W Aquilae
Variable star in the constellation Aquila
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W Aquilae (W Aql) 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 (370 pc) and equatorial location, it is easy to observe and heavily studied.[9]
B:14.8 [3]
W Aquilae showing the close companion Credit: Hubble Legacy Archive | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquila |
| Right ascension | 19h 15m 23.357s[1] |
| Declination | −07° 02′ 50.33″[1] |
| Apparent magnitude (V) | A: 7.0 - 14.6[2] B:14.8 [3] |
| Characteristics | |
| A | |
| Evolutionary stage | asymptotic giant branch[4] |
| Spectral type | S6/6e[4] (S3,9e - S6,9e[2]) |
| B−V color index | +2.58[5] |
| Variable type | Mira[2] |
| B | |
| Evolutionary stage | main sequence[4] |
| Spectral type | F8/9[4] |
| Astrometry | |
| Radial velocity (Rv) | −18.0[6] km/s |
| Proper motion (μ) | RA: 15.713[1] mas/yr Dec.: 0.103[1] mas/yr |
| Parallax (π) | 2.6735±0.1392 mas[1] |
| Distance | 1,220 ± 60 ly (370 ± 20 pc) |
| Absolute magnitude (MV) | A: −0.7 to +6.9[3] B: +7.1[3] |
| Details | |
| A | |
| Mass | 1.04 - 3[4] M☉ |
| Radius | 444[7][a] R☉ |
| Luminosity | 7,500[8] L☉ |
| Temperature | 2,800[7] K |
| B | |
| Mass | 1.04 - 1.09[4] M☉ |
| Temperature | 5,900 - 6,170[4] K |
| Other designations | |
| W Aql, IRAS 19126−0708, TYC 5142-2895-1, 2MASS J19152335−0702503, AAVSO 1910−07, Gaia DR2 420492505899016640 | |
| Database references | |
| SIMBAD | data |
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 4×10−6 solar masses per year.[10] Its effective temperature is about 2,800 K and its radius is equivalent to 440 solar radii.[7][a] It is also a very luminous star, 7,500 times more than the sun.[8]
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.[11] It was listed with its variable star designation, W Aquilae, in Annie Jump Cannon's 1907 Second Catalogue of Variable Stars.[12]
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 (which are named after Mira, the prototype), 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.[14]
Companion
A magnitude 14.8 companion has been detected 0.47" SW of W Aquilae. This is fainter than W Aquilae at minimum and corresponds 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.[3]
Planet X
A 2014 study of W Aquilae and α Centauri with the ALMA array claimed to have accidentally detected a previously-unknown Solar System object. This received widespread press coverage as a potential discovery of planet X. The paper was withdrawn without being accepted for peer-reviewed publication.[15]
Notes
- Radius calculated with angular diameter and distance in Table 1