Are you looking for a beautiful picture? Do you want something that you recognize? Did you expect something else? Is this image already a disappointment? Well, as Jiànzhì Sēngcàn wrote in the XinXin Ming (信心銘): "To set up what you like against what you dislike is the dis-ease of the mind." We are, by nature, pattern seekers. We want patterns, like patterns, expect patterns. However, we can miss important details because we've been conditioned to look at things in a particular way. Sometimes it is our senses that lock us into a preconditioned view, other times it is our very language...

After a general introduction to the Cygnus OB Associations and the showcase of one rather magnificent and optically invisible Type O star in my last image, today I begin a multipart exploration of the Cygnus OB3 Association. 

Cygnus OB3 is one of two historically designated Cygnus OB Associations that actually stand out as real groupings based on the distances, proper motions and velocities of member stars. The Association lies in the area around Sh2-101 (aka Tulip Nebula) and includes the Open Clusters NGC 6871 and NGC 6883. Quintana and Wright  (2021) identify 13 O stars and 112 B stars in Association (which they currently call "Group A", rather than Cyg OB3).

Within the OB Associations, we are conditioned seek out and latch onto the Type O and Type B stars. After all, they "create the beauty" we seek to capture in our imaging. These associations are usually active star-forming regions, too, and, as such, you expect to find various types of young stellar objects (YSO): proto stars and pre-main sequence stars. Naturally, you will find regular, main sequence stars which go largely ignored when discussing the associations. 

Another often overlooked and very rare star type you find in these stellar associations is the Wolf-Rayet (WR) star. WR stars are ultra massive, highly evolved stars that show strong emission spectra of Nitrogen, Carbon or Helium, having depleted most of their surface Hydrogen. The first three WR stars were discovered in 1867 by French astronomers Mssrs. Wolf and Rayet. All three of these stars are in Cygnus and two of those are in this image (WR 134 and WR 135). 

"So what?" you might ask. "What makes WR stars relevant to the Cygnus OB3 Association?" The answer is simple: most Type O stars (and a few Type B stars) evolve into short-lived WR stars. Since these WR stars are manifesting similar distance, motion and velocity as other stars in the OB Association, it is reasonable to assert that they probably have evolved from earlier Type O stars in Cygnus OB3. 

How fascinating! These WR stars give us a possible glimpse into the future of the Type O stars. What an opportunity to look at stellar evolution! Big changes occur during this evolutionary process that we don't fully understand yet. What we do know is that the WR stars are hotter, heavier and more luminous than most other stars (even than their progenitor Type O stars). They are further subdivided by the peculiarities of their emission characteristics. WR 134 is a Type WN6-c star, showing strong lines of Nitrogen (WN) emission and WR 135 is a WC8 star, showing strong Carbon (WC) lines. There are other classifications, as well (such as WO), which need not concern us today.  

Most (not all) WR stars also have associated bubble nebulosity, generated by the stars themselves, usually from ejected material that is subsequently ionized by the stars' high temperatures. Such appears to be the case in this image where WR 134 is assumed to be generating the visible shell. It is not clear just when these bubbles begin to form, but research suggests that it may be in the late O-star phase. 

Wolf-Rayet stars typically end their lives in a supernova, the type of which depends on the weight of the WR star. In the case of WR 134 and WR 135, their weights of 18 M☉ and 13.6 M☉ respectively (very light by WR standards) make them ideal candidates for Type II-L or IIb supernovae.

In studying OB Associations you can not ignore the WR stars. For those WR stars that descend from Type O stars, they are the "old stars" of the association and have much to tell us about the history and the lives of its members. Next time, we'll take a closer look at some of those members in Cygnus OB3.

Finally, just a few words about the image itself: haphazard, chaotic, random, no real object for the mind to latch onto. Really?

In the XinXin Ming, Jiànzhì Sēngcàn goes on to remind us (that): "...the infinite universe stands always before your eyes. Infinitely large and infinitely small..." In each of our images we can find our past, present and future...but where and when, exactly, is that?

Thank you for stopping by and taking a look and spending the time to read and comment.  



Sources:
Gervais and St-Louis, 1999, AJ 118 2394.
Quintana and Wright, 2021, MNRAS 000, 1–15.
Wright N. J., 2020, New Astron. Rev., 90, 101549.