W Aquilae
{{Short description|Variable star in the constellation Aquila}}
{{Starbox begin
| name = W Aquilae
|caption=
}}
{{Starbox image
| image=280px
| caption=W Aquilae showing the close companion
| credit=Hubble Legacy Archive
}}
{{Starbox observe
| epoch=J2000
| appmag_v=A: 7.0 - 14.6
B:14.8
| constell=Aquila
}}
{{Starbox character
| component=A
| type = asymptotic giant branch
| class=S6/6e {{nowrap|(S3,9e - S6,9e)}}
| u-b=
| variable=Mira
}}
{{Starbox character|no_heading=y
| component=B
| type = main sequence
| b-v=
| u-b=
| variable=
}}
{{Starbox astrometry
| parallax=2.6735
| p_error=0.1392
| parallax_footnote={{cite Gaia DR3|4204925063304218880}}
| dist_pc=
| dist_ly=
| absmag_v=A: −0.7 to +6.9
B: +7.1
}}
{{Starbox detail
| component1=A
| radius={{solar radius calculator|type=AD|11|0.375}}{{Cite journal |last1=Wallstrom |first1=S. H. J. |last2=Danilovich |first2=T. |last3=Muller |first3=H. S. P. |last4=Gottlieb |first4=C. A. |last5=Maes |first5=S. |last6=Van de Sande |first6=M. |last7=Decin |first7=L. |last8=Richards |first8=A. M. S. |last9=Baudry |first9=A. |last10=Bolte |first10=J. |last11=Ceulemans |first11=T. |last12=De Ceuster |first12=F. |last13=de Koter |first13=A. |last14=Mellah |first14=I. El |last15=Esseldeurs |first15=M. |date=December 6, 2023 |title=ATOMIUM: Molecular inventory of 17 oxygen-rich evolved stars observed with ALMA |journal=Astronomy & Astrophysics |volume=681 |pages=A50 |doi=10.1051/0004-6361/202347632 |issn=0004-6361|arxiv=2312.03467 }}{{efn|1=Radius calculated with angular diameter and distance in Table 1|name=radius}}
| metal=
| rotation=
| gravity=
| component2=B
| age2=
}}
{{Starbox catalog
| names = W Aql, IRAS 19126-0708, TYC 5142-2895-1, 2MASS J19152335-0702503, AAVSO 1910-07, Gaia DR2 420492505899016640
}}
{{ Starbox reference
| Simbad = W+Aquilae
}}
{{Starbox end}}
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.
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 {{val|4e-6}} solar masses per year.{{Cite journal |arxiv = 1408.1825|doi = 10.1051/0004-6361/201322807|title = Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae|year = 2014|last1 = Danilovich|first1 = T.|last2 = Bergman|first2 = P.|last3 = Justtanont|first3 = K.|last4 = Lombaert|first4 = R.|last5 = Maercker|first5 = M.|last6 = Olofsson|first6 = H.|last7 = Ramstedt|first7 = S.|last8 = Royer|first8 = P.|s2cid = 55615864|journal = Astronomy & Astrophysics|volume = 569|pages = A76|bibcode = 2014A&A...569A..76D}} Its effective temperature is about 2,800 K and its radius is equivalent to {{significant figures|{{solar radius calculator|type=AD|11|0.375}}|2}} solar radii.{{efn|name=radius}} 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 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 (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.
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.
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.
Notes
{{Notelist}}
References
{{reflist|refs=
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{{Stars of Aquila}}
{{DEFAULTSORT:W Aquilae}}
Category:Aquila (constellation)
Category:IRAS catalogue objects