Rho Cassiopeiae
 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) | 0.28 ± 0.58mas |
| Distance | 2,500pc |
| Absolute magnitude (MV) | –9.5 |
| Details | |
| Mass | 14-30 M☉ |
| Radius | 400-500 R☉ |
| Luminosity | ~500,000 L☉ |
| Surface gravity (log g) | 0.1 cgs |
| Temperature | 5777-7200 K |
| Metallicity [Fe/H] | 0.3 dex |
| Rotational velocity (v sin i) | 25 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
Rho Cassiopeiae (/ˌroʊ kæsiəˈpiː.iː/; ρ Cas, ρ Cassiopeiae) is a yellow hypergiant star in the constellation Cassiopeia. It is about 8,200 light-years (2,500 pc) from Earth, yet can still be seen by the naked eye as it is 500,000 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 450 times that of the Sun, approximately 630,000,000 kilometers, or about twice the size of the Earth's orbit.
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 around a dozen are known in the Milky Way, but it is not the only one in its constellation which also contains V509 Cassiopeiae.
The Bayer designation for this star was established in 1603 as part of the Uranometria, a star catalog produced by Johann Bayer. The star catalog by John Flamsteed published in 1712, which orders the stars in each constellation by their right ascension, gave this star the Flamsteed designation 7 Cassiopeiae.
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