STUDY OF THE VARIABLE STARS V10 AND C6 IN MESSIER 13

Abstract

We have studied the variable star V10 and the new variable candidate C6 (announced in 2019), located in Messier 13, using the filtered CCD images -in the V bandobtained in the campaigns of 2019, 2020 and 2021. We have previously determined their precise  and  coordinates (J2000) to identify them in a crowded field. We find the V10 constant in light in the three campaigns: the star is listed in the Catalogue of Variable Stars in Globular Clusters as non-variable. C6 has presented low-level variations from 0.102 to 0.138 mag without regularity; these values are lower than 0.44 mag in the V band detected by its discoverers. Although we find different periods, none draw a coherent light curve. We have also analysed the photometric measurements obtained by ASAS-SN between 2019 and 2023 in the SLOAN-g band, identifying oscillations with a maximum amplitude equal to 0.188 mag;. However, we find two possible periods, none producing a quality light curve. All data suggest that C6 is a new variable star of type L, irregular because no single period fits all of the data: we propose the name V65 for it.