Multi-wavelength photometric study of five contact binaries in the field of globular cluster M4

Abstract

Binary stars are believed to be key determinants in understanding globular cluster evolution. In this paper, we present the Multi-band photometric analyses of five variables in the nearest galactic globular cluster M4, from the observations of CASE, M4 Core Project with HST for four variables (V48, V49, V51, and V55) and the data collected from T40 and C18 Telescopes of Wise Observatory for one variable (NV4). The light curves of five binaries are analysed using the Wilson–Devinney method (WD) and their fundamental parameters have been derived. A period variation study was carried out using times of minima obtained from the literature for four binaries and the nature of the variation observed is discussed. The evolutionary state of systems is evaluated using M-R diagram, correlating with that of a few well-studied close binaries in other globular clusters. Based on the data obtained from the Gaia DR3 database, a three-dimensional Vector-Point Diagrams (VPD) was built to evaluate the cluster membership of the variables, and two out of them (V49 and NV4) were found to be not cluster members.