La Superba
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| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Canes Venatici |
| Right ascension | 12h 45m 07.83s |
| Declination | +45° 26' 24.92" |
| Apparent magnitude (V) | +4.8<m<+6.3 |
| Distance | 711 ± 113 ly (218 ± 35 pc) |
| Spectral type | C7I |
| Other designations | |
La Superba (Y CVn / Y Canum Venaticorum) is a "semi-regular" variable star peaking at about +4.8m and diminishing to around +6.3 over a 160 day cycle. Known in short form as Y CVn, it is one of the reddest stars in the sky, because it is among the brightest of the giant red "carbon stars". La Superba is the sky's brightest "J star", a very rare category of carbon stars that have a puzzlingly large amount of carbon-13 (7 neutrons instead of the usual 6). The 19th century astronomer Father Angelo Secchi, impressed with its beauty, gave the star its common name.
To understand its coloration, it is necessary to understand that massive stars are massive because they are dying (running out of fusionable elements) and that the fused material (in this case helium is fused into carbon) rises to the surface and escapes into space. The apparent red color of Y CVn is caused by tremendous amounts of carbon (in the form of CO, Cyanogen, etc) in the outside layers of the star. These molecules create an absorption spectrum, cutting out the high energy light, giving the star a remarkable spectrum with almost no blue or violet, making the star a very striking red.
Its temperature is believed to be about 2800 K, making Y CVn one of the coldest "true" stars known. This star is normally not viewable with the naked eye because most of its light is outside the visible spectrum, yet when infrared radiation is considered, Y CVn has a luminosity 4400 times that of the Sun. Its radius is approximately 2 AU, meaning if it were placed in our solar system, the star's surface would extend farther than the orbit of Mars. La Superba is most likely finishing the process of fusing the last of its secondary fuel (helium) into carbon and shedding its mass at the rate of about a million times that of the Sun's solar wind. It is also surrounded by a gigantic 2.5 light year-wide shell of its own ejected material, implying that at one point it must have been losing mass even 50 times faster than it is now. La Superba thus appears almost ready to eject its outer layer in a supernova. Afterwards it will end its years as a vanishing white dwarf.