If you've followed my previous work on OB Associations (e.g. this one), you know that they come in a variety of shapes and sizes. Most usually they can be quite large and capturing them requires a very large field, multiple images, or proficiency at mosaic stitching. 

This season, rather than do any of those techniques, I am going to select one or two salient areas of each target OB Association to highlight through imaging. You won't have a single, wide-field picture, but in conjunction with the text should have a good sense of each of the associations.

Our first OB Association is in the constellation Vulpecula. Most people associate this little-known constellation with M27 (the Dumbbell Nebula), but it is also home to a number of other interesting and lesser known DSOs. For me, however, it's all about the largely ignored Vulpecula OB1 Association.

The Association is an active star-forming region about 2.3 kpc from Earth comprising nearly 100 hot and massive O and B Type stars. A number of these stars are ionizing the three most notable HII regions found in the constellation: Sh2-86, Sh2-87 and Sh2-88. There are also a number of SNR (supernova remnants) in the vicinity, indicating earlier explosions of Type O stars in the association.   

Of the three HII regions, Sh2-86 is the most interesting to me (and, coincidentally, the most photogenic). This region hosts the very young (~3 million years old) star cluster NGC 6823, which boasts 3 massive O9V stars and roughly another 60 Type B stars. The ionizing radiation from these stars is responsible for the many pillar structures seen in this image.

The sculpting of these pillars is a very specific process known as Radiation Driven Implosion. This mechanism was first described by Bertoldi (1989). In short, the ionizing radiation from massive Type O and B stars creates a shock-front that can either burn away interstellar gases or can focus the gas into small, dense globules. These globules sit at the heads of the familiar pillars or can float freely and appear as a dark nebulosity (called Bok Globules). Wherever you find these globules--whether at the heads of pillars or as free-floating dark nebulae, new star formation is likely, i.e., there will be the creation of "young stellar objects" (YSO). 

In one of the few articles written about Vulpecula OB1, Billot; et al. (2010) surveyed Vulpecula OB1 and cataloged 856 extant YSO objects  (protostars and pre-main-sequence stars) in Vulpecula OB1. They also confirmed a dozen pillar structures as sites of new star formation, most of which are in Sh2-86. Many of the globules in these pillars have estimated masses from 14 to 700 M⊙, indicating the possibility that Sh2-86 can form the rare, ultra massive, short-lived Type O stars. 

Vulpecula OB1 is one of about 30 stellar associations that remain largely unexamined by researchers. For those of us doing astrophotography, however, a good wide field shot that includes all three Sharpless objects would be a great project to familiarize yourself with the entire association. If the integration times were long enough, you might even be able to discern faint supernova remnants--the telltale evidence of the now-gone progenitor stars of the association.

Is there a Vulpecula OB2 Association? Great question. The answer is "probably so". There is some photometric and spectroscopic evidence that beyond Vul OB1 and partially obscured by interstellar gas is another Association. Time will tell, but in any case it is well beyond the reach of my efforts.

I thank you for stopping by to look and to read. I hope you like the image and found this an informative use of your time. 

Cited Sources:
Bertoldi (1989)
Billot et al (2010)