UOCS-XIX. a multiwavelength study of open cluster Trumpler 5: Cluster properties and exotic populations

Abstract

Trumpler 5 is a populous, intermediate-age (∼3 Gyr), metal-poor ([Fe/H] ∼ −0.4) open cluster, located at a distance of approximately ∼3050 pc. This is a well-studied cluster for its broadened main-sequence (MS) and blue straggler star (BSS) population. We present a UV-based analysis of the BSS and blue lurker (BL) candidates of this cluster using AstroSat/UVIT data along with Gaia DR3 data. We use a machine learning-based algorithm, ML-MOC, on Gaia DR3 data, and identify 3150 high-probability (P > 0.6) cluster members, along with 305 moderate probability (0.2 < P < 0.6) cluster members. Among the cluster members, we identified 32 highprobability BSSs, 13 of which have counterparts in AstroSat/UVIT filters. Additionally, we find 11 MS stars with UVIT counterparts, which we term BL candidates. Upon examining the cumulative radial distribution of various stellar populations, we find the signature of mass segregation in the cluster, with massive stars, including the BSSs and the turnoff stars, found more centrally concentrated than low-mass stars. We investigate the properties of 10 BSS and six BL candidates through multiwavelength spectral energy distributions. We infer the presence of unresolved hot companions in a single BSS and four BL candidates. Our analysis suggests that the hot companion of the BSS is likely a hot subdwarf, whereas the companions of the BL candidates are likely low-mass white dwarfs. We conclude that these five BSS and BL candidates have formed via Case-A/Case-B mass-transfer events, with timescales ranging from ∼26 to 155 Myr.