Object of the Week, January 3rd, 2016 - Abell 24 in Canis Minor

[Paul Alsing]

Object of the Week, January 3rd, 2016 - Abell 24 in Canis Minor
Abell 24 = PN G217.1+14.7, PK 217+14.1, ARO 134
R.A.: 07h51m37.6s
Dec.: +03°00'21" (2000)
Size: 6.0'
Mag: 13.60 photographic

Canis Minor (the smaller dog) is ranked as the 71st constellation, in terms of size. Of course, it features blazing Procyon as its brightest star, and Procyon is the 7th brightest star in the sky; it is a very challenging double star with a huge delta between the bright mag 0.37 primary and the mag 13 secondary, 4.1" distant.

Canis Minor has very few deep sky objects, relatively speaking. SkyTools tells me that there are only 248 galaxies here brighter than mag 16, only 13 with the NGC designation, only 3 IC's, and only 6 brighter than mag 14! Other than galaxies, there are 6 or 7 open cluster and 5 planetary nebulae, but only 2 of these are brighter than mag 16, those being the mag 15.4 Abell 22 and the mag 13.6 Abell 24, the subject of the first OOTW of 2016!

I observed Abell 24 just once, in a nice sky, from my regular spot in the local Anza-Borrego desert, altitude about 2500 feet, in the clear and cold winter sky, using my 25" f/5 Obsession. Without any filter, it was difficult to acquire until I tapped the telescope, and then it was detected only as a faint annular stain on the sky, without any details whatsoever, and with a diffuse edge... and not much more. Hey, this guy has an estimated surface brightness of 16.71 magnitudes per square arcminute! Of course it is difficult to see :>)

I added an NPB filter and the PN became more than just a glow, and I could see a slight brightening in 2 spots, on both the east and west sides, and I didn't note any brightening in the middle. I also didn't see the binary central star, listed at a mere mag 17.1.

During my hunt for photos of Abell 24, I ran across this web page, http://www.darklights.org/gallery/pn/ which has a unique feature; when you hover your mouse over an image you see a different image superimposed, where the imager used either an OIII filter or an Ha filter.

Abell 24- L.2015.03.19.jpgAbell 24-Ha.2015.03.19.jpg

This photo shows lots of tantalizing features which are undoubtedly unavailable to visual observers!

Abell_24.jpg

As always, give it a go and let us know, this guy is a stinker!

[Uwe Glahn]

"Stinker" is a good point Paul.
Although the PN seems to be an easy target when checking pictures you show that the PN mainly glows in the red field.
In practice I had similar problems to detect the nebula. In my Abell PN observing project I wrote:

8", 47x, [OIII], NELM 6m5+
at best a very faint glow suspected; can not hold the glow sure enough, that's why I tend to a negative observation

20", 66x, [OIII], NELM 6m5+
very faint round disk, hardly noticeable only with max. AP, not sharply defined, structureless

[Steve Gottlieb]

I only have one observation, which was made at Jimi's in 2010 with the 48-inch. If this post was a few days earlier I would have taken another look when I observed on the 1st -- we're now in a rainy/cloudy spell in northern California.

At 267x and UHC filter, Abell 24 initially appeared as a large, low surface brightness, roundish glow, ~3' diameter, with the halo fading out at the periphery. A couple of faint stars are superimposed on the south side of the glow. Taking a closer look, I noticed the glow was slightly brighter on the east and west side and extended at least 1' further north than originally seen. This changed the overall shape to an oval, elongated 4'x3' N-S. A pair of mag 12-13 stars is off the southeast side and a close, faint pair is off the west side.

[Clear Skies]

Just wrapped up the Abell PN edition tonight. Here's a screenshot of Abell 24:

Abell24.jpg