Volume 642, October 2020
|Number of page(s)||8|
|Section||Letters to the Editor|
|Published online||22 October 2020|
Letter to the Editor
VVVX-Gaia discovery of a low luminosity globular cluster in the Milky Way disk
Departamento de Ciencias Físicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile
2 Vatican Observatory, Vatican City State 00120, Italy
3 Centro de Astronomía (CITEVA), Universidad de Antofagasta, Av. Angamos 601, Antofagasta, Chile
4 Millennium Institute of Astrophysics, Santiago, Chile
5 Departamento de Astronomía, Av. Cisternas 1200 Norte, La Serena, Chile
6 Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
7 Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, Córdoba, Argentina
8 Gemini Observatory, Northern Operations Center, 670 A’ohoku Place, Hilo, HI 96720, USA
9 Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
10 European Southern Observatory, Karl-Schwarszchild-Strasse 2, 85748 Garching bei Muenchen, Germany
11 Department of Astronomy, University of Hertfordshire, Hertfordshire, UK
12 Mount Saint Vincent University, Halifax, Nova Scotia, Canada
13 Saint Mary’s University, Halifax, Nova Scotia, Canada
14 Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
15 Departamento de Física, Universidade Federal de Santa Catarina, Trinidade 88040-900 Florianópolis, SC, Brazil
16 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
17 Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
18 INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
19 Universidad de Atacama, Copiapó, Chile
Accepted: 29 September 2020
Context. Milky Way globular clusters (GCs) are difficult to identify at low Galactic latitudes because of high differential extinction and heavy star crowding. The new deep near-infrared (IR) images and photometry from the VISTA Variables in the Via Láctea Extended Survey (VVVX) allow us to chart previously unexplored regions.
Aims. Our long term aim is to complete the census of Milky Way GCs. The immediate goals are to estimate the astrophysical parameters for the newly discovered GC candidates, measuring their reddenings, extinctions, distances, total luminosities, proper motions, sizes, metallicities, and ages.
Methods. We used the near-IR VVVX survey database, in combination with the optical photometry and proper motions (PMs) from Gaia Data Release 2 (DR2), and with the Two Micron All Sky Survey photometry to search for and characterise new GCs within the southern Galactic plane (|b| < 5°).
Results. We report the detection of a heretofore unknown Galactic GC at RA = 14:09:00.0; Dec = −65:37:12 (J2000) corresponding to l = 310.828 deg; and b = −3.944 deg in galactic coordinates. We calculate a reddening of E(J − Ks) = (0.3 ± 0.03) mag and an extinction of AKs = (0.15 ± 0.01) mag for this new GC. Its distance modulus and corresponding distance were measured as (m − M) = (15.93 ± 0.03) mag and D = (15.5 ± 1.0) kpc, respectively. We also estimate the metallicity and age by comparison with known GCs and by fitting PARSEC and Dartmouth isochrones, finding [Fe/H] = ( − 0.70 ± 0.2) dex and t = (11.0 ± 1.0) Gyr. The mean GC PMs from Gaia DR2 are μα* = ( − 4.68 ± 0.47) mas yr−1 and μδ = ( − 1.34 ± 0.45) mas yr−1. The total luminosity of our cluster is estimated to be MKs = ( − 7.76 ± 0.5) mag. The core and tidal radii from the radial density profile are rc ∼ 2.1′ (4.6 pc) and rt = 6.5′ (14.6 pc) at the cluster distance.
Conclusions. We have found a new low luminosity, old and metal-rich GC, situated in the far side of the Galactic disk at RG = 11.2 kpc from the Galactic centre and at z = 1.0 kpc below the plane. Interestingly, the location, metallicity, and age of this GC are coincident with the Monoceros ring structure.
Key words: Galaxy: disk / Galaxy: stellar content / globular clusters: general / infrared: stars / surveys
© ESO 2020
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