Alphard is the brightest star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 in the constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

Hydra (constellation)
Hydra is the largest of the 88 modern constellations, measuring 1303 square degrees. It has a long history, having been included among the 48 constellations listed by the 2nd century astronomer Ptolemy. It is commonly represented as a water snake...

. The name Alphard is from the Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 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
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...

 called the "red bird". The European astronomer Tycho Brahe
Tycho Brahe
Tycho Brahe , born Tyge Ottesen Brahe, was a Danish nobleman known for his accurate and comprehensive astronomical and planetary observations...

 dubbed it Cor Hydræ, the heart of the snake.

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Soheil al Fard, which was translated into Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 as Soheil Solitarius, meaning the bright solitary one.

In Chinese
Chinese language
The Chinese language is a language or language family consisting of varieties which are mutually intelligible to varying degrees. Originally the indigenous languages spoken by the Han Chinese in China, it forms one of the branches of Sino-Tibetan family of languages...

, , meaning Star
Star (Chinese constellation)
The Star mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the southern mansions of the Vermilion Bird.- Asterisms :...

, refers to an asterism consisting of Alphard, τ1 Hydrae
Tau Hydrae
The Bayer designation Tau Hydrae is shared by two star systems, τ¹ Hydrae and τ² Hydrae, in the constellation Hydra...

, τ2 Hydrae
Tau Hydrae
The Bayer designation Tau Hydrae is shared by two star systems, τ¹ Hydrae and τ² Hydrae, in the constellation Hydra...

, ι Hydrae, 26 Hydrae, 27 Hydrae
27 Hydrae
27 Hydrae is an evolved yellow giant star in the constellation of Hydra. The star is suspected to host a low-mass companion.-Substellar companion:...

, HD 82477 and HD 82428. Consequently, Alphard itself is known as


Alphard has three times the mass of the Sun
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...

. The estimated age of this star is 420 million years and it has evolved away from the main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...

 to become a giant star
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...

 with a spectral classification of K3 and luminosity class between II and III. The angular diameter of this star has been measured using long baseline interferometry, yielding a value of milliarcseconds. It has expanded to 50 times the radius of the Sun.

Alphard's spectrum shows a mild excess of barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...

, an element that is normally produced by the s-process
The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...

 of nucleosynthesis
Stellar nucleosynthesis
Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the elements heavier than hydrogen. Some small quantity of these reactions also occur on the stellar surface under various circumstances...

. Typically a barium star
Barium star
Barium stars are G to K class giants, whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4nm. Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C2...

 belongs to a binary system
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 and the anomalies in abundances are explained by mass transfer from a companion white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...


Precise radial velocity measurements have shown variations in the stellar radial velocities
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...

 and spectral line
Spectral line
A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from a deficiency or excess of photons in a narrow frequency range, compared with the nearby frequencies.- Types of line spectra :...

 profiles. The oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

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
Asteroseismology also known as stellar seismology is the science that studies the internal structure of pulsating stars by the interpretation of their frequency spectra. Different oscillation modes penetrate to different depths inside the star...


Modern legacy

Alphard appears on the flag of Brazil
Flag of Brazil
The national flag of Brazil is a blue disc depicting a starry sky spanned by a curved band inscribed with the national motto, within a yellow rhombus, on a green field. Brazil officially adopted this design for its national flag on November 19, 1889, replacing the flag of the second Empire of Brazil...

, symbolising the state of Mato Grosso do Sul
Mato Grosso do Sul
Mato Grosso do Sul is one of the states of Brazil.Neighboring Brazilian states are Mato Grosso, Goiás, Minas Gerais, São Paulo and Paraná. It also borders the countries of Paraguay and Bolivia to the west. The economy of the state is largely based on agriculture and cattle-raising...

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