Object of the Week December 11th, 2016 - NGC 1501 The Oyster Nebula

Object of the Week December 11th, 2016 - NGC 1501 The Oyster Nebula


NGC1501
PK144+6.1

Camelopardalis

Planetary Nebula


RA 04 06 59.6
DEC 60 55 11

Mag: 11.5
CS Mag: 14.3

Size: 52.0"

Discovered on November 3rd, 1787 by William Herschel, NGC1501 lies approximately 5000 light years distant in the constellation Camelopardalis. Williams' notes about his discovery that night read "a pretty bright...round, of uniform light and pretty well defined... and a little elliptical."

Visually, NGC1501 can be spotted in scopes as small as 4 inches. Sue French, in her wonderful book, Deep-Sky Wonders, reports that NGC1501 appears as a "small, round and fairly bright" in her 105mm refractor. In larger scopes, NGC 1501, atleast to me, resembles IC418 in Lepus. The resemblance is only similar in structure and not in color, where NGC1501 has a bright gray/green glow in my 25" and IC418 is a beautiful and rare pink/reddish color. NGC1501 does have a very mottled appearance similar to IC418. Larger scopes reveal a subtle oval shape that is aligned northeast to southwest with an apparent central star that shines at 14.3 magnitude. Annularity can be seen in magnifications greater than 350x though don't expect anything like M57. Here, the donut effect is muchmore subtle.

On a more scientific note, NGC 1501 has been a subject of study for quite some time. As printed in the Proceedings of the 180th Symposium of the Astronomical Union under the entry title Asteroseismology of Planetary Nuclei, Bond et al reported that in November of 1991, 5 observatories from around the world were in search of low amplitude pulsations of central stars in 29 known planetary nebulae. Of those 29, 6 were confirmed to have pulsing central stars, NGC 1501 being one of them. NGC1501, whose central star is a Wolf-Rayet star, has a period of 20-30 minutes and a variation of approximately 0.1 magnitude, much to low for us to detect visually of course. But what the researchers found interesting was that this WR star, at the heart of a planetary nebula no less, was a variable; something that isn't known to be too common.

So if you're far enough north, be sure to take a look towards Camelopardalis this winter. NGC 1501 is a beautiful PN visible in all manners of scope, so please don't be shy.

And as always,

Give it a go and let us know!

Attachment 2380
©Hubble/ESA/NASA

Attachment 2381
©Adam Block

Great target. Here are my notes with 16" (I first saw it with 4):

225x with Ethos: Almost round, softly annular. Middle uniformly nebulous. Sharp central star can be held almost continuously. There are small breaks in the enhanced annular edge on the E and W side. The EW axis is a little longer than NS one.

Yes, very cool. I didn't realize 1501's central star was a confirmed variable - that's really interesting! I haven't looked at it in a while, but here's my latest from 2009:

"...1501 has a distinct perimeter that's also the the brightest part of the planetary. This rim gradually dims toward the center, which is obviously dark and features a nice central star that was barely seen with direct vision at 253x. Great view without filters, 21.08 SQM."

Attachment 2382 Attachment 2383

No mention of color though...

Very nice planetary, though seems to be often ignored. Here is my last observation with my 18-inch ...

"Superb view at 450x in good seeing. The 1' diameter disc is slightly elongated ~E-W, ~60"x50" with a very narrow, brighter rim and darker center. The mag 14.4 central star was steadily visible. On closer inspection the thin rim was clearly irregular in surface brightness and slightly brighter along the southwest and northeast sides with a couple of tiny knots embedded in the rim. The slightly darker interior was weakly mottled or patchy with subtle variations in surface brightness."

For comparison, here's how it was described by Lawrence Parsons (William's son) on the 72-inch, back in 1868 ...

"A bright ring and inside it a dark annulus, very decided. A star in the centre seen very clearly and continuously with various powers; suspect variable brightness in the ring, perhaps a dark spot in it nearly on the preceding side. The following side of the ring appears broadest and to approach the central star nearer than the preceding side does. The north and south sides of the ring seem rather brighter than the preceding and following sides. Suspect other bright points in it, but am not at all certain. It is slightly elliptical, its major axis being nearly preceding and following [West and East]."

Hmm, now I'm wondering why I didn't the elliptical shape - better go back for another look.

Very nice planetary.

In the 16" the slightly elliptical shape was clearly noticeable. Like Steve said with irregular rim with knots and brighter structures. The wild inner part merges in two darker holes. CS was steadily visible.

sketch 16", 450x, NELM 6m5+
Attachment 2391

Last new moon period I tried to resolve the inner structure with my 27" under 900x. Because of the soso seeing and the very filigree structure it was not possible to resolve the spectacular structures. Perhaps I tried it with bigger aperture and/or better seeing.

Nice choise Dragan, for sure one of my favorite PNs.

I can contribute an observation using my 12" dobson under pretty good conditions in the Bavarian Alps, about 60 miles south-east of Munich.

http://www.licht-stimmungen.de/01_su...1_10_2011.html

The central star was steadily visible, as well as the slightly oval shape and an irregular rim (two brighter areas). No structure inside the PN.

Power was 500x (Nagler Zoom at 3mm), no filter used.

My observations of Saturday night (25 Feb) from SQM 21.4 skies with excellent seeing:

At 427x a reasonably bright central star (it is the brightest star in the FOV) surrounded by a circular sphere (it is not elongated) that has a bright rim and a mottles disk that is brighter than the sky background. I get the impression of dark spokes in the disk but this is only induced by dark gaps in the rim. To the north lies a star that is slightly fainter than the central star, to the south another one which is the eastern most one of a line of three and a third one to the north west. In the direction of the first star lies a brighter knot in the rim. At first I thought it was a star but it is not. The southern part of the rim also is brighter with two or three knots in it.


Clear skies, Wouter