Tau⁹ Eridani (τ⁹ Eri) is a

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 ...

in the constellation Eridanus. It is visible to the naked eye with an

apparent visual 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 lig ...

of 4.63. The distance to this system can be estimated using the parallax method, which yields a value of roughly 327

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s. This is a single-lined spectroscopic binary system with 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 5.95382 days 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- center, in geometry * Eccentricity (graph theory) of a ...

of 0.12. The primary component, τ⁹ Eri A, is a magnetic

chemically peculiar star In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual metal abundances, at least in their surface layers. Classification Chemically peculiar stars are common among hot main-sequence (hydrogen-burning) stars. Thes ...

with a

stellar classification 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 t ...

of , indicating that it is a

B-type main sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...

that shows abundance anomalies in its silicon

absorption lines A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identif ...

. It is an Alpha² Canum Venaticorum variable with a rotational periodicity of 5.954 days. The averaged strength of the stellar effective

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 t ...

is . The primary component Tau⁹ Eridani A has an estimated 326% the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass of ...

and 3.1 times the Sun's radius. It shines with 166 times the

solar luminosity The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nomin ...

from an outer atmosphere 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 10,866 K. The star is spinning 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 bulge ...

of 30 km/s. The secondary star, designated Tau⁹ Eridani B, is a late A-type or early F-type star with a mass of 1.6 solar masses and an effective temperature of 7530 K.

References

{{DEFAULTSORT:Tau9 Eridani B-type main-sequence stars Ap stars Eridanus (constellation) Eridani, Tau9 Eridani, 36 025267 018673 01240 Durchmusterung objects Alpha2 Canum Venaticorum variables Spectroscopic binaries