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Old 01-03-2022, 10:41 AM
EpickCrom (Joe)
Epick Crom

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Ngc 2818

Hi all. Last night I observed NGC 2818, a planetary nebula and open cluster combination. I identified NGC 2828 the planetary with difficulty, it looked like a diffuse haze at 267x. However I saw no trace of the open cluster that the planetary is embedded in. What is your guys experience in observing this two for one combo object? How difficult is it for you too see the open cluster specifically? Thanks and clear skies
Joe.
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Old 01-03-2022, 03:36 PM
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ngcles
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Hi Joe,

Very interesting object in some ways -- the PNe is much, much the better of the two objects that share one designation.

It was discovered by James Dunlop at Paramatta (not the government observatory but his own observing site) on 28 May 1826.

According to Steve Gottlieb's NGC notes: "His (Dunlop's) summary description (based on two observations) reads "a pretty large faint nebula [star cluster] of a round figure, 6' or 8' diameter; the nebulosity is faintly diffused to a considerable extent. There is a small nebula [PN] in the north preceding edge, which is probably a condensation of the faint diffused nebulous matter; The large nebula is resolvable into stars with small nebula remaining." He clearly described both the PN and the cluster".

Dunlop observed with a small speculum-mirror reflector approximately the equivalent of a modern 15cm reflector.

Again from Steve's NGC notes: "Sir John Herschel recorded on 7 Aug 1837 (sweep 787): "A very curious object which reminds me strongly of M46 and IV. 39 [NGC 2438]. It is a rich cluster of the VI class, stars 12..14m; about 8' dia, gpmbM; all but a sort of vacuity, in which is situated a pB, R, neb; 40" diam; of a character approaching to planetary, having its edges shading off very rapidly, and being but very little brighter in the middle." His sketch is reproduced on plate V, figure 8 of the CGH Observations. A second observation on 22 Jan 1838 (sweep 809) describes the planetary first and the NGC summary refers to the planetary (in a large cluster)".


The two objects, the cluster and the PNe are not physically associated, reside at different distances and have differing radial velocities.


The cluster itself is far from being a conspicuous one and most of the stars are around the 12th and 15th magnitude range. Because it is a milky way field, it doesn't stand out from the surroundings very well (if indeed at all).

If you were observing using your 25cm telescope (particularly if it were suburban conditions) I'm hardly surprised it escaped your attention. The PNe is actually a genuinely spectacular object in truly large apertures under rural or pristine skies -- particularly if you have a UHC eyepiece nebula filter and the seeing permits high magnifications.

Here are my own observing notes using 25 and 46cm. Both were from rural sites, the latter on a night with exceptional seeing:

NGC 2818 + NGC 2818A OC +PNe Pyxis
25cm x86: Quite a small cluster which is no more than 10' diameter. The 4 brightest stars seem to mark boundaries, and a magnitude 11 star in the centre. Scattering of maybe 50 stars magnitude 11.5 to threshold and a bit of weak milkiness in the centre. Moderately range in brightness, More faint stars in the S end. On the outer halo in NW corner is NGC 2818A, and associated PNe. NGC 2818A: Easily visible at x86 without filtration. Sort of "U" shaped and open to the NE. Roundish, unevenly lit. S side is distinctly brightest. Bright spot or stellaring there. Dark area (ie inside the "U", intrudes from the NE toward centre. A very pleasing object. No central star is evident. Diffuse edges.

46cm x247 + x317: NGC 2818A is a very interesting and unusual PNe. The brighter areas look like a pair of longish butterfly wings without the butterfly body in the centre -- longish opposing mirrored triangles with the long axis in PA 90. Each long triangle is about 30" long and 10" wide at the widest and the N one is slightly the weaker in brightness and definition. The short sides of the triangle are the best defined but the two long hypotenuse much less defined on their edges. An area around this is very weakly nebulous out to 60" diameter. Moderately bright. Good response to OIII and UHC. Some bluish/smoky bluish colouration Best at x247.

