PZ Cassiopeiae

 ( M-type Supergiants ) 

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

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Characteristics PZ Cassiopeiae is a luminous red supergiant star, one of the largest stars currently known with a radius over 1,200 times the solar radii (), and also one of the most luminous of its type, over 200,000 times Sun luminosity (). It is likely to be part of the Cas OB5 stellar association although apparently much younger than the other stars in the association. The star is losing mass at around per year and has also once been described as a red hypergiant.

Its distance from Earth was initially estimated to be around 7,800 (2.4 kiloparsecs). Subsequent studies of the star using the water that surround it have allowed to refine both the distance and the parameters of this star, deriving an accurate parallax of , corresponding to a distance of 9,160 (2.81 kiloparsecs), that translates a luminosity for it around , 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.

A Gaia Data Release 2 parallax of gives the star a luminosity below with a corresponding radius of .

In 1956, R. Weber announced his discovery that the star's brightness varies. 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.

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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 possible less massive O-rich S- or SC-type Asymptotic Giant Branch (AGB) or post-AGB star. It shows enrichment of Zr and Ba, but not Li as would be expected for a true supergiant.

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

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Notes

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