DH Cephei is a variable

binary star A binary star or binary star system 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 as separate stars us ...

system in the northern

circumpolar constellation A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. Circumpolar stars are therefore visible from said location toward the nearest p ...

Cepheus Cepheus (Ancient Greek: Κηφεύς ''Kepheús'') may refer to: In Greek mythology * Cepheus (father of Andromeda), and King of Aethiopia * Cepheus (son of Aleus), a king of Tegea, Arcadia In astronomy * Cepheus (constellation), one of the 88 m ...

, positioned about two degrees to the east of the star system

Delta Cephei Delta Cephei (δ Cep, δ Cephei) is a quadruple star system located approximately 887 light-years away in the northern constellation of Cepheus (constellation), Cepheus, the King. At this distance, the visual magnitude of the star is di ...

. With an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 8.61, it is too faint to be visible without a telescope. Based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

measurements, this system is located at a distance of approximately from the Sun. At present it is moving closer to the Earth with a

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of −33 km/s. DHCepLightCurve

This is a double-lined

spectroscopic binary A binary star or binary star system 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 as separate stars us ...

system consisting of two near-identical, massive,

O-type main sequence star An O-type main-sequence star (O V) is a main-sequence (core hydrogen-burning) star of spectral type O and luminosity class V. These stars have between 15 and 90 times the mass of the Sun and surface temperatures between 30,000 and 50,000 K. Th ...

Evolutionary track In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

s place the stars close to the zero age main sequence, with an age of less than two million years. This is a detached binary with a close orbit having a period of 2.11 days, and the orbit is assumed to have circularized. The

orbital plane The orbital plane of a revolving body is the geometric plane in which its orbit lies. Three non-collinear points in space suffice to determine an orbital plane. A common example would be the positions of the centers of a massive body (host) a ...

is estimated to be inclined by an angle of to the line of sight from the Earth, which yields mass estimates of 38 and 34 times the

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

. In 1949,

Joseph Algernon Pearce Joseph Algernon Pearce (February 7, 1893 – September 8, 1988) was a Canadian astrophysicist, who was notable for studies on the structure of Milky Way and O-type stars. Born in Brantford, Ontario, Pearce enlisted in the Canadian Expedition ...

derived the

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 o ...

for DH Cephei (then known as HD 215835) and predicted that the binary pair would show eclipses, although he had no data to prove that. Graham Hill ''et al.'' confirmed the predicted

variability Variability is how spread out or closely clustered a set of data is. Variability may refer to: Biology *Genetic variability, a measure of the tendency of individual genotypes in a population to vary from one another *Heart rate variability, a phy ...

of star's brightness, in 1976. Although initially suspected to be an

eclipsing binary A binary star or binary star system is a Star system, system of two 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 ...

and given a

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

, it doesn't appear to be eclipsing. Instead, the system displays

ellipsoidal An ellipsoid is a surface that can be obtained from a sphere by deforming it by means of directional scalings, or more generally, of an affine transformation. An ellipsoid is a quadric surface; that is, a surface that may be defined as the ze ...

light variations that are caused by tidal distortions. This system lies at the center of the young

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

NGC 7380. It is the primary ionizing source for the surrounding

H II region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...

designated S142. The pair are a source of X-ray emission, which may be the result of colliding

stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...

s. Their measured X-ray luminosity is . The location and rare class of these stars make them an important object for astronomical studies.

References

{{DEFAULTSORT:DH Cephei O-type main-sequence stars Rotating ellipsoidal variables Spectroscopic binaries Cepheus (constellation) BD+57 2607 215835 112470 Cephei, DH