A comprehensive Gaia DR3 study of the open cluster NGC 6134: Bayesian distances, present-day mass function, mass segregation, and structural decomposition
Open clusters are key laboratories for studying the formation and dynamical evolution of stellar populations. We present a comprehensive characterization of the intermediate-age open cluster NGC 6134 using Gaia DR3 astrometry and photometry. Adopting the 890-member Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) membership catalog, we determine the cluster distance and individual member distances with the Bayesian hierarchical code Kalkayotl under a King spatial prior, derive the fundamental parameters with the automated isochrone-fitting code ASteCA, quantify mass segregation, and decompose the projected spatial distribution into structural components. We obtain a Bayesian cluster distance of $1070.8^{+21.0}_{-19.0}$ pc (mode and 68\% credible interval), consistent with the ASteCA value ($d = 1064.4 \pm 15.2$ pc), with member distances peaking at $1071.2 \pm 2.5$ pc. ASteCA yields $\mathrm{[Fe/H]} = 0.08 \pm 0.06$, $\log(t) = 9.14 \pm 0.01$, and $A_\mathrm{V} = 1.03 \pm 0.05$ mag. The present-day mass function (PDMF) follows a broken power law with slopes $Γ_A = -2.10^{+0.10}_{-0.10}$ and $Γ_B = 1.59^{+0.14}_{-0.14}$ and break mass $M_c = 0.95^{+0.02}_{-0.02}\ M_\odot$, with a negative low-mass slope and a high-mass slope steeper than the canonical Salpeter value ($Γ= 1.35$), consistent with the preferential loss of the most massive stars through stellar evolution rather than with dynamical depletion. The observed mass segregation is consistent with an origin in long-term dynamical evolution. The cluster comprises a core, a diffuse halo, and a coherent plane-of-sky elongated feature that is unlikely to arise from noise based on a size-matched isotropic null test, and that lies beyond the radius at which masses are available. The observed main-sequence gap is closely linked to the cluster's binary fraction.