The Metropolitan Museum opens its performance season on Sept. 11 at the Temple of Dendur with an eightieth-birthday tribute to composer Arvo Pärt that features members of the New Juilliard Ensemble as well as the New York City Ballet principal dancers Amar Ramasar and Rebecca Krohn, who will physicalize the hard-won serenity of Pärt’s “Fratres,” in choreography by Christopher Wheeldon (“Liturgy”).