AX Circini

AX Circini is a binary star[4] 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]

AX Circini
Observation data
Epoch J2000      Equinox J2000
Constellation Circinus
Right ascension  14h 52m 35.25324s[1]
Declination −63° 48′ 35.4172″[1]
Apparent magnitude (V) 5.91[2] (5.69 – 6.19)[3]
Characteristics
Spectral type F8 II + B6 V[4]
U−B color index +0.2[5]
B−V color index +0.8[5]
Variable type δ Cep[6]
Astrometry
Radial velocity (Rv)−20.9±4.6[7] km/s
Proper motion (μ) RA: −4.779[1] mas/yr
Dec.: −5.108[1] mas/yr
Parallax (π)1.7449 ± 0.3450[1] mas
Distanceapprox. 1,900 ly
(approx. 600 pc)
Absolute magnitude (MV)−3.37[8]
Orbit[9]
Period (P)6,532±25 d
Eccentricity (e)0.19±0.02
Longitude of the node (Ω)231±8°
Periastron epoch (T)2448500±60 JD
Semi-amplitude (K1)
(primary)		10.0±0.5 km/s
Details
AX Cir A
Mass11.56[10] M☉
Radius45.68[1] R☉
Luminosity2,050[9] L☉
Surface gravity (log g)2.00[11] cgs
Temperature5,443±21[11] K
Metallicity [Fe/H]−0.05[12] dex
Rotational velocity (v sin i)7.4±0.4[13] km/s
AX Cir B
Mass5.57[10] M☉
Other designations
26 G. Cir, AX Cir, CD−63° 1029, HD 130701/2, HIP 72773, HR 5527, SAO 252928, WDS J14526-6349AB[14]
Database references
SIMBADdata
Light curve of AX Circini recorded by NASA's Transiting Exoplanet Survey Satellite (TESS)

This is a spectroscopic binary with an orbital period of 17.88 yr 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 2014[4] 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] and it is a classical Cepheid variable.[11] 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
  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.
  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.
  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, L3
  5. Lloyd Evans, T (1968). "The frequency of Cepheid binaries". Monthly Notices of the Royal Astronomical Society. 141: 109. 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.
  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, 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.
  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. 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.
  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.
  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. 51.
  13. Ammler-von Eiff, M.; Reiners, A. (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.
  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. 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.
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