4 Ursae Majoris (sometimes abbreviated 4 Uma) is the Flamsteed designation of a

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in the

northern Northern may refer to the following: Geography * North, a point in direction * Northern Europe, the northern part or region of Europe * Northern Highland, a region of Wisconsin, United States * Northern Province, Sri Lanka * Northern Range, a ra ...

circumpolar constellation of Ursa Major. It also bears the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

of Pi² Ursae Majoris (Pi² UMa, π² Ursae Majoris, π² UMa) and is traditionally named Muscida. With an apparent visual magnitude of +4.6, this star is visible from suburban or darker skies based upon the Bortle Dark-Sky Scale. From

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements made during the ''

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

'' mission, this star is at a distance of from Earth. , one extrasolar planet has been confirmed to be orbiting the star.

Properties

This star has a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of K2 III, indicating that, at an estimated age of around four billion years, it is an

evolved star Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

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. The

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of the star's outer atmosphere is . This heat gives it the cool, orange-hued glow of a K-type star. Pi² Ursae Majoris is a member of the Milky Way galaxy's

thin disk population This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

. It is following an orbit through the galaxy with an eccentricity of 0.10, which carries it as close to the Galactic Center as and as far as . The inclination of this orbit lies close to the galactic plane, so it departs this plane by no more than .

Planetary system

Based upon observed

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

changes in the star, in 2007 the presence of a planetary companion was announced. The planet, designated

4 Ursae Majoris b 4 Ursae Majoris (sometimes abbreviated 4 Uma) is the Flamsteed designation of a star in the northern circumpolar constellation of Ursa Major. It also bears the Bayer designation of Pi2 Ursae Majoris (Pi2 UMa, π2 Ursae Majoris, ...

, is at least seven times more massive than Jupiter. Its orbit is

eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...

, 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 In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

. This is curious, because most main-sequence stars with planets tend to have a higher abundance of metals.

Naming and etymology

With π¹, σ¹, σ², ρ, A and d, it composed the Arabic asterism Al Ṭhibā᾽, the Gazelle. According to the catalogue of stars in the ''Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars'', ''Al Ṭhibā'' were the title for seven stars: A as ''Althiba I'', π¹ as ''Althiba II'', this star (π²) as ''Althiba III'', ρ as ''Althiba IV'', σ¹ as ''Althiba V'', σ² as ''Althiba VI'', and d as ''Althiba VII''.

References

External links

* {{DEFAULTSORT:Pi2 Ursae Majoris Ursae Majoris, Pi2 Ursae Majoris, 04 073108 042527 3403 Ursa Major (constellation) K-type giants Althiba III Durchmusterung objects

Properties

Planetary system

Naming and etymology

See also

References

External links