (50'') planetary nebula. Its ring structure displays 6 bright knots. The [NII] and [OIII] condensations more obviously outline the circular ring (smaller ring in oxygen)

3.5 DS 2 - PN G 335.5 + 12.4

This is probably the first monochromatic image (Fig. 5a) of DS 2 obtained since its discovery by Drilling in 1983. [NII]6583 and [OIII]5007 were not detected (nitrogen and oxygen probably absent). The H $\alpha$ image with its 190'' diameter suggests Rayleigh-Taylor instabilities. In absence of the distance's measurement, we were not able to derive its ionized mass.

3.6 DuRe 1 - PNG 302.3 - 01.3

The H $\alpha$ image (Fig. 5b) shows a prominent central star. The [NII] (Fig. 5c) emission is more conspicuous with faint filament tied up westwards. As for DS 2, we cannot compute the ionized mass without knowledge of the PN distance.

$\begin{figure} \psfig {figure=ds7743f5.eps,height=20cm} \end{figure}$

Figure 5: a) DS 2 in H $\alpha$ . The inner network structure (alike A 43) spreading over 190'' of the H $\alpha$ image suggests Rayleigh-Taylor instabilities. [NII] and [OIII] emissions were not detected. b) DuRe 1 in H $\alpha$ . The faint emission around a bright central star is a diffuse disk of 55''. c) DuRe 1 in [NII]: A faint NE filament is probably present in [NII]. [OIII] was not detected

3.7 He 2-70 - PNG 293.6 + 01.2

This planetary nebula, observed at MJUO, displays a 60'' "crab'' structure surrounded by a fuzzy emission (Figs. 6). The [NII] image is slightly more extended, and the [OIII] image is smaller than the two other emission lines. Using d = 1900 pc (Maciel 1984) we obtain $M\rm _i$ = 3.085 10^-3 $\epsilon$ $N\rm _e$ .

$\begin{figure} \psfig {figure=ds7743f7.eps,height=20cm} \end{figure}$

Figure 6: He 2-70. a) H $\alpha$ . b) [NII]. c) [OIII]. This planetary nebula also displays a "crab'' or "spider''-structure. Nitrogen is much stronger than H $\alpha$ and [OIII]

3.8 He 2-72 - PNG 294.9 - 00.6

This planetary nebula was observed only in [NII]6583 Å (Fig. 7a) and [OIII]5007 Å (Fig. 7b). Its distance is unknown, one cannot estimate the ionized mass.

$\begin{figure} \psfig {figure=ds7743f8.eps,height=6.6cm} \parbox{\textwidth}{} \end{figure}$

Figure 7: He 2-72. a) [NII]: Two lobes provide the bipolar shape along the minor axis of a ring structure. Two ansae end the major axis (NS). b) The [OIII] image is smaller and rather circular

3.9 He 2-119 - PNG 317.1 - 05.7

A large circular halo (diameter $\sim\!215''$ ) was detected around the 53'' core. Rather faint in H $\alpha$ , much stronger in [NII] and diffuse in [OIII], this explosive structure (Figs. 8) could be the remnant of the early ejections of stellar material. The spheroidal envelope resembles the overall appearance of NGC 6543 (Hua 1997). The absolute calibration is quite difficult (see below for SaWe 3 for instance), due to the presence of number of stars in the field. The values given in Table 3 are estimated within 20% uncertainty. For the inner elliptical area (80 $\times$ 120) $F\rm _i$ (H $\alpha$ ) = 1.47 10^-11 erg cm^-2 s^-1; $F\rm _i$ ([NII]) = 3.1 10^-11 erg cm^-2 s^-1; $F\rm _i$ ([OIII]) = 5.87 10^-11 erg cm^-2 s^-1. In Table 3 we give flux values including the halo for three filters. When subtracting the central nebula and stellar contributions, one obtains an upper limit of 3 10^-12 erg cm^-2 s^-1 for the faint halo. For [NII], $F\rm _h$ ([NII]) = 3. 10^-11 erg cm^-2 s^-1. For oxygen, $F\rm _h$ ([OIII]) = 7.6 10^-12 erg cm^-2 s^-1. Using the H $\alpha$ diameter (215''), the ionized mass is equal to 5.19 10^-2 $\times$ $\epsilon$ $\times$ $N\rm _e$ , leading to $M\rm _i$ $\sim\!1$ $M_{\odot }$ if $\epsilon$ = 0.3 and $N\rm _e$ = 65 cm^-3.

