The Tokyo String Quartet will perform at 8 p.m. Thursday, Feb. 21, in the UGA Performing Arts Center’s Hodgson Concert Hall in Athens. Long regarded as one of the world’s premier chamber ensembles, the Tokyo String Quartet has announced that the 2012-2013 season will be its last. For its final appearance in Athens, the ensemble will perform a program of quartets by Beethoven, Webern and Schubert.