DH Cephei is a variable

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 circumpolar constellation of Cepheus, positioned about two degrees to the east of the star system

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

. With an apparent visual magnitude 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 lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

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, 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 −33 km/s. DHCepLightCurve

This is a double-lined

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 ...

system consisting of two near-identical, massive, O-type main sequence stars.

Evolutionary track 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 He ...

s place the stars close to the

zero age 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 He ...

, with an age of less than two million years. This is a

detached binary 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 ...

with a close orbit having a period of 2.11 days, and the orbit is assumed to have circularized. The orbital plane 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 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 ...

. Although initially suspected to be an eclipsing binary and given a

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

, it doesn't appear to be eclipsing. Instead, the system displays ellipsoidal light variations that are caused by tidal distortions. This system lies at the center of the young open cluster

NGC 7380 NGC 7380 is a young open cluster of stars in the northern circumpolar constellation of Cepheus, discovered by Caroline Herschel in 1787. The surrounding emission nebulosity is known colloquially as the Wizard Nebula, which spans an angle of . Ge ...

. It is the primary ionizing source for the surrounding H II region designated S142. The pair are 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), ...

, which may be the result of colliding

stellar wind A stellar wind is a flow of gas ejected from the 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 spherically symmetric. D ...

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