Plotting Oddities on H-R Diagrams (B-V): What's Going On?

[vociferous]

I was plotting the color magnitude diagram of a globular cluster and I noticed something odd. On most H-R diagrams, the turn-off from the main sequence to the giant branch is somewhere between (B-V) magnitude values of about .5-1.0.

On my plot, the turn-off is between about -.4 and -0.1.

I am assuming that there is some data adjustment being done that I have missed.

I am also kind of puzzled by the presence of what appear to be a few hot stars, either super-giants or stars that are much hotter than the sun, neither of which should be present in a globular cluster where the stars are about the age of the Milky Way.

 

[lippyka]

It is possible that the cluster has been contaminated by a few foreground stars, or perhaps there are some more massive stars within the cluster that have evolved quickly and are now on their way to becoming white dwarfs. If this is the case, they will be located on the cooler side of the color magnitude diagram. It is also possible that the data you are using has been affected by some kind of observational bias that has resulted in the unusual shape of the turn-off. It is important to investigate further to determine the cause of the unusual turn-off.