Sigma Aquilae, Latinized from σ Aquilae, is the

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. ...

for a

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

equatorial Equatorial may refer to something related to: *Earth's equator **the tropics, the Earth's equatorial region **tropical climate *the Celestial equator ** equatorial orbit **equatorial coordinate system ** equatorial mount, of telescopes * equatorial ...

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 ...

of Aquila. The baseline apparent magnitude of the pair is +5.17, which, according to the Bortle Dark-Sky Scale, is bright enough to be seen with the naked eye from suburban skies. Because of the Earth's orbit about the Sun, this system has an annual

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 ...

shift of . This provides a distance estimate of approximately . SigAqlLightCurve

Sigma Aquilae 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 massive B-type main sequence stars; each has a

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 ...

of B3 V. They are detached components, which means the two stars are sufficiently distant from each other that neither fills its Roche lobe. Because the orbital plane lies close to the line of sight with the Earth, they form an eclipsing binary system. The two components are each distorted by the gravity of the other star, and their shapes mean that the magnitude of the star system varies constantly even outside of the eclipses, an arrangement known as a Beta Lyrae variable. The brightness of the pair decreases during each

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 ...

, which occurs with a frequency determined by their orbital period of 1.95026 days. During the eclipse of the primary component the net magnitude decreases by 0.20 to 5.37; the eclipse of the secondary component results in a magnitude decrease of 0.10 to 5.27.

References

External links

Image ADS 12737

HR 7474

CCDM 19392+0524
{{DEFAULTSORT:Sigma Aquilae Aquila (constellation) Beta Lyrae variables 185507 Aquilae, Sigma B-type main-sequence stars Eclipsing binaries Spectroscopic binaries 096665 Aquilae, 44 7474 BD+05 4225