EDP Sciences
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Volume 390, Number 1, July IV 2002
Page(s) 267 - 279
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20020685

A&A 390, 267-279 (2002)
DOI: 10.1051/0004-6361:20020685

The CORALIE survey for southern extra-solar planets

VIII. The very low-mass companions of HD 141937 , HD 162020 , HD 168443 and HD 202206 : Brown dwarfs or "superplanets"?
S. Udry, M. Mayor, D. Naef, F. Pepe, D. Queloz, N. C. Santos and M. Burnet

Observatoire de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland

(Received 26 February 2002 / Accepted 22 April 2002)

Doppler CORALIE measurements of the solar-type stars HD 141937 , HD 162020 , HD 168443 and HD 202206 show Keplerian radial-velocity variations revealing the presence of 4 new companions with minimum masses close to the planet/brown-dwarf transition, namely with $m_2\sin{i}=$ 9.7, 14.4, 16.9, and 17.5 $M_{\rm Jup}$, respectively. The orbits present fairly large eccentricities ( $0.22\leq e \leq 0.43$). Except for HD 162020 , the parent stars are metal rich compared to the Sun, as are most of the detected extra-solar planet hosts. Considerations of tidal dissipation in the short-period HD 162020 system points towards a brown-dwarf nature for the low-mass companion. HD 168443 is a multiple system with two low-mass companions being either brown dwarfs or formed simultaneously in the protoplanetary disks as superplanets. For HD 202206 , the radial velocities show an additional drift revealing a further outer companion, the nature of which is still unknown. Finally, the stellar-host and orbital properties of massive planets are examined in comparison to lighter exoplanets. Observed trends include the need of metal-rich stars to form massive exoplanets and the lack of short periods for massive planets. If confirmed with improved statistics, these features may provide constraints for the migration scenario.

Key words: techniques: radial velocities -- stars: binaries: spectroscopic -- stars: individual: HD 141937 -- stars: individual: HD 162020 -- stars: individual: HD 168443 -- stars: individual: HD 202206

Offprint request: S. Udry, stephane.udry@obs.unige.ch

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