How accurately can we age-date solar-type dwarfs using activity/rotation
  diagnostics?
  It is well established that activity and rotation diminishes during the life
of sun-like main sequence (~F7-K2V) stars. Indeed, the evolution of rotation
and activity among these stars appears to be so deterministic that their
rotation/activity diagnostics are often utilized as estimators of stellar age.
A primary motivation for the recent interest in improving the ages of
solar-type field dwarfs is in understanding the evolution of debris disks and
planetary systems. Reliable isochronal age-dating for field, solar-type main
sequence stars is very difficult given the observational uncertainties and
multi-Gyr timescales for significant structural evolution. Observationally,
significant databases of activity/rotation diagnostics exist for field
solar-type field dwarfs (mainly from chromospheric and X-ray activity surveys).
But how well can we empirically age-date solar-type field stars using
activity/rotation diagnostics? Here I summarize some recent results for F7-K2
dwarfs from an analysis by Mamajek & Hillenbrand (2008), including an improved
"gyrochronology" [Period(color, age)] calibration, improved chromospheric
(R'_HK and X-ray (log Lx/Lbol) activity vs. rotation (via Rossby number)
relations, and a chromospheric vs. X-ray activity relation that spans four
orders of magnitude in log Lx/Lbol. Combining these relations, one can produce
predicted chromospheric and X-ray activity isochrones as a function of color
and age for solar type dwarfs.
