  We report spectra of the overtone and fundamental bands of CO in the eruptive
variable V838 Mon, which trace the recent evolution of the star and allow its
ejecta to be characterized. The data were obtained at the United Kingdom
Infrared Telescope on fourteen nights from 2002 January, shortly after the
first outburst of the star, to 2006 April. Although the near-infrared stellar
spectrum superficially resembled a cool supergiant after both the first and
third of its outbursts in 2002, its infrared "photosphere" at that time
consisted of highly blueshifted gas that was moving outward from the original
stellar surface. A spectrum obtained during the third outburst reveals a
remarkable combination of emission and absorption in the CO first overtone
bands. The most recent observations show a composite spectrum that includes a
stellar-like photosphere at a temperature similar to that seen just after the
initial outburst, but at a radial velocity redshifted by 15 km/s relative to
the stellar velocity determined from SiO maser emission, suggesting that the
atmosphere is now contracting. Three shell components, corresponding to
expansion velocities of 15, 85, and 145 km/s, also are present, but absorption
is seen at all expansion velocities out to 200km/s. Weak absorption features of
fundamental band lines of 13CO have been detected. However, the large
uncertainty in the value of [12C/13C] does not constrain the evolutionary
status of the progenitor.