$\begin{figure} \psfig {figure=ds7743f6.eps,height=20cm} \end{figure}$

Figure 8: He 2-119. a) H $\alpha$ . b) [NII]. c) [OIII]. The outer big halo is more prominent in [NII] and [OIII] than in H $\alpha$ . Radial structures are present around the inner [NII] core. The [OIII] outer halo is more diffuse

3.10 Hf 48 - PN G 290.1 - 00.4

This planetary nebula is characterized by a quite strong reddening, since the Balmer decrement is rather high (10.17), and by a strong [NII] emission. The major part consists of a rectangular (10'' $\times$ 15'') core. The fuzzy (20'' $\times$ 25'') envelope is very faint. The surrounding fuzz (Figs. 9) emits a flux $\sim$ 2 10^-13 erg cm^-2 s^-1. In nitrogen, the central area has the same dimensions (2.94 10^-12 erg cm^-2 s^-1) but the outer extensions are larger. The surrounding fuzz then emits a flux $\sim\!1\ 10^{-13}$ erg cm^-2 s^-1. In [OIII] (2.2 10^-12 erg cm^-2 s^-1 for the centre), 1.10^-12 erg cm^-2 s^-1 are due to the surrounding envelope. At the distance of 2000 pc (Maciel 1984), 1'' = 2.99 10¹⁶ cm, the nebular radius (12''5) measures 3.74 10¹⁷ cm. One obtains for the ionized mass 2.5 10^-4 $\times$ $\epsilon$ $\times$ $N\rm _e$ which could amount roughly $\leq$ 0.1 $M_{\odot }$ , if $\epsilon$ = 0.3 and $N\rm _e$ = 1000.

$\begin{figure} \psfig {figure=ds7743f9.eps,height=20cm}\end{figure}$

Figure 9: Hf 48. a) H $\alpha$ . b) [NII]. c) [OIII]. The rectangular core is seen in three wavelengths, with east-west emissions, more extended in [NII] and [OIII]

3.11 IC 4406 - PN 319.6 + 15.7

What is the real structure of the PN IC 4406? Discovered almost a hundred years ago (Stewart 1898), this PN shows low and high ionization species. The narrow-band filter photographs (Warner 1974) display the bright central bulk in [OIII]5007, H $\alpha$ , [NII]6583, [OI]6300 and [SII]6717-6731 as well, with this remark that the central region does not appear to be completely filled in (Warner 1974). Its apparent "cigar-shape'' resembles NGC 6905. The outer emission was reported as due to low ionization potential ions ([SII], [NII] and [OI]). Nonetheless, spectroscopic data giving [OIII]5007/H $\beta$ = 12.67 clearly demonstrate that IC 4406 belongs to the high excitation class (Acker93).

As a matter of fact, our monochromatic H $\alpha$ and [OIII] images (obtained first at MJUO then at SSO) show (Figs. 10) condensations in the central area, separated by a north-south absorbing lane, whereas the outer extension spreads even farther than the western star, as seen in low-ionization transition by Warner 1974. In fact, its looks like a broken ring rather than a dense concentration towards the centre. Therefore, our observations do not agree with the Warner's geometry, since we notice three superposed structures. This result evidences the nonuniform distribution of matter in the very centre of the PN. The central area is formed with a bright centre crossed by an absorbing lane. In addition, a peculiar feature is present in [NII] and not seen in the two other lines (see Figs. 10). The absolute calibration is quite satisfactory between the data obtained first at MJUO and later at SSO, and provides for the for the bright centre F(H $\alpha$ ) = 4.35 10^-11 erg cm^-2 s^-1. Table 3 gives total fluxes emitted by the whole bright rectangle of 105'' $\times$ 35''. The ionized mass estimated with the overall H $\alpha$ diameter (120'') equals 5.12 10^-2 $\times$ $\epsilon$ $\times$ $N\rm _e$ , or 1.9 $M_{\odot }$ assuming $\epsilon$ = 0.3 and $N\rm _e$ = 125.

