binary star
A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
system in the southern
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 first constellati ...
of Indus. It is visible to the naked eye with a combined apparent visual magnitude of +4.40. The brighter primary, designated component A, is magnitude 4.80 while the companion, component B, is magnitude 5.96. Based upon an annual parallax shift of 17.34 mas as measured from Earth, the system is located about 188
light year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...
s from the Sun.
The binary nature of this system was discovered by South African astronomer William Stephen Finsen from 1936 onward, with his published orbital elements appearing in 1956. The pair have an
orbital period
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...
of 12.2 years, a
semimajor axis
In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...
of 0.176
arc second
A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
s, and an
eccentricity
Eccentricity or eccentric may refer to:
* Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal"
Mathematics, science and technology Mathematics
* Off-Centre (geometry), center, in geometry
* Eccentricity (g ...
of around 0.03. They have been listed with a
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 gratin ...
of F0 IV by multiple authors, suggesting they are yellow-white hued F-typesubgiant stars. However, their estimated masses don't match this classification, so Docobo and Andrade (2013) suggest the Hipparcos parallax may have been underestimated. One paper has published separate spectral classes of A8(V) and F3(V) respectively for the two components.