MCAO near-IR photometry of the Globular Cluster NGC 6388: MAD observations in crowded fields

Abstract

Deep photometry of crowded fields, such as Galactic Globular Clusters, is severely limited by the actual resolution of ground-based telescopes. On the other hand, the Hubble Space Telescope does not provide the near-infrared (NIR) filters needed to allow large color baselines. In this work we aim at demonstrating how ground based observations can reach the required resolution when using Multi-Conjugated Adaptive Optic (MCAO) devices in the NIR, such as the experimental infrared camera (MAD) available on the VLT. This is particularly important since these corrections are planned to be available on all ground--based telescopes in the near future. We do this by combining the infrared photometry obtained by MAD/VLT with ACS/HST optical photometry of our scientific target, the bulge globular cluster NGC 6388, in which we imaged two fields. In particular, we constructed color-magnitude diagrams with an extremely wide color baseline in order to investigate the presence of multiple stellar populations in this cluster. From the analysis of the external field, observed with better seeing conditions, we derived the deepest optical-NIR CMD of NGC 6388 to date. The high-precision photometry reveals that two distinct sub-giant branches are clearly present in this cluster. We also use the CMD from the central region to estimate the distance ((m-M)=15.33) and the reddening (E(B-V)=0.38) for this cluster. We estimate the age to be ~11.5+/- 1.5 Gyr. The large relative-age error reflects the bimodal distribution of the SGB stars. This study clearly demonstrates how MCAO correction in the NIR bands implemented on ground based telescopes can complement the high-resolution optical data from HST.

9 pages, 10 figures. Accepted for publication on A. & A

References in corpus (10)

• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• The ACS Survey of Galactic Globular Clusters. III. The Double Subgiant Branch of NGC 1851
• Near-IR properties of 24 Globular Clusters in the Galactic Bulge
• The double Subgiant Branch of NGC 1851: the role of the CNO abundance
• NGC 6441: another indication for a very high helium content in Globular Cluster stars
• The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations
• On the Origin of Bimodal Horizontal-Branches in Massive Globular Clusters: The Case of NGC 6388 and NGC 6441
• The link between chemical anomalies along the red giant branch and the horizontal branch extension in globular clusters
• Resolving Stellar Populations outside the Local Group: MAD observations of UKS2323-326
• Multiple stellar populations in Globular Clusters: collection of information from the Horizontal Branch

Cited by in corpus (8)

• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• Ultra-deep GEMINI near-infrared observations of the bulge globular cluster NGC 6624
• A Highly Eccentric 3.9-Millisecond Binary Pulsar in the Globular Cluster NGC 6652
• Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441
• GeMS/GSAOI photometric and astrometric performance in dense stellar fields
• A stellar population synthesis approach to the Oosterhoff dichotomy
• Stellar photometry with Multi Conjugate Adaptive Optics
• Prediction of Multi-Wavelength Afterglows Associated with FRB 20200120E and FRB 20201124A