$\begin{figure} \psfig {figure=ds7743f10.eps,height=20cm} \end{figure}$

Figure 10: IC 4406. a) H $\alpha$ . b) [NII]. c) [OIII]. Left: Overall field of view; right: the inner core. The rectangular and bright inner core is surrounded by a $\sim\!120''$ circular faint halo. The inner core in [NII] shows a different structure even though the EW dusty patch is still present. The rather prominent NE feature seen in [NII] was not detected in the two other filters. We initially attributed it to the "ghost'' image due to the bright centre. However, after careful examination of the previous images taken at MJUO, with the Mc-Lellan 1 metre telescope, this emission nebulosity may be real. [OIII] displays the same structure as for H $\alpha$

3.12 IC 5148 - 50 - PNG 002.7 - 52.4

Already observed at MJUO, this planetary nebula was reimaged at SSO. No new structure was detected in the present larger field of view (Figs. 11). The PN displays a double ring structure with 135'' diameter. The ionized mass amounts 6.54 10^-3 $\times$ $\epsilon$ $\times$ $N\rm _e$ , or $\leq$ 0.2 $M_{\odot }$ assuming $\epsilon$ = 0.3 and $N\rm _e$ = 100.

$\begin{figure} \psfig {figure=ds7743f11.eps,height=20cm} \end{figure}$

Figure 11: IC 5148-50. a) H $\alpha$ . b) [NII]. c) [OIII]. The H $\alpha$ displays a multiple-shell structure with a bright inner ring. The [NII] image is marked by a mulptiple-ring and helical structure. [OIII] shows almost the same morphology as for H $\alpha$ . The major axis is oriented NS (North at the up right corner)

3.13 K 1-3 - PNG 346.9 + 12.4

The overall dimensions (120'' $\times$ 160'') are larger than the 92'' quoted (Figs. 12). On underexposed image, only the bright inner (broken) ring would show up, giving K 1-3 a bipolar structure shape. But deep exposures reveal outer emissions. Oxygen is restricted in a circular shape with smaller dimensions. The ionized mass for a 160'' diameter amounts 1.86 10^-3 $\times$ $\epsilon$ $\times$ $N\rm _e$ , or 0.058 $M_{\odot }$ with $\epsilon$ = 0.3 and $N\rm _e$ = 100.

$\begin{figure} \psfig {figure=ds7743f12.eps,height=20cm} \end{figure}$

Figure 12: K 1-3. a) H $\alpha$ . b) [NII]. c) [OIII]. This double-shell planetary nebula displays a "shark-jaws'' structure. The major axis is along the E-W direction. Two N-S blobs end the minor axis. Nitrogen is much stronger. Only the two inner peaks are seen superimposed on a diffuse and smaller emission in [OIII]. North at the up right corner

3.14 K 2-7 - PN G 019.4 - 19.6

Surprisingly, few measurements were done on this PN since its discovery by Kohoutek on 1963. We could only observe the planetary nebula with the H $\alpha$ filter (Fig. 13a) just before the clouds came in. Two distance measurements are available but with a factor 2 of discrepancy: from 1.27 kpc (Cahn & Kaler 1971) to 2.6 kpc (Maciel 1984). Therefore its ionized mass would amount 1.4 10^-2 $\times$ $\epsilon$ $\times$ $N\rm _e$ and 0.12 $\times$ $\epsilon$ $\times$ $N\rm _e$ respectively. Assuming $\epsilon$ = 0.3 and $N\rm _e$ = 100, one obtains 0.04 $M_{\odot }$ and ... 3.6 $M_{\odot }$ !

$\begin{figure} \psfig {figure=ds7743f13.eps,height=6.6cm} \parbox{\textwidth}{ } \end{figure}$

Figure 13: a) K 2-7. Only the H $\alpha$ image was obtained for this almost perfectly circular and faint planetary nebula. b) SaWe 4. Only the H $\alpha$ image was obtained showing a circular shape

3.15 Lo 17 - PN G 356.8 - 11.7

The H $\alpha$ and [NII] (2400s integration) images which were first acquired at MJUO (1993), then completed with [OIII] (600s) at SSO (1997), display a "donut" shape (Figs. 14), with the overall diameter of 110''. The ionized mass could not be computed without knowledge of the distance. Its circular annulus shape resembles A 39.