Steve Gottlieb's notes with various apertures:

14.5" (4/10/21): at 140x, the open cluster appeared as a sprinkling of mostly fainter mag 13-14 stars spread over a 7' region, along with a few brighter mag 12 stars. Increasing to 226x, the cluster appeared fairly rich, with close to 50 stars resolved, including many in the mag 14-14.5 range that popped in an out of view.

The planetary nebula is situated along the west side of the cluster and displayed an excellent response to an NPB filter at 140x. It appeared relative bright and large, ~50" diameter, with an irregular shape (elongated ~N-S) that was hard to pin down, and an uneven surface brightness.


17.5" (3/25/00): NGC 2818 refers to both an open cluster and a superimposed planetary nebula (identified as NGC 2818A in the RNGC). The moderately bright PN is nestled on the west side of a faint but fairly rich open cluster. At 220x it appeared moderately bright, irregularly shaped, ~1.0'x0.8' and elongated roughly N-S. Excellent view at 280x with a UHC filter and unfiltered at 380x. The rim is irregularly brighter and gave a weak annular appearance; brightest at the south and southwest rim. The center is slightly darker but there was no well-defined central hole. The outline was not crisp and seemed to change orientation somewhat with averted vision.


13.1" (4/10/86): the cluster appears as a faint group of 25-30 stars mag 12 to 15, over unresolved haze, though good seeing might resolve more. Includes a fairly faint planetary (NGC 2818A) on the west side. At 166x using a Daystar 300 filter, the planetary appeared moderately bright and large, elongated ~N-S. Also responds well to an OIII filter at 79x.


13.1 (1/28/84): the cluster is a faint group of two dozen stars mag 12 and fainter. The planetary on the west side of the cluster is a pretty sight using a UHC filter at 79x. It appeared fairly faint, moderately large, 1.0'x0.8', elongated N-S or SSW-NNE.

Hope all that helps,

Best,

L.
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Old 01-03-2022, 04:35 PM
EpickCrom (Joe)
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Quote:
Originally Posted by ngcles View Post
Hi Joe,

Very interesting object in some ways -- the PNe is much, much the better of the two objects that share one designation.

It was discovered by James Dunlop at Paramatta (not the government observatory but his own observing site) on 28 May 1826.

According to Steve Gottlieb's NGC notes: "His (Dunlop's) summary description (based on two observations) reads "a pretty large faint nebula [star cluster] of a round figure, 6' or 8' diameter; the nebulosity is faintly diffused to a considerable extent. There is a small nebula [PN] in the north preceding edge, which is probably a condensation of the faint diffused nebulous matter; The large nebula is resolvable into stars with small nebula remaining." He clearly described both the PN and the cluster".

Dunlop observed with a small speculum-mirror reflector approximately the equivalent of a modern 15cm reflector.

Again from Steve's NGC notes: "Sir John Herschel recorded on 7 Aug 1837 (sweep 787): "A very curious object which reminds me strongly of M46 and IV. 39 [NGC 2438]. It is a rich cluster of the VI class, stars 12..14m; about 8' dia, gpmbM; all but a sort of vacuity, in which is situated a pB, R, neb; 40" diam; of a character approaching to planetary, having its edges shading off very rapidly, and being but very little brighter in the middle." His sketch is reproduced on plate V, figure 8 of the CGH Observations. A second observation on 22 Jan 1838 (sweep 809) describes the planetary first and the NGC summary refers to the planetary (in a large cluster)".


The two objects, the cluster and the PNe are not physically associated, reside at different distances and have differing radial velocities.


The cluster itself is far from being a conspicuous one and most of the stars are around the 12th and 15th magnitude range. Because it is a milky way field, it doesn't stand out from the surroundings very well (if indeed at all).

