Probing the Galactic Bulge with deep Adaptive Optics imaging: the age of NGC 6440

Abstract

We present first results of a pilot project aimed at exploiting the potentiality of ground based adaptive optics imaging in the near infrared to determine the age of stellar clusters in the Galactic Bulge. We have used a combination of high resolution adaptive optics (ESO-VLT NAOS-CONICA) and wide-field (ESO-NTT-SOFI) photometry of the metal rich globular cluster NGC 6440 located towards the inner Bulge, to compute a deep color magnitude diagram from the tip of the Red Giant Branch down to J~22$, two magnitudes below the Main Sequence Turn Off (TO). The magnitude difference between the TO level and the red Horizontal Branch has been used as an age indicator. It is the first time that such a measurement for a bulge globular cluster has been obtained with a ground based telescope. From a direct comparison with 47 Tuc and with a set of theoretical isochrones, we concluded that NGC 6440 is old and likely coeval to 47 Tuc. This result adds a new evidence that the Galactic Bulge is ~2 Gyr younger at most than the pristine, metal poor population of the Galactic Halo.

References in corpus (18)

• A large stellar evolution database for population synthesis studies. I. Scaled solar models and isochrones
• Analysis of isoplanatic high resolution stellar fields by Starfinder code
• Distances, ages, and epoch of formation of globular clusters
• Distances and ages of NGC 6397, NGC 6752 and 47 Tuc
• Homogeneous age dating of 55 Galactic globular clusters. Clues to the Galaxy formation mechanisms
• Galactic Globular Cluster Relative Ages. II
• Galactic Globular Cluster Relative Ages
• Near-IR properties of 24 Globular Clusters in the Galactic Bulge
• Building up the globular cluster system of the Milky Way. The contribution of the Sagittarius galaxy
• Low-extinction windows in the inner Galactic Bulge
• Formation & evolution of the Galactic bulge: constraints from stellar abundances
• The First Empirical Mass Loss Law for Population II Giants
• Transformations between the theoretical and observational planes in the HST-NICMOS and WFPC2 photometric systems
• High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters
• A new, cleaner colour-magnitude diagram for the metal-rich globular cluster NGC 6528 - Velocity dispersion in the Bulge, age and proper motion of NGC 6528
• HST NICMOS Photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4
• HST-NICMOS Observations of Terzan 5: Stellar Content and Structure of the Core
• A Near-Infrared Photometric Study of the Low Latitude Globular Clusters Liller 1, Djorgovski 1, HP 1, and NGC 6528

Cited by in corpus (12)

• The mass and the radius of the neutron star in the transient low mass X-ray binary SAX J1748.9-2021
• The WAGGS project - I. The WiFeS Atlas of Galactic Globular cluster Spectra
• Globular Cluster Abundances from High-Resolution, Integrated-Light Spectroscopy. II. Expanding the Metallicity Range for Old Clusters and Updated Analysis Techniques
• An E-ELT Case Study: Colour-Magnitude Diagrams of an Old Galaxy in the Virgo Cluster
• Terzan 5: an alternative interpretation for the split horizontal branch
• A new identity card for the bulge globular cluster NGC 6440 from resolved star counts
• The Optical Counterpart to the Accreting Millisecond X-ray Pulsar SAX J1748.9-2021 in the Globular Cluster NGC 6440
• Gamma-ray spectral properties of the Galactic globular clusters: constraint on the numbers of millisecond pulsars
• The near-IR counterpart of IGR J17480-2446 in Terzan 5
• Modeling Gas Evacuation Mechanisms in Present-Day Globular Clusters: Stellar Winds from Evolved Stars and Pulsar Heating
• Inferring the Helium abundance of extragalactic Globular Clusters using Integrated Spectra
• Challenges in Stellar Population Studies