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tokens: leads to the inclusion of a number of RGB stars that are located close to the selection boundary, while retaining the color selection in ( m F435W − m F555W ) will still lead to rejection of RC stars. The RGB sample resulting from this updated selection run includes 207 stars. We repeated all of our subsequent analysis and found a new C index value of 0.063 mag, which is almost the same as our initial result, C index = 0.062 mag. We therefore conclude that the potential loss of a small number of genuine RGB stars by our initial selection method does not significantly influence our measurement of the cluster’s RGB broadening, nor our final results. 4. Discussion Our results show that the artificial stellar population is characterized by a similar dispersion in C F336W,F435W,F814W as the observed RGB sequence of NGC 1783. This demonstrates that the photometric uncertainties fully account for the RGB’s broadening in NGC 1783. The color index used, C F336W,F435W,F814W , is sensitive to the stellar N and He abundances, which are two of the most representative elements that exhibit large abundance variations in star clusters (Gratton et al. 2004 ). The consistency of the observed RGB’s width with that defined by our artificial SSP therefore indicates that our RGB sample is best represented by single-valued N and He abundances. There are a small number of outliers in the observed RGB distribution, in particular two stars at the far left (see the top panel of Figure 6 ). These objects are unlikely statistical fluctuations, given that they deviate by >5 σ from the Gaussian peak. Alternatively, they might be field stars that have not been properly removed by our field star decontamination algorithm. If they were cluster members, they would need to have unrealistically extreme metallicities. Note that these two data points appear both in the scatter diagram in the top panel of Figure 6 and in the observed histogram in the figure’s bottom panel. We suspect that these two stars might result from stochasticity in the field’s RGB sample (see Figure 5 ), rather than from random effects associated with our field star decontamination. We explored whether these objects might be binary systems instead. If we assume that the primary components ( M 1 ) of such binary systems are genuine RGB stars, the secondary components ( M 2 ) must have lower masses. We tested the appearance of binary systems with different mass ratios, M 2 / M 1 . For very low-mass companions, the change in color is almost negligible, while for equal-mass binaries no color difference is expected, compared with the single-star case. The top panel of Figure 6 includes binary sequences for M 2 / M 1 = 0.7, 0.8, and 0.9. It is clear that the outliers at the far left cannot be binary systems. An intermediate-age cluster with an age of 1.8 Gyr and a mass of 1.8 × 10 5 M ⊙ , NGC 1783 is comparably as massive as other star clusters that show clear evidence of MSPs (e.g., Martocchia et al. 2018 ). If