We have performed a careful investigation of the 74 candidate variable stars
presented by Safanova & Stalin (2011). For this purpose we used our data base
of imaging and light curves from Arellano Ferro et al. (2011) and Arellano
Ferro et al. (2012). We find that two candidates are known variable stars,
eight candidates were discovered first by Arellano Ferro et al. (2011) but
would not have been known to Safanova & Stalin (2011) at the time of their
paper submission, while four candidates are new variables. Three of the new
variables are SX Phe type and one is a semi-regular red giant variable (SR
type). We also tentatively confirm the presence of true variability in two
other candidates and we are unable to investigate another four candidates
because they are not in our data base. However, we find that the remaining 54
candidate variable stars are spurious detections where systematic trends in the
light curves have been mistaken for true variability. We believe that the
erroneous detections are caused by the adoption of a very low detection
threshold used to identify these candidates.Comment: MNRAS accepte