Iota Cassiopeiae (ι Cas, ι Cassiopeiae) is a

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

in the

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 ...

Cassiopeia. The system has a combined

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of 4.53, making it visible to the naked eye. Based on its

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

, it is located about 133 light-years (41 parsecs) from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

Components

Iota Cassiopeiae is known to be a quintuple star system. The brightest star system, ι Cassiopeiae A, contains a white-colored

A-type main-sequence star An A-type main-sequence star (A V) or A dwarf star is a main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1 ...

with a mean

of +4.61. The primary is itself a tighter

binary star A binary star 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 using a telescope as separate stars, in wh ...

system. The two stars were resolved by

adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...

. These are designated Aa and Ab (although confusingly they may also be labeled as A and Aa, respectively). The primary is classified as an Alpha² Canum Venaticorum-type

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

and the brightness of the system varies from magnitude +4.45 to +4.53 with a period of 1.74 days, because of its

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 ...

. The fainter companion is a

G-type star A G-type main-sequence star (Spectral type: G-V), also often, and imprecisely called a yellow dwarf, or G star, is a main-sequence star (luminosity class V) of spectral type G. Such a star has about 0.9 to 1.1 solar masses and an effective tempe ...

with a mass of . The orbital period of the system is about 49 years. ι Cassiopeiae B is a yellow-white F-type main sequence dwarf with an apparent magnitude of +6.87. It orbits around ι Cassiopeiae A approximately every 2,400 years with a

semi-major 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 around 6.5

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

s, but the orbit is not very well constrained. This object may be causing Kozai–Lidov cycles in the inner orbital pair. ι Cassiopeiae C is itself another binary, designated Ca and Cb, or just C and c. It comprises two stars, a

K-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

and an

M-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

. It is currently at an angular distance of about 7

s from the AB pair. Since the semimajor axis of the AB orbit is about 6.5 arcseconds, the true semimajor axis of C's orbit around them is thought to be significantly larger than 7 arcseconds.

References

Alpha2 Canum Venaticorum variables Cassiopeiae, Iota Cassiopeia (constellation) 4 Spectroscopic binaries A-type main-sequence stars F-type main-sequence stars G-type main-sequence stars 0707 015089 011569 Durchmusterung objects Ap stars {{Multi-star-stub