Alpha Serpentis or α Serpentis, formally named Unukalhai (), is a star in the head (Serpens Caput) of the equatorial

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Serpens Serpens () is a constellation in the northern celestial hemisphere. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations designated by the International Astronomical Union. It ...

. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 2.6, this star is the brightest in the constellation and it can be viewed with the naked eye from most of the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements yield an estimated distance of about from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

Properties

Alpha Serpentis is a

giant star A giant star has a substantially larger radius and luminosity than a main-sequence (or ''dwarf'') star of the same surface temperature. They lie above the main sequence (luminosity class V in the Yerkes spectral classification) on the Hertzsp ...

with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of K2IIIbCN1, having consumed the hydrogen at its core and

evolved Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

away from the

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

. It has 1.6 times the mass and 13.5 times the radius of the Sun. It is most likely a

horizontal branch The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red-giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha proc ...

or red clump star, fusing helium into carbon and heavier elements within its core. The

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of the outer envelope is 4,687 K, giving it an orange hue that is characteristic of a K-type star. It has been classified as a strong CN star, showing a higher than expected strength in the

cyanogen Cyanogen is the chemical compound with the chemical formula, formula . Its structure is . The simplest stable carbon nitride, it is a Transparency and translucency, colorless and highly toxic gas with a pungency, pungent odor. The molecule is a ...

bands. This star is radiating about 30 times the

luminosity of the Sun The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

, while a further 32 times the Sun's luminosity is being emitted in the

infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...

, for 70-fold total.

Nomenclature

''α Serpentis'' ( Latinised to ''Alpha Serpentis'') is the system's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

. It bore the traditional names ''Unukalhai'' (alternatively spelt ''Unuk al Hay'' or ''Unuk Elhaija'') from the

Arabic Arabic (, , or , ) is a Central Semitic languages, Central Semitic language of the Afroasiatic languages, Afroasiatic language family spoken primarily in the Arab world. The International Organization for Standardization (ISO) assigns lang ...

عنق الحيّة ''ʽunuq al-ḥayyah'' "the serpent's neck", and ''Cor Serpentis'' from the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

"the Heart of the Serpent". In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

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 catalogue and standardize proper names for stars. The WGSN approved the name ''Unukalhai'' for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names. Alpha Serpentis is a member of the indigenous Arabic asterism ''al-Nasaq al-Yamānī'' "the Southern Line" of ''al-Nasaqān'' "the Two Lines", along with Delta Serpentis, Epsilon Serpentis, Delta Ophiuchi, Epsilon Ophiuchi, Zeta Ophiuchi and Gamma Ophiuchi. According to a 1971

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

catalogue, ''al-Nasaq al-Yamānī'' or ''Nasak Yamani'' was the name for two stars: Delta Serpentis as ''Nasak Yamani I'' and Epsilon Serpentis as ''Nasak Yamani II''. In Chinese, (), meaning '' Right Wall of Heavenly Market Enclosure'', refers to an asterism which represents eleven old states in China and which is marking the right borderline of the enclosure, consisting of Alpha Serpentis, Beta Herculis,

Gamma Herculis Gamma Herculis, Latinisation of names, Latinized from γ Herculis, is a Magnitude (astronomy), magnitude 3.74 binary star system in the northern constellation of Hercules (constellation), Hercules. It is easily visible to the naked eye un ...

, Kappa Herculis,

Gamma Serpentis Gamma Serpentis (γ Serpentis, γ Ser) is a star in the equatorial constellation Serpens, in the part of the constellation that represents the serpent's head (Serpens Caput). It has an apparent visual magnitude +3.85, which means it is vis ...

Beta Serpentis Beta Serpentis, Latinized from β Serpentis, also named Zhou, is a binary star system in the constellation Serpens, in its head (Serpens Caput). It is visible to the naked eye with a combined apparent visual magnitude of +3.65. Based u ...

, Delta Serpentis, Epsilon Serpentis, Delta Ophiuchi, Epsilon Ophiuchi and Zeta Ophiuchi. Consequently, the

Chinese name Chinese may refer to: * Something related to China * Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity **Han Chinese, East Asian ethnic group native to China. **'' Zhonghua minzu'', the supra-ethni ...

for Alpha Serpentis itself is (, ), and represents the state Shu (蜀) (or Shuh)English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name
, Hong Kong Space Museum. Accessed on line November 23, 2010. (together with Lambda Serpentis in R.H.Allen's works).

References

{{DEFAULTSORT:Alpha Serpentis K-type giants CN stars Serpens Serpentis, Alpha BD+06 3088 Serpentis, 24 140573 077070 5854 Unukalhai Horizontal-branch stars