$\begin{figure} \psfig {figure=ds7743f14.eps,height=20cm} \end{figure}$

Figure 14: Lo 17. a) H $\alpha$ . b) [NII]. c) [OIII]. The three images show a nearly perfect circular ring, with probably an outer diffuse shell

3.16 NGC 246 - PNG 118.8 - 74.7

This high-excitation PN shows no [NII] emission. Three monochromatic images were obtained: H $\alpha$ (Figs. 15), [OIII] and HeII much smaller and fainter. With 265'' diameter, its ionized mass equals 4.08 10^-3 $\times$ $\epsilon$ $\times$ $N\rm _e$ , or 0.16 $M_{\odot }$ with $\epsilon$ = 0.3 and $N\rm _e$ = 150.

$\begin{figure} \psfig {figure=ds7743f15.eps,height=20cm} \end{figure}$

Figure 15: NGC 246 a) H $\alpha$ . b) [OIII]. c) HeII 4686 Å. This high-excitation PN has a similar structure in H $\alpha$ and [OIII]. Nitrogen was not detected. HeII $\lambda$ 4686 shows up very weak and has almost the same volume

3.17 NGC 3699 - PNG 292.6 + 01.2

The H $\alpha$ image (Figs. 16) of this planetary nebula displays a $\sim\!145''$ dimension, leading to $M\rm _i$ = 2.63 10^-3 $\times$ $\epsilon$ $\times$ $N\rm _e$ , i.e. $\sim\!0.7$ $M_{\odot }$ , assuming $\epsilon$ = 0.3 and $N\rm _e$ = 100. The [NII] image shows a spectacular extension which would be larger than our field of view (6'5). In addition, we have detected a faint emission nebula 50'' west of NGC 3699. For nitrogen, the computations of absolute flux were more difficult due to the overall extensions. Nevertheless, we obtain F([NII]) = 2.5 10^-11 erg cm^-2 s^-1 for the main nebula, while the newly detected nebulosity emits F([NII]) = 8 10^-13 erg cm^-2 s^-1. In [OIII] (Fig. 16c) we get F([OIII]) = 5.21 10^-13 erg cm^-2 s^-1 for the new object. The overall fluxes are given in Table 3.

$\begin{figure} \psfig {figure=ds7743f16.eps,height=20cm} \parbox{\textwidth}{} \end{figure}$

Figure 16: NGC 3699. a) H $\alpha$ . b) [NII]. c) [OIII]. Left: Overall field of view. Right: Enlargements for the bright central area. The two-lobe structure in the central area is probably due to a strong absorbing lane nearly oriented E-W, and superimposed on a fainter underlying emission. The nitrogen emission is much more prominent and much more extended than the two other emission lines. Notice a bright emission nebula at the W-side in the total field of view, still much brighter in [NII]. A faint and large loop spreads over $\sim\!6$ arcmin, in three wavelengths

3.18 NGC 5189 - PN G 307.2 - 03.4

Strong IRAS emissions were reported 12/25/60/100 = 1.26/13.47/33.73/31.29 as well as strong S(6 cm). The [SII] intensity ratio would imply $N\rm _e$ $\approx$ 10³ cm^-3. The largest dimension (Figs. 17) in the H $\alpha$ image (195'') leads to the ionized mass 5.3 10^-3 $\times$ $\epsilon$ $\times$ $N\rm _e$ , or 1.5 $M_{\odot }$ if $\epsilon$ = 0.3 and the above electron density.

$\begin{figure} \psfig {figure=ds7743f17.eps,height=20cm} \end{figure}$

Figure 17: NGC 5189. a) H $\alpha$ . b) [NII]. c) [OIII]. This "Z-shape'' already observed at MJUO is confirmed with SSO's images for this planetary nebula which displays a strong filamentary structure

3.19 NGC 6302 - PNG 349.5 + 01.0

This PN was already observed at MJUO (Hua 1997). New monochromatic images (Figs. 18 & 19) were again performed at SSO through four filters H $\alpha$ , H $\beta$ , [NII]6583 Å, [OIII]5007 Å, and [SII]6717/6731 with the AAT 2.3-m telescope confirming an explosive structure surrounding a compact central core divided into two areas by an absorbing lane. The central area is much more brighter than the peripheral zones. Thanks to the larger field of view at SSO, we were able to outline the outermost extensions. The H $\alpha$ and [OIII]5007 images have similar structures, whereas the [NII]6583 image displays condensations, and possibly the presence of a surrounding halo.

