Alpha Circini
{{Short description|Star in the constellation Circinus}}
{{Starbox begin
| name = α Circini
}}
{{Starbox image
| image=
{{Location mark
|image=Circinus constellation map.svg|alt=|float=center|width=240
|label=|position=right
|mark=Red circle.svg|mark_width=12|mark_link=α Circini
|x=520|y=674
}}
|caption=Location of α Circini (circled)
}}
{{Starbox observe
| epoch = J2000.0
| constell = Circinus
| dec = {{DEC|-64|58|30.4934}}
}}
{{Starbox character
| variable = roAp
}}
{{Starbox astrometry
| parallax = 60.35
| p_error = 0.14
}}
{{Starbox detail
| radius = {{val|1.967|0.066}}
| luminosity = {{val|10.51|0.60}}
| rotational_velocity = {{val|13.0|1.5}}
| rotation = {{val|4.4790|0.0001}} days
}}
{{Starbox catalog
| names=Xami, α Cir, 17. G Circini, CD−64°867, HD 128898, HIP 71908, HR 5463, SAO 252853
}}
{{Starbox reference
| Simbad=alf+Cir
}}
{{Starbox end}}
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 {{Convert|54.0|ly|pc|abbr=off|lk=on}} from the Earth.
File:AlphaCirLightCurve.png 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 {{nowrap|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 {{Convert|91|ly|pc|abbr=on}} 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.)
References
{{Reflist|refs=
| last1=Ammler-von Eiff | first1=Matthias | last2=Reiners | first2=Ansgar
| title=New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?
| journal=Astronomy & Astrophysics | arxiv=1204.2459
| volume=542 | page=A116 | date=June 2012 | postscript=.
| doi=10.1051/0004-6361/201118724 | bibcode=2012A&A...542A.116A | s2cid=53666672 }}
{{citation | last1=Evans | first1=D. S. | date=June 20–24, 1966 | editor1-last=Batten | editor1-first=Alan Henry | editor2-last=Heard | editor2-first=John Frederick | title=The Revision of the General Catalogue of Radial Velocities | journal=Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30 | volume=30 | pages=57| location=University of Toronto | publisher=International Astronomical Union | bibcode=1967IAUS...30...57E }}
{{cite simbad | title=* alf Cir | access-date=2012-01-04 }}
{{citation | display-authors=1 | last1=Bruntt | first1=H. | last2=Kurtz | first2=D. W. | last3=Cunha | first3=M. S. | last4=Brandão | first4=I. M. | last5=Handler | first5=G. | last6=Bedding | first6=T. R. | last7=Medupe | first7=T. | last8=Buzasi | first8=D. L. | last9=Mashigo | first9=D. | last10=Zhang | first10=I. | last11=Van Wyk | first11=F. | title=Asteroseismic analysis of the roAp star α Circini: 84d of high-precision photometry from the WIRE satellite | journal=Monthly Notices of the Royal Astronomical Society | volume=396 | issue=2 | pages=1189–1201 |date=June 2009 | doi=10.1111/j.1365-2966.2009.14804.x | doi-access=free | bibcode=2009MNRAS.396.1189B |arxiv = 0903.3967 | s2cid=119292022 }}
{{citation | first1=James B. | last1=Kaler | title=ALPHA CIR (Alpha Circini) | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/alphacir.html | access-date=2012-01-04 }}
{{citation|title=The Colour of Stars |date=December 21, 2004 |work=Australia Telescope, Outreach and Education |publisher=Commonwealth Scientific and Industrial Research Organisation |url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |access-date=2012-01-16 |url-status=dead |archive-url=https://web.archive.org/web/20120222183238/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html |archive-date=February 22, 2012 }}
| title=Uranometria Argentina
| last1=Gould | first1=Benjamin Apthorp
| journal=Resultados del Observatorio Nacional Argentino en Cordoba
| volume=1 | location=Buenos Aires | pages=385 | year=1879
| bibcode=1879RNAO....1.....G | postscript=. }} See [http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=V/135A VizieR catalogue V/135A].
}}
{{Stars of Circinus}}
{{Authority control}}
{{DEFAULTSORT:Alpha Circini}}
Category:A-type main-sequence stars