We present a new method to estimate the absolute ages of stellar systems. This method is based on the difference in magnitude between the main-sequence turnoff (MSTO) and a well-defined knee located along the lower main sequence (MSK). This feature is caused by the collisionally induced absorption of molecular hydrogen, and it can easily be identified in near-infrared (NIR) and in optical-NIR color-magnitude diagrams of stellar systems. We took advantage of deep and accurate NIR images collected with the Multi-Conjugate Adaptive Optics Demonstrator temporarily available on the Very Large Telescope and of optical images collected with the Advanced Camera for Surveys Wide Field Camera on the Hubble Space Telescope and with ground-based telescopes to estimate the absolute age of the globular NGC 3201 using both the MSTO and the Delta(MSTO-MSK). We have adopted a new set of cluster isochrones, and we found that the absolute ages based on the two methods agree to within 1 sigma. However, the errors of the ages based on the Delta(MSTO-MSK) method are potentially more than a factor of 2 smaller, since they are not affected by uncertainties in cluster distance or reddening. Current isochrones appear to predict slightly bluer (approximate to 0.05 mag) NIR and optical-NIR colors than observed for magnitudes fainter than the MSK.
ON A NEW NEAR-INFRARED METHOD TO ESTIMATE THE ABSOLUTE AGES OF STAR CLUSTERS: NGC 3201 AS A FIRST TEST CASE
DEGL'INNOCENTI, SCILLA;PRADA MORONI, PIER GIORGIO;
2010-01-01
Abstract
We present a new method to estimate the absolute ages of stellar systems. This method is based on the difference in magnitude between the main-sequence turnoff (MSTO) and a well-defined knee located along the lower main sequence (MSK). This feature is caused by the collisionally induced absorption of molecular hydrogen, and it can easily be identified in near-infrared (NIR) and in optical-NIR color-magnitude diagrams of stellar systems. We took advantage of deep and accurate NIR images collected with the Multi-Conjugate Adaptive Optics Demonstrator temporarily available on the Very Large Telescope and of optical images collected with the Advanced Camera for Surveys Wide Field Camera on the Hubble Space Telescope and with ground-based telescopes to estimate the absolute age of the globular NGC 3201 using both the MSTO and the Delta(MSTO-MSK). We have adopted a new set of cluster isochrones, and we found that the absolute ages based on the two methods agree to within 1 sigma. However, the errors of the ages based on the Delta(MSTO-MSK) method are potentially more than a factor of 2 smaller, since they are not affected by uncertainties in cluster distance or reddening. Current isochrones appear to predict slightly bluer (approximate to 0.05 mag) NIR and optical-NIR colors than observed for magnitudes fainter than the MSK.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
