Article · Wikipedia archive · Last revised Jun 23, 2026

AX Circini

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 1.7 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.

Last revised
Jun 23, 2026
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AX Circini
Observation data
Epoch J2000      Equinox J2000
Constellation Circinus
Right ascension 14h 52m 35.25324s1
Declination −63° 48′ 35.4172″1
Apparent magnitude (V) 5.912 (5.69–6.19)3
Characteristics
Spectral type F8 II + B6 V4
U−B color index +0.25
B−V color index +0.85
Variable type δ Cep6
Astrometry
Radial velocity (Rv)−20.9±4.67 km/s
Proper motion (μ) RA: −4.7791 mas/yr
Dec.: −5.1081 mas/yr
Parallax (π)1.7449±0.3450 mas1
Distanceapprox. 1,900 ly
(approx. 600 pc)
Absolute magnitude (MV)−3.378
Orbit9
Period (P)6,532±25 d
Eccentricity (e)0.19±0.02
Longitude of the node (Ω)231±8°
Periastron epoch (T)2,448,500±60 JD
Semi-amplitude (K1)
(primary)		10.0±0.5 km/s
Details
AX Cir A
Mass11.5610 M☉
Radius45.681 R☉
Luminosity2,0509 L☉
Surface gravity (log g)2.0011 cgs
Temperature5,443±2111 K
Metallicity [Fe/H]−0.0512 dex
Rotational velocity (v sin i)7.4±0.413 km/s
AX Cir B
Mass5.5710 M☉
Other designations
26 G. Cir, AX Cir, CD−63° 1029, HD 130701/2, HIP 72773, HR 5527, SAO 252928, WDS J14526-6349AB14
Database references
SIMBADdata
Light curve of AX Circini recorded by NASA's Transiting Exoplanet Survey Satellite (TESS) source ↗

AX Circini is a binary star4 system in the southern constellation of Circinus. It has a nominal magnitude of 5.91,2 which is bright enough to be visible to the naked eye. Based upon an annual parallax shift of 1.7 mas,1 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.7

This is a spectroscopic binary with an orbital period of 17.88 years and an eccentricity of 0.19.9 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 20144 and 2015.15 The system has an a sin i value of 6.05 AU, where a is the semimajor axis and i is the (unknown) orbital inclination.4

The primary, component A, is a yellow-white-hued bright giant with a stellar classification of F8 II,16 Walter Strohmeier discovered that it is a variable star, in 1964, but could not classify it initially.17 By 1966 he had classified it as a classical Cepheid variable.1819 The combined apparent magnitude of the system ranges from 5.69 to 6.19 over 5.273 days.3 The secondary companion, component B, is a main-sequence star with a class of B6 V and an absolute magnitude of about −0.12.4

References

References

  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
  3. Klagyivik, P.; Szabados, L. (September 2009). "Observational studies of Cepheid amplitudes. I. Period-amplitude relationships for Galactic Cepheids and interrelation of amplitudes". Astronomy and Astrophysics. 504 (3): 959–972. arXiv:0908.3561. Bibcode:2009A&A...504..959K. doi:10.1051/0004-6361/200811464. S2CID 18283579.
  4. Gallenne, A.; et al. (January 2014), "Multiplicity of Galactic Cepheids from long-baseline interferometry. II. The Companion of AX Circini revealed with VLTI/PIONIER", Astronomy & Astrophysics, 561: 5, arXiv:1312.1950, Bibcode:2014A&A...561L...3G, doi:10.1051/0004-6361/201322883, S2CID 14282671, L3
  5. Lloyd Evans, T (1968). "The frequency of Cepheid binaries". Monthly Notices of the Royal Astronomical Society. 141: 109–142. Bibcode:1968MNRAS.141..109L. doi:10.1093/mnras/141.1.109.
  6. Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  7. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  8. Evans, Nancy Evans; Bond, Howard E; Schaefer, Gail H; Mason, Brian D; Karovska, Margarita; Tingle, Evan (2013). "Binary Cepheids: Separations and Mass Ratios in 5 M ☉ Binaries". The Astronomical Journal. 146 (4): 93. arXiv:1307.7123. Bibcode:2013AJ....146...93E. doi:10.1088/0004-6256/146/4/93. S2CID 34133110.
  9. Petterson, O. K. L.; et al. (May 2004). Kurtz, Donald W.; Pollard, Karen R. (eds.). A spectroscopic study of southern binary Cepheids. Variable Stars in the Local Group, IAU Colloquium 193, Proceedings of the conference held 6-11 July, 2003 at Christchurch, New Zealand. ASP Conference Proceedings. Vol. 310. San Francisco: Astronomical Society of the Pacific. p. 403. Bibcode:2004ASPC..310..403P.
  10. Tokovinin, A. (2008). "Comparative statistics and origin of triple and quadruple stars". Monthly Notices of the Royal Astronomical Society. 389 (2): 925–938. arXiv:0806.3263. Bibcode:2008MNRAS.389..925T. doi:10.1111/j.1365-2966.2008.13613.x. S2CID 16452670.
  11. Usenko, I. A.; et al. (July 2011). "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". Astronomy Letters. 37 (7): 499–507. Bibcode:2011AstL...37..499U. doi:10.1134/S1063773711070061. S2CID 122968535.
  12. Luck, R. E.; et al. (August 2011). "The Distribution of the Elements in the Galactic Disk. II. Azimuthal and Radial Variation in Abundances from Cepheids". The Astronomical Journal. 142 (2): 12. arXiv:1106.0182. Bibcode:2011AJ....142...51L. doi:10.1088/0004-6256/142/2/51. S2CID 119288363. 51.
  13. Ammler-von Eiff, Matthias; Reiners, Ansgar (June 2012), "New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?", Astronomy & Astrophysics, 542: A116, arXiv:1204.2459, Bibcode:2012A&A...542A.116A, doi:10.1051/0004-6361/201118724, S2CID 53666672.
  14. "26 Cir". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 28 August 2018.
  15. Gallenne, A.; et al. (July 2015). "Robust high-contrast companion detection from interferometric observations. The CANDID algorithm and an application to six binary Cepheids". Astronomy & Astrophysics. 579: 12. arXiv:1505.02715. Bibcode:2015A&A...579A..68G. doi:10.1051/0004-6361/201525917. S2CID 1118066. A68.
  16. Gallenne, A; Mérand, A; Kervella, P; Breitfelder, J; Le Bouquin, J.-B; Monnier, J. D; Gieren, W; Pilecki, B; Pietrzyński, G (2013). "Multiplicity of Galactic Cepheids from long-baseline interferometry". Astronomy & Astrophysics. 561: L3. arXiv:1312.1950. Bibcode:2014A&A...561L...3G. doi:10.1051/0004-6361/201322883. S2CID 14282671.
  17. Strohmeier, W. (June 1964). "Bright Southern BV-Stars". Information Bulletin on Variable Stars. 55: 1. Bibcode:1964IBVS...55....1S. Retrieved 26 January 2025.
  18. Strohmeier, W. (September 1966). "The Cepheid BV 428 = 26 Cir". Information Bulletin on Variable Stars. 159: 1. Bibcode:1966IBVS..159....1S. Retrieved 26 January 2025.
  19. Mauder, H.; Schöffel, E. (1968). "Lichtelektrische Drei-Farben-Photometrie des Cepheiden AX Cir = BV 428 (in German)". Zeitschrift für Astrophysik. 69: 258–264. Bibcode:1968ZA.....69..258M. Retrieved 26 January 2025.