Fr.: EX Lupi
A classical → T Tauri star, and the EXor prototype, subject to sporadic outbursts. It remains at about V = 13.2 mag for extended periods to brighten to as much as V = 8.4 mag (1955-1956). When EX Lupi is at minimum, it resembles a classical T Tauri star of type M0. At outburst this spectrum is veiled by a hot continuum, 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. → FU Orionis objects.
E and X, letters of alphabet; Lupi, genitive of → Lupus.