Sigma Aquarii
Sigma Aquarii is the Bayer designation for a double star in the equatorial constellation of Aquarius. It is visible to the naked eye with an apparent visual magnitude of 4.81. Based upon parallax measurements, the distance to this star is roughly .
Sigma Aquarii has a stellar classification of A0 IVs, indicating that it is a subgiant star. The s qualifier indicates that its absorption lines are sharp in comparison with standard stars, caused by relatively slow rotation. It has been categorized as a hot Am star, meaning that it is a chemically peculiar, although this is now considered doubtful. The spectrum displays at least double the normal abundances of elements like magnesium, aluminum and silicon, while helium and scandium are under-abundant. Calcium, normally deficient in Am stars, has near-normal abundance.
The Hipparcos catalogue identified Sigma Aquarii as a possible astrometric binary with an orbital period of 654 days.
