Object of the Week, November 10, 2019 – NGC 7635, the Bubble Nebula

[Howard B]

Wolf-Rayet / HII nebula
Cassiopeia
RA 23 20 48
DEC +61 12 06
Size 15’ x 8’

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NGC 7635, the Bubble Nebula, is one of those iconic deep sky objects that’s more difficult to see as well as I’d like. Even so, it’s a fascinating object, and especially deserves attention on the darkest and most transparent nights – which unfortunately I have yet to do!

Not surprisingly, William Herschel is the discoverer, finding it in 1787. We now know it’s a rather exotic object – the nebula is created by the interaction of the strong stellar wind of a Wolf-Rayet star, BD+60°2522, as it meets the interstellar medium. 7635 is also classified as an HII nebula.

BD+60°2522 is the brightest star within the Bubble, and although it’s located well off-center, toward the brightest arc of the Bubble, we can still consider it the central star of 7635. BD+60°2522 is a huge star that's around 45 times the mass of our sun, and we see it shine at magnitude 8.67v from 7100 light years away. It's moving through space in the direction of the brightest arc.

My observation and sketch dates to 2008 and shows what I saw with my 28-inch scope:
“Surprisingly prominent given the so-so darkness and seeing. The bright part of the arc shows well, with the associated nebula (to the left of the Bubble in the sketch) looks fainter. The Bubble looks more like a backward comma, and it’s best seen with the UHC filter. The OIII is close, but it suppresses the associated nebula. The comma part is fairly well seen without filters too. 253x, 21.10 SQM.”

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I hope to get a better view of this beautiful nebula sometime this fall or winter, and of course, hope you’ll give it a go too.

[Raul Leon]

Hi here's my observation from 10/25/2014 on ngc 7635 aka the Bubble nebula, emission nebula in Cassiopeia magnitude :11 ; Using an OIII filter I observed a really faint, elliptical fan shape ,that I believe to be part of the bubble itself.I used a 10mm Ethos at 158x magnification with my 14.5 Starstructure Dob f/4.33707

[obrazell]

I was always under the impression the exciting star here is an O star not a WR star, unless it has changed spectral type in the recent past. I think it is an O6.5 star

Owen

[Howard B]

Thanks for the heads up, I think you're correct. I found info that BD+60 2522 is a WR star here:

https://www.constellation-guide.com/bubble-nebula-ngc-7635/

but with more research today I think this site is mistaken.

[Clear Skies]

Here's the one observation I logged for the Bubble. 16 October 2017 in the French Ardennes, SQM 21.03.

14" SCT @ 168x / 29' - unfiltered
Surrounding a white mag. 8.5 star (SAO20575) is a slightly oval-shaped, ESE-WNW (almost east-west) elongated glow with a mag. 13.5 star on the NNW edge and a part on the SE side that subtly curves towards the SE.

14" SCT @ 168x / 29' - Lumicon UHC
Using this filter the nebula is much clearer and the SE curving part is longer. To the north of the brightest part of the nebula, after an interruption, is a small nebulous area. The central part of the nebula has a curved shape on the NNE side. The extension towards the SE is clear. This part of the nebula is the "bubble". Quite faint but with a notable shape. The faint NW part of the nebula is not visible.

Rated it 6/10.

[wvreeven]

With my old home made 6" Newtonian telescope using OIII at 25x I noted down in August 2005 that "In the field of M 52 I see quite a lot of nebulosity. The Bubble Nebula is visible as a straight line close to the star where it should be visible."

[Uwe Glahn]

Very cool object Howard.

With my old 16-inch I could follow the bubble at around 120°. The 27-inch shows the arc at around 180°. I wonder if it is possible to see the whole bubble with large aperture or some structure within the arc?

sketch 16", 129x-225x, UHC, NELM 6m5+
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[Paul Alsing]

Thanks for the heads up, I think you're correct. I found info that BD+60 2522 is a WR star here:

https://www.constellation-guide.com/bubble-nebula-ngc-7635/

but with more research today I think this site is mistaken.

Hi Howard,

On the other hand, SIMBAD says that BD+60 2522 is an Emission-line Star...

http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=BD%2B60+2522&submit=SIMBAD+search

... and Wiki says, of Emission-line Stars...

https://en.wikipedia.org/wiki/Emission-line_star

... "An emission-line star is a star whose spectrum exhibits emission lines. Common types include:

Be star
Herbig Ae/Be star
Shell star
Wolf–Rayet star"

So, if BD+60 2522 is really an emission-line Star, and if Emission-line Stars come in one of four flavors... well, which one of the four is it? Hmmmmm? Perhaps it is not one of the 'common' types...

Just food for thought.

[Bertrand Laville]

Hi All,

Here is my observation and drawing of the bubble, with my 25" Obsession, in average good sky (NELM +/-7.0v, SQM 21.55) of the french Alps.
Report here: http://www.deepsky-drawings.com/ngc-7635/dsdlang/fr

Clear skies


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Bertrand
http://www.deepsky-drawings.com

[Howard B]

Hey Paul, I came across this information as well, but I also gathered that a WR star is labeled as such even though it shares an emission line type sprectra with other types of stars However, I'm not an expert on this and I could be completely wrong again!