Object of the Week, July 14, 2024 - IRAS 17150-3224 the "Cotton Candy Nebula"

[Uwe Glahn]

IRAS 17150-3224 "Cotton Candy Nebula" (PN G353.8+02.9, RAFGL 6815S, GLMP 540)

= Protoplanetary Nebula (Post AGB-star)

RA: 17h 18m 19.8s
DEC: -32° 27' 21.5"
Vmag: 14.3
Size:
- 6,6"x2,4" (main lobes)
- 9,4" (arcs)
- 13,8"x15,8" (halo)

After posting some easy OOTW last times, we go harder today.

The current object was missed by Herschel but discovered by the IRAS satellite, which was searching after infrared sources. After selecting objects by its IRAS colour to find another "Egg Nebula" to prove the protoplanetary nebula theory, Hu et al. [1993A&A...273..185H] and Kwok et al. [1996ApJ...472..287K] photographed IRAS 17150-3224. Equipped with the best ground-based telescopes both groups could verify two lobes with a dark dust lane in the middle. Later on, the revolutionary image of the HST shows the two lobes in all its beauty and detail [1998ApJ...501L.117K]. Sun Kwok invented the name "Cotton Candy". Later on, Su et al. [2003AJ....126..848S] and other scientific papers, even SIMBAD refer to this designation.

But what is this object? To make the loooong story short - our Candy belongs to the protoplanetary nebula (PPN), that means the evolutionary stage between the end of the asymptotic giant branch (AGB) stage and the planetary nebula (PN) stage of an intermediate-mass star.
Somewhat longer, but without getting a scientific paper - within this short period, the strong infrared shining central star (CS) illuminates the ejected shells. The envelope shape changes from spherically symmetric (concentric rings) to axially symmetric and forms the frequently observed bipolar structures, depending on the line of sight. The remaining dust, usually donut-shaped around the CS, blocks the light and forms the constricted morphology between the bipolar outflows. The star itself is still not hot enough to ionize the surrounding remnants, causing the visible nebula to be a reflection nebula.
The special of our Candy are the series of concentric, circular arcs. As with the objects NGC 6543, NGC 7027 or the Egg Nebula they suggest that the wind of the AGB is not steady and causes these "puffs".

But what about observing this small thing? I recorded two observations in my PPN project (http://www.deepsky-visuell.de/Projekte/PPN.htm), both from the pristine sky of Namibia with larger telescopes. Believing reports in the internet, the object should be visible from up to 15-inch. But hopefully you know it better and let us know.

picture: HST
5486

sketch: Uwe Glahn, 28", 1248x, NELM 7m5+, Seeing I-II
5487
home (http://www.deepsky-visuell.de/Zeichnungen/IRAS17150-3224.htm)

As always, give it a go and let us know.

[ScottH]

Nice pick, Uwe! But at a declination of -32.5, you aren't going to get many takers since it's 6.5* farther south than my recent OotW! However, it's only 0.1-magnitude fainter than PDS 144N, so at least there's that.

I saw it back in the spring of 2022 for the first time. I used my 16-inch first and then, when I found how "easy" it was, I tried and succeeded in sighting it at 260x in my 10-inch SCT. It was my fifth PPNe at the time (I've now seen over a dozen...largely thanks to your PPNe Project).

Scott H.

[Steve Gottlieb]

I have a single observation of the pre-PN Cotton Candy nebula with my 18" Starmaster back in July 2010. The seeing conditions probably weren't great from +41° latitude (Golden State Star Party), and I used a maximum of 285x.

At the position of the nebula, I found two similar faint "stars" forming a wide double [18" separation] oriented WSW to ENE. The western of the pair is a 14th magnitude star, but the eastern object had a soft appearance and on close inspection was seen as a very small glow, ~ 5" diameter.

I didn't resolve the bipolar wings at 285x, so either I noticed a single lobe or they were merged. I would assume good seeing and high power are necessary.

[Uwe Glahn]

Thanks Scott and Steve for your response. You showed, that this thing is doable, even from the US.

I'm aware of the southern declination but was hoping that the forum consist also from observer from the southern hemisphere, or people from the US who travel far more south. For Europeans it is nearly impossible to go so deep south (Germany ~50°N, UK ~53°N) but again, I know many people who travel to La Palma (29°N) or Namibia (23°S).