Alpha Circini

Lore & Background

Alpha Circini belongs to a class of variables known as rapidly oscillating Ap stars, oscillating with multiple, non-radial pulsation cycles and a dominant cycle of 6.8 minutes. Its spectrum shows peculiar features caused by chemical stratification of the outer atmosphere, displaying a moderate deficiency of carbon, nitrogen and oxygen, while there is an overabundance of chromium. The stellar classification A7 Vp SrCrEu indicates it is a main sequence star with enhanced levels of strontium, chromium, and europium 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, it has double the Sun's radius, and its luminosity is more than 10 times that of the Sun. The effective 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 37 ± 4° to the line of sight from the Earth. Based upon its location and motion through space, Alpha Circini is a candidate member of the Beta Pictoris moving group, which 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 91 ly (28 pc) from the center of the assemblage. The IAU Working Group on Star Names approved the name Xami for this star on 12 December 2024, referring to an indigenous South African asterism 'Eyes of the Lion', consisting of Alpha and Beta Centauri; if these stars are the lion's eyes, the lion's face covers Alpha Circini.

Reader's Guide

Alpha Circini is significant as the brightest star in the faint constellation Circinus, readily visible to the naked eye from the southern hemisphere to as far north as 25° north latitude. Its membership in the rare class of rapidly oscillating Ap stars makes it a valuable object for studying stellar pulsation and chemical peculiarity. The star's multiple non-radial pulsation cycles, with a dominant period of 6.8 minutes, provide insights into the internal structure of A-type stars. The chemical stratification in its atmosphere, showing deficiencies in carbon, nitrogen, and oxygen alongside overabundances of chromium, strontium, and europium, offers a laboratory for understanding diffusion and magnetic processes in main-sequence stars. Its candidacy as a member of the Beta Pictoris moving group, with an estimated age of about 12 million years, links it to a young stellar association of common origin. The proper name Xami, approved in December 2024, connects the star to indigenous South African astronomy, specifically the 'Eyes of the Lion' asterism involving Alpha and Beta Centauri, with Alpha Circini representing the lion's face. The star also has a K dwarf companion, Alpha Circini B.

Did You Know?

• Alpha Circini oscillates with a dominant pulsation cycle of 6.8 minutes.
• It has a K dwarf companion star named Alpha Circini B.
• The star's proper name Xami was approved by the IAU Working Group on Star Names on 12 December 2024.