Constraining the Age of the Oldest Stars from the White Dwarf Cooling Sequence in M4

Details Constraining the Age of the Oldest Stars from the White Dwarf Cooling Sequence in M4 Constraining the Age of the Oldest Stars from the White Dwarf Cooling Sequence in M4

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000hst..prop.8679r&link_type=abstract

HST Proposal ID #8679

Physics

Hst Proposal Id #8679 Stellar Populations

Scientific paper

We propose to search for the oldest and hence coolest white dwarfs {WDs} in M4, the nearest Galactic globular cluster to the Sun. New models for cooling hydrogen white dwarfs predict that their colors should become bluer, rather than redder, with increasing age. Our goal is to test these models and at the same time constrain the age of M4. This would be the first test of globular cluster ages ever done that would not depend on the timescale to exhaust the hydrogen core of a main sequence star. New revised distance moduli and stellar evolution models now support an age of 11.5+/- 1.5 Gyr for the globular clusters. If we can reach V=30, we can solidly measure the turnover in the M4 WD luminosity function for an age of 12 Gyr, and we will get meaningful constraints on larger ages. The images will be taken in a single field of the cluster using the WFPC2 and the F606W and F814W filters. If we are successful in reaching the termination point of the WD cooling sequence in this cluster we will be able to derive an accurate estimate for the age of the cluster and, with only a mild extrapolation, for the Universe itself. Further, if it is indeed correct that the lensing objects in the various microlensing experiments in the direction of the Magellanic Clouds are old WDs, then these data will also prove to be critical in guiding the extensive searches that are now being carried out to find local examples of these MACHOs.

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