Beta Tauri

Beta Tauri is the second-brightest star in the constellation of Taurus. It has the official name Elnath; Beta Tauri is the current Bayer designation, which is Latinised from β Tauri and abbreviated Beta Tau or β Tau. The original designation of Gamma Aurigae is now rarely used. It is a chemically peculiar B7 giant star, 134 light years away from the Sun with an apparent magnitude of 1.65.

Nomenclature

This star has two Bayer designations: β Tauri (Latinised to Beta Tauri) and γ Aurigae (Latinised to Gamma Aurigae). Ptolemy considered the star to be shared by Auriga, and Johann Bayer assigned it a designation in both constellations. When the modern constellation boundaries were fixed in 1930, the designation γ Aurigae largely dropped from use.<ref name=ridpath/>

The traditional name Elnath, variously El Nath or Alnath, comes from the Arabic word النطح an-naţħ, meaning "the butting" (i.e. the bull's horns). As in many other Arabic star names, the article ال is transliterated literally as el, yet overwhelmingly in Arabic pronunciation it is assimilated to the n, meaning it is omitted. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN"/> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1"/> included a table of the first two batches of names approved by the WGSN; which included Elnath for this star.<ref name="IAU-CSN"/>

In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Five Chariots, refers to an asterism consisting of β Tauri, ι Aurigae, Capella, β Aurigae and θ Aurigae.<ref>Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.</ref> Consequently, the Chinese name for β Tauri itself is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}; Template:Langx.)<ref>Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>

Physical properties

The absolute magnitude of Beta Tauri is −1.34, similar to another star in Taurus, Maia in the Pleiades star cluster. Like Maia, β Tauri is a B-class giant with a luminosity 700 times solar (Template:Solar luminosity).<ref name="kaler" /> It has evolved to become a giant star, larger and cooler than when it was on the main sequence.<ref name=knyazeva/> However, being approximately 130 light-years distant compared to Maia's estimated 360 light-years, β Tauri ranks as the second-brightest star in the constellation.

It is a mercury-manganese star, a type of non-magnetic chemically peculiar star with unusually large signatures of some heavy elements in its spectrum.<ref name=hgmn/> Relative to the Sun, β Tauri is notable for a high abundance of manganese, but little calcium and magnesium.<ref name="kaler" /><ref name="aj41" /> However, the lack of strong mercury signatures, together with notably high levels of silicon and chromium, have led some authors to give other classifications, including as a "SrCrEu star" or even an Ap star.<ref name=chen/><ref name=bychkov/> Its limb-darkened angular diameter has been measured at Template:Val. At a distance of Template:Val, this corresponds to a linear radius of Template:Val.<ref name=Baines2025/>

At the southern edge of the narrow plane of the Milky Way Galaxy a few degrees west of the galactic anticenter, β Tauri figures (appears) as a foreground object south of many nebulae and star clusters such as M36, M37, and M38.<ref name="ApopPik"/> It is 5.39 degrees north of the ecliptic, still few enough to be occultable by the Moon. Such occultations occur when the Moon's ascending node is near the March equinox, as in 2007. Most are visible only in the Southern Hemisphere, because the star is at the northern edge of the lunar occultation zone – but rarely as far north as southern California.<ref name=abrams/>

Companions

A faint star is, angularly from our viewpoint, close enough for astronomers to consider, and guides to mention, the pair as a double star. This visual companion, BD+28°795B, has a position angle of 239 degrees and is separated from the main star by 33.4 arcseconds (″).<ref name=VizieR/><ref name="Alcyone"/> Six angularly closer, even fainter stars have been found in a search for brown dwarf and planetary companionsTemplate:Sndall considered background objects.<ref name=janson/>

A very close companion was reported from lunar occultation measurements at a distance of Template:Val, but not confirmed by other observers. Radial velocity measurements indicate that Beta Tauri is a single-lined spectroscopic binary, but there is no published information about the companion or orbit.<ref name=adelman2006/><ref name=gordon2019/>