Presumably young (OH 1612 MHz detection by Payne et al. 1988), and due to its location near the galactic plane, this bipolar PN is strongly affected by high interstellar absorption since E(B-V) = 0.93 from the flux(radio)/flux(H $\beta$ )ratio. The "strong physical condition'': excitation class 10⁺, the helium abundance He/H being twice (0,182) the average value for known PNe, are certainly related to the (invisible) central star with B $\geq$ 21.1, Acker93) the Stoy temperature of which is about 3 10⁵ K, and even higher, up to 4.3 10⁵ K (Ashley & Hyland 1988). Furthermore, nitrogen N/H (85 10^-5) is 10 times the average value (CKS92 and Pottasch 1984). Fast motions were detected in the [NeV]3426 Å line profile (Meaburn & Walsh 1980) with velocities approaching 800 km s^-1.

$\begin{figure} \psfig {figure=ds7743f18.eps,height=11.6cm} \end{figure}$

Figure 18: NGC 6302. a) H $\alpha$ . b) [NII]. c) [OIII]. d) The [SII]6717/6731 intensity ratio. The remarkable "butterfly-shape" appears in three emission lines, but more extended in [NII]. The electron density is rather high in the very centre which is seen in white, whereas the outer area corresponds to $N\rm _e$ < 10³

$\begin{figure} \psfig {figure=ds7743f19.eps,height=12.8cm} \end{figure}$

Figure 19: NGC 6302 inner regions. a) H $\alpha$ . b) [NII]. c) [OIII]. d) [SII]6717 ( $\Delta$ $\lambda$ = 4.7 Å)

This very dusty PN with strong IRAS data 12/25/60/100 = 32.08/335.90/849.70/537.40 and S(6 cm) = 3100 mJy shows an outstanding "butterfly'' morphology. In addition, it is overabundant in nitrogen (H $\alpha$ /[NII]/[OIII] = 704/1758/1354). The [SII] intensity ratio (64/99) implies a high electron density. As a matter of fact, our narrowband images clearly demonstrate that this parameter is far from uniform across the nebula. The plot of the intensity ratio [SII]6717/6731 (Fig. 18d) shows the variation of $N\rm _e$ , from $\sim$ 10⁴ cm^-3 in the very bright centre (in white; the [SII]6717/6731 ratio is $\leq$ 0.5) to a few hundreds cm^-3 (in black; [SII]6717/6731 $\sim$ 1.2).

The absolute calibration gives for the bright rectangular area F₁(H $\alpha$ ) = 1.71 10^-10 erg cm^-2 s^-1. This determination is in very good agreement with that (2.10 10^-10 erg cm^-2 s^-1) reported by Hua 1997, considering the fact one cannot adjust quite exactly the integration contour around the nebula. Including the outermost extensions, one gets 1.77 10^-10 erg cm^-2 s^-1. The important thing to emphasize is that our images are absolutely calibrated, so that every pixel provides an absolute flux value for various interference filters in use. It is always possible to use isophotal contours to obtain the total flux values.

For the "same'' bright area F(H $\beta$ ) = 2.07 10^-11 erg cm^-2 s^-1, leading to a Balmer decrement of 8.21, so that we derive E(B-V) = 1.05 (in the case B assumption). This result is not so discrepant with above radio determination. For the same region, F([NII]) = 4.53 (4.64 including the outermost extensions) 10^-10 erg cm^-2 s^-1, leading to the following intensity ratios: F([NII])/F(H $\beta$ ) $\sim$ 22, instead of 17.58 (Acker93, but this "discrepancy is not significant due to the irregular shape of the planetary nebula); F([NII])/F(H $\alpha$ ) = 2.65 instead of 2.5 (Acker93). F([OIII]) = 3.86 (3.93 with extensions) 10^-10 erg cm^-2 s^-1 leading to F([OIII])/ F(H $\beta$ ) = 18.7 (13.5 Acker93) and F([OIII])/ F(H $\alpha$ ) = 2.26 (1.92 Acker93). F([SII]6717) = 3.66 (3.93) 10^-12 erg cm^-2 s^-1; F([SII]6731) = 3.85 (3.97) 10^-12 erg cm^-2 s^-1, so that the average intensity ratio equals 0.95.

