V810 Centauri
V810 Centauri is a double star consisting of a yellow hypergiant primary and blue giant secondary. It is a small amplitude variable star, entirely due to the supergiant primary which is visually over three magnitudes brighter than the secondary. It is the MK spectral standard for class G0 0-Ia. A 5th magnitude star, it is visible to the naked eye under good observing conditions.
Maurice Pim FitzGerald announced that the star's brightness varies, in 1973. It was given its variable star designation, V810 Centauri, in 1979.
V810 Cen A shows semi-regular variations with several component periods. The dominant mode is around 156 days and corresponds to Cepheid fundamental mode radial pulsation. Without the other stellar pulsation modes it would be considered a Cepheid variable">Cepheid variable">Cepheid variable. Other pulsation modes have been detected at 89 to 234 days, with the strongest being a possible non-radial p-mode at 107 days and a possible non-radial g-mode at 185 days.
The blue giant secondary has a similar mass and luminosity to the supergiant primary, but is visually much fainter. The primary is expected to have lost around since it was on the main sequence, and has expanded and cooled so it lies at the blue edge of the Cepheid instability strip. It is expected to get no cooler and may perform a blue loop while slowly increasing in luminosity.
V810 Cen was once thought to be a member of the Stock 14 open cluster at 2.6 kpc, but appears to be more distant based on spectrophotometric study. The distance derived from Gaia parallax measurements is even larger, between 4 kpc and 16 kpc.