Beta Cassiopeiae

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Caph, Beta Cassiopeiae
Cassiopeia constellation map.svg
Red circle.svg

Location of β Cassiopeiae (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 00h 09m 10.68518s[1]
Declination +59° 08′ 59.2120″[1]
Apparent magnitude (V) +2.28 (2.25–2.31)[2]
Characteristics
Spectral type F2 III[3]
U−B color index 0.11[4]
B−V color index 0.34[4]
Variable type Delta Scuti[5]
Astrometry
Radial velocity (Rv) 11.3[6] km/s
Proper motion (μ) RA: 523.50[1] mas/yr
Dec.: -179.77[1] mas/yr
Parallax (π) 59.58 ± 0.38[1] mas
Distance 54.7 ± 0.3 ly
(16.8 ± 0.1 pc)
Absolute magnitude (MV) +1.3[7]
Details
Mass 1.91 ± 0.02[8] M☉
Radius 3.43–3.69[8] R☉
Luminosity 27.3[8] L☉
Surface gravity (log g) 3.40[5] cgs
Temperature 7,079[5] K
Metallicity [Fe/H] 0.03[8] dex
Rotational velocity (v sin i) 71.0[9] km/s
Age 1.09–1.18[8] Gyr
Other designations
Caph, Chaph, Kaff, Al Sanam al Nakah,[10] 11 Cas, Gl 8, HR 21, BD+58°3, HD 432, LHS 1027, GCTP 16.00, SAO 21133, FK5 2, HIP 746, GC 147, ADS 107, CCDM J00092+5909[11]
Database references
SIMBAD data

Beta Cassiopeiae (β Cas, β Cassiopeiae) is a Delta Scuti variable star in the constellation Cassiopeia. It is a subgiant or giant star belonging to the spectral class F2. The white star of second magnitude (+2.27 mag) has an absolute magnitude of +1.16 mag. It has the traditional name Caph, from the Arabic word كف kaf, "palm" (i.e. reaching from the Pleiades).

Visibility

With a mean apparent magnitude (V-band) of +2.27, it is one of the five stars which make up the 'W' of Cassiopeia, adjacent to the just brighter Schedar (Alpha Cassiopeiae).[12] SN 1572, traditionally known as Tycho's Star, appeared about 5 degrees to the northwest of Caph in 1572.[10]

As a star in the deep northern hemisphere of the sky, Beta Cassiopeiae is prominent to viewers in the northern hemisphere but not often seen by those in the southern hemisphere. The constellation of Cassiopeia does not rise above the horizon to viewers in Tasmania, and only low if one were in Cairns.[13]

System

β Cassiopeiae is a yellow-white hued subgiant or giant of stellar class F2III-IV, with a surface temperature of 6,700 Kelvin.[12] More than three times the size of and 28 times brighter than the Sun, Caph has an absolute magnitude of +1.16. It was once an A-type star with about double the Sun's mass.[8] It is now in the process of cooling and expanding to become a red giant. Its core is likely to have used up its hydrogen and is shrinking and heating, while its outer envelope of hydrogen is expanding and cooling. Stars do not spend much time in this state and are relatively uncommon. Caph's corona is unusually weak.[12]

β Cassiopeiae is a variable star of the Delta Scuti type, in fact the second brightest of such stars in the sky after Altair.[14] It is a monoperiodic pulsator,[15] with a brightness that ranges from magnitude +2.25 to +2.31 with a period of 2.5 hours.[12] This type of variables includes subgiant or main sequence stars of spectral classes F5–A0, having masses between 1.5–2.5 solar masses and nearing the end of their core hydrogen fusion lifetime.[15] Their pulsations are related to the same helium instability strip on the Hertzsprung–Russell diagram as that of classical Cepheids. Delta Scuti stars are located at the intersection of the strip with the main sequence.[16]

This star is rotating at about 92% of its critical speed, completing a full rotation every 1.12–1.16 days. This is giving the star an oblate spheroid shape with an equatorial bulge that is 24% larger than the polar radius. This shape is causing the polar region to have a higher temperature than the equator: the temperature difference is about 1,000 K. The axis of rotation is inclined about 20° to the line of sight from the Earth.[8]

β Cassiopeiae is a binary star, with a faint companion, which orbits it every 27 days. Little else is known about this companion.[17]

Etymology and cultural significance

Originally, the pre-Islamic Arabic term al-Kaff al-Khadib "the stained hand" referred to the five stars comprising the 'W' of the constellation Cassiopeia, and depicted a hand stained with henna. The term was abbreviated and somehow came to signify β Cassiopeiae alone. The old "stained hand" was part of an asterism stretching from the Pleiades, which signified the "head" through Taurus and Perseus and into Cassiopeia, while the other "hand" was in Cetus.[18]

Alternate common names are Chaph and Kaff, as well as al-Sanam al-Nakah "the Camel's Hump".[10]

In Chinese, 王良 (Wáng Liáng), meaning Wang Liang[19], refers to an asterism consisting of β Cassiopeiae, κ Cassiopeiae, η Cassiopeiae, α Cassiopeiae and λ Cassiopeiae.[20] Consequently, β Cassiopeiae itself is known as 王良一 (Wáng Liáng yī, English: the First Star of Wang Liang.)[21]

Together with Alpha Andromedae (Alpheratz) and Gamma Pegasi (Algenib), Beta Cassiopeiae was one of three bright stars known as the "Three Guides" marking the equinoctial colure.[10] This is an imaginary line running due south from Beta Cassiopeiae through Alpha Andromedae to the celestial equator, at a point where the Sun's path (the ecliptic) crosses it each autumn and spring equinox.[12]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ 4.0 4.1 Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 5.2 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 8.6 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ 10.0 10.1 10.2 10.3 Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ 15.0 15.1 Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Wang Liang was a famous charioteer during the Spring and Autumn Period
  20. ↑ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  21. ↑ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.

External links

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