V838 Mon has undergone one of the most mysterious stellar outbursts on
record, with (a) a large amplitude (Delta B ~ 10 mag) and multi-maxima
photometric pattern, (b) a cool spectral type at maximum becoming cooler and
cooler with time during the descent, until it reached the never-seen-before
realm of L-type supergiants, never passing through optically thin or nebular
stages, (c) the development of a spectacular, monotonically expanding
light-echo in the circumstellar material, and (d) the identification of a
massive and young B3V companion, unaffected by the outburst. In this talk we
review the photometric and spectroscopic evolution during the first three full
years of outburst, the light-echo development and infer the nature of the
progenitor, which was brighter and hotter in quiescence than the B3V companion
and with an inferred ZAMS mass of about 65 Msun.Comment: to appear in the Proceedings of the Colloquium "Interacting Binaries:
Accretion, Evolution and Outcome", held in Cefalu' (Sicily) July 4-10, 2004,
L.A. Antonelli et al. eds., American Institute of Physics Conf. Proc. series,
in press. 6 pages, 4 figure
