4 Ursae Majoris

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Pi² Ursae Majoris
Diagram showing star positions and boundaries of the Ursa Major constellation and its surroundings
Cercle rouge 100%.svg

Location of π² Ursae Majoris (circled) near the center
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension 08h 40m 12.81767s[1]
Declination +64° 19′ 40.5700″[1]
Apparent magnitude (V) +4.620[2]
Spectral type K2 III[3]
U−B color index +1.193[2]
B−V color index +1.159[2]
Radial velocity (Rv) +14.62[4] km/s
Proper motion (μ) RA: –60.05[1] mas/yr
Dec.: +26.40[1] mas/yr
Parallax (π) 12.74 ± 0.26[1] mas
Distance 256 ± 5 ly
(78 ± 2 pc)
Absolute magnitude (MV) 0.150[3]
Mass 1.234 ± 0.15[5] M
Radius 18.11 ± 1.47[5] R
Surface gravity (log g) 1.8 ± 0.15[5] cgs
Temperature 4,415 ± 70[5] K
Metallicity [Fe/H] -0.25 ± 0.04[5] dex
Rotational velocity (v sin i) 8[6] km/s
Age 4.18 ± 1.95[3] Gyr
Other designations
π² Ursae Majoris, π² UMa, Pi² UMa, 4 Ursae Majoris, BD+64°698, FK5 2677, GC 11850, HD 73108, HIP 42527, HR 3403, PPM 16713, SAO 14616.
Database references

Pi² Ursae Majoris (Pi² UMa, π² Ursae Majoris, π² UMa), also known as 4 Ursae Majoris (sometimes abbreviated 4 Uma) or traditionally named Muscida, is the Bayer designation for a star in the northern circumpolar constellation of Ursa Major. With an apparent visual magnitude of +4.6,[2] this star is visible from suburban or darker skies based upon the Bortle Dark-Sky Scale. From parallax measurements made during the Hipparcos mission, this star is at a distance of 256 light-years (78 parsecs) from Earth.[1] As of 2011, one extrasolar planet has been confirmed to be orbiting the star.


This star has a stellar classification of K2 III,[3] indicating that, at an estimated age of around four billion years,[3] it is an evolved star that has reached the giant stage. It has a mass about 1.2 times larger than the Sun, but has expanded to 18 times the Sun's girth.[5] The effective temperature of the star's outer atmosphere is 4,415 K.[5] This heat gives it the cool, orange-hued glow of a K-type star.[7]

Pi² Ursae Majoris is a member of the Milky Way galaxy's thin disk population. It is following an orbit through the galaxy with an eccentricity of 0.10, which carries it as close to the Galactic Center as 27.7 kly (8.5 kpc) and as far as 34.1 kly (10.5 kpc). The inclination of this orbit lies close to the galactic plane, so it departs this plane by no more than 260 light-years (80 parsecs).[3]

Planetary system[edit]

Based upon observed radial velocity changes in the star, in 2007 the presence of a planetary companion was announced. The planet, designated 4 Ursae Majoris b, is at least seven times more massive than Jupiter. Its orbit is eccentric, orbiting 4 Ursae Majoris at 87% the distance from Sun to Earth. Compared to the Sun, this star has a lower abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity. This is curious, because most main sequence stars with planets tend to have a higher abundance of metals.[5]

The 4 Ursae Majoris planetary system[5]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b >7.1 ± 1.6 MJ 0.87 ± 0.04 269.3 ± 1.96 0.432 ± 0.024

See also[edit]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society 172: 667–679, Bibcode:1975MNRAS.172..667J 
  3. ^ a b c d e f Soubiran, C. et al. (2008), "Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants", Astronomy and Astrophysics 480 (1): 91–101, arXiv:0712.1370, Bibcode:2008A&A...480...91S, doi:10.1051/0004-6361:20078788 
  4. ^ Famaey, B. et al. (January 2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics 430: 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272 
  5. ^ a b c d e f g h i Döllinger, M. P. et al. (2007), "Discovery of a planet around the K giant star 4 Ursae Majoris", Astronomy and Astrophysics (abstract) 472 (2): 649–652, arXiv:astro-ph/0703672, Bibcode:2007A&A...472..649D, doi:10.1051/0004-6361:20066987 
  6. ^ Bernacca, P. L.; Perinotto, M. (1970), "A catalogue of stellar rotational velocities", Contributi Osservatorio Astronomico di Padova in Asiago 239 (1): 1, Bibcode:1970CoAsi.239....1B 
  7. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 

External links[edit]

Coordinates: Sky map 08h 40m 12.8s, +64° 19′ 40″