  The intriguing binary LS V +22 25 (LB-1) has drawn much attention following
claims of it being a single-lined spectroscopic binary with a 79-day orbit
comprising a B-type star and a ~70 Msun black hole. Recent analyses have
implied that the visible primary star is a stripped He-rich star. However, the
nature of the secondary, which was proposed to be a black hole, a neutron star,
or a main sequence star, remains unknown. Based on 26 newly acquired
spectroscopic observations, we perform an orbital analysis and spectral
disentangling of LB-1 to elucidate the nature of the system. Our analysis
reveals that LB-1 contains two components of comparable brightness in the
optical. The narrow-lined primary, which we estimate to contribute ~55% in the
optical, has spectral properties that suggest that it is a stripped star: it
has a small spectroscopic mass (~1 Msun) for a B-type star and it is He- and
N-rich. The "hidden" secondary, which contributes about 45% of the optical
flux, is a rapidly rotating (vsini ~ 300 km/s) B3 V star with a decretion disk
-- a Be star. Hence, LB-1 does not contain a compact object. Instead, it is a
rare Be binary system consisting of a stripped star (the former mass donor) and
a Be star rotating at near its critical velocity (the former mass accretor).
This system is a clear example that binary interactions play a decisive role in
the production of rapid stellar rotators and Be stars.
