Rho Cassiopeiae
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Graphic: Harvard-Smithsonian Center for Astrophysics, Lobel et al |
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| Observation data Epoch J2000 |
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|---|---|
| Constellation (pronunciation) |
Cassiopeia |
| Right ascension | 23h 54m 23.0s |
| Declination | +57° 29′ 58″ |
| Apparent magnitude (V) | 4.52 |
| Characteristics | |
| Spectral type | G2Ia0e |
| U-B color index | 1.12 |
| B-V color index | 1.20 |
| Variable type | semiregular |
| Astrometry | |
| Radial velocity (Rv) | −43.1 km/s |
| Proper motion (μ) | RA: −4.54 mas/yr Dec.: −3.45 mas/yr |
| Parallax (π) | 0.28 ± 0.58 mas |
| Distance | approx. 12000 ly (approx. 4000 pc) |
| Absolute magnitude (MV) | −7.48 |
| Details | |
| Mass | 40 M☉ |
| Radius | 450 R☉ |
| Luminosity | 5.5 × 105 L☉ |
| Temperature | (7,500 +/- 200) K |
| Metallicity | 110% Sun |
| Rotation | 29 km/s |
| Age | ? years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Rho Cassiopeiae (ρ Cas / ρ Cassiopeiae) is a yellow hypergiant in the constellation Cassiopeia. It is about 11,650 light-years away, yet can still be seen by the naked eye (in the Northern Hemisphere only), as it is 550,000 times as luminous as the Sun. Its surface diameter is 450 times that of our sun's. On average, it has an absolute magnitude of −7.5, making it one of the most luminous stars known. Even though its surface temperature is similar to the Sun, its comfort zone for an Earthlike planet would be 450AU, which is more than 10 times the distance from the sun to Pluto. Being a yellow hypergiant, it is one of the rarest types of stars, one of only seven that are currently known.
Rho Cassiopeiae is somewhat unstable in its luminosity. Its apparent magnitude is currently about 4.5, but in 1946 it dimmed to 6th magnitude, before returning to its previous brightness. This happened again in 2000–2001, when it produced one of the largest outbursts known, ejecting 3% of a solar mass, the equivalent of 10,000 Earths. During the summer of 2000 it was observed (by the William Herschel Telescope) to have cooled from 7000 to 4000 degrees in the course of a few months. It seems to undergo these eruptions approximately once every 50 years (data suggests previous eruptions in 1893 and 1945).
Astronomers predict Rho Cassiopeiae may become a supernova in the near future because it will soon have consumed most of its nuclear fuel.
[edit] External links
- Press release from the William Herschel Telescope team about their findings.
- Rho Cassiopeiae fact sheet
- David Darling site
- Big and Giant Stars: Rho Cassiopeiae
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