3 Comparison with photographic photometry from Menzies 1974

Figures 2a,b show the results of the comparison (based upon 108 stars in common) between our photometry and that published by Menzies (1974). It is clearly seen that, in some cases, the deviations of V magnitudes are much larger than the errors of CCD and photographic photometry, reaching almost 0.5 mag, with magnitudes from Menzies always brighter. The deviations exceed 0.2 mag in almost 20 percent of the cases. Such deviations cannot be due to random errors. Actually, our analysis of individual deviant cases shows that they always occur when Menzies measured a blend of two or more close stellar images, whereas our PSF photometry enables us to measure the magnitudes of the blended stars separately.

  

Figure 2: Comparison of our photometry and that by Menzies (1974). a) Comparison of V magnitudes; crosses, blends not separated by Menzies; b) comparison of (B-V) colors. Our values are plotted along the x axis; differences (in the sense our value minus that from Menzies) are plotted along y. The straight line in panel (2) is the regression $\Delta(B-V)=+0.084-0.019(B-V)$

If we reject all cases when Menzies reported combined magnitudes of blended photographic stellar images, we find that the standard deviation between the two sets of measurements is $0\hbox{$.\!\!^{\rm m}$}05$, a typical random error of the photographic method. In most cases, we are able to reproduce combined magnitudes of blends measured by Menzies using our CCD magnitudes of their components, with deviations not exceeding $0\hbox{$.\!\!^{\rm m}$}1$.

The comparison of (B-V) color indices shows that the values given by Menzies are systematically bluer by approximately $0\hbox{$.\!\!^{\rm m}$}08$.

Unfortunately, magnitudes of the cluster's individual stars obtained in Martins & Fraquelli (1987) and in Fullton & Carney (1993), Fullton & Carney (1996), Fullton (1996) have not been published. The CMDs shown in the figures in these papers are very similar to our results.