Bibcode
Di Cecco, A.; Bono, G.; Prada Moroni, P. G.; Tognelli, E.; Allard, F.; Stetson, P. B.; Buonanno, R.; Ferraro, I.; Iannicola, G.; Monelli, M.; Nonino, M.; Pulone, L.
Bibliographical reference
The Astronomical Journal, Volume 150, Issue 2, article id. 51, 13 pp. (2015).
Advertised on:
8
2015
Citations
18
Refereed citations
16
Description
We investigated the absolute age of the Galactic globular cluster M71
(NGC 6838) using optical ground-based images (u\prime
,g\prime ,r\prime ,i\prime
,z\prime ) collected with the MegaCam camera at the
Canada–France–Hawaii Telescope (CFHT). We performed a robust
selection of field and cluster stars by applying a new method based on
the 3D (r\prime ,u\prime -g\prime
,g\prime -r\prime )
color–color–magnitude diagram. A comparison between the
color–magnitude diagram (CMD) of the candidate cluster stars and a
new set of isochrones at the locus of the main sequence turn-off (MSTO)
suggests an absolute age of 12 ± 2 Gyr. The absolute age was also
estimated using the difference in magnitude between the MSTO and the
so-called main sequence knee, a well-defined bending occurring in the
lower main sequence. This feature was originally detected in the
near-infrared bands and explained as a consequence of an opacity
mechanism (collisionally induced absorption of molecular hydrogen) in
the atmosphere of cool low-mass stars. The same feature was also
detected in the r‧, u\prime -g\prime , and
in the r\prime ,g\prime -r\prime CMD,
thus supporting previous theoretical predictions by Borysow et al. The
key advantage in using the {{{Δ
}}}{TO}{Knee} as an age diagnostic is that it is
independent of uncertainties affecting the distance, the reddening, and
the 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 on average a factor of two smaller. We also found that
the {{{Δ }}}{TO}{Knee} is more sensitive to
the metallicity than the MSTO, but the dependence vanishes when using
the difference in color between the MSK and the MSTO.
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Galaxy formation and evolution is a fundamental Astrophysical problem. Its study requires “travelling back in time”, for which there are two complementary approaches. One is to analyse galaxy properties as a function of red-shift. Our team focuses on the other approach, called “Galactic Archaeology”. It is based on the determination of galaxy
Matteo
Monelli