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Delta Arietis
	Location of δ Arietis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Aries
Right ascension	03h 11m 37.76465s
Declination	+19° 43′ 36.0397″
Apparent magnitude (V)	4.349
Characteristics
Spectral type	K2 III
U−B color index	+0.914
B−V color index	+1.035
R−I color index	0.51
Variable type	Suspected
Astrometry
Radial velocity (Rv)	23.05 ± 0.20 km/s
Proper motion (μ)	RA: +153.33 mas/yr ; Dec.: –8.28 mas/yr
Parallax (π)	19.22 ± 0.19 mas
Distance	170 ± 2 ly ; (52.0 ± 0.5 pc)
Absolute magnitude (MV)	+0.77
Details
Mass	1.91 M☉
Radius	10.42 ± 0.97 R☉
Luminosity	45 ± 6 L☉
Surface gravity (log g)	2.93 cgs
Temperature	4,810 K
Metallicity [Fe/H]	–0.03 dex
Rotational velocity (v sin i)	4.3 km/s
Other designations
	Botein, Botejn, 57 Arietis, BD+19° 477, FK5 114, HD 19787, HIP 14838, HR 951, SAO 93328.
Database references
SIMBAD	data

Delta Arietis (δ Arietis, abbreviated Delta Ari, δ Ari), officially named Botein /ˈboʊtiːn/,^[9] is a star in the northern constellation of Aries, 1.8 degrees north of the ecliptic. The apparent visual magnitude is 4.35,^[2] so it is visible to the naked eye. It has an annual parallax shift of 19.22 mas;^[1] corresponding to a distance of about 170 ly (52 pc) from the Sun.

Nomenclature

δ Arietis (Latinised to Delta Arietis) is the star's Bayer designation.

It bore the traditional name Botein which is derived from Al Bīrūnī's Al Buṭayn (Arabic: البُطَين), the diminutive of Al Baṭn, "the Belly". This is the name of a star association consisting of this star, Epsilon Arietis, Zeta Arietis, Pi Arietis, and Rho³ Arietis^[10] According to a 1971 NASA catalogue of stars, Al Buṭain was the title for five stars: Delta Arietis (listed as Botein), Pi Arietis (as Al Buṭain I), Rho3 Arietis (Al Buṭain II), Epsilon Arietis (Al Buṭain III) and Zeta Arietis (Al Buṭain IV).^[11] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)^[12] to catalogue and standardize proper names for stars. The WGSN approved the name Botein for this star on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.^[9]

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Nir al Botain, which was translated into Latin as Lucida Ventris, meaning "the brightest of the belly".^[13]

In Chinese, 天陰 (Tiān Yīn), meaning Yin Force, refers to an asterism consisting of Delta Arietis, 63 Arietis, Zeta Arietis, Tau Arietis and 65 Arietis.^[14] Consequently, the Chinese name for Delta Arietis itself is 天陰四 (Lóu Su sì, English: the Fourth Star of Yin Force.)^[15]

Properties

Delta Arietis is an evolved giant star with a stellar classification of K2 III.^[3] It belongs to a population known as red clump giants, which means it is generating energy through the fusion of helium at its core.^[16] With close to twice the mass of the Sun,^[3] the outer envelope has expanded until it is around ten^[6] times the Sun's radius. It shines with 45^[6] times the Sun's luminosity at an effective temperature of 4,810 K,^[6] giving it the orange-hued glow of a K-type star.^[17] It is a suspected variable star that ranges in magnitude from 4.33 to 4.37.^[4]