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 toward the inner bulge, to compute a deep color-magnitude diagram from the tip of the red giant branch down to J~22, 2 magnitudes below the main-sequence turnoff (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.
Origlia L., Lena S., Diolaiti E., Ferraro F. R., Valenti E., Fabbri S., et al. (2008). Probing the Galactic Bulge with Deep Adaptive Optics Imaging: The Age of NGC 6440. THE ASTROPHYSICAL JOURNAL, 687, 79-82 [10.1086/593351].
Probing the Galactic Bulge with Deep Adaptive Optics Imaging: The Age of NGC 6440
FERRARO, FRANCESCO ROSARIO;FABBRI, SARA;
2008
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 toward the inner bulge, to compute a deep color-magnitude diagram from the tip of the red giant branch down to J~22, 2 magnitudes below the main-sequence turnoff (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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
