GEMINI/GeMS Observations Unveil the Structure of the Heavily Obscured Globular Cluster Liller 1

Journal
Date Issued
2015
Author(s)
Saracino, S.
•
•
Ferraro, F. R.
•
Lanzoni, B.
•
Geisler, D.
•
Mauro, F.
•
Villanova, S.
•
Moni Bidin, C.
•
Miocchi, P.
•
Massari, D.
DOI
Abstract
By exploiting the exceptional high-resolution capabilities of the near-IR camera GSAOI combined with the Gemini Multi-Conjugate Adaptive System at the GEMINI South Telescope, we investigated the structural and physical properties of the heavily obscured globular cluster Liller 1 in the Galactic bulge. We have obtained the deepest and most accurate color-magnitude diagram published so far for this cluster, reaching {{K}s}∼ 19 (below the main-sequence turnoff level). We used these data to redetermine the center of gravity of the system, finding that it is located about 2.″2 southeast from the literature value. We also built new star density and surface brightness profiles for the cluster and rederived its main structural and physical parameters (scale radii, concentration parameter, central mass density, total mass). We find that Liller 1 is significantly less concentrated (concentration parameter c=1.74) and less extended (tidal radius {{r}t}=298\prime\prime and core radius {{r}c}=5\buildrel{\prime\prime}\over{.} 39) than previously thought. By using these newly determined structural parameters, we estimated the mass of Liller 1 to be {{M}tot}=2.3+0.3-0.1× {{10}6} {{M}☉ } ({{M}tot}=1.5+0.2-0.1× {{10}6} {{M}☉ } for a Kroupa initial mass function), which is comparable to that of the most massive clusters in the Galaxy (ω Centari and Terzan 5). Also, Liller 1 has the second-highest collision rate (after Terzan 5) among all star clusters in the Galaxy, thus confirming that it is an ideal environment for the formation of collisional objects (such as millisecond pulsars).

Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). Based on observations gathered with the ESO-VISTA telescope (program ID 179.B-2002).

Volume
806
Issue
2
Start page
152
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2015ApJ...806..152S
Rights
open.access
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