If you check his picture out - please do! - you will see that the Cone and Christmas Tree cluster appear to be part of a huge dusty arc. It looks as if the area encompassed by this arc has been pretty much evacuated, and much of the gas and dust that used to be inside it have been piled up along the rim of it. And smack in the middle of this arc sits an old open cluster, Trumpler 5.
Photograph from UK Schmidt plates by David Malin
Now look at Marcin Paciorek's picture again, and do look at this 3 MB larger version of it. I can't help thinking that it looks as if Trumpler 5 is somehow responsible for producing the relatively evacuated area around itself, and the piled-up rim och gas and dust which has produced the Cone Nebula and Christmas Tree cluster.
But how would Trumpler 5 be able to create an evacuated bubble and a long rim of piled-up gas? Simple, if one of its stars went supernova! A type Ia supernova does not seem impossible for a rich old open cluster.
I googled Trumpler 5 and came up pretty empty. Not quite empty, though, because I found this, an arxiv.org paper. According to this paper, Trumpler 5 is a metal-poor (Z=Fe/H]=−0.403±0.006), reddened (E(B−V) in the range 0.60 to 0.66 mag) cluster whose age is between 2.9 and 4 billion years. The paper also says that the distance modulus of Trumpler 5 is (m−M)0=12.4±0.1 mag.
What does that mean???? AAARRGHH!!! I googled "distance modulus" and got some horrible equations.
Can anyone help me? How far away is Trumpler 5? If this cluster has anything to do with NGC 2264, the Cone Nebula and the Christmas Tree cluster, it shouldn't too far away from them. In my opinion, it isn't impossible that Trumpler 5 has produced a moderately recent type Ia supernova, which might just possibly have acted like a snowplow and piled up the rim of gas where the Cone Nebula and the Christmas Tree cluster were born. But this is only possible if Trumpler 5 isn't too far away from the celestial Cone and Christmas Tree.
So, please! If the distance modulus of Trumpler 5 is (m−M)0=12.4±0.1 mag, how far away is it really?
P.S. Okay, I admit it - the area around Trumpler 5, and the rim where the Cone and Christmas Tree have formed, don't look much like a classic supernova remnant at all. And I guess there should be elevated levels of X-rays if a supernova had exploded there. Right?
But isn't it totally weird that a rich old cluster like Trumpler 5 appears to sit smack in the middle of a bubble whose rim has prduced new star formation?