Phecda

Phecda Template:IPAc-en, also called Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa),<ref name=Kunitzsch>Template:Cite book</ref><ref name="IAU-CSN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> is a star in the constellation of Ursa Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.<ref name=baas25_1319/> Based upon parallax measurements with the Hipparcos astrometry satellite,<ref name=aaa323_L49/><ref name=GSM/> it is located at a distance of around Template:Convert from the Sun.<ref name=aaa474_2_653/>

It is more familiar to most observers in the northern hemisphere as the lower-left star forming the bowl of the Big Dipper, together with Alpha Ursae Majoris (Dubhe, upper-right), Beta Ursae Majoris (Merak, lower-right) and Delta Ursae Majoris (Megrez, upper-left). Along with four other stars in this well-known asterism, Phecda forms a loose association of stars known as the Ursa Major moving group.<ref name=aj125_4_1980/> Like the other stars in the group, it is a main sequence star, as the Sun is, although somewhat hotter, brighter and larger.

Phecda is located in relatively close physical proximity to the prominent Mizar–Alcor star system. The two are separated by an estimated distance of Template:Cvt; much closer than the two are from the Sun. The star Merak is separated from Phecda by Template:Cvt.<ref name=apjss192_1_2/>

Nomenclature

γ Ursae Majoris (Latinised to Gamma Ursae Majoris) is the star's Bayer designation.

It bore the traditional names Phecda or Phad, derived from the Arabic phrase {{#invoke:Lang|lang}} fakhth al-dubb ('thigh of the bear').<ref name=garfinkle/> In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016<ref name="WGSN1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> included a table of the first two batches of names approved by the WGSN, which included Phecda for this star.

To the Hindus this star was known as Pulastya, one of the seven rishis.<ref name=allen1899/>

In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Gamma Ursae Majoris itself is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx) and {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx).<ref>Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 15 日 Template:Webarchive</ref>

Properties

Phecda is an Ae star, which is surrounded by an envelope of gas that is adding emission lines to the spectrum of the star;<ref name=aas130_507/> hence the 'e' suffix in the stellar classification of A0 Ve.<ref name=apjss192_1_2/> It is 2.4 times more massive than the Sun and is 333 million years old. It rotates rapidly with a rotational velocity of 386 km/s at its equator, which causes it to have an oblate shape. The equatorial radius measures Template:Solar radius, while the polar radius measures Template:Solar radius. The effective temperature varies as well, from 6,750 K in the equator to 10,520 K in the poles.<ref name=Jones/>

Phecda is also an astrometric binary: the companion star regularly perturbs the Ae-type primary star, causing the primary to wobble around the barycenter. From this, an orbital period of 20.5 years has been calculated.<ref name=Gontcharov/> The secondary star is a K-type main-sequence star that is 0.79 times as massive as the Sun, and with a surface temperature of Template:Val.<ref name=Eggl/>