Those that are familiar with my work know that I am keenly interested in stellar associations. I am particularly fascinated in the OB Associations that are the catalyst for most types of star formation. These loosely-bound clusters of massive, hot, and short-lived Type O and B stars, and their attendant ionizing effects on the regions in which they exist, never cease to amaze.

In keeping with my abiding fascination, this Winter I had intended to make a thorough study of the Perseus OB2 Association (Per OB2), but to quote a beloved song by Joni Mitchell, "so many things I would have done, but clouds got in my way". 

The Per OB2 Association is nearly 50 parsecs in diameter and contains over a dozen of my cherished Type OB stars. As is always the case with these volatile OB stars, they are prone to supernova. Sometime in the past one of these stars must have exploded, sending a shockwave out that disrupted the trajectory of another member of the cluster: 46 ξ Persi (aka Menkib). Menkib is considered a "runaway" star from the Association; nobody really knows what caused it to leave the cluster, but a supernova is the most likely cause. It is just another example of how powerful these Type O stars really are.

Menkib itself is a class O7.5III star, weighing in at about 30 times heavier than Sol and is one of the hottest stars visible to the naked eye, with a surface temperature reported to be 35k Kelvin (our sun is "only" about 6k Kelvin). More importantly is the fact that it is ionizing the interstellar medium in front of it as it streaks away from the Association. The ionized gas in the path of Menkib is a structure that is popularly known as the California Nebula (NGC1499). I think it is easy to look at this nebula. I think it is much harder to understand that a single Type O star is responsible.

I think it bears repeating: Menkib is "doing" this! In this image I framed Menkib and the nebula in such a way as to underscore the ionizing shockwave that results in this fantastic nebula. When I contemplate the power of these stars and the resulting nebulae, I am dumbstruck. To continue with the Joni Mitchell reference, "I really don't know clouds, at all..."

Sadly, the Perseus OB2 Association is setting earlier and earlier now and I won't have a chance to complete my Association project this year. In the meantime, , however, I leave you with this one "small" part of the huge Perseus Molecular Cloud for you to ponder and, as always, wish you the clearest of skies.