Unresolved triples in the open cluster NGC 2437 (M 46) confirmed by the KMOS VVVX-GalCen Spectroscopic Survey

D. Minniti; T. Palma; C. O. Obasi; M. Gómez; R. K. Saito; J. G. Fernández-Trincado; J. Alonso-García; E. R. Garro; J. Corral-Santana; A. Luna; P. W. Lucas; M. G. Navarro; V. D. Ivanov; Z. Guo; J. Borissova; R. Kurtev; C. Morris; V. Fermiano; J. Osses; P. Esteves; C. Cáceres; B. Dias; S. Saroon; S. Federle; M. Lad; I. Petralia; P. Rodriguez Cuevas; J. B. Pullen; D. Bhadrakumar Sindhu; L. Gramajo; L. Baravalle; D. Galdeano; M. V. Alonso; J. L. Nilo Castellon

arXiv · 2610.00659

Unresolved triples in the open cluster NGC 2437 (M 46) confirmed by the KMOS VVVX-GalCen Spectroscopic Survey

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Abstract

Recent optical and near-IR photometric databases like Gaia data release 3 (DR3) and the VISTA Variables in the Vía Láctea eXtended (VVVX) ESO public survey allow the exploration of candidate unresolved multiple systems (binaries, triples, quadruples, etc.) in nearby clusters, that need spectroscopic confirmation. NGC 2437 (M 46) is a benchmark open cluster with well determined physical parameters. Its relative proximity (D=1.6 kpc) makes this cluster an ideal laboratory to measure the fractions of unresolved multiple systems. We aim here to identify unresolved triple and higher order systems that are reliable members of the open cluster NGC 2437, and provide the spectroscopic confirmation using radial velocities. We confirm that there is a sequence of unresolved binaries in NGC 2437, and report the discovery of a sequence of unresolved triple systems in this cluster. We corroborate membership for 13 binary systems and 8 triple systems using radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. We further select stars with colors consistent with K-dwarfs, in order to have a controlled sample, comparable to the Solar neighborhood. We also find that the fraction of unresolved triples and quadruples is higher than that of the older open cluster Trumpler 19, studied using a similar setup, suggesting that these systems merge to form blue stragglers or get dissolved with time. We report the spectroscopic confirmation of 95% of the selected VVVX targets, thereby securing the presence of a sequence of unresolved triple systems in NGC 2437, located above the sequence of equal-mass binaries. The single stars constitute 60% of the mass of the cluster, while the rest of the mass (40%) is lodged in the unresolved multiple systems.

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D. Minniti, T. Palma, C. O. Obasi, M. Gómez, R. K. Saito, J. G. Fernández-Trincado, J. Alonso-García, E. R. Garro, J. Corral-Santana, A. Luna, P. W. Lucas, M. G. Navarro, V. D. Ivanov, Z. Guo, J. Borissova, R. Kurtev, C. Morris, V. Fermiano, J. Osses, P. Esteves, C. Cáceres, B. Dias, S. Saroon, S. Federle, M. Lad, I. Petralia, P. Rodriguez Cuevas, J. B. Pullen, D. Bhadrakumar Sindhu, L. Gramajo, L. Baravalle, D. Galdeano, M. V. Alonso, J. L. Nilo Castellon. 2026-09-30. Unresolved triples in the open cluster NGC 2437 (M 46) confirmed by the KMOS VVVX-GalCen Spectroscopic Survey. https://arxiv.org/abs/2610.00659

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