2001PASP..113.1547H

EX Lupi is a classical T Tauri star (and the EXor prototype) subject to sporadic outbursts. The historic record shows that it remains at about V=13.2 (or m_pg=14.7:) for extended periods, from which it has been observed to brighten to as much as V=8.4 (on one occasion in 1955-1956). During 1993-1994 the star remained slightly above normal minimum, at about V=12.8, and from that level rose to three maxima at V=11.4 and on other occasions to about V=12.0. At minimum light an M0 V absorption spectrum is present. At outburst this spectrum is veiled by a hot continuum (well shown by an IUE exposure), the equivalent widths of the optical-region emission lines decrease, and reverse P Cygni absorption components appear at the higher Balmer lines. The outbursts are believed to be due to episodic infall onto the M0 star.