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 (4)

• Near-IR properties of 24 Globular Clusters in the Galactic Bulge
• Formation & evolution of the Galactic bulge: constraints from stellar abundances
• The First Empirical Mass Loss Law for Population II Giants
• High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular Clusters

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• The Optical Counterpart to the Accreting Millisecond X-ray Pulsar SAX J1748.9-2021 in the Globular Cluster NGC 6440
• A new identity card for the bulge globular cluster NGC 6440 from resolved star counts
• 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
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