Alpha Circini

α Circini

Template:Location mark Location of α Circini (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Circinus
Right ascension	Template:RA
Declination	Template:DEC
Apparent magnitude (V)	3.18 - 3.21
Characteristics
Spectral type	A7 Vp SrCrEu
U−B Template:Engvar	+0.12
B−V Template:Engvar	+0.24
Variable type	roAp
Astrometry
Radial velocity (Rv)	+7.2 km/s
Proper motion (μ)	RA: −192.53 mas/yr Dec.: −233.51 mas/yr
Parallax (π)	60.35±0.14 mas
Distance	Template:Rnd ± Template:Rnd ly (Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)	+2.18
Details
Mass	1.5–1.7 Template:Solar mass
Radius	Template:Solar radius
Luminosity	Template:Solar luminosity
Surface gravity (log g)	4.1 cgs
Temperature	7,500 K
Metallicity [Fe/H]	0.13 dex
Rotation	days
Rotational velocity (v sin i)	km/s
Age	~12 million years
Metallicity [Fe/H]	{{{metal_fe2}}} dex
Other designations
Template:Odlist
Database references
SIMBAD	A
	B

Alpha Circini (α Cir, α Circini), also named Xami, is a variable star 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 to as far north as 25° north latitude. Parallax measurements of this star yield an estimated distance of from the Earth. There is a K dwarf companion star, Alpha Circini B.

File:AlphaCirLightCurve.png

A light curve for Alpha Circini, adapted from Bruntt et al. (2009)

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 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 (Cr). The stellar classification of A7 Vp SrCrEu indicates that this is a main sequence star with enhanced levels of strontium (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 and it has double the Sun's radius, while the 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 a stellar kinematic group 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.

The IAU Working Group on Star Names approved the name Xami for this star on 12 December 2024 and it is now so entered in the IAU Catalog of Star Names. This refers 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. (See also Xamidimura.)