Alpha Circini

α Circini
Location of α Circini (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Circinus
Right ascension 14h 42m 30.41958s[1]
Declination −64° 58′ 30.4934″[1]
Apparent magnitude (V) 3.18 - 3.21[2]
Characteristics
Spectral type A7 Vp SrCrEu[3]
U−B color index +0.12[4]
B−V color index +0.24[4]
Variable type roAp[2]
Astrometry
Radial velocity (Rv)+7.2[5] km/s
Proper motion (μ) RA: −192.53[1] mas/yr
Dec.: −233.51[1] mas/yr
Parallax (π)60.35 ± 0.14 mas[1]
Distance54.0 ± 0.1 ly
(16.57 ± 0.04 pc)
Absolute magnitude (MV)+2.18[6]
Details
Mass1.5–1.7[7] M☉
Radius1.967 ± 0.066[8] R☉
Luminosity10.51 ± 0.60[7] L☉
Surface gravity (log g)4.1[7] cgs
Temperature7,500[7] K
Metallicity [Fe/H]0.13[9] dex
Rotation4.4790 ± 0.0001 days[10]
Rotational velocity (v sin i)13.0 ± 1.5[10] km/s
Age~12 million[11] years
Other designations
17. G Circini,[12] CD−64° 86, HD 128898, HIP 71908, HR 5463, SAO 252853.[13]
Database references
SIMBADdata

Alpha Circini (α Cir, α Circini) is a variable star in the faint, southern, circumpolar constellation of Circinus. At an apparent visual magnitude of 3.19,[4] 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 54.0 light-years (16.6 parsecs) from the Earth.[1]

A light curve for Alpha Circini, adapted from Bruntt et al. (2009)[10]

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.[10] 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).[7] The stellar classification of A7 Vp SrCrEu[3] 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).[14]

The mass of Alpha Circini is about 150% to 170% the mass of the Sun[7] and it has double the Sun's radius,[8] 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.[7][15] 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.[10]

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 91 ly (28 pc) from the center of the assemblage.[11]

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