Alphard

Coordinates: Sky map 09h 27m 35.2433s, −08° 39′ 30.969″
Source: Wikipedia, the free encyclopedia.
This article is about the star. For the programming language, see
Alpharadin
.
Alphard
Location of Alphard (circled)
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]
Distance
177 ± 8 ly
(54 ± 2 pc)
Absolute magnitude (MV)−1.69 ± 0.09[5]
Details
Rotational velocity (v sin i)
1.1[7] km/s
Age(4.2 ± 1.6) × 108[5] years
HIP 46390[8]
Database references
SIMBADdata

Alphard /ˈælfɑːrd/,[9] designated Alpha Hydrae (α Hydrae, abbreviated Alpha Hya, α Hya), is the brightest star in the constellation of Hydra. It is a single giant star, cooler than the Sun but larger and more luminous. It is about 177 light-years away.

Nomenclature

α Hydrae (Latinised to Alpha Hydrae) is the star's Bayer designation.

The traditional name Alphard is from the

Working Group on Star Names (WGSN)[11] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[12] included a table of the first two batches of names approved by the WGSN; which included Alphard for this star. It is now so entered in the IAU Catalog of Star Names.[13]

The European astronomer Tycho Brahe dubbed it Cor Hydræ, Latin for 'the heart of Hydra'.[14]

In

ι Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428.[15] Consequently, Alphard itself is known as 星宿一 (Xīng Xiù yī), "the First Star of Star".[16] In ancient China
it formed part of an asterism called the "red bird".

Properties

The western portion of Hydra, with Alphard the brightest star near the centre

Alphard has three 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.[18]

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.[19]

Modern legacy

Alphard appears on the flag of Brazil, symbolising the state of Mato Grosso do Sul.[20]

The Toyota Alphard is a minivan named after this star.

The character Roy Alphard from Japanese light novel series Re:Zero is named after this star.

References

  1. ^
    Bibcode:1997A&A...323L..49P
  2. ^
    S2CID 118533297
  3. ^
    doi:10.1086/111186
    .
  4. Bibcode:1967IAUS...30...57E
    .
  5. ^
    S2CID 9341088
    .
  6. ^
    S2CID 119428437
    .
  7. ^
    doi:10.1051/0004-6361:20041042-1
  8. Centre de Données astronomiques de Strasbourg
    . Retrieved 2009-10-09.
  9. ISBN 978-1-931559-44-7
    .
  10. doi:10.1093/mnras/55.8.429
    .
  11. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  12. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  13. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  14. ISBN 0-486-43581-4
    .
  15. ISBN 978-986-7332-25-7
    .
  16. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2008-10-25 at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  17. S2CID 10478557
    .
  18. Bibcode:1997A&A...326..722M
    . Retrieved 2009-10-09.
  19. Bibcode:2006MmSAI..77..510S
    . Retrieved 2009-10-09.
  20. ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. 1 January 2019. Retrieved 3 May 2019.
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