Epsilon Equulei, Latinized from ε Equulei, is a

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

of apparent magnitude +5.23 in the constellation of

Equuleus Equuleus ( ) is a constellation of stars that are visible in the night sky. Its name is Latin for "little horse", a foal. Located just north of the celestial equator, it was one of the 48 constellations listed by the 2nd century astronomer Ptolem ...

. It is located 180 light years away from the Solar System, based on its

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 ...

Star system

Two stars make up the brighter part of the Epsilon Equulei star system. They are called Epsilon Equulei A and B and are

main-sequence star 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 Hert ...

s of spectral type of F5 and F6, respectively. The orbital period of this binary is about 101.5 years. Although the average separation between the two stars is about , the orbit is remarkably

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 ...

, at 0.705. The two stars passed their

periastron An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...

in 1920. Finally, it is thought that Epsilon Equulei A may be, in turn, a

spectroscopic binary A binary star is a system of two star, stars that are gravity, 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 separa ...

. The orbital period of the latter would be 2.03133 days. Approximately 10 arcseconds away from A and B is Epsilon Equulei C (HIP 103571), with an apparent magnitude of 7.35. It is another

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 ...

s, and based on its similar distance and

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

to A and B, it is assumed to be associated. The Epsilon Equulei system is thought to be approximately 1.5 billion years old.

References

{{DEFAULTSORT:Epsilon Equulei Equuleus Triple star systems Equulei, 01 Equulei, Epsilon F-type main-sequence stars Durchmusterung objects 103569 199766 8034