Alphard , 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 A giant star is a star with substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moore, New York: Oxford University Press ...

, cooler than the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

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

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

الفرد (''al-fard''), "the individual", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the

Arabs The Arabs (singular: Arab; singular ar, عَرَبِيٌّ, DIN 31635: , , plural ar, عَرَب, DIN 31635: , Arabic pronunciation: ), also known as the Arab people, are an ethnic group mainly inhabiting the Arab world in Western Asia, ...

. In the catalogue of stars in the ''Calendarium of Al Achsasi Al Mouakket'', it was designated ''Soheil al Fard'', which was translated into

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

as ''Soheil Solitarius'', meaning ''the bright solitary one''. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 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. The European astronomer

Tycho Brahe Tycho Brahe ( ; born Tyge Ottesen Brahe; generally called Tycho (14 December 154624 October 1601) was a Danish astronomer, known for his comprehensive astronomical observations, generally considered to be the most accurate of his time. He was ...

dubbed it ''Cor Hydræ'', Latin for 'the heart of Hydra'. In

Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...

, (), meaning '' Star'', refers to an asterism consisting of Alphard, τ¹ Hydrae, τ² Hydrae,

ι Hydrae Iota Hydrae (ι Hydrae, abbreviated Iota Hya, ι Hya), formally named Ukdah , is a star in the constellation of Hydra, about 8° to the north-northwest of Alphard (Alpha Hydrae) and just to the south of the celestial equator. Visible to ...

26 Hydrae 26 Hydrae is a binary star system located 334 light years away from the Sun in the equatorial constellation of Hydra. It is visible to the naked eye as a faint, yellow-hued point of light with a combined apparent visual magnitude ...

27 Hydrae 27 Hydrae is a member of a triple star system system in the equatorial constellation of Hydra, located 222 light years away from the Sun. It is visible to the naked eye as a faint, orange-hued star with a combined apparent visual ...

, HD 82477 and HD 82428. Consequently, Alphard itself is known as (), "the First Star of Star". In ancient China it formed part of an asterism called the "red bird".

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

with a

spectral classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of K3 and

luminosity class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

between II and III. The angular diameter has been measured using long-baseline interferometry, yielding a value of

milliarcseconds A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...

, only beaten in it by Betelgeuse and

R Doradus R Doradus (HD 29712 or P Doradus) is a red giant variable star in the far-southern constellation Dorado. Its distance from Earth is . Having a uniform disk diameter of , it is thought to be the extrasolar star with the largest apparent ...

. It has expanded to 50 times the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.957\t ...

. Alphard's

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...

shows a mild excess of barium, an element that is normally produced by the s-process of

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

. Typically a

barium star Barium stars are spectral class G to K stars whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4 nm. Barium stars also show enhanced spectral features of carbon, the ...

belongs to a

binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that th ...

and the anomalies in abundances are explained by mass transfer from a companion

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...

star. Precise radial velocity measurements have shown variations in the stellar

radial velocities The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection o ...

and

spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to iden ...

profiles. The

oscillation Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

s 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.

Modern legacy

Alphard appears on the

flag of Brazil The national flag of Brazil ( pt, bandeira do Brasil), is a blue disc depicting a starry sky (which includes the Southern Cross) spanned by a curved band inscribed with the national motto "''Ordem e Progresso''" ("Order and Progress"), within a ...

, symbolising the state of Mato Grosso do Sul. The

Toyota Alphard The is a minivan produced by the Japanese automaker Toyota since 2002. It is available as a seven or eight-seater with petrol and hybrid engine options. Hybrid variants have been available since 2003, which incorporates Toyota's Hybrid Synergy ...

is a

minivan Minivan (sometimes called simply as van) is a North American car classification for vehicles designed to transport passengers in the rear seating row(s), with reconfigurable seats in two or three rows. The equivalent classification in Europe is ...

named after this star. The character Roy Alphard from Japanese

light novel A light novel (, Hepburn: ''raito noberu'') is a style of young adult novel primarily targeting high school and middle school students. The term "light novel" is a '' wasei-eigo'', or a Japanese term formed from words in the English languag ...

series '' Re:Zero'' is named after this star.

References

{{Stars of Hydra Hydrae, Alpha Hydra (constellation) K-type bright giants K-type giants

Alphard Alphard , 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-year ...

Hydrae, 30 046390 081797 BD-08 2680 3748