Alpha Cephei

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Alpha Cephei (α Cephei, abbreviated Alpha Cep, α Cep), officially named Alderamin Template:IPAc-en,<ref name=Kunitzsch/><ref name="IAU-CSN"/> is a second magnitude star in the constellation of Cepheus near the northern pole. The star is relatively close to Earth at 49 light years (ly) and drifting closer with a heliocentric radial velocity of about −16 km/s.

NomenclatureEdit

α Cephei (Latinised to Alpha Cephei) is the star's Bayer designation. It has a Flamsteed designation of 5 Cephei.

It bore the traditional name Alderamin, a contraction of the Arabic phrase الذراع اليمين al-dhirā‘ al-yamīn, meaning "the right arm". 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 Alderamin for this star.

VisibilityEdit

With a declination in excess of 62 degrees north, Alpha Cephei never rises south of −27° latitude, which means for much of South America, Australia, South Africa, and all of New Zealand, the star stays below the horizon. The star is circumpolar throughout all of Europe, northern Asia, Canada, and American cities as far south as San Diego. Since Alpha Cephei has an apparent magnitude of about 2.5, the star is the brightest in the constellation and is easily observable to the naked eye, even in light-polluted cities.

Pole starEdit

Alpha Cephei is located near the precessional path traced across the celestial sphere by the Earth's North pole. That means that it periodically comes within 3° of being a pole star,<ref name="KALER"/> a title currently held by Polaris. Alpha Cephei will next be the North Star in about the year 7500 AD.<ref name=Monthly1871/> The north pole of Mars points to the midpoint of the line connecting the star and Deneb.<ref name="Barlow"/>

Preceded by	Pole Star	Succeeded by
Iota Cephei	circa 19,000BC and 7500AD to 8700AD	Deneb

PropertiesEdit

File:AlphaCepLightCurve.png

A light curve for Alpha Cephei, plotted from TESS data<ref name=MAST/>

Alderamin is a white class A star, evolving off the main sequence into a subgiant, probably on its way to becoming a red giant as its hydrogen supply runs low. On average, Alderamin has an apparent magnitude of 2.46.<ref name=AAVSO/> In 2007, the star's parallax was measured at Template:Val yielding a distance of 15 parsecs or approximately 49 light years from Earth.<ref name="LEEUWEN"/>

Interferometry by the CHARA array show that Alderamin has an oblate shape, its equatorial size measures Template:Solar radius and the polar radius measures Template:Solar radius. The star's temperature varies as well, from 8,440 K in the poles to 7,600 K in the equator.<ref name=vanBelle2006/> A more recent but less detailed measurement by the Navy Precision Optical Interferometer gives Template:Solar radius, which likely corresponds to the equatorial radius.<ref name=npoi/> Like other stars in its class, it is slightly variable with a range in brightness of 0.06 magnitude, and is listed as a Delta Scuti variable.

Alderamin has a very high rotation speed of at least 246 km/s, completing one complete revolution in less than 12 hours, with such a rapid turnover appearing to inhibit the differentiation of chemical elements usually seen in such stars.<ref name="HR1"/> By comparison, the Sun takes almost a month to turn on its axis. Alpha Cephei is also known to emit an amount of X radiation similar to the Sun, which along with other indicators suggests the existence of considerable magnetic activity—something unexpected (though not at all unusual) for a fast rotator.

Etymology and cultural significanceEdit

This star, along with Beta Cephei (Alfirk) and Eta Cephei (Alkidr) were al-Kawākib al-Firq (الكواكب الفرق), meaning "the Stars of the Flock" by Ulug Beg.<ref name=allen1963/><ref name=PopAst/>

In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Celestial Hook, refers to an asterism consisting of α Cephei, 4 Cephei, HD 194298, Eta Cephei, Theta Cephei, Xi Cephei, 26 Cephei, Iota Cephei and Omicron Cephei.<ref name=zh/> Consequently, the Chinese name for Alpha Cephei itself is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}, Template:Langx.).<ref name=lcsd/>