EDP Sciences
Free access
Volume 467, Number 2, May IV 2007
Page(s) 721 - 727
Section Planets and planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20066845

A&A 467, 721-727 (2007)
DOI: 10.1051/0004-6361:20066845

A new Neptune-mass planet orbiting HD 219828

C. Melo1, N. C. Santos2, 3, 4, W. Gieren5, G. Pietrzynski5, M. T. Ruiz6, S. G. Sousa2, 7, 8, F. Bouchy9, C. Lovis3, M. Mayor3, F. Pepe3, D. Queloz3, R. da Silva3, and S. Udry3

1  European Southern Observatory, Casilla 19001, Santiago 19, Chile
    e-mail: cmelo@eso.org
2  Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
3  Observatoire de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland
4  Centro de Geofisica de Évora, Rua Romão Ramalho 59, 7002-554 Évora, Portugal
5  Universidad de Concepcion, Departamento de Fisica, Casilla 160-C, Concepcion, Chile
6  Departamento de Astronomia, Universidad de Chile, Casilla Postal 36D, Santiago, Chile
7  Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
8  Departamento de Matemática Aplicada, Faculdade de Ciências da Universidade do Porto, Portugal
9  Institut d'Astrophysique de Paris, 98bis Bd. Arago, 75014 Paris, France

(Received 30 November 2006 / Accepted 28 January 2007 )

Two years ago a new benchmark for the planetary survey was set with the discoveries of three extrasolar planets with masses below 20 $M_\oplus$. In particular, the serendipitous discovery of the 14 $M_\oplus$ planet around $\mu$ Ara found with HARPS with a semi-amplitude of only 4 m s-1 put in evidence the tremendous potential of HARPS for the search of this class of very low-mass planets. Aiming to discovering new worlds similar to $\mu$ Ara b, we carried out an intensive campaign with HARPS to observe a selected sample of northern stars covering a range of metallicity from about solar to twice solar. Two stars in our program were found to present radial velocity variations compatible with the presence of a planet-mass companion. The first of these, HD 219828, was found to be orbited by a planet with a minimum mass of 19.8 $M_\oplus$ and an orbital period of 3.83 days. It is the 11th Neptune-mass planet found so far orbiting a solar-type star. The radial velocity data clearly show the presence of an additional body to the system, likely of planetary mass. The second planet orbits HD 102195, has a mass of 0.45  $M_{\rm Jup}$ and an orbital period of 4.11 days. This planet has been already announced by Ge et al. (2006, ApJ, 648, 683). Our data confirm and improve the orbital solution found by these authors. We also show that the high residuals of the orbital solution are caused by stellar activity, and use the bisectors of the HARPS cross-correlation function to correct the noise introduced by stellar activity. An improved orbital solution is obtained after this correction. This kind of analysis may be used in the future to correct the radial-velocities for stellar activity induced noise.

Key words: stars: individual: HD 219828 -- stars: planetary systems -- planetary systems: formation -- techniques: radial velocities

© ESO 2007