Rho Cassiopeiae

Bayer name	ρ Cassiopeiae
Flamsteed name	7 Cassiopeiae
Bonn survey	BD + 56 ° 3111
Bright Star Catalog	HR 9045 [1]
Henry Draper Catalog	HD 224014 [2]
Hipparcos catalog	HIP 117863 [3]
SAO catalog	SAO 35879 [4]
Tycho catalog	TYC 4009-2605-1 [5]
2MASS catalog	2MASS J23542302 + 5729578 [6]
Other names	FK5 899

ρ Cassiopeiae ( rho Cassiopeiae , short ρ Cas , also called Rhocas ) is a yellow hypergiant in the constellation Cassiopeia and about 3500 light years away from our solar system. It is the brightest star in the Cas OB5 star association .

In 2003, an international team of astronomers named ρ Cas as the best candidate for an imminent supernova explosion. With the William Herschel telescope on the Canary Island of La Palma , strong changes in the giant star ρ Cas were observed.

Surname

The first part of the name “rho” (ρ) follows the rules of the Bayer name . It says that the brightest star in a constellation as seen from Earth is usually designated with α, the next brightest with β, etc. However, there are slight deviations in the constellation Cassiopeia: Although the letter ρ is only in the seventeenth position of the Greek alphabet , ρ is Cas itself is the fourteenth brightest star that can be found in this constellation. The second part of the name "Cassiopeiae" corresponds to the genitive of the Latin name of the constellation Cassiopeia.

The Flamsteed designation of ρ Cas (7 Cas) is less common, as a Bayer designation already exists for the star, which is usually better known.

Physical Properties

Due to its instability, the surface temperature and thus also the spectral class varies between F8 and K0.

ρ Cas belongs to the yellow hypergiant, a very rare class of stars, of which only a few are known in the galaxy. With an absolute visual brightness of −9.6 M _V , it is one of the brightest stars of all, it has about 500,000 times the luminosity of the sun. Although its surface temperature is not much higher than that of the Sun, the Habitable Zone only begins at a massive 450 AU .

The mass of ρ Cas is approx. 40 solar masses, making it one of the heaviest stars in the Milky Way . Such stars only live a few million years before they explode as a supernova or a hypothetical hypernova and finally end up as pulsars or neutron stars or even as black holes .

The apparent magnitude of ρ Cas is 4.5 mag. Presumably, clouds of dust that are between him and the sun weaken the light. Yet it is faintly visible to the naked eye even under poor conditions.

Age

Hypergiants use up their nuclear fuel very quickly; therefore they are only a few million years old. Presumably only very few massive stars like ρ Cas, which do not have the mass to become a luminous blue variable (LBV), as hypergiant a white, yellow or even an orange or red phase like RW Cephei shortly before their end before they explode. Due to the current pulsations of ρ Cas, it can be assumed that it will no longer reach spectral class M.

Discoveries

Astronomers assume that stars of the type ρ Cas are well developed stars that are about to start a supernova explosion. The stars are in a very unstable state, which inevitably leads to a supernova explosion.

The environment of the sun, ρ Cas is on the lower left edge of the picture.

Researchers found that in 2000 ρ Cas cooled from 7000 to 4000 degrees within a few months. This very strong cooling is explained by the fact that 0.1 solar masses were probably expelled into space in the form of a gas envelope. The nuclear fuel is almost used up. Older observations from the years 1893 and 1945 have shown that there must have been an extreme loss of mass at ρ Cas. It is further assumed that such mass losses occur approximately every 50 years.

The atmosphere of ρ Cas has been pulsing since 2000, which is why astronomers expect a new loss of mass. Due to the great distance of ρ Cas, it is very likely that the star has already exploded and became a black hole or a neutron star . If the star loses 10 percent of the sun's mass every 50 years, that would be 20 solar masses in 10,000 years. Therefore it is very likely that ρ Cas no longer exists.

Web links

Commons : ρ Cassiopeiae - collection of images, videos and audio files

Individual evidence

↑ ^a ^b rho Cas. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed October 29, 2018 .
^ Hipparcos catalog (ESA 1997)
↑ ^a ^b rho Cas. In: VSX. AAVSO, accessed October 29, 2018 .
↑ ^a ^b ^c Bright Star Catalog
↑ Pulkovo radial velocities for 35493 HIP stars
^ Hipparcos, the New Reduction (van Leeuwen, 2007)
↑ ^a ^b ^c ^d Rho Cas. Jim Kaler, accessed October 29, 2018 .
↑ Dr. Garik Israelian (Instituto de Astrofísica de Canarias).

[Simbad-1] rho Cas. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed October 29, 2018 .

[hip1-2] Hipparcos catalog (ESA 1997)

[VSXEntry-3] rho Cas. In: VSX. AAVSO, accessed October 29, 2018 .

[hr-4] Bright Star Catalog

[Pulkovo-5] Pulkovo radial velocities for 35493 HIP stars

[hip2-6] Hipparcos, the New Reduction (van Leeuwen, 2007)

[Kaler-7] Rho Cas. Jim Kaler, accessed October 29, 2018 .

[8] Dr. Garik Israelian (Instituto de Astrofísica de Canarias).