13 Ceti
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13 Ceti is a triple star system in the equatorial
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
Cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus (mythology), Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the sky that contains other water- ...
. It is dimly visible to the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...
with a combined apparent visual magnitude of 5.20. The system is located at a distance of approximately 69 
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 Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
based on
stellar parallax Stellar parallax is the apparent shift of position (''parallax'') of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the stel ...
, and is drifting further away with a
radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...
of +10.4 km/s. It shares a common motion with the Hyades moving group, although it is too old to be a member. This star was identified as a visual binary system by G. W. Hough in 1844 and given the identifier HO 212. 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 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 0.77. The brighter member, designated component A, is an F-type main-sequence star 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 F6 V and a visual magnitude of 5.61. It appears to have an active chromosphere and is classified as an
RS Canum Venaticorum variable An RS Canum Venaticorum variable is a type of variable star. The variable type consists of close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity. ...
with a
variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...
of BU Cet. The star was detected as a source of soft X-ray emission by EXOSAT. It has 18% more mass than the Sun and is estimated to be about four billion years old. In 1907, E. B. Frost discovered the primary is a
spectroscopic binary 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 ...
, making this a triple star system. This is a double-lined spectroscopic binary with a period of 2.1 days and a circularized orbit. The companion signature was confirmed using the separated fringe packet technique with the CHARA array. It is most likely a
K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ...
with a class of K3.5 V and 70% of the mass of the Sun. The secondary member of the visual binary, designated component B, is a
G-type main-sequence 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, main-sequence star (luminosity class V) of stellar classification, spectral type G. Such a star has about 0.9 to ...
with a class of G4 V. It has 90% of the Sun's mass and a visual magnitude of 6.90. A distant visual companion to this system was detected by S. W. Burnham in 1877. Designated component C, this star is a background object of magnitude 12.50. As of 1999, it was located at an angular separation of from the primary along a
position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...
of 322°.


References

{{DEFAULTSORT:13 Ceti F-type main-sequence stars G-type main-sequence stars K-type main-sequence stars RS Canum Venaticorum variables Triple stars Spectroscopic binaries Cetus BD-04 0062 Ceti, 13 0023 003196 002762 0142 Ceti, BE