Spin-forbidden pyroxene absorptions in the vir-spectra of 4Vesta. - Katrin Stephan; Ralf Jaumann; Maria Cristina De Sanctis; Eleonora Ammannito; Thomas Roatsch; Klaus-Dieter Matz; Lucy A. McFadden; Rachel L. Klima; Carol A. Raymond; Christopher T. Russell (WHISPERS, 2015)