Article · Wikipedia archive · Last revised Jul 29, 2026

HD 121056

HD 121056, or HIP 67851, is an aging giant star with a pair of orbiting exoplanets located in the southern constellation of Centaurus. This star is dimly visible to the naked eye with an apparent visual magnitude of 6.17. It is located at a distance of 209 light-years from the Sun, based on parallax measurements, and is drifting further away with a radial velocity of 5.6 km/s.

Last revised
Jul 29, 2026
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HD 121056
Observation data
Epoch J2000      Equinox ICRS
Constellation Centaurus1
Right ascension 13h 53m 52.06131s2
Declination −35° 18′ 51.6918″2
Apparent magnitude (V) 6.173
Characteristics
Evolutionary stage red giant branch2
Spectral type K0 III4
B−V color index 1.015
Astrometry
Radial velocity (Rv)5.60±0.132 km/s
Proper motion (μ) RA: −295.304 mas/yr2
Dec.: −68.458 mas/yr2
Parallax (π)15.6261±0.0418 mas2
Distance208.7 ± 0.6 ly
(64.0 ± 0.2 pc)
Absolute magnitude (MV)+2.081
Details
Mass1.394±0.0526 M☉
Radius5.948±0.0776 R☉
Luminosity18.2+2.0
−1.86 L☉
Surface gravity (log g)3.034±0.0056 cgs
Temperature4,867±493 K
Metallicity[Mg/H] 0.286±0.05 dex3
Metallicity [Fe/H]0.020±0.0313 dex
Rotational velocity (v sin i)2.38±0.513 km/s
Age5.467 Gyr
Other designations
CD−34 9223, GJ 532.1, HD 121056, HIP 67851, HR 5224, TYC 7287-1874-1, 2MASS J13535209-35185178
Database references
SIMBADdata
Exoplanet Archivedata

HD 121056, or HIP 67851, is an aging giant star with a pair of orbiting exoplanets located in the southern constellation of Centaurus. This star is dimly visible to the naked eye with an apparent visual magnitude of 6.17.3 It is located at a distance of 209 light-years from the Sun, based on parallax measurements, and is drifting further away with a radial velocity of 5.6 km/s.2

The spectrum of HD 121056 presents as an evolved K-type giant star with a stellar classification of K0 III.9 It is presently ascending the red-giant branch, having exhausted the supply of hydrogen at its core.5 The star is about 5.57 billion years old and is spinning with a projected rotational velocity of 2.4 km/s. HD 121056's concentration of heavy elements is similar to the Sun, with a metallicity Fe/H index of 0.020±0.031, although the star is enriched in lighter rock-forming elements like magnesium and aluminum.3 It has 1.610 times the mass of the Sun and has expanded to 5.72 times the Sun's radius.7 The star is radiating 15.87 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,867 K.3

Planetary system

In 2014, two planets orbiting HD 121056 were discovered by the radial velocity method,5 and were confirmed a few months later.9 The orbits of these planets are stable on astronomical timescales,11 although the periods are not in orbital resonance.12 In 2022, the inclination and true mass of HD 121056 c were measured via astrometry, indicating a nearly edge-on orbit.13 Subsequent studies have provided further updates to the planetary parameters.614

The planetary system configuration is favorable for direct imaging of exoplanets in the near future, being included in the top ten easiest targets in 2018.15

The HD 121056 planetary system14a
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination
(°) 		Radius
b ≥1.15±0.04 MJ 0.42±0.0002 89.23±0.06 0.13±0.04 — —
c 4.97+0.22
−0.21 MJ 		4.55±0.05 3,128.41+52.09
−47.13 		0.30±0.03 89.86+28.38
−24.7313 		—
Notes

Notes

  1. Most parameters are taken from the most recent study of the system, Fontanet et al. 2025. This does not incorporate astrometry, hence the mass of planet c is technically a minimum mass, but since the inclination measured by Feng et al. 2022 is nearly edge-on, the true mass is about the same as this value.
References

