PZ Cassiopeiae
Star in the constellation Cassiopeia
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PZ Cassiopeiae is a red supergiant or hypergiant[5] star located in the constellation of Cassiopeia, and a semi-regular variable star.
PZ Cassiopeiae is the bright star towards the upper right in this WISE infrared image of the nebula LBN 114.55+00.22 and the bright red star in the lower left corner of this image IRAS 23304+6147. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia[1] |
| Right ascension | 23h 44m 03.28104s[2] |
| Declination | +61° 47′ 22.1823″[2] |
| Apparent magnitude (V) | 8.2 – 10.2[3] |
| Characteristics | |
| Evolutionary stage | Red supergiant[4] or hypergiant[5] |
| Spectral type | M3Iab[6] |
| U−B color index | +1.32[7] |
| B−V color index | +2.58[7] |
| Variable type | SRc[8] + Cepheid[9] |
| Astrometry | |
| Radial velocity (Rv) | –45.68[10] km/s |
| Proper motion (μ) | RA: −4.15[2] mas/yr Dec.: −3.55[2] mas/yr |
| Parallax (π) | 0.356±0.026 mas[4] |
| Distance | 2,810+220 −190[4] pc |
| Absolute magnitude (MV) | −7.89[11] |
| Details | |
| Mass | 20 or 25 (initial mass)[4] M☉ |
| Radius | 1,260—1,340[4][a] R☉ |
| Luminosity | 229,000,[12] (240,000 – 270,000[4]) L☉ |
| Surface gravity (log g) | −0.5[11] cgs |
| Temperature | 3,605[6] K |
| Age | 8 or 10[4] Myr |
| Other designations | |
| PZ Cas, IRC +60417, HIP 117078, BD+60°2613, RAFGL 3138 | |
| Database references | |
| SIMBAD | data |
Characteristics
PZ Cassiopeiae is a luminous red supergiant star, one of the largest stars currently known with a radius over 1,200 times the Sun's radius (R☉), and also one of the most luminous of its type, over 200,000 times more luminous than the Sun (L☉).[13] It is likely to be part of the Cas OB5 stellar association although apparently much younger than the other stars in the association.[4] The star is losing mass at around 2.6×10−5 M☉ per year and has also once been described as a hypergiant.[14][5]
Its distance from Earth was initially estimated to be around 7,800 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 an accurate parallax of 0.356±0.026 mas, corresponding to a distance of 9,160 light-years (2.81 kiloparsecs), that translates a luminosity for it around 229,000 L☉, 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.[4][12]
A Gaia Data Release 2 parallax of 0.42±0.09 mas gives the star a luminosity below 180,000 L☉ with a corresponding radius of 1,062 R☉.[15]
In 1956, R. Weber announced his discovery that the star's brightness varies.[17] PZ Cas is a slow semi-regular variable star with the period quoted as 925 days in the General Catalogue of Variable Stars,[18] although periods of 850 and 3,195 days have been derived.[8][3] The visual range is approximate magnitude 8–10, large for this type of variable.[3]
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.[19]
Companion
PZ Cas has a Cepheid variable companion, a 13th magnitude star 12" away.[9]
Notes
- Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
- .
.
- .
