Theta Capricorni, Latinized from θ Capricorni, is a
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 ...
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
Capricornus
Capricornus is one of the constellations of the zodiac. Its name is Latin for "horned goat" or "goat Horn (anatomy), horn" or "having horns like a goat's", and it is commonly represented in the form of a sea goat: a mythical creature that is hal ...
, positioned 0.58° south of the
ecliptic
The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making.
Fr ...
. Sometimes, this star is called by the name Dorsum, meaning ''the back (of the goat)'' in
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
. It can be seen with the naked eye, having an
apparent visual magnitude
Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...
of +4.07. Based upon an annual
parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
shift of 20.11 mas as seen from the Earth, the star is about 162
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 ...
. It is drifting closer 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 −11 km/s.
Characteristics
Radial velocity variations indicated it may be a
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, but when the system was examined in the
infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
, no companion was detected. However, a companion was subsequently confirmed in 2023 by direct observations by an
interferometer
Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...
.
The main component of this system is an
A-type main sequence star
An A-type main-sequence star (A) or A dwarf star is a main-sequence (hydrogen burning) star of spectral type A and luminosity class (five). These stars have spectra defined by strong hydrogen Balmer absorption lines. They measure between 1.7 ...
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 A1 V. Theta Capricorni has an estimated 2.54 times the
mass of the Sun
The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies a ...
and around 2.35 times the
Sun's radius
Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3:
1\,R_ = 6.957\ti ...
. It is 280 million years old and is spinning fairly rapidly with 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 bu ...
of 104 km/s. The star is radiating 65 times the
solar luminosity
The solar luminosity () is a unit of radiant flux (Power (physics), power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxy, galaxies and other celestial objects in terms of the output of ...
from its
photosphere
The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
at an
effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...
of around 10,000 K.
The secondary component does not have a known stellar classification, but is much smaller and cooler than its primary, with about 50% the mass and radius of the Sun, and a temperature of 3,900 K. It takes to complete an orbit around the barycenter, and is separated from its primary by 0.78
astronomical unit
The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
s.
Night viewing
The star or star system is almost eclipsed by the Sun on about 3 February, when it will figure behind the Sun's corona if there is a full solar eclipse. Thus the star can be viewed the whole night, crossing the sky, in early August (in the current epoch).
Chinese name
In Chinese, (), meaning '' Twelve States'', refers to an asterism which represents twelve ancient states in the
Spring and Autumn period
The Spring and Autumn period () was a period in History of China, Chinese history corresponding roughly to the first half of the Eastern Zhou (256 BCE), characterized by the gradual erosion of royal power as local lords nominally subject t ...
and the
Warring States period
The Warring States period in history of China, Chinese history (221 BC) comprises the final two and a half centuries of the Zhou dynasty (256 BC), which were characterized by frequent warfare, bureaucratic and military reforms, and ...
ι Capricorni
Iota Capricorni (ι Cap, ι Capricorni) is a solitary, yellow-hued star in the southern constellation of Capricornus. It can be seen with the naked eye, having an apparent visual magnitude of +4.3. Based upon an annual parallax shift of 16 ...
26 Capricorni
6 (six) is the natural number following 5 and preceding 7. It is a composite number and the smallest perfect number.
In mathematics
A six-sided polygon is a hexagon, one of the three regular polygons capable of tiling the plane. A hexagon a ...
,
27 Capricorni
This is the list of notable stars in the constellation Capricornus, sorted by decreasing brightness.
See also
*List of stars by constellation
References
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{{Stars of Capricornus
Capricornus, *List
Lists of stars by constel ...
Chinese name
Chinese may refer to:
* Something related to China
* Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity
**Han Chinese, East Asian ethnic group native to China.
**'' Zhonghua minzu'', the supra-ethni ...