  Stellar ages are extremely difficult to determine and often subject to large
uncertainties, especially for field low-mass stars. We plan to carry out a
calibration of the decrease in high-energy emissions of low-mass GKM stars with
time, and therefore precise age determination is a key ingredient. The overall
goal of our research is to study the time evolution of these high-energy
emissions as an essential input to studing exoplanetary atmospheres.
  We propose to determine stellar ages with a methodology based on wide
binaries. We are interested in systems composed of a low-mass star and a white
dwarf (WD), where the latter serves as a stellar chronometer for the system. We
aim at obtaining reliable ages for a sample of late-type stars older than 1
Gyr.
  We selected a sample of wide binaries composed by a DA type WD and a GKM
companion. High signal-to-noise, low-resolution spectroscopic observations were
obtained for most of the WD members of the sample. Atmospheric parameters were
determined by fitting the spectroscopic data to appropiate WD models. The total
ages of the systems were derived by using cooling sequences, an initial-final
mass relationship and evolutionary tracks, to account for the progenitor life.
  The spectroscopic observations have allowed us to determine ages for the
binary systems using WDs as cosmochronometers. We obtained reliable ages for 27
stars between 1 and 5 Gyr, which is a range where age determination becomes
difficult for field objects.
