There's a good article on some of the research on this at
http://www.as.arizona.edu/1045059820
Apparently, these helium burning stars have lost their "red giant
atmospheres," exposing the blue helium rich core.
----- Original Message -----
From: "Richard Crisp" <rdcrisp@No-Spam>
To: <sf-bay-tac@No-Spam>
Sent: Sunday, April 20, 2003 11:35 PM
Subject: [TAC] M53, a glob I seldom see
Friday night I did a bit of imaging from my backyard in Castro Valley. Among
the targets that night were NGC4490 and M53.
I don't think I have seen M53 too many times. One thing I noticed was a
large number of blue stars in it.
I had recently read in the book "The Big Bang" by Joseph Silk of Oxford that
Globs contain a lot of old blue stars. Old blue stars: I always had thought
blue stars were young hot stars.
Well as it turns out, when a star depletes its hydrogen fuel, it can resort
to fusing Helium and if it does, the stars get a lot hotter and look blue.
Instead of the Blue Straggler theory I had heard before, it appears that the
blue stars are just helium burning stars. That makes sense when you consider
that Globular Clusters are some of the oldest objects in the universe. It
did not make sense to me that ancient globs would have young hot blue stars
in them.
Here is a link to my M53 image:
http://www.rdcrisp.darkhorizons.org/m53_globular_cluster_page.htm
and NGC4490:
http://www.rdcrisp.darkhorizons.org/ngc4490_rgb_page.htm
Both of these were taken with my newly refurbished C14. I had been fighting
mirror flop with it for some time and finally applied a lot of grease to the
central focus tube and that seemed to greatly improve the situation. It is
not 100% gone, but it is usable now where it was really not before.
rdc