The HARPS search for southern extra-solar planets. V. A 14 Earth-masses planet orbiting HD 4308
Abstract
We present here the discovery and characterisation of a very light planet around HD 4308. The planet orbits its star in 15.56 days. The circular radial-velocity variation presents a tiny semi-amplitude of 4.1 m s-1 that corresponds to a planetary minimum mass m_2sin{i} = 14.1 Moplus (Earth masses). The planet was unveiled by high-precision radial-velocity measurements obtained with the HARPS spectrograph on the ESO 3.6-m telescope. The radial-velocity residuals around the Keplerian solution are 1.3 m s-1, demonstrating the very high quality of the HARPS measurements. Activity and bisector indicators exclude any significant perturbations of stellar intrinsic origin, which supports the planetary interpretation. Contrary to most planet-host stars, HD 4308 has a marked sub-solar metallicity ([Fe/H] = -0.31), raising the possibility that very light planet occurrence might show a different coupling with the parent star's metallicity than do giant gaseous extra-solar planets. Together with Neptune-mass planets close to their parent stars, the new planet occupies a position in the mass-separation parameter space that is constraining for planet-formation and evolution theories. The question of whether they can be considered as residuals of evaporated gaseous giant planets, ice giants, or super-earth planets is discussed in the context of the latest core-accretion models.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- February 2006
- DOI:
- 10.1051/0004-6361:20054084
- arXiv:
- arXiv:astro-ph/0510354
- Bibcode:
- 2006A&A...447..361U
- Keywords:
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- stars: individual: HD 4308;
- methods: observational;
- techniques: radial velocities;
- techniques: spectroscopic;
- instrumentation: spectrographs;
- Astrophysics
- E-Print:
- Accepted for publication in A&