English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We investigated the absolute age of the Galactic globular cluster M71 (NGC6838) by using optical ground-based images (u',g',r',i',z') collected with theMegaCam camera at the Canada-France-Hawaii-Telescope (CFHT). We performed arobust selection of field and cluster stars by applying a new method based onthe 3D (r',u'-g',g'-r') Color-Color-Magnitude-Diagram. The comparison betweenthe Color-Magnitude-Diagram of the candidate cluster stars and a new set ofisochrones, at the locus of the Main Sequence Turn Off (MSTO), suggests anabsolute age of 12+/-2 Gyr. The absolute age was also estimated using thedifference in magnitude between the MSTO and the so-called main sequence knee,a well defined bending occurring in the lower main sequence. This feature wasoriginally detected in the near-infrared (NIR) bands and explained as aconsequence of an opacity mechanism (collisionally induced absorption ofmolecular hydrogen) in the atmosphere of cool low-mass stars (Bono et al.2010). The same feature was also detected in the r',u'-g' and in the r',g'-r'CMD, thus supporting previous theoretical predictions by Borysow et al. (1997).The key advantage in using the Delta^(Knee)_(TO) as an age diagnostic is thatit is independent of uncertainties affecting the distance, the reddening andthe photometric zero-point. We found an absolute age of 12+/-1 Gyr that agrees,within the errors, with similar age estimates, but the uncertainty is onaverage a factor of two smaller. We also found that the Delta^(Knee)_(TO) ismore sensitive to the metallicity than the MSTO, but the dependence becomesvanishing using the difference in color between the MSK and the MSTO.

On the absolute age of the metal-rich globular M71 (NGC 6838): I. optical photometry