RW Cephei
RW Cephei is a K-type hypergiant and a semirregular variable star in the constellation Cepheus, at the edge of the Sharpless 132 H II region and close to the small open cluster Berkeley 94. It is among the largest stars known with a radius of almost 1,000 times that of the Sun (R☉), nearly as large as the orbit of Jupiter.
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cepheus |
| Right ascension | 22h 23m 07.01521s |
| Declination | +55° 57′ 47.6244″ |
| Apparent magnitude (V) | +6.65 (6.0–7.6) |
| Characteristics | |
| Evolutionary stage | Red or yellow hypergiant |
| Spectral type | K2 0-Ia (G8 - M2Ia-0) |
| Apparent magnitude (K) | 1.88 |
| U−B color index | 2.38 |
| B−V color index | 2.22 |
| Variable type | SRd |
| Astrometry | |
| Radial velocity (Rv) | −56.00 km/s |
| Proper motion (μ) | RA: −3.606 mas/yr Dec.: −2.881 mas/yr |
| Parallax (π) | 0.1140 ± 0.0342 mas |
| Distance | 3,400+220 −200 pc |
| Absolute magnitude (MV) | −8.0 – −9.4 |
| Details | |
| Radius | 900–1,760, 940 R☉ |
| Luminosity | 300,000 L☉ |
| Surface gravity (log g) | 0.2 cgs |
| Temperature | 4,200–4,400, 3,900 (during the dimming) K |
| Metallicity [Fe/H] | +0.17±0.20 dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
In 2022, the star underwent a "great dimming" event similar to Betelgeuse.
The temperature intermediate between the red supergiants and yellow hypergiants has led to it being variously considered as a red hypergiant or yellow hypergiant.
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