The high-altitude, inner-disc, and chemically peculiar open cluster UBC 1052^★

¹ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), Martí i Franquès 1, 08028 Barcelona, Spain
² Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), Martí i Franquès 1, 08028 Barcelona, Spain
³ Institut d’Estudis Espacials de Catalunya (IEEC), Esteve Terradas, 1, Edifici RDIT, Campus PMT-UPC, 08860 Castelldefels, Spain
⁴ LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
⁵ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁶ Faculty of Psychology, UniDistance Suisse, Brig, Switzerland
⁷ GRANTECAN, Cuesta de San José s/n, 38712 Breña Baja, La Palma, Spain
⁸ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁹ Institut d’Estudis Catalans (IEC), Carrer del Carme, 47, 08001 Barcelona, Spain
¹⁰ INAF – Osservatorio di Astrofisica e Fisica dello Spazio, via P. Gobetti 93/3, 40129 Bologna, Italy

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 8 January 2026
Accepted: 27 March 2026

Abstract

Context. Of the thousands of newly discovered open clusters (OCs) thanks to the exquisite precision of the Gaia mission data, only a small fraction has been observed with high-resolution spectroscopy. Particularly, the population of OCs in the inner disc at relatively high altitudes (Z) from the Galactic plane remains poorly studied. Few such high-|Z| inner-disc OCs have been detected, and most are sparse groupings of stars that still await confirmation as real OCs.

Aims. We performed a detailed spectroscopic analysis of the high-|Z| inner-disc OC UBC 1052, an old cluster located at a cylindrical Galactocentric radius R_GC = 6.1 kpc, where it is one of a few OCs situated at a considerable altitude (Z = 340 pc).

Methods. We used FLAMES/VLT to acquire high signal-to-noise ratio UVES spectra of four red clump (RC) members (G ∼ 14 mag), from which we derived high-precision radial velocities and local thermodynamic equilibrium chemical abundances for 23 elements. A strict line-by-line differential analysis was carried out using a reference RC star and a solar analogue in the OC M 67, allowing us to derive very precise abundances for each star (a median precision in [X/H] of ≃0.06 dex). We also acquired GIRAFFE spectra for other candidate member stars and derived their radial velocities.

Results. We determine that UBC 1052 has an age of 2.25 ± 0.25 Gyr, a distance of 3.11 ± 0.07 kpc, an extinction of A_V = 1.23 mag, and a mean radial velocity of v. We find that the four RC stars have fully compatible chemical abundances, thus confirming UBC 1052 as a real OC. It has [Fe/H] = +0.05 ± 0.01 dex, and with [X/H] dispersions among the four stars <0.03 dex for 20 elements, we give conservative limits for chemical inhomogeneities at ≃0.05 dex for these species.

Conclusions. UBC 1052 stands out as the oldest and highest-|Z| inner-disc OC studied at high resolution to date, being located in the poorly sampled inner Galactic region where old OCs and OCs with large maximum excursions from the plane are scarce. Its relatively low [Fe/H] at its R_GC suggests it is a rare candidate for an inward-migrated OC in the inner disc. Its detailed abundance pattern (e.g. [Ba/Zr] and [Nd/Y]) shows some interesting features that appear to be unique in the current census of OCs studied at high resolution, making it an interesting object for potential strong chemical-tagging searches for already dispersed member stars.