VW Cephei (VW Cep) is an eclipsing

contact binary In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontac ...

W Ursae Majoris W Ursae Majoris (W UMa) is the variable star designation for a binary star system in the northern constellation of Ursa Major. It has an apparent visual magnitude of about 7.9, which is too faint to be seen with the naked eye. However, i ...

-type located roughly at 90.6 light years from the Sun, whose two component stars share a common outer layer. Because the two components share their outer layers, as the components of

do, they have the same

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 ...

, and are classified as yellow G-type

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 ...

dwarfs. The components take 0.2783 days (roughly 6.7 hours) to revolve around a common

barycentre In astronomy, the barycenter (or barycentre; ) is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit. A barycenter is a dynamical point, not a physical object. It is an important co ...

. Orbital period variations suggest the presence of one more additional perturbing objects of likely low-mass

stellar Stellar means anything related to one or more stars (''stella''). The term may also refer to: Arts, entertainment, and media * ''Stellar'' (magazine), an Irish lifestyle and fashion magazine * Stellar Loussier, a character from ''Mobile Suit Gun ...

nature.

Unseen companion(s)

Orbital period variations suggest the presence of one more perturbing unseen object around the eclipsing binary. Several publications have tried to set constrains to putative orbital period and minimum mass for unseen component. The most recent article proposes an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of 29.8 years for a stellar object with roughly three fourths the Sun's mass and high

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...

(e=0.66). Inclination is assumed being 33.6

degree Degree may refer to: As a unit of measurement * Degree (angle), a unit of angle measurement ** Degree of geographical latitude ** Degree of geographical longitude * Degree symbol (°), a notation used in science, engineering, and mathematics ...

s. Nevertheless, hints of an additional body in the system still subsist and the authors infer a period of 77.46 years and eccentricity of 0.54 for unseen fourth component. Minimum mass is unclear, tentatively assumed being as small as 0.19 solar masses, as inferred by Pribulla et al. in 2000. In any case orbital solutions are still blurry and further calculations are needed to provide a more robust model. With the release of

Gaia DR2 The ''Gaia'' catalogues are star catalogues created using the results obtained by ''Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, especia ...

, the presence of any stellar companions was ruled out.The recorded excess noise for the stars is 0.398 ± 0.008 mas, which corresponds to an angular size of 0.0106 ± 0.0002 AU at the stars' distance. This rules out any bodies capable of perturbing the stars by more than 0.0106 AU from their current velocities over the 2-year observation period. The stars, for comparison, orbit each other 0.0083 AU apart.

Notes

References

Cepheus (constellation) Cephei, VW W Ursae Majoris variables 197433 G-type main-sequence stars 101750 Durchmusterung objects 9703 {{Multi-star-stub