PZ Cassiopeiae
 Location of PZ Cas |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 23h 44m 03.28104s |
| Declination | +61° 47′ 22.1823″ |
| Apparent magnitude (V) | 8.90(8.2 - 10.2) |
| Characteristics | |
| Spectral type | M3I |
| U−B color index | +1.32 |
| B−V color index | +2.58 |
| Variable type | SRc |
| Astrometry | |
| Radial velocity (Rv) | -45.68 ± 0.68 km/s |
| Proper motion (μ) |
RA: −4.15 mas/yr Dec.: −3.55 mas/yr |
| Parallax (π) | 0.356 ± 0.026mas |
| Distance |
2,810+220 −190pc |
| Absolute magnitude (MV) | −7.89 |
| Details | |
| Radius | 1,190 (-1,940) R☉ |
| Luminosity | 240,000–270,000 L☉ |
| Surface gravity (log g) | −0.5 cgs |
| Temperature | 3,600 K |
| Age | 8 – 10 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
PZ Cassiopeiae is a red supergiant star located in the Cassiopeia constellation, and a semi-regular variable star.
PZ Cas is an extreme luminous red supergiant star, one of the largest stars currently known with estimates at 1,190–1,940 times the Sun's radius. Its distance from Earth was initially estimated to be around 7800 light-years (2.4 kiloparsecs). 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 (2.81 kiloparsecs) that translates into a luminosity for it of between 240,000 and 270,000 times the Sun's luminosity, a radius 1,260–1,340 the solar one, and an initial mass 25 times that of the Sun. These parameters are all similar to those estimated for the red hypergiant VY Canis Majoris. 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.
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 (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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