I decided to do some detective work and see if I couldn't figure out how to find Barnard 29 and the green star. The green star appears to be star 202 on Barnard's M13 list. It's variable. I wonder how many days it was between your first and last exposure? I downloaded the APOD hires BMP and looked at it in MS Paint. Star 29 (the blue one) is at x=1068, y=1117. You can see all of this for yourself by looking at Publications of the Yerkes Obs., Vol. 6. Look here:
http://articles.adsabs.harvard.edu/c...MB&classic=YES
The section on M13 starts on p. 62. M13 star positions start on p. 67.
Randy