APOD: Globular Star Cluster NGC 6752 (2013 Jul 05)

[Ann]

I'm certainly not trying to suggest that there are no blue stragglers in this cluster. However, the straggler stars are far less conspicuous than the blue horizontal branch stars, which means that most or all the blue stars that we see so clearly in this picture are likely to be horizontal branch stars.

But the blue stars near the center of NGC 6752 aren't very conspicuous (except for their color)

http://outreach.atnf.csiro.au/education ... sters.html

Your link contains this Hubble picture of the central parts of globular cluster NGC 6397. The blue straggler stars have sunk to the center of the cluster, since they are the most massive of the surviving members of this cluster. NGC 6397 is likely to about twelve billion years old, and all of its really massive members have died. The blue stragglers are so massive that they, too, should have died, but they survive since they are almost certainly the products of two or even three low-mass stars that have recently merged.

Sources: http://www.mso.anu.edu.au/~jerjen/resea ... ggler.html,
B.J. Mochejska, J. Kaluzny, 1 m Swope Telescope

Your link also contains this diagram. It shows that the blue straggler stars are fainter and generally less blue than the blue horizontal branch stars.










Ann

[neufer]

I'm certainly not trying to suggest that there are no blue stragglers in this cluster. However, the straggler stars are far less conspicuous than the blue horizontal branch stars, which means that most or all the blue stars that we see so clearly in this picture are likely to be horizontal branch stars.

But the blue stars near the center of NGC 6752 aren't very conspicuous (except for their color)

http://outreach.atnf.csiro.au/education ... sters.html

Your link... contains this diagram.

It shows that the blue straggler stars are fainter and generally less blue than the blue horizontal branch stars.

But do you (or don't you) agree that the blue stars near the center of
APOD's NGC 6752 aren't very conspicuous (except for their color)

[Ann]

Click to view full size image

neufer wrote:
But do you (or don't you) agree that the blue stars near the center of
APOD's NGC 6752 aren't very conspicuous (except for their color)

They are certainly not very conspicuous. This Hubble picture of NGC 6397 shows a bit more of the globular's core. The blue straggler stars can be seen at the upper left, looking like small blue pearls on a string. The much brighter blue stars farther from the core are blue horizontal branch stars.

Ann