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RickJ
2011-Nov-01, 01:38 AM
NGC 7419 is the richest known coeval (all stars are the same age) cluster of red super giants in the galaxy. Or so one paper says. It doesn't take many for this distinction as it has only 5. Most clusters of this type have a ratio of blue super giants to red ones of almost 2:1. This cluster the ratio is 0.2:1, that is it has only one. That one is questionable so it may contain none. And no that star is not at all obvious, in fact it is very red! Why I can only guess, though the entire cluster is obviously severely reddened by dust. Apparently little of its blue light is getting through the dust. In fact none its blue stars shines with a blue color. The best they can do is a slightly reddish white in my image. The blue stars you see are foreground stars it would appear.
http://iopscience.iop.org/1538-3881/126/3/1415/pdf/1538-3881_126_3_1415.pdf

One paper puts the reddening at 1.65 magnitudes and gives a distance of 9500 1300 light-years. The reddening varies quite a bit across the cluster but on average the dust dims the cluster by 5.1 0.4 That doesn't seem enough to explain why its hottest and bluest star is so red. It is red on the POSS plates as well. Many of its blue B stars are Be stars meaning they have emission lines. The age of the cluster appears to be about 25 million years but the Be stars are far younger, 0.3 to 3 million years old. The cluster may have had two periods of star formation. So it isn't coeval after all? I'm confused. The article also indicates the dust from this formation is still reddening the cluster. The super giant blue star is not one of these young stars however. http://arxiv.org/PS_cache/astro-ph/pdf/0605/0605017v2.pdf

In the annotated image the red super giants are denoted by R, (MY Cephi is the one furthest to the NE--upper left) the possible single blue super giant by BSG? (it is certainly not a Be star) and three young blue emission line stars by Be. One of those is also questionable so I've added a question mark for it. B denotes ordinary blue giant stars. There is one carbon star, MZ Cephi, in the cluster. It is denoted by C. It confused me at first as the cluster appeared to have 6 red super giants until I saw one was a bright carbon star instead. G denotes a background galaxy that looks much like a star that's a member of the cluster. It is 2MASX J22541342+6048221. NED has no distance or even magnitude estimate for it. There are a couple other galaxies in the image as well. They too look like faint stars. They are labeled in the annotated image with a G.

14" LX200R @ f/10, L=4x10' RGB=2x10'x3, STL-11000XM, Paramount ME

Full image
http://www.spacebanter.com/attachment.php?attachmentid=3792&stc=1

Annotated
http://www.spacebanter.com/attachment.php?attachmentid=3794&d=1320080900

Rick