Alphard

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For the programming language, see Alphard (programming language). For the vehicle, see Toyota Alphard.
Alpha Hydrae
Alphard is located in 100x100
Alphard

Alphard = α Hya (circled) in the constellation Hydra.
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 09h 27m 35.2433s[1]
Declination −08° 39′ 30.969″[1]
Apparent magnitude (V) +2.00[2]
Characteristics
Spectral type K3 II-III[2]
U−B color index +1.73[3]
B−V color index +1.44[3]
Astrometry
Radial velocity (Rv) −4.3[4] km/s
Proper motion (μ) RA: −14.49[1] mas/yr
Dec.: 33.25[1] mas/yr
Parallax (π) 18.40 ± 0.78[1] mas
Distance 177 ± 8 ly
(54 ± 2 pc)
Absolute magnitude (MV) −1.69 ± 0.09[5]
Details
Mass 3.03 ± 0.36[5] M☉
Radius 50.5 ± 4.0[5] R☉
Luminosity 780 ± 78[2] L☉
Surface gravity (log g) 1.54[6] cgs
Temperature 4,120[6] K
Metallicity [Fe/H] −0.06[6] dex
Rotation 2,991 days[7]
Rotational velocity (v sin i) 1.1[7] km/s
Age (4.2 ± 1.6) × 108[5] years
Other designations
Alphard, Alfard, Alphart, Kalbelaphard, Cor Hydrae, 30 Hydrae, HR 3748, BD−08° 2680, HD 81797, SAO 136871, FK5 354, HIP 46390.[8]

Alphard (α Hya, α Hydrae, Alpha Hydrae) is the brightest star in the constellation Hydra. The name Alphard is from the Arabic الفرد (al-fard), "the solitary one", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the Arabs. In ancient China it formed part of an asterism called the "red bird". The European astronomer Tycho Brahe dubbed it Cor Hydræ, the heart of the snake.[9]

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, it was designated Soheil al Fard, which was translated into Latin as Soheil Solitarius, meaning the bright solitary one.[10]

In Chinese, 星宿 (Xīng Xiù), meaning Star, refers to an asterism consisting of Alphard, τ1 Hydrae, τ2 Hydrae, ι Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428.[11] Consequently, Alphard itself is known as 星宿一 (Xīng Xiù yī), "the First Star of Star".[12]

Properties

Alphard has three times the mass of the Sun. Its estimated age is 420 million years and it has evolved away from the main sequence to become a giant star with a spectral classification of K3 and luminosity class between II and III.[5] The angular diameter has been measured using long baseline interferometry, yielding a value of 9.09 ± 0.09 milliarcseconds, only beaten in it by Betelgeuse and R Doradus.[13] It has expanded to 50 times the radius of the Sun.[5]

Alphard's spectrum shows a mild excess of barium, an element that is normally produced by the s-process of nucleosynthesis. Typically a barium star belongs to a binary system and the anomalies in abundances are explained by mass transfer from a companion white dwarf star.[14]

Precise radial velocity measurements have shown variations in the stellar radial velocities and spectral line profiles. The oscillations are multi-periodic with periods from several hours up to several days. The short-term oscillations were assumed to be a result of stellar pulsations, similar to the solar ones. A correlation between the variations in the asymmetry of the spectral line profile and the radial velocity has also been found. The multi-periodic oscillations make HD 81797 (Alphard) an object of interest for asteroseismologic investigations.[15]

Modern legacy

Alphard appears on the flag of Brazil, symbolising the state of Mato Grosso do Sul.[16]

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. ↑ 2.0 2.1 2.2 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 6.2 Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 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. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ (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.
  12. ↑ (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.
  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. ↑ 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.
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