Alpha Circini (α Cir, α Circini) is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

in the faint, southern, circumpolar constellation of Circinus. At an apparent visual magnitude of 3.19, it is the brightest star in the constellation and can be readily seen with the naked eye from the southern hemisphere.

Parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby object ...

measurements of this star yield an estimated distance of from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

This star belongs to a class of variables known as rapidly oscillating Ap stars. It oscillates with multiple, non-radial pulsation cycles and a dominant cycle of 6.8 minutes. The

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of color ...

shows peculiar features caused by chemical stratification of the outer atmosphere. It displays a moderate deficiency of carbon, nitrogen and oxygen, while there is an overabundance of

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and h ...

(Cr). The

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 A7 Vp SrCrEu indicates that this is a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star with enhanced levels of

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ...

(Sr), chromium, and europium (Eu) in its atmosphere (compared to a typical star like the Sun). The mass of Alpha Circini is about 150% to 170% 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 it has double the Sun's radius, while the luminosity is more than 10 times that of the Sun. The

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 the outer envelope is about 7,500 K, giving it the white hue typical of A-type stars. It is rotating with a period of 4.5 days and the pole is inclined by about to the line of sight from the Earth. Based upon its location and motion through space, Alpha Circini is a candidate member of a

stellar kinematic group In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as t ...

known as the Beta Pictoris moving group. This group shares a common origin and has an estimated age of about 12 million years. At the birth of this group, Alpha Circini was estimated to be located at a distance of about from the center of the assemblage.

References

{{DEFAULTSORT:Alpha Circini Circinus (constellation) A-type main-sequence stars Suspected variables Circini, Alpha Durchmusterung objects 128898 071908 5463 Circini, 17 Rapidly oscillating Ap stars