3.20 NGC 6853 - PNG 060.8 - 03.6

The Dumbbell nebula has been extensively investigated by several teams during the last two decades (Hua & Louise 1970, 1981; Moreno-Corral et al. 1992). However, one may ask a question as to whether this planetary nebula has so far revealed all its overall structure.

New monochromatic images (Figs. 20) were taken in H $\alpha$ , H $\beta$ , [NII] and [OIII] emission lines. The overall dimensions are much larger than the 12' field of view offered by the 120-cm telescope (f/6). NGC 6853 probably should have the same intrinsic morphology as Sh 1-89 (Hua 1997) but seen pole-on, the outer emission corresponding to an equatorial confinement (gravitational breaking) due to a massive central star. Our monochromatic pictures suggest shock mechanism, along with the ISM influence. An extended halo was detected around the "dumbbell'' centre, with this particularity that this halo is not the same in H $\alpha$ , [NII] or in [OIII]. Radial structures show up with "cometary dust'' features outwards. A prominent dusty patch crosses the [OIII] image, which has not the same morphology as in the two other lines. Even S⁺⁺ ion is seen outwards, of course quite much fainter. Due to the non-photometric conditions during the absolute calibration, we prefer not to provide uncertain flux values, and do hope to be able to do such calibration shortly in better conditions. Nonetheless, attempts to estimate ionized mass were done using the measured H $\alpha$ dimensions. The major axis of the bright main nebula (470'') would infer $M\rm _i$ = 3.89 10^-3 $\epsilon$ $N\rm _e$ , at the distance of 262 pc. Assuming $\epsilon$ $\times$ $N\rm _e$ = 0.3 $\times$ 1000, one gets 1.16 $M_{\odot }$ . The overall diameter is much larger (720''), leading to $M\rm _i$ = 0.11 $\epsilon$ $\times$ $N\rm _e$ , so that the total ionized mass would be 3.3 $M_{\odot }$ if $\epsilon$ $\times$ $N\rm _e$ = 0.3 $\times$ 100.

$\begin{figure} \psfig {figure=ds7743f20.eps,height=12.8cm} \end{figure}$

Figure 20: NGC 6853. a) H $\alpha$ . b) [NII]. c) [OIII]. The well-known "dumbbell'' shape of the central area is not reproduced here. The emission structures of the outer halo detected in these images do not have the same origin. The dusty patch is well outlined in [OIII]. The overall dimensions should be larger than our present field of view (12')

3.21 SaWe 3 - PNG 013.8 - 02.8

This outstanding planetary nebula displays a bipolar shape in H $\alpha$ , and [NII] (Figs. 21) more obviously than in [OIII]. In absence of some useful parameters (distance, radio flux, etc.) we could only provide the absolute fluxes (Table 3). The H $\alpha$ /[NII] intensity ratio slightly differs with spectroscopic data (see Table 2); as a matter of fact, after superimposing the [NII] and H $\alpha$ images, we measured this ratio varying from 0.7 (outermost area) to 3.6 (in the central bright filament).

$\begin{figure} \psfig {figure=ds7743f21.eps,height=20cm} \end{figure}$

Figure 21: SaWe 3. a) H $\alpha$ . b) [NII]. c) [OIII]. A knotty core is surrounded with extended EW diffuse emissions. Probably seen edge-on, SaWe 3's intrinsic structure should resemble Sh 1-89

3.22 SaWe 4 - PNG 014.7 - 11.8

The H $\alpha$ image (Fig. 13b) shows two small condensations over a roundish (40'' diameter) and diffuse nebula emitting a flux F(H $\alpha$ ) = 4.44 10^-13 erg cm^-2 s^-1. Without knowledge of its distance, we cannot derive the corresponding ionized mass.