V509 Cassiopeiae (= V509 Cas = HR 8752) is a star in the constellation Cassiopeia.
V509 Cassiopeiae is yellow hypergiant with a G-type and an apparent magnitude that has varied from below +6 in historical times to a peak of +4.3 and now around +5.2. It is around 4,500 light years from Earth. It is classified as a semiregular variable star and is undergoing strong mass loss. It has recently passed through the yellow evolutionary void by ejecting around a solar mass of material in less than 50 years.
This type of star has evolved from an initial mass of 25-40 times the sun to a red hypergiant and is now shedding its remaining outer layers in a series of dramatic explosions, progressively increasing in temperature. It may become a blue supergiant or luminous blue variable before declining in luminosity as a late type Wolf–Rayet star, but is expected to explode as a supernova before that point.