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

Time evolution of high-energy emissions of low-mass stars:I. Age determination using stellar chronology with white dwarfs in wide binaries