UVIT magellanic BRidge analysis (UMBRA) – I. Far-UV–Gaia study of seven star clusters

Abstract

We present the first high spatial resolution far-ultraviolet (FUV; F148W) images of seven star clusters in the Magellanic Bridge using the UltraViolet Imaging Telescope (UVIT) on the Indian multiwavelength space observatory AstroSat. These observations emphasize UVIT’s unique capability to resolve individualstellar populations at the distance of the Magellanic Clouds (50–60 kpc). Using probable cluster members, we constructed colour–magnitude diagrams using UVIT and Gaia data to estimate key cluster parameters such as age, distance, and extinction. We assessed the likelihood that these are genuine star clusters and carried outstellar parameter estimation of individual hot main-sequence (MS)stars. Our analysis confirms that four objects, BS 245, L 144, OGLE-MBR-CL-0075, and OGLE-MBR-CL-0084, are bona fide clusters. The remaining objects are likely OB associations or field stars. For three, OGLE-MBR-CL-0026, OGLE-MBR-CL-0030, and OGLE-MBR-CL-0084, we provide age estimates for the first time. All seven objects have ages between 15 and 70 Myr, supporting an in situ star formation scenario triggered by tidal interactions between the Magellanic Clouds. We further model the spectral energy distribution of 51 MS stars by combining photometric data from UVIT, the GALaxy Evolution eXplorer (GALEX), Gaia, and two near-infrared surveys: the VISTA Survey of the Magellanic Clouds and Two Micron All Sky Survey. The modelling reveals five hot MS stars with Teff ranging between 32 500 (±1250) K to 42 500 (±1250) K and log g from 3.5 (±0.1) dex to 4.0 (±0.1) dex, consistent with late O-type stars. We release an FUV photometric catalogue of all MS stars to enable future studies of stellar abundances and binarity in the Bridge.