Theta Tucanae (θ Tuc, θ Tucanae) is a
star
A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
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 first constellati ...
Tucana
Tucana (The Toucan) is a constellation in the southern sky, named after the toucan, a South American bird. It is one of twelve constellations conceived in the late sixteenth century by Petrus Plancius from the observations of Pieter Dirkszoon K ...
.
Like other stars in Tucana, it was given its
Bayer designation
A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
by French explorer and astronomer
Nicolas Louis de Lacaille
Abbé Nicolas-Louis de Lacaille (; 15 March 171321 March 1762), formerly sometimes spelled de la Caille, was a French astronomer and geodesist who named 14 out of the 88 constellations. From 1750 to 1754, he studied the sky at the Cape of Goo ...
in 1756.
It was found to be variable in 1971.
Theta Tucanae is a white
A-type subgiant
A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution ...
of spectral type A7IV with a mean
apparent magnitude
Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...
of +6.11, located approximately 423
light years
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astro ...
from
Earth
Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
.
It is classified as a
Delta Scuti type variable star
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...
and its brightness varies from magnitude +6.06 to +6.15 with periods of around 70 to 80 minutes.
The Delta Scuti variables are a class of short-period (six hours at most) pulsating stars that have been used as
standard candles
The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...
and as subjects to study
astroseismology
Asteroseismology is the study of oscillations in stars. Stars have many resonant modes and frequencies, and the path of sound waves passing through a star depends on the local speed of sound, which in turn depends on local temperature and chemical ...
.
Observations over the decades have shown that its colour slightly changes and it exhibits variation in light that indicate the star is actually an ellipsoidal binary with a period of seven days.
The system is more luminous than expected, given the
spectrum
A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...
and distance of the primary star, indicating that the companion star must be contributing a good proportion of its light. Stellar evolution modelling has concluded that the system likely begun as a
binary system
A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.)
The most common ki ...
, with one star about double the
Sun's mass
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 the other roughly equivalent to that of the sun. The larger star eventually aged and expanded as it used up its core hydrogen, and begun having its mass siphoned off by the smaller star; the system is likely to have been an
Algol-type eclipsing binary at this stage. This star appears now to be an aged star composed mostly of helium with very little hydrogen and with a mass of 0.2
solar mass
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, galaxie ...
es and around 37 times the luminosity of 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 ...
and surface temperature of 7000 K, while the once-smaller star is the Delta Scuti variable that is now around two solar masses.
Around 0.8 solar masses has been lost from the system over time.
References
{{DEFAULTSORT:Theta Tucanae
Tucanae, Theta
Tucana
Delta Scuti variables
A-type subgiants
002629
003112
0139
Durchmusterung objects