Place: Baltimore, Maryland, USA
How old is that star? That is one of the most difficult questions to
answer in Galactic astrophysics. We have ways of determining the ages of
ensembles of stars (groups and clusters), but critical astrophysical questions
can only be addressed if we can estimate the ages of individual stars in the
field. Stellar ages lie at the heart of astrophysics, and stellar evolution
is all about time and how stars change with time. We want to know time-scales
for physical processes such as angular momentum loss, nucleosynthetic
processing, changes in magnetic fields, and the like, or we wish to compare
objects or groups of objects at different stages in their lives. Stellar and
galactic evolution cannot be understood without some knowledge of ages.
If we could pin ages on individual stars we could determine the star formation
history of the Galaxy and its principal components, and we could understand
the physics of low-mass stars much better. The well-studied spin-down of stars
like the Sun and the concomitant decline of observed activity indices makes it
possible to estimate rough ages for individual stars, but the scarcity and
remoteness of older clusters makes calibrating and testing the activity-age
relation problematic.
Ages of Resolved Populations: The discovery and study of multiple
populations of stars in clusters and other resolved objects in recent years
has been a major accomplishment of HST and has led to changing views on how
clusters form and evolve. In some cases there is evidence for multiple ages,
in others for differences in composition. A full and complete understanding
of the nature and ages of groups of stars is vital to stellar astrophysics.
Now is an appropriate time to examine the problem of stellar ages in detail.
It is time to bring together astronomers from the around the world to discuss
the current state of the problem of estimating ages of individual stars and
of populations, where the advances are now being made, and what the near
future offers.
