8 Figures

 

Figure 1: A 13 in H$\alpha$ with equatorial coordinates

  

Figure 2: This H$\alpha$ image of A 13 displays an elliptical ring which resembles that of NGC 6720. However, the outer emission is by far less extended. The image frame covers 350 square arc seconds. North is at the top, East to the left for all figures, unless otherwise stated

  

Figure:3 The [N II] image of A 13, represented in the same image frame scale as for H$\alpha$. Diffuse extensions can be seen spreading to radii as large as $\sim$12', comparable to that given by Rosado & Moreno (1991). The faint fuzzy outward radial structures could result from a projection of bubble-like emissions - like in Sh1-89 (Hua & al. 1998) on the plane of sky. In nitrogen, A 13 appears as a multiple-shell planetary nebula

  

Figure 4: Variation of the [NII] to H$\alpha$ intensity ratio with a maximum of 2.5 in the SW area

 

Figure:5 Isophotal contours of the intensity ratio map with start/end/step = 0.4/2.5/0.3, showing that the outer faint extension PA is perpendicular to that of the bright ring (in agreement with Rosado & Moreno 1991). See A 24 below. Coordinates are in arc seconds. A EW cross-section through the central star (line 340) shows the two peaks separated by 115''

  

Figure 6: A EW cross-section through the central star (line 340) shows the two intensity ratio peaks separated by 115''

 

Figure 7: A 21 in H$\alpha$ with equatorial coordinates

  

Figure 8: The overall dimensions of A 21 are certainly much larger than this H$\alpha$ image spreading over 700'' as indicated in our field of view

  

Figure 9: The [NII] image of A 21 with the same remarks as for H$\alpha$

  

Figure 10: Variation of the [NII] to H$\alpha$ intensity ratio of A 21

 

Figure 11: Isophotal contours for the [NII]/H$\alpha$ intensity ratio of A 21, with 0.7 start, and 0.2 step. Numbers and tick marks are in arc seconds

 

Figure 12: A 24 in H$\alpha$ with equatorial coordinates

  

Figure 13: The H$\alpha$ image A 24. Numbers are expressed in arc seconds, as for all figures presented

  

Figure 14: The [N II] image A 24. Both the lobes and the radial structures are more prominent in the [N II] than in H$\alpha$ images

 

Figure 15: Ratio of the [N II]/H$\alpha$ images of A 24. This ratio varies from 0.6 in the light shadowed areas to 2.5 (maximum = 3.5) within the two lobes

  

Figure 16: Isophotal contours (start/step = 0.5/0.2) of the [N II]/H$\alpha$ intensity ratio of A 24. This ratio varies from 0.6 in the light shadowed areas to 2.5 (maximum = 3.5) within the two lobes. A 24 also has the outer extension PA almost perpendicular to that of the bright inner blobs (see above A 13). Coordinates are indicated in arc seconds

 

Figure 17: A 28 with equatorial coordinates

  

Figure 18: The H$\alpha$ image of A 28. Fragments of an outer shell can be seen in the south-west side of this nearly circular PN

  

Figure 19: The [N II] image of A 28 shows a ring-like shape with a bipolar structure. The line from NW to SE is the trace of a satellite trajectory

  

Figure 20: The [O III] image of A 28. The [OIII] emission is faint and well confined to the vicinity of the central star

 

Figure 21: A 30 with equatorial coordinates

  

Figure 22: The H$\alpha$ image of A 30. The almost perfectly circular shape shows four fragments with enhanced intensity along the ring. The core is composed with two bright knots close to the central star. The [N II] structure only consists of the same "ansae'' but much brighter, see isophotes below

  

Figure 23: The [NII] image of A 30: The spherical shell is not detected (even though very faint "traces'' can be suspected against the noise level) in the [N II] image, suggesting that the shell may be nitrogen poor. The [N II] structure only consists of the same "ansae'' but much brighter, see isophotes below

  

Figure 24: The [O III] image of A 30. The four enhancements along the ring seen in H$\alpha$ are still visible in [O III]. Yet, the inner "spider'' feature seems to whirl around the central knots

  

Figure 25: The central part of A 30 in (from left to right) H$\alpha$, [N II], and [O III] in grey scale (upper panel) and contour (lower panel) representations. The scales on the contour maps are in arc seconds

 

Figure 26: A 33 with equatorial coordinates

  

Figure 27: This H$\alpha$ image of A 33 nicely illustrates the "diamond ring'' structure, while the almost perfectly spherical shape reflects a uniform shell, and the inner structure rather suggests a bipolar morphology

  

Figure 28: The [O III] image of A 33 displays a similar structure as for H$\alpha$, but with a stronger intensity. The inner area resembles NGC 3587, the "Owl Nebula''

  

Figure 29: This [O III] to H$\alpha$ intensity ratio of A 33, varying from 0.6 to 1.5 reached on the double-ring structure, reveals a double-shell structure. The circular diffuse emission is due to the bright foreground star

 

Figure 30: A 36 with equatorial coordinates

 

Figure 31: The H$\alpha$ image, in logscale, of A 36 shows a helical structure resembling the "Cat Eye'' nebula as seen by HST

 

Figure 32: The [O III] image of A 36 also displays a similar helical inner region as in the H$\alpha$ image but with a fainter emission along with outer "spiraling arms''