Astronomy and Astrophysics – Astrophysics
Scientific paper
1996-04-30
Astronomy and Astrophysics
Astrophysics
16 pages, plain LaTeX, plus 1 .ps figure uuencoded, gzipp'ed tar file -- accepted by ApJLett
Scientific paper
Deep Hubble Space Telescope (HST) observations with WFPC2 of the nearby globular cluster NGC 6752 have allowed us to obtain accurate photometry for the cluster white dwarfs (WD). A sample of local WDs of known trigonometric parallax and mass close to that of the cluster WDs have also been observed with WFPC2. Matching the cluster and the local WD sequences provides a direct measure of the distance to the cluster: $(m-M)_\circ=13.05$, with an uncertainty less than $\pm0.1$ mag which allows a substantial reduction in the uncertainty in the age of the cluster. Indeed, coupling this value of the cluster distance to the cluster metallicity, helium abundance and $\alpha$-element enhancement [$\alpha$/Fe]=0.5 yields an age of 15.5 Gyr and 14.5 Gyr using evolutionary models that do not include or do include helium diffusion, respectively. The uncertainty affecting these age determinations is $\sim 10\%$. The majority of the cluster WDs appear to be of the DA variety, while the color-magnitude location of two WDs is consistent with the DB type. This suggests a cluster DB/DA ratio similar to that of WDs in the solar neighborhood.
Bohlin Ralph Charles
Bragaglia Angela
Ferraro Francesco R.
Gilmozzi Roberto
Holberg Jay Brian
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