Issue |
A&A
Volume 390, Number 3, August II 2002
|
|
---|---|---|
Page(s) | 961 - 965 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20020858 | |
Published online | 14 August 2002 |
The white dwarf cooling sequence in the old open cluster NGC 188*
1
INAF-Astronomical Observatory of Rome, via di Frascati I-33, 00040 Monteporzio Catone, Roma, Italy
2
Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
3
University of California, UCO/Lick Observatory, Santa Cruz, CA 95064, USA
Corresponding author: G. Andreuzzi, gloria@coma.mporzio.astro.it
Received:
17
January
2002
Accepted:
6
June
2002
We develop the white dwarf luminosity function (LF) of the old
open cluster NGC 188 in order to determine a lower limit to the age
of the cluster by using the faint end of the cooling sequence.
To produce an extensive sequence of the cooling white dwarfs we imaged
four contiguous HST-WFPC2 fields in the center of the cluster in the
F555W and F814W filters. After imposing selection criteria on the
detected objects we found a white dwarf cooling sequence (down to ) including 28 candidate white dwarfs in the cluster. The
exposures are not deep enough to reach the end of this sequence, but
the results of our analysis allow us to establish a lower limit to the
age of the cluster independently of the isochrone fit to the cluster
turnoff.
The most ancient white dwarfs found are
4 Gyr old, an age that
is set solely by the photometric limit of our data. Classical methods
provide an estimate of
7 Gyr (Sarajedini et al. 1999).
Key words: open clusters and associations: individual: NGC 188 / stars: white dwarfs / stars: luminosity function
© ESO, 2002
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