AX Circini
{{Short description|Binary star system in the constellation Circinus}}
{{Starbox begin
| name = AX Circini
}}
{{Starbox observe
| epoch = J2000
| constell = Circinus
| dec = {{DEC|-63|48|35.4172}}
| appmag_v = 5.91 {{nowrap|(5.69–6.19)}}
}}
{{Starbox character
| type =
| class = {{nowrap|F8 II + B6 V}}
| variable = δ Cep
}}
{{Starbox astrometry
| radial_v = {{Val|−20.9|4.6}}
| parallax = 1.7449
| p_error = 0.3450
}}
{{Starbox orbit
| period_unitless = {{Val|6532|25|u=day|fmt=commas}}
| eccentricity = {{Val|0.19|0.02}}
| node = {{Val|231|8}}
| periastron = {{Val|2448500|60|u=JD|fmt=commas}}
| k1 = {{Val|10.0|0.5}}
}}
{{Starbox detail
| source =
| component1 = AX Cir A
| temperature = {{Val|5443|21|fmt=commas}}
| rotational_velocity = {{Val|7.4|0.4}}
| age_gyr =
| component2 = AX Cir B
}}
{{Starbox catalog
| names={{odlist | name=26 G. Cir | V=AX Cir | CD=−63° 1029 | HD=130701/2 | HIP=72773 | HR=5527 | SAO=252928 | WDS=J14526-6349AB }}
}}
{{Starbox reference
| Simbad = 26+Cir
}}
{{Starbox end}}
File:AX Circini TESS lightcurve.png of AX Circini recorded by NASA's Transiting Exoplanet Survey Satellite (TESS)]]
AX Circini is a binary star system in the southern constellation of Circinus. It has a nominal magnitude of 5.91, which is bright enough to be visible to the naked eye. Based upon an annual parallax shift of {{Val|1.7|ul=mas}}, it is located roughly 1,900 light-years from the Earth. The system is moving closer with a heliocentric radial velocity of −21 km/s.
This is a spectroscopic binary with an orbital period of {{Convert|6532|d|year|disp=out|abbr=off}} and an eccentricity of 0.19. A binary companion was first suspected in 1960, as the spectrum was considered to be composite and there is an ultraviolet excess. The companion was confirmed in 1982, and it was resolved using long baseline interferometry in 2014 and 2015. The system has an a sin i value of {{Val|6.05|ul=AU}}, where a is the semimajor axis and i is the (unknown) orbital inclination.
The primary, component A, is a yellow-white-hued bright giant with a stellar classification of F8 II, Walter Strohmeier discovered that it is a variable star, in 1964, but could not classify it initially. By 1966 he had classified it as a classical Cepheid variable. The combined apparent magnitude of the system ranges from 5.69 to 6.19 over 5.273 days. The secondary companion, component B, is a main-sequence star with a class of B6 V and an absolute magnitude of about −0.12.
References
{{reflist|refs=
{{cite simbad | title=26 Cir | access-date=28 August 2018 }}
{{cite DR2|5873984023533350400}}
| last1=Strohmeier | first1=W. | title=Bright Southern BV-Stars | journal=Information Bulletin on Variable Stars
| date=June 1964 | volume=55 | page=1 | bibcode=1964IBVS...55....1S
| url=https://articles.adsabs.harvard.edu/pdf/1964IBVS...55....1S | access-date=26 January 2025}}
| last1=Strohmeier | first1=W. | title=The Cepheid BV 428 = 26 Cir | journal=Information Bulletin on Variable Stars
| date=September 1966 | volume=159 | page=1 | bibcode=1966IBVS..159....1S
| url=https://articles.adsabs.harvard.edu/pdf/1966IBVS..159....1S | access-date=26 January 2025}}
| last1=Mauder | first1=H. | last2=Schöffel | first2=E.
| title=Lichtelektrische Drei-Farben-Photometrie des Cepheiden AX Cir = BV 428 (in German)
| journal=Zeitschrift für Astrophysik | date=1968 | volume=69 | pages=258-264 | bibcode=1968ZA.....69..258M
| url=https://articles.adsabs.harvard.edu/pdf/1968ZA.....69..258M | access-date=26 January 2025}}
| title=XHIP: An extended hipparcos compilation
| last1=Anderson | first1=E. | last2=Francis | first2=Ch.
| journal=Astronomy Letters | arxiv=1108.4971
| volume=38 | issue=5 | pages=331 | year=2012
| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | s2cid=119257644 }}
| title=General catalogue of variable stars: Version GCVS 5.1
| last1=Samus' | first1=N. N | last2=Kazarovets | first2=E. V
| last3=Durlevich | first3=O. V | last4=Kireeva | first4=N. N
| last5=Pastukhova | first5=E. N | journal=Astronomy Reports
| volume=61 | issue=1 | pages=80 | year=2017
| doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=125853869 }}
| title=Spectroscopic studies of Cepheids (S Cru, AP Pup, AX Cir, S TrA, T Cru, R Mus, S Mus, U Car) and semiregular bright supergiants (V382 Car, HD 75276, R Pup) in the southern hemisphere
| last1=Usenko | first1=I. A. | last2=Kniazev | first2=A. Yu.
