HD 121056#Planetary system
{{Short description|Star in the constellation Centaurus}}
{{Starbox begin}}
{{Starbox observe
| epoch = J2000
| constell = Centaurus
| dec = {{DEC|−35|18|51.6918}}
}}
{{Starbox character
| type = giant star
| variable =
}}
{{Starbox astrometry
| radial_v = {{val|5.60|0.13}}
| prop_mo_ra = {{val|−295.304}}
| prop_mo_dec = {{val|−68.458}}
| parallax = 15.6261
| p_error = 0.0418
}}
{{Starbox detail
| source =
| radius = {{val|5.948|0.077}}
| temperature = {{val|4,867|49|fmt=commas}}
| luminosity = {{val|18.2|2.0|1.8}}
| gravity = {{val|3.034|0.005}}
| metal_fe = {{val|0.020|0.031}}
| metal = [Mg/H] {{val|0.286|0.05}} dex
| rotation =
| rotational_velocity = {{val|2.38|0.51}}
}}
{{Starbox catalog
| names = {{odlist | CD=−34 9223 | 2MASS=J13535209-3518517 | TYC=7287-1874-1 | HD=121056 | HIP=67851 | HR=5224 | GJ=532.1 }}
}}
{{Starbox reference
| Simbad = HD+121056
| NSTED = HIP-67851
}}
{{Starbox end}}
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.
The spectrum of HD 121056 presents as an evolved K-type giant star with a stellar classification of K0 III. It is presently ascending the red-giant branch, having exhausted the supply of hydrogen at its core. The star is about 5.5 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. It has 1.6 times the mass of the Sun and has expanded to 5.72 times the Sun's radius. The star is radiating 15.8 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,867 K.
Planetary system
In 2014, two planets orbiting HD 121056 were discovered by the radial velocity method, and were confirmed a few months later. The orbits of these planets are stable on astronomical timescales, although the periods are not in orbital resonance. In 2022, the inclination and true mass of HD 121056 c were measured via astrometry, indicating a nearly edge-on orbit. Subsequent studies have provided further updates to the planetary parameters.
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.
{{OrbitboxPlanet begin
| name = HD 121056
| table_ref = {{efn|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.}}
}}
{{OrbitboxPlanet
| exoplanet = b
| mass = {{val|1.15|0.04|p=≥}}
| radius =
| semimajor = {{val|0.42|0.0002}}
| period = {{val|89.23|0.06}}
| eccentricity = {{val|0.13|0.04}}
| inclination =
}}
{{OrbitboxPlanet
| exoplanet = c
| mass = {{val|4.97|0.22|0.21}}
| radius =
| semimajor = {{val|4.55|0.05}}
| period = {{val|3128.41|52.09|47.13|fmt=commas}}
| eccentricity = {{val|0.30|0.03}}
| inclination = {{val|89.86|28.38|24.73}}
}}
{{Orbitbox end}}
Notes
{{Notelist}}
References
{{Reflist|refs=
{{cite simbad|title=HD 121056|accessdate=2021-05-13}}
{{Cite Gaia DR3|6169943210465504384}}
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| bibcode=1999MSS...C05....0H }}
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| bibcode=2021A&A...647A.157S | s2cid=221534230 }}
| title=Catalog for the ESPRESSO blind radial velocity exoplanet survey
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| last3=Santos | first3=N. C. | last4=Adibekyan | first4=V.
| last5=Sousa | first5=S. G. | last6=Delgado-Mena | first6=E.
| last7=Alibert | first7=Y. | last8=Cristiani | first8=S.
| last9=González Hernández | first9=J. I. |last10=Lanza | first10=A. F.
| last11=Di Marcantonio | first11=P. | last12=Martins | first12=J. H. C.
| last13=Micela | first13=G. | last14=Molaro | first14=P.
| last15=Neves | first15=V. | last16=Oshagh | first16=M.
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| last19=Rojas-Ayala | first19=B. | last20=Rebolo | first20=R.
| last21=Suárez Mascareño | first21=A. | last22=Zapatero Osorio | first22=M. R.
| display-authors=1 | journal=Astronomy & Astrophysics
| volume=629 | pages=A80 | year=2019
| arxiv=1908.04627 | doi=10.1051/0004-6361/201834729
| bibcode=2019A&A...629A..80H | s2cid=199552090 }}
| title=The Pan-Pacific Planet Search. II. Confirmation of a Two-planet System around HD 121056
| last1=Wittenmyer | first1=Robert A. | last2=Wang | first2=Liang
| last3=Liu | first3=Fan | last4=Horner | first4=Jonathan
| last5=Endl | first5=Michael | last6=Johnson | first6=John Asher
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| display-authors=1 | journal=The Astrophysical Journal
| volume=800 | issue=1 | page=74 | year=2015
| arxiv=1412.6889 | doi=10.1088/0004-637X/800/1/74
| bibcode=2015ApJ...800...74W |s2cid=53684180 }}
{{cite journal | display-authors=1
| title=Predicting multiple planet stability and habitable zone companions in the TESS era
| last1=Kane | first1=Stephen R. | last2=Horner | first2=Jonathan
| last3=Maddison | first3=Sarah T. | last4=Agnew | first4=Matthew T.
| journal=Monthly Notices of the Royal Astronomical Society
| volume=485 | issue=4 | pages=4703–4725 | year=2019
| doi=10.1093/mnras/stz345 | doi-access=free
| arxiv=1901.11297
| bibcode=2019MNRAS.485.4703A }}
| title=Secular spin-axis dynamics of exoplanets
| display-authors=1 | last1=Saillenfest | first1=M.
| last2=Laskar | first2=J. | last3=Boué | first3=G.
| journal=Astronomy & Astrophysics
| volume=623 | pages=A4 | year=2019
| arxiv=1901.02831 | doi=10.1051/0004-6361/201834344
| bibcode=2019A&A...623A...4S | s2cid=119073661 }}
| title=3D Selection of 167 Substellar Companions to Nearby Stars
| last1=Feng | first1=Fabo | last2=Butler | first2=R. Paul | display-authors=etal
| journal=The Astrophysical Journal Supplement Series
| volume=262 | issue=21 | page=21 | date=August 2022
| doi=10.3847/1538-4365/ac7e57 | arxiv=2208.12720 | doi-access=free
| bibcode=2022ApJS..262...21F | s2cid=251864022 }}
| title=Kernel-nulling for a robust direct interferometric detection of extrasolar planets
| last1=Martinache | first1=Frantz | last2=Ireland | first2=Michael J.
| journal=Astronomy & Astrophysics
| volume=619 | pages=A87 | year=2018
| doi=10.1051/0004-6361/201832847 | arxiv=1802.06252
| bibcode=2018A&A...619A..87M | s2cid=118882482 }}
{{cite journal |last1=Fontanet |first1=E. |last2=Udry |first2=S. |display-authors=etal |date=May 2025 |title=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 |journal=Astronomy & Astrophysics |volume= |issue= |pages= |doi= |arxiv=2505.14317}}
}}
{{Stars of Centaurus}}
{{Sky|13|53|52.0610|-|35|18|51.6809}}
{{DEFAULTSORT:HD 121056}}