Berkeley 32: A Metal-poor and Dynamically Evolved Open Cluster with Evidence of Radial Migration

Abstract

We present a comprehensive chemo-dynamical analysis of the old, metal-poor open cluster Berkeley 32 based on Gaia DR3 astrometry and Gaia-ESO Survey DR5.1 spectroscopy. Cluster membership is determined using a Gaussian Mixture Model applied to proper-motion components and trigonometric parallaxes. Isochrone fitting yields an age of 4.9 +/- 0.5 Gyr, a heliocentric distance of 3325 pc, and an extinction of A_V = 0.38 +/- 0.12 mag. Spectroscopic member stars exhibit a mean metallicity of [Fe/H] = -0.39 +/- 0.02 dex, near-solar alpha-element abundances, and a weighted mean radial velocity of V_rad = 106.26 +/- 0.03 km s^-1. The [Y/Mg] chemical clock yields an age of 4.73 +/- 2.39 Gyr, consistent with the isochrone estimate. Orbital integration indicates a moderately eccentric orbit (e = 0.268 +/- 0.004) with a guiding radius of R_g = 8.82 kpc. The inferred chemical birth radius, R_b = 9.82 kpc, together with DeltaR ~ -1 kpc, suggests moderate inward radial migration, while the offsets among R_b, R_g, and R_GC are consistent with both churning and blurring processes. A photometric analysis identifies a binary fraction of f_b = 0.449 +/- 0.017 for systems with mass ratios q >= 0.5, implying a substantial unresolved binary population. Radial cumulative distribution functions further reveal significant mass segregation, with evolved stars more centrally concentrated than main-sequence stars. These results indicate that Berkeley 32 is a dynamically evolved old-disk cluster whose present-day structure and orbit preserve signatures of both internal dynamical evolution and radial migration within the Galactic disk.

27 pages, including 15 figures and 4 tables, accepted for publication in the The Astronomical Journal (AJ)

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