Gamma Delphini, which is Latinized from γ Delphini, is a wide

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

system in the northern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Delphinus Delphinus (Pronounced or ) is a small constellation in the Northern Celestial Hemisphere, close to the celestial equator. Its name is the Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-Europea ...

. The star marks one corner of the asterism " Job's Coffin". The pair can be split with a modest

amateur telescope ''Amateur Telescope Making'' (''ATM'') is a series of three books edited by Albert G. Ingalls between 1926 and 1953 while he was an associate editor at ''Scientific American''. The books cover various aspects of telescope construction and observ ...

and have been described as "one of the prettier pairs in the sky", with their contrasting colors said to be orange and lime in appearance. Together, the system is visible to the naked eye with a combined

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

of 3.87.

Space motion

The system is located at a distance of 115

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

based on

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 ...

, but is drifting closer with a

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 ...

of −7 km/s. It is a member of the

thin disk The thin disk is a structural component of spiral and S0-type galaxies, composed of stars, gas and dust. It is the main non-centre (e.g. galactic bulge) density, of such matter. That of the Milky Way is thought to have a scale height of around i ...

population, and is a proposed member of the

Wolf 630 moving group V1054 Ophiuchi, together with the star Gliese 643, is a nearby quintuple star system, in the constellation Ophiuchus at a distance of 21.19 light-years. It consists of five stars, all of which are red dwarfs. The alternative designat ...

. This star was found to be a

double A double is a look-alike or doppelgänger; one person or being that resembles another. Double, The Double or Dubble may also refer to: Film and television * Double (filmmaking), someone who substitutes for the credited actor of a character * Th ...

by Christian Mayer and later observed by William Herschel on Sept 27th, 1779. It was later included as STF 2727 in the catalogue compiled by F. G. W. Struve and can be found under this name in the Washington Double Star Catalog. At the time, the components had an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of along a

position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the north celestial pole (NCP), turning positive into the d ...

(PA) of 280°. As of 2019, they are separated by with a PA of 265°. The fainter component, designated γ¹ Delphini, is of

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

5.03. Its companion is a magnitude 4.360 star designated γ² Delphini. A fit of

orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...

to the available positional data provides a

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

of 3,249 years with a high

eccentricity 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 ...

(ovalness) of 0.88. Their physical separation ranges from roughly 40 out to .

Physical properties

The

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 γ¹ Delphini is F7V, which matches an

F-type main-sequence star An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K.Tables VII ...

with a yellow-white hue. It is about 1.8 billion years old and is spinning with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of 7.8 km/s. The star has 1.6 times the mass and 2.6 times the radius of the Sun. It is radiating 10 times the Sun's luminosity from its

photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

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 6,295 K. The brighter component, γ² Delphini, has an orange hue with a class of K1IV. Being the more massive star of the pair, it is the more

evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...

star and is currently on the

subgiant branch A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of ...

. It has double the mass of the Sun but has expanded to over eight times the Sun's radius. The star is radiating 33 times the luminosity of the Sun at 4,798 K. It is spinning with a

of 3.6 km/s. The star displays a radial acceleration with a periodicity of 1.44 years, which may be the effect of an orbiting companion. The system is a source of

X-ray emission Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays. Several types of astrophysical objects emit X-rays. They include galaxy clusters, black holes in active galactic nuclei (AGN), ...

with high probability.

Possible planetary system

In 1999, the presence of a planetary companion was inferred around Gamma² Delphini as one possible explanation for the radial velocity variations. Such a planet would have a minimum mass of 0.7

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

masses, orbital period of 1.44 years and separation of nearly 1.5

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s (almost the orbital separation of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

from the

). The planetary candidate has not been confirmed. McDonald Observatory researches have set mass limits for potential planetary companions in orbit around the star Gamma² Delphini.

References

External links

* {{DEFAULTSORT:Gamma Delphini F-type main-sequence stars K-type subgiants Hypothetical planetary systems Binary stars Delphinus (constellation) Delphini, Gamma BD+15 4255 Delphini, 12 197963 4 102531/2 7947/8