16 Sagittarii is a multiple

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

system in the southern zodiac

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Sagittarius. It is near the lower limit of brightness for stars that can be seen with the naked eye, having an apparent visual magnitude of 6.02. The estimated distance to this system is about 4,600

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s. It is a member of the Sgr OB7 cluster. Along with the O-type star 15 Sgr, it is ionizing an H II region along the western edge of the molecular cloud L291. Mason et al. (1998) found this to be a member of a speckle binary with an estimated orbital period of roughly 130 years and a magnitude difference of 0.4. Both components show indications of a variable radial velocity, suggesting that they are spectroscopic binaries – making it a candidate quadruple star system. However, Tokovinin (2008) considers it a triple star system.

Orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...

for the main spectroscopic binary, components Aa and Ab, were published by Mayer et al. (2014), giving an orbital period of 12.76 days and an eccentricity of 0.18. This system displays a merged

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of O9.5 III, matching a blue-hued O-type giant star. It shows a longitudinal

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

strength of and a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of 51 km/s. Tokovinin (2008) gives an estimated mass of 50 times the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

for the primary, and 3.72 for the secondary. The tertiary member, component B, has 2.54 times the Sun's mass.

References

{{DEFAULTSORT:16 Sagittarii O-type giants Spectroscopic binaries Triple star systems Sagittarius (constellation) Durchmusterung objects Sagittarii, 16 167263 089440