Gamma Pegasi is a

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

in the constellation of

Pegasus Pegasus ( grc-gre, Πήγασος, Pḗgasos; la, Pegasus, Pegasos) is one of the best known creatures in Greek mythology. He is a winged divine stallion usually depicted as pure white in color. He was sired by Poseidon, in his role as hor ...

, located at the southeast corner of the asterism known as the Great Square. It has the formal name Algenib ; 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. T ...

Gamma Pegasi is Latinized from γ Pegasi and abbreviated Gamma Peg or γ Peg. The average apparent visual magnitude of +2.84 makes this the fourth-brightest star in the constellation. The distance to this star has been measured using the

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 object ...

technique, yielding a value of roughly .

Nomenclature

''Gamma Pegasi'' is the star's

. Although it also had the traditional name ''Algenib'', this name was also used for Alpha Persei. In 2016, the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize List of proper names of stars, proper names for stars for the international astronomical community. It operates under ...

(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 ''Algenib'' for this star (Alpha Persei was given the name ''Mirfak''). The asterism of γ Pegasi and α Andromedae, in Hindu astronomy, is called Uttara Bhādrapadā (उत्तरभाद्रपदा) or Uttṛṭṭāti. It is the 26th

nakshatra Nakshatra ( sa, नक्षत्रम्, translit=Nakṣatram) is the term for lunar mansion in Hindu astrology and Indian Astronomy. A nakshatra is one of 27 (sometimes also 28) sectors along the ecliptic. Their names are related to ...

. In Chinese, (), meaning ''

Wall A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative. There are many kinds of walls, including: * Walls in buildings that form a fundamental part of the su ...

(asterism)'' refers to an asterism consisting of γ Pegasi and α Andromedae . Consequently, the

Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are oft ...

for γ Pegasi itself is (, en, the First Star of Wall.)

Properties

In 1911, American astronomer Keivin Burns discovered that the

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 rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

of Gamma Pegasi varied slightly. This was confirmed in 1953 by American astronomer

D. Harold McNamara D. Harold McNamara, Ph.D. (June 28, 1923 - January 9, 2014) was an American astronomer at Brigham Young University and an internationally recognized authority in intrinsic variable and eclipsing binary stars."1967 Faculty Lecturer Chosen", ''Da ...

, who identified it as a Beta Cephei variable. (At the time he actually identified it as a Beta Canis Majoris star, which was subsequently designated a Beta Cephei variable.) It has a radial pulsation period of 0.15175 days (3.642 hours), but also shows the behavior of a slowly pulsating B star (SPB) with three additional pulsational frequencies. Its magnitude varies between +2.78 and +2.89 over the course of each pulsation cycle. This is a large star with almost nine times the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass of ...

and close to five times the Sun's radius. The

stellar classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting t ...

of B2 IV suggests this is a subgiant star that is exhausting the hydrogen at its core and is in the process of evolving away from the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

. It is either rotating very slowly with no measurable

rotational velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...

or else it is being viewed from nearly pole-on. Gamma Pegasi has a total

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a s ...

of 5,840 times that of the Sun, which is being radiated from its outer atmosphere at an

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 more than 21,000 K. At this temperature, the star glows with a blue-white hue. The star has a weak

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

(from -10 G to 30 G, an upper bound on a dipolar magnetic field strength of about ).

References

External links

* {{DEFAULTSORT:Gamma Pegasi B-type subgiants Beta Cephei variables Pegasus (constellation) Pegasi, Gamma 0039 Durchmusterung objects Pegasi, 88 000886 001067 Algenib