The Age of Gl879 and Fomalhaut

We estimate here the age of one of the prototypes of the Beta Pic-like stars, Fomalhaut, based on the properties of its common proper motion companion Gl879. By combining constraints derived from the lithium abundance, rotational velocity, HR diagram position, and coronal activity we conclude that the age for Gl879, and hence the age for Fomalhaut, is 200$\pm$100 Myr. This age estimate agrees quite well with the completely independent age estimate derived directly from isochrone–fitting to Fomalhaut’s position in an HR diagram, and thus confirms that circumstellar dust disks can persist in A stars for several hundred Myr.