Alpha Serpentis or α Serpentis, formally named Unukalhai (), is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...

in the head (Serpens Caput) of the equatorial constellation of Serpens. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

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. Parallax measurements yield an estimated distance of about from 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 ...

Properties

Alpha Serpentis is a giant star with a

stellar 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 th ...

of K2IIIbCN1, having consumed the hydrogen at its core and

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variati ...

away from the

main sequence In astronomy, 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 H ...

. It has 1.7 times the mass and 13.5 times the radius of the Sun. 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 4,498 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 formula ( C N)2. It is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecules ...

bands. This star is radiating about 38 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 ...

, while a further 32 times the Sun's luminosity is being emitted in the infrared, for 70-fold total. A magnitude +11.8 companion is at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in ...

of 58

arcsecond 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 ...

s from Alpha Serpentis, while a 13th magnitude star lies 2.3

arcminute 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 ...

s distant.

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 or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. T ...

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

عنق الحيّة ''ʽunuq al-ḥayyah'' "the serpent's neck", and ''Cor Serpentis'' from the Latin "the Heart of the Serpent". 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, outreach ...

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 Delta Serpentis, Latinized from δ Serpentis, is a binary star system in the constellation Serpens, in its head (Serpens Caput). The light from the two stars in the system give a combined apparent magnitude of +3.80, which is bright enou ...

Epsilon Serpentis Epsilon Serpentis, Latinized from ε Serpentis, is a single, white-hued star in the constellation Serpens, in its head (Serpens Caput). It is visible to the naked eye with an apparent visual magnitude of +3.69. Based upon an annual parall ...

Delta Ophiuchi Delta Ophiuchi (δ Ophiuchi, abbreviated Delta Oph, δ Oph), formally named Yed Prior , is a star in the constellation of Ophiuchus. It forms a naked-eye optical double with Epsilon Ophiuchi (named ''Yed Posterior''). The apparent visual ...

Epsilon Ophiuchi Epsilon Ophiuchi or ε Ophiuchi, formally named Yed Posterior (), is a red giant star in the constellation of Ophiuchus. Located less than five degrees south of the celestial equator in the eastern part of the constellation, it forms a n ...

Zeta Ophiuchi Zeta Ophiuchi (ζ Oph, ζ Ophiuchi) is a single star located in the constellation of Ophiuchus. It has an apparent visual magnitude of 2.6, making it the third-brightest star in the constellation. Parallax measurements give an estimate ...

and

Gamma Ophiuchi Gamma Ophiuchi, Latinized from γ Ophiuchi, is a fourth-magnitude star in the constellation Ophiuchus. Together with Beta Ophiuchi, it forms the serpent-holder's right shoulder. The staris visible to the naked eye with an apparent visual ...

. According to a 1971 NASA catalogue, ''al-Nasaq al-Yamānī'' or ''Nasak Yamani'' was the name for two stars:

as ''Nasak Yamani I'' and

as ''Nasak Yamani II''. 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 v ...

, (), 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 Beta Herculis (β Herculis, abbreviated Beta Her, β Her), formally named Kornephoros , or Rutilicus, is a binary star and the brightest star in the northern constellation of Hercules at a base apparent visual magnit ...

Gamma Herculis Gamma Herculis, Latinized from γ Herculis, is a magnitude 3.74 binary star system in the northern constellation of Hercules. Properties This is known to be a spectroscopic binary system, although there is no information about the seco ...

Kappa Herculis Kappa Herculis (κ Herculis, abbreviated Kappa Her, κ Her) is an optical double star in the constellation of Hercules. The two components, Kappa Herculis A (Marsic , the traditional name of the system) and B, were 27.3 arc seconds apa ...

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 visi ...

Beta Serpentis Beta Serpentis, Latinized from β Serpentis, 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 upon an annual paral ...

and

. Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are often a ...

for Alpha Serpentis itself is (, en, the Seventh Star of Right Wall of Heavenly Market Enclosure), 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 Triple star systems Serpens (constellation) Serpentis, Alpha BD+06 3088 Serpentis, 24 140573 077070 5854 Unukalhai