Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A156 | |
Number of page(s) | 12 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/202453482 | |
Published online | 18 March 2025 |
The bulge globular cluster Terzan 6 as seen from multi-conjugate adaptive optics and HST★
1
Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna,
Via Piero Gobetti 93/2,
40129
Bologna, Italy
2
INAF – Astrophysics and Space Science Observatory Bologna,
Via Piero Gobetti 93/3,
40129
Bologna, Italy
3
Departamento de Astronomia, Casilla 160-C,
Universidad de Concepcion, Chile
4
Departamento de Astronomía, Facultad de Ciencias, Universidad de La Serena.
Av. Juan Cisternas 1200,
La Serena, Chile
5
Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Ciencias Físicas – Instituto de Astrofísica,
Autopista Concepcion-Talcahuano 7100,
Talcahuano, Chile
★★ Corresponding author; martina.loriga2@unibo.it
Received:
17
December
2024
Accepted:
12
February
2025
This work consists of the first detailed photometric study of Terzan 6, one of the least known globular clusters in the Galactic bulge. Through the analysis of high angular resolution and multiwavelength data obtained from adaptive optics corrected and space observations, we built deep, optical and near-infrared color-magnitude diagrams reaching ≈4 magnitudes below the main-sequence turnoff. Taking advantage of four different epochs of observations, we measured precise relative proper motions for a large sample of stars, from which cluster members have been solidly distinguished from Galactic field interlopers. A noncanonical reddening law (with RV = 2.85) and high-resolution differential reddening map, with color excess variations up to δE(B − V) ≈ 0.8 mag, have been derived in the direction of the system. According to these findings, new values for the extinction and distance modulus have been obtained: E(B − V) = 2.36 ± 0.05 and (m − M)0 = 14.46 ± 0.10 (corresponding to d = 7.8 ± 0.3 kpc), respectively. We also provide the first determinations of the cluster center and projected density profile from resolved star counts. The center is offset by more than 7″ to the east from the literature value, and the structural parameters obtained from the King model fitting to the density profile indicate that Terzan 6 is in an advanced stage of its dynamical evolution, with a large value for the concentration parameter (c = 1.94−0.26+0.24) and a small core radius (rc = 2.6−0.7+0.09 arcsec). We also determined the absolute age of the system, finding t = 13 ± 1 Gyr, in agreement with the old ages found for the globular clusters in the Galactic bulge. From the redetermination of the absolute magnitude of the red giant branch bump and the recent estimate of the cluster global metallicity, we find that Terzan 6 nicely matches the tight relation between these two parameters drawn by the Galactic globular cluster population.
Key words: Hertzsprung-Russell and C-M diagrams / stars: Population II / globular clusters: general / Galaxy: stellar content
Based on observations collected at the GEMINI South Observatory under program GS-2013A-Q23 (PI: Geisler), with the HST (GO14074, GO15616 and GO16420, PI:Cohen and Homan) and at the Very Large Telescope of the European Southern Observatory at Cerro Paranal (Chile) under Program 091.D-0115 (PI:Ferraro).
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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