02/22/2014:
Hi Steve, and thanks for the question. Harris 2000 quotes an HB mag of 16.15. Mochesjka et al 2000
http://adsabs.harvard.edu/abs/2000AcA....50..105M measured an MSTO of 19.5, 3.35 mag fainter than the HB. CMD data from p.110 the Mochesjka paper plot 6 stars in the range of mag 15.5 to mag 16. Three of them are >0.5 (B - V) blueward of the RGB which indicates field star contamination. This paper has quite a lot of magnitude derivation detail, though it was compiled from a 2048 px imager at 0.41” arcsec/pixel—coarse by today’s standards. The 1985 McClure
http://adsabs.harvard.edu/abs/1985PASP...97..665M CMD plots only two red giants definitively on the RGB (Table III p.673); the other four between mag 15.5 and 16.0 are >0.5 mag (B - V) blueward and thus suspect. Les Dalrymple may well have been seeing some of these six, so he had a 50/50 assurance of resolving actual cluster stars. Les likely gets the gold for at least three as definite members in his report. Dadgum better than the averted-only glow I can see. I wish I could put a ‘1’ in front of the ‘8’ in my largest aperture.
I don’t know why Harris 2000 listed the extinction of E(B - V) as 0.81 when the 1984-85 papers he likely drew upon said 0.3. E3 data has a lot of blank spots in Harris, esp all the luminosities rightward to the absol. mag -4.12 in Sect 2 and every item leftward of the core concentration in Sect. 3. The core surf brightness is mag 23.1, which makes it an elusive visual object using any aperture.
I sure appreciate the detail and accuracy of your myriad visual reports. I think you’ve single-handedly invented a whole scientific / literary cross-breed. Certainly a lot more credible than most of the fiction my wife tries to cajole me into reading.