Epoch J2000 Equinox J2000
|Right ascension||22h 25m 16.62285s|
|Declination||+01° 22′ 38.6346″|
|Apparent magnitude (V)||+4.66|
|Spectral type||B1 Ve|
|U−B color index||–0.98|
|B−V color index||–0.03|
|Variable type||γ Cas|
|Radial velocity (Rv)||+4.0 km/s|
|Proper motion (μ)||RA: +17.83 mas/yr
Dec.: +2.41 mas/yr
|Parallax (π)||4.17 ± 0.28 mas|
|Distance||780 ± 50 ly
(240 ± 20 pc)
|Mass||10.7 ± 0.7 M☉|
|Rotational velocity (v sin i)||215 km/s|
|Age||10.0 ± 5.0 Myr|
Pi Aquarii (π Aqr, π Aquarii) is the Bayer designation for a binary star in the equatorial constellation of Aquarius. It shares the traditional name Seat with Delta Aquarii, where it has long been misspelled Skat. It may be from the Arabic word ši'at, meaning "a wish". This system has an apparent visual magnitude of a mean apparent magnitude of +4.57. Based upon parallax measurements, it is located at a distance of roughly 780 light-years (240 parsecs) from Earth.
This is a binary star system with an orbital period of 84.1 days. The primary component is a B-type main sequence star with a stellar classification of B1 Ve. This is a large star with nearly eleven times the mass and over six times the radius of the Sun. Pi Aquarii shines about 7,300 times as brightly as the Sun. This energy is being radiated from its outer atmosphere at an effective temperature of 27,094, giving it the blue-hued glow of a B-type star. It is spinning rapidly with a projected rotational velocity of 215 km/s.
Pi Aquarii is notable for having undergone a transition from a Be star (showing hydrogen emission lines) into an ordinary B-type star. It is classified as a Gamma Cassiopeiae type variable star and its brightness varies from magnitude +4.45 to +4.71; a range of 0.28. The dominant variability period, 83.8 ± 0.8 days, is nearly the same as the orbital period. Pi Aquarii has a reasonable chance of becoming a supernova some day.
In Chinese, 墳墓 (Fén Mù), meaning Tomb, refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii. Consequently, π Aquarii itself is known as 墳墓四 (Fén Mù sì, English: the Fourth Star of Tomb.)
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Wasat al Achbiya (وسط الأخبية - wasath al ahbiyah), which was translated into Latin as Media Tabernaculorum, meaning the middle of luck of the homes (tents). This star, along with γ Aqr (Sadachbia), ζ Aqr (Sadaltager / Achr al Achbiya) and η Aqr (Hydria), were al Aḣbiyah (الأخبية), the Tent.
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- γ Aqr as Aoul al Achbiya or Prima Tabernaculorum (the first of luck of the homes or tents), π Aqr as Wasat al Achbiya or Media Tabernaculorum (the middle of luck of the homes or tents) and ζ Aqr as Achr al Achbiya or Postrema Tabernaculorum (the end of luck of the homes or tents). η Aqr should be designated as al Achbiya consistently, but it was not designated as the Arabic name except the name Hydria (Greek) or Deli (Hebrew)