PZ Cassiopeiae


PZ Cassiopeiae is a red supergiant star located in the Cassiopeia constellation, and a semi-regular variable star.

Characteristics

PZ Cas is an extreme luminous red supergiant star, one of the largest stars currently known with an estimate of 1,062 times the Sun's radius, and also one of most luminous of its type, 229,000 times more luminous than the Sun. Its distance from Earth was initially estimated to be around 7,800 light-years. Subsequent studies of the star using the water masers that surround it have allowed to refine both the distance and the parameters of this star, deriving a distance of 9,160 light-years that translates into a luminosity for it of between 240,000 and 270,000 times the Sun's luminosity, and an initial mass of 20 to 25 times that of the Sun. These parameters are all similar to those estimated for the red hypergiant VY Canis Majoris. More recent measurements based on a Gaia Data Release 2 parallax of gives a luminosity below with a corresponding radius of. It is likely to be part of the Cas OB5 stellar association although apparently much younger than the other stars in the association.
PZ Cas is a slow semi-regular variable star with the period quoted as 925 days in the General Catalogue of Variable Stars, although periods of 850 and 3,195 days have been derived. The visual range is approximate magnitude 8-10, large for this type of variable.

Supergiant or AGB star

PZ Cas has traditionally been treated as a massive supergiant, comparable to others such as VY CMa, but there is some evidence that it is a less massive Asymptotic Giant Branch or post-AGB star. It shows enrichment of Zr and Ba, but not Li as would be expected for a true supergiant.

Companion

PZ Cas has a companion, a 13th magnitude star 12" away.