Phecda

Phecda

Template:Location mark Location of Phecda (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Ursa Major
Right ascension	Template:RA
Declination	Template:DEC
Apparent magnitude (V)	2.438
Characteristics
Spectral type	A0 Ve + K2 V
U−B Template:Engvar	+0.008
B−V Template:Engvar	–0.013
Astrometry
Radial velocity (Rv)	−12.6 km/s
Proper motion (μ)	RA: +107.68 mas/yr Dec.: +11.01 mas/yr
Parallax (π)	39.21±0.40 mas
Distance	Template:Rnd ± Template:Rnd ly (Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)	0.4
Orbit
Period (P)	20.5 ± 1 yr
Semi-major axis (a)	0.460″
Eccentricity (e)	0.3 ± 0.3
Inclination (i)	51 ± 15°
Longitude of the node (Ω)	6 ± 61°
Periastron epoch (T)	B 1984.0 ± 2.0
Argument of periastron (ω) (secondary)	185 ± 37°
Details
γ UMa A
Mass	Template:Val Template:Solar mass
Radius	3.385 (equatorial) 2.186 (polar) Template:Solar radius
Luminosity	Template:Val Template:Solar luminosity
Surface gravity (log g)	3.79 cgs
Temperature	6,751 (equatorial) 10,520 (polar) K
Rotational velocity (v sin i)	Template:Val km/s
Age	Template:Val Myr
γ UMa B
Mass	0.79 Template:Solar mass
Luminosity	0.397 Template:Solar luminosity
Temperature	4,780 K
Metallicity [Fe/H]	{{{metal_fe2}}} dex
Other designations
Phad, Phecda, Phekda, Phegda, Phekha, Phacd, Fekda, γ Ursae Majoris, γ UMa, Gamma UMa, 64 Ursae Majoris, BD+54 1475, FK5 447, GC 16268, HD 103287, HIP 58001, HR 4554, PPM 33292, SAO 28179.
Database references
SIMBAD	data

Phecda Template:IPAc-en, also called Gamma Ursae Majoris (γ Ursae Majoris, abbreviated Gamma UMa, γ UMa), 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. Based upon parallax measurements with the Hipparcos astrometry satellite, it is located at a distance of around Template:Convert from the Sun.

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. 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.

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 fakhth al-dubb ('thigh of the bear'). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 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.

In Chinese, (), meaning Northern Dipper, refers to an asterism equivalent to the Big Dipper. Consequently, the Chinese name for Gamma Ursae Majoris itself is (, Template:Langx) and (, Template:Langx).

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; hence the 'e' suffix in the stellar classification of A0 Ve. 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.

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. 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.