W Aquilae
A heavily studied Mira variable star in Aquila.
W Aquilae is a variable star located in the constellation Aquila, about 1,200 light-years from Earth. It is an evolved S-type star, a type of red giant similar to M-type stars, but its spectrum is dominated by oxides of metals from the fifth period of the periodic table. The star is notably rich in technetium. Its effective temperature is roughly 2,800 K, and its radius is many times that of the Sun. It is highly luminous, shining with about 7,500 times the Sun’s brightness. The star also loses mass at a rate estimated in solar masses per year.
First identified as a variable in 1893 by Leo Anton Carl de Ball, its brightness was found to vary by at least one magnitude. It received the designation W Aquilae in Annie Jump Cannon’s 1907 Second Catalogue of Variable Stars. As a Mira variable, its brightness fluctuates between magnitudes +7.3 and +14.3 over a period of 490.43 days. This instability is caused by pulsations in the star’s surface, which also produce changes in color and brightness. W Aquilae exhibits silicon monoxide maser emission.
A faint companion star, with a magnitude of 14.8, lies 0.47 arcseconds southwest of W Aquilae. This companion is fainter than W Aquilae at its minimum brightness, corresponding to an absolute magnitude of +7.1. While that absolute magnitude would suggest a K4 main-sequence star, its spectrum has been classified as F5 or F8. The two stars are separated by about 160 astronomical units.
In 2014, a study using the ALMA array claimed to have accidentally detected a previously unknown object in the Solar System while observing W Aquilae and Alpha Centauri. This received widespread media attention as a possible discovery of Planet X, but the paper was withdrawn before peer-reviewed publication.
- Distance
- 1,200 light-years (370 pc)
- Spectral type
- S3,9e to S6,9e
- Effective temperature
- 2,800 K
- Luminosity
- 7,500 times the Sun
- Brightness range
- magnitude +7.3 to +14.3
- Period
- 490.43 days
- Companion magnitude
- 14.8
Lore & Background
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. W Aquilae is a Mira variable, whose brightness oscillates between magnitude +7.3 and +14.3 over a period of 490.43 days. This instability comes from pulsation in the stellar surface, causing changes in color and brightness. The star shows silicon monoxide maser emission. W Aquilae is rich in the element technetium and has an estimated mass loss rate. Its effective temperature is about 2,800 K and its radius is equivalent to solar radii. A magnitude 14.8 companion has been detected 0.47" SW of W Aquilae, corresponding to an absolute magnitude of +7.1. Although that absolute magnitude would correspond to a K4 main sequence star, a spectrum was classified as F5 or F8. The separation between the two stars is 160 AU.
Reader's Guide
W Aquilae is notable as a well-studied Mira variable and S-type star, providing insights into evolved stellar atmospheres and mass loss. Its relatively close distance and equatorial location make it a frequent target for observation. The star's variability, discovered in the late 19th century and cataloged by Annie Jump Cannon, has been monitored extensively, contributing to the understanding of long-period pulsating variables. The detection of silicon monoxide maser emission highlights its complex circumstellar chemistry. The presence of a companion star, though fainter and with a spectral classification that does not match its absolute magnitude, adds to the system's interest. A 2014 study using the ALMA array claimed accidental detection of a previously-unknown Solar System object while observing W Aquilae, receiving widespread press coverage as a potential discovery of Planet X, but the paper was withdrawn without peer-reviewed publication. This episode underscores the star's role in serendipitous astronomical discoveries.
Did You Know?
- W Aquilae is an S-type star, rich in the element technetium.
- Its brightness varies between magnitude +7.3 and +14.3 over 490.43 days.
- A companion star of magnitude 14.8 lies 0.47" SW, with a spectral classification of F5 or F8.
- A 2014 ALMA study of W Aquilae claimed accidental detection of a potential Planet X, but the paper was withdrawn.
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