  The F8Ia supergiant V810 Centauri is part of a long-term high-precision
photometric monitoring program on long period variables started twenty years
ago. Time series analysis of this unique set of 500 data points, spanning
almost fifteen years in the homogeneous Geneva photometric system, is
presented. Cluster membership, physical parameters and evolutionary status of
the star are reinvestigated. Radial velocity data do not support the cluster
membership to Stock 14}. Ultraviolet and optical spectrophotometry is combined
with optical and infrared photometry to evaluate the physical parameters of the
yellow supergiant (Teff = 5970 K, M_bol = -8.5, R = 420 R_sun) and of its B0III
companion. From theoretical stellar evolutionary tracks, an initial mass of 25
M_sun is estimated for V810 Cen, which is actually at the end of its first
redward evolution.
  V810 Cen is a multi-periodic small amplitude variable star, whose amplitudes
are variable with time. The period of the main mode, 156 d, is in agreement
with the Period--Luminosity--Colour relation for supergiants. This mode is most
probably the fundamental radial one. According to the theoretical pulsation
periods for the radial modes, calculated from a linear non-adiabatic analysis,
the period of the observed second mode, 107 d, is much too long to correspond
to the first radial overtone . Thus, this second mode could be a non-radial
p-mode. Other transient periods are observed, in particular at 187 d. The l
ength of this period suggests a non-radial g-mode. Then, the complex
variability of V810 Cen could be due to a mixing of unstable radial and
non-radial p- and g-modes.
