W Serpentis is an

eclipsing 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 ...

in the

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 ...

Serpens. It is always too faint to be seen with the naked eye, varying between apparent magnitudes 8.42 and 10.2 with a period of just over 14 days. This is mainly due to

eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...

s; however, variations in its period indicate there are some innate changes in

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

of one or both component stars as they interact with each other, and it has been difficult to disentangle the light to determine their nature. The period is increasing by 14 seconds a year, indicating that a massive amount of material is being transferred from the larger fainter star to the smaller brighter one. The system has been found to contain an

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other fo ...

, and was one of the first discovered W Serpentids, which are eclipsing binaries containing exceptionally strong

far-ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

spectral lines. These systems have a high rate of mass transfer between one star and the other, and are thought to evolve first into

double periodic variable A Double Periodic Variable (DPV) is a type of binary star. As the name implies, the systems vary in brightness not only due to eclipses of one star by the other, but also on a cycle of roughly 33 times longer than the orbit. The star gaining mass f ...

s and then classical Algol variables. In the late stages of mass transfer, such systems can develop an optically thick disc and are segregated as a separate class of W Serpentis stars. The classes may also represent different types of system altogether, with the W Serpentis type being younger and more massive. The spectral types of the component stars are not known; the hotter brighter component appears spectrally similar to an F-type giant. However, the central star appears to be completely obscured by material and may be a B-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 ...

star. The spectrum of the cooler fainter star has not been identified. Examining the polarised light shows that a jet of material is probably coming from the primary star as well. The properties of the two components are highly uncertain. Their orbital separation has been calculated to be or . The orbit is generally assumed to be circular, although the 9th catalogue of spectroscopic binary orbits gives an eccentric orbit from a very old source. The accretion disc has been calculated at across, The sizes of the two stars are disputed: different sources give masses of and or and for the hot and cool components respectively, and radii of and or and for the hot and cool components respectively.

References

Further reading