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 5.5^[7] 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 1.6^[10] times the mass of the Sun and has expanded to 5.72 times the Sun's radius.^[7] The star is radiating 15.8^[7] 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.^[6][14]

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]

Notes

References