| last3=Berdnikov | first3=L. N. | last4=Kravtsov | first4=V. V.
| journal=Astronomy Letters | display-authors=1
| volume=37 | issue=7 | pages=499–507 | date=July 2011
| doi=10.1134/S1063773711070061 | bibcode=2011AstL...37..499U | s2cid=122968535 }}
| title=Robust high-contrast companion detection from interferometric observations. The CANDID algorithm and an application to six binary Cepheids
| last1=Gallenne | first1=A. | last2=Mérand | first2=A.
| last3=Kervella | first3=P. | last4=Monnier | first4=J. D.
| last5=Schaefer | first5=G. H. | last6=Baron | first6=F.
| last7=Breitfelder | first7=J. | last8=Le Bouquin | first8=J. B.
| last9=Roettenbacher | first9=R. M. | last10=Gieren | first10=W.
| last11=Pietrzyński | first11=G. | last12=McAlister | first12=H.
| last13=ten Brummelaar | first13=T. | last14=Sturmann | first14=J.
| last15=Sturmann | first15=L. | last16=Turner | first16=N.
| last17=Ridgway | first17=S. | last18=Kraus | first18=S.
| journal=Astronomy & Astrophysics | display-authors=1
| volume=579 | id=A68 | pages=12 | date=July 2015
| doi=10.1051/0004-6361/201525917 | bibcode=2015A&A...579A..68G | arxiv=1505.02715 | s2cid=1118066 }}
| title=Comparative statistics and origin of triple and quadruple stars
| journal=Monthly Notices of the Royal Astronomical Society
| last1=Tokovinin | first1=A.
| volume=389 | issue=2 | pages=925–938 | year=2008
| bibcode=2008MNRAS.389..925T | arxiv=0806.3263
| doi=10.1111/j.1365-2966.2008.13613.x | doi-access=free
| s2cid=16452670
}}
| title=Multiplicity of Galactic Cepheids from long-baseline interferometry. II. The Companion of AX Circini revealed with VLTI/PIONIER
| display-authors=1 | last1=Gallenne | first1=A.
| last2=Mérand | first2=A. | last3=Kervella | first3=P.
| last4=Breitfelder | first4=J. | last5=Le Bouquin | first5=J. -B.
| last6=Monnier | first6=J. D. | last7=Gieren | first7=W.
| last8=Pilecki | first8=B. | last9=Pietrzyński | first9=G.
| journal=Astronomy & Astrophysics
| volume=561 | id=L3 | pages=5 | date=January 2014
| doi=10.1051/0004-6361/201322883 | bibcode=2014A&A...561L...3G | arxiv=1312.1950 | s2cid=14282671 }}
| title=The Distribution of the Elements in the Galactic Disk. II. Azimuthal and Radial Variation in Abundances from Cepheids
| display-authors=1 | last1=Luck | first1=R. E.
| last2=Andrievsky | first2=S. M. | last3=Kovtyukh | first3=V. V.
| last4=Gieren | first4=W. | last5=Graczyk | first5=D.
| journal=The Astronomical Journal
| volume=142 | issue=2 | id=51 | pages=12 | date=August 2011
| doi=10.1088/0004-6256/142/2/51 | bibcode=2011AJ....142...51L | arxiv=1106.0182 | s2cid=119288363 }}
| 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 }}
| last1=Klagyivik | first1=P. | last2=Szabados | first2=L.
| title=Observational studies of Cepheid amplitudes. I. Period-amplitude relationships for Galactic Cepheids and interrelation of amplitudes
| journal=Astronomy and Astrophysics
| volume=504 | issue=3 | pages=959–972 | date=September 2009
| doi=10.1051/0004-6361/200811464 | bibcode=2009A&A...504..959K
| arxiv=0908.3561 | s2cid=18283579 }}
| last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C.
| title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project
| journal=Astronomy & Astrophysics
| volume=546 | id=A61 | pages=14 | date=October 2012
| doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D
| arxiv=1208.3048 | s2cid=59451347 | postscript=. }}
{{cite conference | display-authors=1
| title=A spectroscopic study of southern binary Cepheids
| last1=Petterson | first1=O. K. L. | last2=Albrow | first2=Michael D.
| last3=Cottrell | first3=P. L. | last4=Fokin | first4=A.
| conference=Variable Stars in the Local Group, IAU Colloquium 193, Proceedings of the conference held 6-11 July, 2003 at Christchurch, New Zealand
| editor1-first=Donald W. | editor1-last=Kurtz
| editor2-first=Karen R. | editor2-last=Pollard
| series=ASP Conference Proceedings | volume=310
| location=San Francisco | page=403
| publisher=Astronomical Society of the Pacific
| date=May 2004 | bibcode=2004ASPC..310..403P }}
}}
{{Stars of Circinus}}
{{DEFAULTSORT:AX Circini}}
Category:B-type main-sequence stars
Category:Classical Cepheid variables