W Aquilae
W Aquilae is a variable star in the constellation of Aquila. It is a type of evolved star known as an S-type star. Due to its relatively close distance of 1,200 light-years and equatorial location, it is easy to observe and heavily studied.
Description
W Aquilae is an S-type star with a spectral type of S3,9e to S6,9e, a red giant similar to M-type stars, but in which the dominant spectrum oxides are formed by metals of the fifth period of the periodic table. W Aquilae is also rich in the element technetium. Another feature of this class of stars is the stellar mass loss, in the case of W Aquilae is estimated at solar masses per year. Its effective temperature is about 2,800 K and its radius is equivalent to solar radii. It is also a very luminous star, 7,500 times more than the sun.Variability
In 1893, Leo Anton Carl de Ball announced that the then unnamed star was a variable star, whose brightness varied by at least one magnitude. It was listed with its variable star designation, W Aquilae, in Annie Jump Cannon's 1907 Second Catalogue of Variable Stars.File:WAqlLightCurve.png|thumb|left|The visual band light curve of W Aquilae, from AAVSO data
W Aquilae is a variable whose brightness oscillates between magnitude +7.3 and +14.3 over a period of 490.43 days. In Mira variables, this instability comes from pulsation in the stellar surface, causing changes in color and brightness. W Aquilae, a Mira variable, shows silicon monoxide maser emission.