Pi Aquarii
Pi Aquarii is a binary star system in the equatorial constellation of Aquarius. Its name is a Bayer designation that is Latinized from π Aquarii, and abbreviated Pi Aqr or π Aqr. This system has a combined apparent visual magnitude of +4.57, which is bright enough to be faintly visible to the naked eye. Based upon parallax measurements, it is located at a distance of approximately from the Sun. It is drifting further away with a radial velocity of.
Properties
This is a binary star system with a period of 84.1 days in a circular orbit. The primary component is a B1 giant or subgiant star. This is a massive star with 11 times the mass of the Sun, and is luminous with 8,300 times the Sun's luminosity. It is spinning rapidly with a projected rotational velocity of. The fast rotation make the star ellipsoidal rather than spherical, its radius at equator is 5.8 times that of the Sun, while its polar radius is 5.0 times solar. Gravity darkening make the temperature at the equator to be about colder than the temperature at the poles.The secondary is likely a white dwarf star with a strong magnetic field and a mass of. It is an X-ray source which is probably coming from accretion onto this object, making this an intermediate polar system. The accretion rate is ·yr−1.
Pi Aquarii is notable for having undergone a transition from a Be star 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, days, is nearly the same as the orbital period. Pi Aquarii has a reasonable chance of becoming a supernova some day.
Infrared images from WISE at a wavelength of 22 µm reveal a bow shock located approximately 100″ from the star in the direction of its proper motion. In optical range, a weakly ionized emission nebula with a diameter of about 5° is visible. There also appears to be some interaction with the surrounding interstellar medium. Notably, the rectangular shape of the nebula is not aligned with the current orientation of the circumstellar disk.
In culture
Pi Aquarii was called Seat by Grotius in the 17th century, but the name has rarely been used since.In Chinese, 墳墓, meaning Tomb, refers to an asterism consisting of π Aquarii, γ Aquarii, ζ Aquarii, η Aquarii. Consequently, the Chinese name for π Aquarii itself is 墳墓四
In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Wasat al Achbiya, which was translated into Latin as Media Tabernaculorum, meaning the middle of luck of the homes . This star, along with γ Aqr, ζ Aqr and η Aqr, were al Aḣbiyah, the Tent.