Characterization of blue and yellow straggler stars of Berkeley 39 using Swift/UVOT

TL;DR

This study characterizes blue and yellow straggler stars in the open cluster Berkeley 39 using multi-wavelength data, identifying candidates and analyzing their spectral energy distributions to understand their properties.

Contribution

It is the first to combine multi-wavelength observations with machine learning to identify and analyze BSS and YSS candidates in Berkeley 39.

Findings

Identified 17 BSS and 4 YSS candidates in Berkeley 39.

Successfully fitted SEDs for 8 BSS and 2 YSS candidates.

Detected UV excess in some BSS candidates indicating possible companions or activity.

Abstract

We characterize blue straggler stars (BSS) and yellow straggler stars (YSS) of an open cluster (OC) Berkeley 39 using multi-wavelength observations including Swift/UVOT. Our analysis also makes use of ultraviolet (UV) data from GALEX, optical data from Gaia DR3 and Pan-STARRS, and infrared data from 2MASS, Spitzer/IRAC, and WISE. Berkeley 39 is a ~6 Gyr old Galactic OC located at a distance of ~4200 pc. We identify 729 sources as cluster members utilizing a machine learning algorithm, ML-MOC, on Gaia DR3 data. Of these, 17 sources are classified as BSS candidates and four as YSS candidates. We construct multi-wavelength spectral energy distributions (SEDs) of 16 BSS and 2 YSS candidates, within the Swift/UVOT field, to analyze their properties. Out of these, 8 BSS candidates and both the YSS candidates are successfully fitted with single-component SEDs. Five BSS candidates show marginal excess in the near-UV (fractional residual < 0.3 in all but one UVOT filter), whereas three BSS candidates show moderate to significant excess in the near-UV (fractional residual > 0.3 in at least two UVOT filters). We present the properties of the BSS and YSS candidates, estimated based on the SED fits.