If you were observing using your 25cm telescope (particularly if it were suburban conditions) I'm hardly surprised it escaped your attention. The PNe is actually a genuinely spectacular object in truly large apertures under rural or pristine skies -- particularly if you have a UHC eyepiece nebula filter and the seeing permits high magnifications.

Here are my own observing notes using 25 and 46cm. Both were from rural sites, the latter on a night with exceptional seeing:

NGC 2818 + NGC 2818A OC +PNe Pyxis
25cm x86: Quite a small cluster which is no more than 10' diameter. The 4 brightest stars seem to mark boundaries, and a magnitude 11 star in the centre. Scattering of maybe 50 stars magnitude 11.5 to threshold and a bit of weak milkiness in the centre. Moderately range in brightness, More faint stars in the S end. On the outer halo in NW corner is NGC 2818A, and associated PNe. NGC 2818A: Easily visible at x86 without filtration. Sort of "U" shaped and open to the NE. Roundish, unevenly lit. S side is distinctly brightest. Bright spot or stellaring there. Dark area (ie inside the "U", intrudes from the NE toward centre. A very pleasing object. No central star is evident. Diffuse edges.

46cm x247 + x317: NGC 2818A is a very interesting and unusual PNe. The brighter areas look like a pair of longish butterfly wings without the butterfly body in the centre -- longish opposing mirrored triangles with the long axis in PA 90. Each long triangle is about 30" long and 10" wide at the widest and the N one is slightly the weaker in brightness and definition. The short sides of the triangle are the best defined but the two long hypotenuse much less defined on their edges. An area around this is very weakly nebulous out to 60" diameter. Moderately bright. Good response to OIII and UHC. Some bluish/smoky bluish colouration Best at x247.

Steve Gottlieb's notes with various apertures:

14.5" (4/10/21): at 140x, the open cluster appeared as a sprinkling of mostly fainter mag 13-14 stars spread over a 7' region, along with a few brighter mag 12 stars. Increasing to 226x, the cluster appeared fairly rich, with close to 50 stars resolved, including many in the mag 14-14.5 range that popped in an out of view.

The planetary nebula is situated along the west side of the cluster and displayed an excellent response to an NPB filter at 140x. It appeared relative bright and large, ~50" diameter, with an irregular shape (elongated ~N-S) that was hard to pin down, and an uneven surface brightness.


17.5" (3/25/00): NGC 2818 refers to both an open cluster and a superimposed planetary nebula (identified as NGC 2818A in the RNGC). The moderately bright PN is nestled on the west side of a faint but fairly rich open cluster. At 220x it appeared moderately bright, irregularly shaped, ~1.0'x0.8' and elongated roughly N-S. Excellent view at 280x with a UHC filter and unfiltered at 380x. The rim is irregularly brighter and gave a weak annular appearance; brightest at the south and southwest rim. The center is slightly darker but there was no well-defined central hole. The outline was not crisp and seemed to change orientation somewhat with averted vision.


13.1" (4/10/86): the cluster appears as a faint group of 25-30 stars mag 12 to 15, over unresolved haze, though good seeing might resolve more. Includes a fairly faint planetary (NGC 2818A) on the west side. At 166x using a Daystar 300 filter, the planetary appeared moderately bright and large, elongated ~N-S. Also responds well to an OIII filter at 79x.


13.1 (1/28/84): the cluster is a faint group of two dozen stars mag 12 and fainter. The planetary on the west side of the cluster is a pretty sight using a UHC filter at 79x. It appeared fairly faint, moderately large, 1.0'x0.8', elongated N-S or SSW-NNE.

Hope all that helps,

Best,

L.
Excellent NgcLes! That sure helps a lot! I'm observing from the inner suburbs using my 25cm dob, my only scope for now. My skies are bortle 7/6. This explains why I only saw the planetary ( with real difficulty using high magnification and averted vision) but not the fainter smaller open cluster. Very nice observations you have of this interesting cluster/ planetary. Thanks.
Joe
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