References

  1. 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. XHIP record for this object at VizieR.
  2. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  3. Hojjatpanah, S.; et al. (2019). "Catalog for the ESPRESSO blind radial velocity exoplanet survey". Astronomy & Astrophysics. 629: A80. arXiv:1908.04627. Bibcode:2019A&A...629A..80H. doi:10.1051/0004-6361/201834729. S2CID 199552090.
  4. Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars". Michigan Spectral Survey. 5. Bibcode:1999MSS...C05....0H.
  5. Jones, M. I.; et al. (2015). "A planetary system and a highly eccentric brown dwarf around the giant stars HIP 67851 and HIP 97233". Astronomy & Astrophysics. 573: A3. arXiv:1409.7429. Bibcode:2015A&A...573A...3J. doi:10.1051/0004-6361/201424771. S2CID 53638707.
  6. Lin, Wen-Xu; Qian, Sheng-Bang; Zhu, Li-Ying; Liao, Wen-Ping; Li, Fu-Xing (2024-07-01). "Using Asteroseismology to Calibrate the Physical Parameters of Confirmed Exoplanets and Their Evolved Host Stars". The Astronomical Journal. 168 (1): 27. arXiv:2405.15162. Bibcode:2024AJ....168...27L. doi:10.3847/1538-3881/ad4ffc. ISSN 0004-6256.
  7. Soto, M. G.; et al. (2021). "SPECIES. II. Stellar parameters of the EXPRESS giant star sample". Astronomy and Astrophysics. 647: A157. arXiv:2009.03371. Bibcode:2021A&A...647A.157S. doi:10.1051/0004-6361/202039357. S2CID 221534230.
  8. "HD 121056". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-05-13.
  9. Wittenmyer, Robert A.; et al. (2015). "The Pan-Pacific Planet Search. II. Confirmation of a Two-planet System around HD 121056". The Astrophysical Journal. 800 (1): 74. arXiv:1412.6889. Bibcode:2015ApJ...800...74W. doi:10.1088/0004-637X/800/1/74. S2CID 53684180.
  10. Sousa, S. G.; et al. (2018). "SWEET-Cat updated". Astronomy & Astrophysics. 620: A58. arXiv:1810.08108. Bibcode:2018A&A...620A..58S. doi:10.1051/0004-6361/201833350. S2CID 119374557.
  11. Kane, Stephen R.; et al. (2019). "Predicting multiple planet stability and habitable zone companions in the TESS era". Monthly Notices of the Royal Astronomical Society. 485 (4): 4703–4725. arXiv:1901.11297. Bibcode:2019MNRAS.485.4703A. doi:10.1093/mnras/stz345.
  12. Saillenfest, M.; et al. (2019). "Secular spin-axis dynamics of exoplanets". Astronomy & Astrophysics. 623: A4. arXiv:1901.02831. Bibcode:2019A&A...623A...4S. doi:10.1051/0004-6361/201834344. S2CID 119073661.
  13. Feng, Fabo; Butler, R. Paul; et al. (August 2022). "3D Selection of 167 Substellar Companions to Nearby Stars". The Astrophysical Journal Supplement Series. 262 (21): 21. arXiv:2208.12720. Bibcode:2022ApJS..262...21F. doi:10.3847/1538-4365/ac7e57. S2CID 251864022.
  14. Fontanet, E.; Udry, S.; et al. (May 2025). "CORALIE radial-velocity search for companions around evolved stars (CASCADES) IV: New planetary systems around HD 87816, HD 94890, and HD 102888 and an update on HD 121056". Astronomy & Astrophysics. arXiv:2505.14317.
  15. Martinache, Frantz; Ireland, Michael J. (2018). "Kernel-nulling for a robust direct interferometric detection of extrasolar planets". Astronomy & Astrophysics. 619: A87. arXiv:1802.06252. Bibcode:2018A&A...619A..87M. doi:10.1051/0004-6361/201832847. S2CID 118882482.