Lambda Eridani (λ Eri) is a

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

in the constellation Eridanus. It is visible to the naked eye on a dark night with an apparent visual magnitude of 4.27. The distance to this star, based upon an annual parallax shift of 0.00402

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, is roughly 810 light years. λ Eri is classified in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and th ...

as a Beta Cephei variable. The AAVSO International Variable Star Index defines a LERI type of variation. λ Eri is classified as LERI + GCAS since it shows both short term periodic variations and longer timescale eruptive variation. It was one of the first stars where short-period variations were found. The line profile variability periods are 0.702d and 0.269d, with intermittently present periods of 0.6d and 0.75d. The photometric

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of a ...

of the variation is 0.010 magnitude. This is a

giant In folklore, giants (from Ancient Greek: '' gigas'', cognate giga-) are beings of human-like appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''giant'' is first attested in 1297 fr ...

or subgiant Be star 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 B2 IVne or B2 III(e)p, depending on the source. It is spinning 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 bulge ...

of 327 km/s. Compare this to the estimated

break-up velocity This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsid ...

of 440 km/s. This rotation is giving the star an oblate shape with an equatorial bulge that is 25% larger than the polar radius. The most likely rotation period is deemed to be twice the period of variation, or 1.4 days. The star also possesses a rotating circumstellar disc, seen edge on, which makes Lambda Eri a "shell star", where the disk appears more opaque than usual. Like most Be stars, Lambda Eridani emits soft

X-rays X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

. In 1993, a giant X-ray flare was observed in which the X-ray luminosity increased by a factor of six over a 39-hour period. Lambda Eridani has about nine times 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 seven times the Sun's radius. It radiates 14,700 times the solar luminosity from its 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 .

References

{{DEFAULTSORT:Lambda Eridani B-type subgiants Be stars Eridanus (constellation) Lambda Eridani variables Eridani, Lambda Eridani, 69 033328 023972 01679 Durchmusterung objects