Mu2 Octantis (μ2 Oct) is a binary star system in the constellation Octans, whose primary and secondary stars have apparent magnitudes of +6.481 and 7.153, respectively.[1] Based on parallax measurements, it lies 130.3 light-years away.[2][3]

The two stars, HD 196067 and HD 196068 (also named μ2 Oct A and μ2 Oct B), are separated at 17 arcseconds in the sky, corresponding to 740 astronomical units (AU). The semimajor axis of the stars' orbit is 932 AU.[4]

Component A is a G-dwarf star with 1.33 and 1.73 times of the Sun's mass and radius, respectively. Component B also a G-type main-sequence star with a radius 1.19 times larger than the Sun. Their effective temperatures are similar. HD 196068 has a higher metallicity than its companion, the reasons for this are uncertain.[5]

Planetary system

From 1998 to 2012, the system was observed using the CORALIE instrument, at the ESO's La Silla Observatory.[4]

In November 2012, a long-period, wide-orbiting planet was deduced by radial velocity around HD 196067. The planet has been pulled to an eccentric orbit by the B star HD 196068. The planet's true mass, as measured by astrometry, is , placing it right on the traditionally adopted boundary between planets and brown dwarfs.[6]

A second, innermost planet was detected using radial velocity observations with the CORALIE, HARPS, and ESPRESSO observatories. Despite its small orbit, it does not transit the host star.[7]

References

  1. ^ Paunzen, E. (2015-08-01). "A new catalogue of Strömgren-Crawford uvbyβ photometry". Astronomy and Astrophysics. 580: A23. arXiv:1506.04568. Bibcode:2015A&A...580A..23P. doi:10.1051/0004-6361/201526413. ISSN 0004-6361
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  4. ^ Marmier, M. et al. (2013). "The CORALIE survey for southern extrasolar planets XVII. New and updated long period and massive planets". Astronomy and Astrophysics. 551: A90. arXiv:1211.6444. Bibcode:2013A&A...551A..90M. doi:10.1051/0004-6361/201219639. S2CID 59467665
  5. ^ Flores, M; Yana Galarza, J; Miquelarena, P; Saffe, C; Jaque Arancibia, M; Ibañez Bustos, R V; Jofré, E; Alacoria, J; Gunella, F (2023-12-06). "Elemental abundance differences in the massive planet-hosting wide binary HD 196067−68". Monthly Notices of the Royal Astronomical Society. 527 (4): 10016–10024. arXiv:2311.17272. doi:10.1093/mnras/stad3714. ISSN 0035-8711
  6. ^ Li, Yiting; Brandt, Timothy D.; Brandt, G. Mirek; Dupuy, Trent J.; Michalik, Daniel; Jensen-Clem, Rebecca; Zeng, Yunlin; Faherty, Jacqueline; Mitra, Elena L. (2021). "Precise Masses and Orbits for Nine Radial-velocity Exoplanets". The Astronomical Journal. 162 (6): 266. arXiv:2109.10422. Bibcode:2021AJ....162..266L. doi:10.3847/1538-3881/ac27ab. S2CID 237592581
  7. ^ Delisle, J.-B.; Faria, J. P.; Ségransan, D.; Fontanet, E.; Ceva, W.; Barbato, D.; Sousa, S. G.; Unger, N.; Leleu, A. (2025-09-30). "Architecture of planetary systems with and without outer giant planets I. Inner planet detections around HD 23079, HD 196067, and HD 86226". Astronomy & Astrophysics. arXiv:2509.26232