August 19, 2009: A new bubble nebula in Cygnus

Steve Gottlieb

On Wednesday (Aug 19th), I took advantage of the good weather prospects and the waning days of summer vacation and met Mark Johnston (probably playing hooky from work) at Bob Ayer's remote 3000' astro-site at Willow Springs in the Diablo range. We were treated to a fairly warm, dry and steady night with SQM readings around 21.50. We may have had a little residual haze very low from the Lockheed fire in the Santa Cruz mountains, but I still had no problems picking off galaxies below -40 degrees dec, so the skies were pretty transparent.

Mark spent the evening hunting down galaxy groups, though we picked on him for chasing objects in the west that were not in prime observing position. I'm sure he'll post his results later. Bob spent time hunting down emission objects at low power with his innovative duo 8-inch folded refractor/4-inch reflector. My listed included a number of quasars, blazars and other odd animals in the astrophysical zoo.

A few weeks ago on the Cloudy Nights deep sky forum, German amateur Reiner Vogel mentioned observing an obscure Wolf-Rayet nebula in Cygnus surrounding HD 191765 = WR 134. As there only a handful of known Wolf-Rayet shells I was surprised I hadn't heard of this object. Austrian observer Matthias Kronberger provided me with an image and mentioned he had also seen it in a 10". How could such a relatively bright object slip by virtually unnoticed until now?

I did a little searching online and found this object was first listed by David Crampton in 1971 (MNRAS 153, 303 ). Several papers in the early 1980's on W-R shell nebulae listed this object as "Anon around MR 100" -- the number from a 1962 paper by Roberts on galactic Wolf-Rayet stars. In fact, SIMBAD still lists this object as "Bubble around HD 191765". Interestingly, a very recent study concluded the bubble is actually associated with HD 192103 (WR 135) so perhaps it should be named the WR 135 nebula. Although, I must have run across this object while researching for the article I wrote for Astronomy magazine on observing W-R nebulae, I probably ignored it and assumed it wasn't a visual target.

Although this object has been overlooked it looked promising on the DSS and Reiner mentioned it was fairly easy in his 22" using an OIII filter. Visually, the center of the nebula is roughly at 20 09.4 +36 08, just two degrees SSW of the Crescent Nebula, so I knew it wouldn't be difficult to find. I put it high on my observing list and wasn't disappointed.

At 73x I was amazed to find a thick crescent extending 15'-20' in length, elongated N-S and opening to the east. It varies in brightness and thickness along its length and has a slightly sharper edge along the west (outer) side. The OIII filter provided an excellent contrast gain -- in fact, I didn't notice it initially unfiltered at 73x though once it was viewed using the filter I could vaguely make out some nebulosity unfiltered.

If you want to take a look, WR 134 shell is situated between a 3' string of four bright stars including mag 8 HD 191765 to the east and a 1' pair of bright stars including mag 7.3 HD 191493 to the west. These groups of stars are roughly 18' apart and oriented nearly E-W. The south end of the crescent begins south of a line connecting these groups of stars and curves north bending towards the east and thickening on the north side.

I'm sure this object is bright enough to be seen in an 8-inch in good conditions although you won't find it plotted on any atlas or listed in any major catalogue. Check it out!