Telescope Reviews: New Cosmic Bubble in Cygnus

This object is one of a handful of Wolf-Rayet shell nebulae (the two best known are the Crescent Nebula, NGC 6888, in Cygnus and Thor's Helmet, NGC 2359, in Canis Major). These shocked shells of ionized gas are ejected from rare, short-lived supergiant W-R stars -- only a couple of hundred of these stars are known in our galaxy!

While not a new discovery -- it was first catalogued in 1971 -- the shell surrounding HD 191765 = WR 134 at 20 10.2 +36 11 is virtually unknown as an amateur target. But a few weeks ago Reiner Vogel mentioned he observed this partial shell and it was fairly easy in his 22" with 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, the best northern Wolf-Rayet shell nebula.

Although the WR 134 nebula has been overlooked, it looked promising on the DSS (image below) so it was high on my observing list on Wednesday night 8/21 from Willow Springs (SQM-L 21.5). As soon as I looked in the 73x field of my 18-inch Starmaster with an OIII filter, I was amazed to find a remarkable, thick crescent, extending ~17' in length, elongated N-S and opening to the east.

This unknown nebula 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 OIII filter I could vaguely make out some nebulosity unfiltered.

The 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 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 or 10-inch in good conditions although you won't find it plotted on any atlas or listed in any major catalogue. It reminds me of another obscure Wolf-Rayet crescent nebula -- Sh 2-308 in Canis Major. A very recent study concluded the bubble is actually associated with HD 192103 (WR 135) so perhaps it should be called the WR 135 shell, but you won't find any more info online. Just go and check it out!

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Steve Gottlieb
18" f/4.3 Starmaster
Adventures In Deep Space
7500+ NGC/IC Visual Descriptions
NGC/IC Project

Edited by sgottlieb (08/21/09 07:50 PM)