Volume 447, Number 1, February III 2006
|Page(s)||361 - 367|
|Section||Planets and planetary systems|
|Published online||27 January 2006|
The HARPS search for southern extra-solar planets
V. A 14 Earth-masses planet orbiting HD 4308
Observatoire de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: firstname.lastname@example.org
2 Physikalisches Institut Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
3 Service d'Aéronomie du CNRS, BP 3, 91371 Verrières-le-Buisson, France
4 Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, 13013 Marseille, France
Accepted: 28 September 2005
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 = 14.1 (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.
Key words: stars: individual: HD 4308 / methods: observational / techniques: radial velocities / techniques: spectroscopic / instrumentation: spectrographs
© ESO, 2006
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.