Cousin Ricky wrote: ↑
Sun Feb 09, 2020 4:41 pm
Ann wrote: ↑
Sat Feb 08, 2020 9:26 pm
Cousin Ricky wrote: ↑
Sat Feb 08, 2020 4:39 pm
I’m trying to find out how Tr 5 is so orange and still an open cluster, but I can’t find anything on the Web that isn’t an abstruse science paper or behind a subscription wall.
Take a look at the picture at left of the Hyades Cluster. The Hyades is a much younger cluster than Trumpler 5, about 625 million years
, while Trumpler 5 is at least two billion years. Also Trumpler 5 is much farther away than the Hyades, because the Hyades is a nearby cluster at only about 153 light-years, while Trumpler 5 is certainly at least a thousand light-years away, and probably more.
Thanks. I didn’t realize open clusters could last 2 billion years without dispersing.
Note that Trumpler 5 is an anticenter cluster:
et al. wrote:
As part of a long-term programme, we analyse the evolutionary status and properties of the old and populous open cluster Trumpler 5
(Tr 5), located in the Galactic anticentre direction, almost on the Galactic plane.
I think this means that Trumpler 5 is located in the very outskirts of the spiral system of the Milky Way, which in that case would place it in a position where it would enjoy an unusual amount of "peace and quiet" and little harassment of giant molecular clouds and other obstacles which would normally hasten the demise of an open cluster.
There is another interesting open cluster which we may compare Trumpler 5 to, which is even older than Tr 5. It's the fascinating open cluster M67.
M67. Processing: Noel Carboni, Imaging: Greg Parker.
M67. Image credit: Palomar Observatory / STScI / WikiSky.
M67 is believed to be 4 billion years old, which is extremely old for an open cluster. As you can see it is rich, and like Trumpler 5, it is located in a "peaceful" part of the galaxy, far away from the galactic center. Unlike Trumper 5, it is relatively unreddened.
According to Messier Monday
, there are about 500 stars in M67 (after 4 billion years!) and all the A-type stars have evolved off the main sequence, leaving only F-type and later main sequence stars left.
I want to protest a little there, however. As you can see, there is one strikingly blue star in M67. The way this star stands out is seen better in another picture:
Ultraviolet image of M67. Photo: GALEX.
The bright blue star in M67 is called HIP 43465
. Note the GALEX image, which measured the ultraviolet light emanating from the stars of M67. All the yellow stars in the GALEX image are non-blue, but the very blue star is UV-bright, hot and blue. Without a doubt, this is a B-type star, otherwise it couldn't possibly be so blue. (It is in fact a B8V-type star with a B-V index of -0.07.)
How can a 4 billion-year-old cluster contain a B8V star, which should have died when M67 was perhaps a tenth of its current age? In my opinion, HIP 43465 can only be a blue straggler star. It has gained mass from another star, gradually or suddenly becoming massive enough (at least 3 solar masses) to shine with the blue light of a B-type star. It wouldn't surprise me in the slightest if HIP 4365 is (or was) an Algol-type star, where a main sequence star is close enough to its red giant companion (which must have filled its Roche lobe
) to start accreting matter from its swollen companion, eventually almost sucking it dry while putting on more and more mass itself.
So M67 is somewhat similar to Trumpler 5, but it is even older. M67 is also relatively unreddened, unlike Trumpler 5, and it contains a very hot and blue "blue straggler", which Trumpler 5 doesn't.