The Comprehensive Investigations of the NGC 7419 Open Cluster and the New Perspective on Mass Populations

Abstract

We present a structural, kinematic, and photometric analysis of the young, red supergiant- and Be star-rich open cluster NGC 7419 using Gaia DR3 and 2MASS data. This cluster is located at equatorial coordinates α= 343.58 ± 0.06◦and δ= 60.81 ± 0.03◦. By applying the HDBSCAN algorithm and adopting a conservative membership selection, we identify a high-probability sample of 734 members, effectively disentangling the cluster from the dense Perseus Arm background. Treating the classical Be star population separately to mitigate their circumstellar disk excess, isochrone fitting to the Gaia DR3 CMD yields an age of 15 ± 2 Myr, a distance of d iso = 3161± 261 pc ((m − M) 0 = 12.50± 0.08 mag), and a mean colour excess of E (G BP − G RP ) = 2.58 ± 0.06 mag. An independent near-infrared CMD constructed from 2MASS photometry yields a consistent distance modulus of (m − M) 0 = 12.53 mag and E (J − Ks ) = 0.99 mag, providing an independent photometric-band consistency check of the Gaia-based parameters. The Be stars are found to exhibit a prominent infrared colour excess in the J − Ks band, consistent with free–free and bound–free emission from their circumstellar disks rather than thermal dust emission. Astrometrically, we derive mean proper motions (μα cos δ = -2.738 ± 0.115, μδ = -1.604 ± 0.149 mas yr−1) and a trigonometric parallax of ω = 0.288 ± 0.062 mas, corresponding to a trigonometric distance of dω = 3316 ± 317 pc. The photometric isochrone distance is the primary distance estimate. Structural modelling via the generalized King profile yields a core radius of rc = 1.53 ± 0.08′ and a limiting radius of rcl = 8.16 ± 1.1′, corresponding to a concentration parameter of C = 5.33 and a density contrast of δc = 11.62, describing a moderately concentrated system with a well-defined core. The stellar mass distribution deviates from a simple power-law profile and is best represented empirically by a multi-component Gaussian function, which can be interpreted as representing multiple mass populations. Our analysis shows that the stellar mass distribution of NGC 7419 is best described by a three-component Gaussian model, which we interpret as three distinct mass populations. A similar result was previously reported for NGC 2168, suggesting that multiple mass populations may not be unique to a single cluster. Hierarchical formation provides a plausible framework for the origin of these populations. Moreover, these mass populations coexist within NGC 7419 but have not yet become fully mixed, in agreement with the young age of the cluster