Rho Cassiopeiae
Rho Cassiopeiae (/ˌroʊ kæsiəˈpiːaɪ, -sioʊ-, -iː/; ρ Cas, ρ Cassiopeiae) is a yellow hypergiant star in the constellation Cassiopeia. It is about 3,400 light-years (1,000 pc) from Earth, yet can still be seen by the naked eye as it is over 300,000 times brighter than the Sun. On average it has an absolute magnitude of −9.5, making it visually one of the most luminous stars known. Its diameter measures between 636 and 981 times that of the Sun, approximately 1,125,000,000 kilometers (7.52 AU; 699,000,000 mi), or almost four times the size of Earth's orbit.
Location of Rho Cassiopeiae in the Cassiopeia constellation. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 23h 54m 23.0s |
| Declination | +57° 29′ 58″ |
| Apparent magnitude (V) | 4.1 to 6.2 |
| Characteristics | |
| Spectral type | G2Iae (F8pIa-K0pIa-0) |
| U−B color index | 1.15 |
| B−V color index | 1.26 |
| Variable type | SRd |
| Astrometry | |
| Radial velocity (Rv) | −47 km/s |
| Proper motion (μ) | RA: −4.54 mas/yr Dec.: −3.45 mas/yr |
| Parallax (π) | 0.9470 ± 0.2021 mas |
| Distance | 3,400 ly (1,050±210 pc) |
| Absolute magnitude (MV) | –9.5 |
| Details | |
| Mass | 40 M☉ |
| Radius | 636–981 R☉ |
| Luminosity | 302,000–530,000, 129,000 L☉ |
| Surface gravity (log g) | 0.1 cgs |
| Temperature | 4,571–6,044 K |
| Metallicity [Fe/H] | 0.3 dex |
| Rotational velocity (v sin i) | 25 km/s |
| Age | 4-6 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
Rho Cassiopeiae is a single star, and is categorized as a semiregular variable. As a yellow hypergiant, it is one of the rarest types of stars. Only a few dozen are known in the Milky Way, but it is not the only one in its constellation which also contains V509 Cassiopeiae.