Rho Cassiopeiae
File:Rho Cassiopeiae.jpeg 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[1] |
| Characteristics | |
| Spectral type | G2Ia0e(F8Ia0-M2I) |
| U−B color index | 1.12 |
| B−V color index | 1.20 |
| Variable type | semiregular (SRD)[1] |
| 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 | 2,500[2] pc |
| Absolute magnitude (MV) | –-9.5[3] |
| Details | |
| Mass | 14-30[4] M☉ |
| Radius | 400-500[3] R☉ |
| Luminosity | ~500,000[3] L☉ |
| Temperature | 6500-7200[3] K |
| Metallicity | 110% Sun |
| Rotation | 29 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) away from Earth, yet can still be seen by the naked eye (in the Northern Hemisphere only), as it is 500,000 times more luminous than the Sun. On average, it has an absolute magnitude of −9.5, making it one of the most luminous stars known. Its surface diameter measures 450 times that of the Sun, or approximately 630,000,000 kilometers. Being a yellow hypergiant, it is one of the rarest types of stars, one of only twelve in the Milky Way that are currently known,[5] though it is not the only one in its constellation, which also includes V509 Cassiopeiae.[6] Rho Cassiopeiae is a single star, and is categorized as a semiregular variable.
Observation
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.
Like other yellow hypergiants, Rho Cassiopeiae is somewhat unstable. Its apparent magnitude is usually about 4.5, but in 1946 it unexpectedly dimmed to 6th magnitude and cooled by over 3,000 Kelvin, before returning to its previous brightness. A similar eruption was recorded in 1893, suggesting that it undergoes these eruptions approximately once every 50 years.[7]
This happened again in 2000–2001, when it was observed (by the William Herschel Telescope) to have cooled from 7,000K to 4,250K in the course of a few months. This was one of the largest outbursts observed for any star, ejecting approximately 3% of a solar mass or 10,000 Earth masses at rates comparable to Eta Carinae during its great outburst. Such mass loss rates are thousands of times higher than the rates between eruptions and would be the dominant mechanism for mass loss in this type of star, possibly providing a mechanism for such stars to lose enough mass to explode as a supernova.[7]
Naming
In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of ρ Cassiopeiae, α Lacertae, 4 Lacertae, π2 Cygni, π1 Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, λ Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, ρ Cassiopeiae itself is known as 螣蛇十二 (Téng Shé shíèr, English: the Twelfth Star of Flying Serpent)[8]
References
- ^ a b "GCVS Query=Rho Cas". General Catalogue of Variable Stars @ Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2010-11-24.
- ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1086/168496, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
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|doi=10.1086/507590instead. - ^ Bibcode:1992A&A...254..280G
- ^ Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1086/312283, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1086/312283instead. - ^ http://jumk.de/astronomie/big-stars/v509-cassiopeiae.shtml
- ^ a b Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1086/345503, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with
|doi=10.1086/345503instead. - ^ Template:Zh icon AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
