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Centro de Astrofísica da Universidade do Porto

The HARPS search for southern extra-solar planets
XXXI. The M-dwarf sample

X. Bonfils, X. Delfosse, S. Udry, T. Forveille, M. Mayor, C. Perrier, F. Bouchy, M. Gillon, C. Lovis, F. Pepe, D. Queloz, N. C. Santos, D. Ségransan, J.-L. Bertaux

Resumo
Context. Searching for planets around stars with different masses probes the outcome of planetary formation for different initial conditions. The low-mass M dwarfs are also the most frequent stars in our Galaxy and potentially therefore, the most frequent planet hosts.
Aims. This drives observations of a sample of 102 southern nearby M dwarfs, using a fraction of our guaranteed time on the ESO/HARPS spectrograph. We observed 460 hours and gathered 1965 precise (∼ 1 - 3 m/s) radial velocities, spanning the period from Feb. 11th, 2003 to Apr. 1st 2009.
Methods. This paper makes available the sample’s time series, presents their precision and variability. We apply systematic searches for long-term trends, periodic signals and Keplerian orbits (from 1 to 4 planets). We analyze the subset of stars with detected signals and apply several diagnostics to discriminate whether the observed Doppler shifts are caused by stellar surface inhomogeneities or by the radial pull of orbiting planets. To prepare for the statistical view of our survey we also compute the limits on possible unseen signals, and derive a first estimate of the frequency of planets orbiting M dwarfs.
Results. We recover the planetary signals corresponding to 9 planets already announced by our group (Gl 176 b, Gl 581 b, c, d & e, Gl 674 b, Gl 433 b, Gl 667C b and Gl 667C c). We present radial velocities that confirm GJ 849 hosts a Jupiter-mass planet, plus a long-term radial-velocity variation. We also present RVs that precise the planetary mass and period of Gl 832b. We detect longterm RV changes for Gl 367, Gl 680 and Gl 880 betraying yet unknown long-period companions. We identify candidate signals in the radial-velocity time series of 11 other M dwarfs. Spectral diagnostics and/or photometric observations demonstrate however that they are most probably caused by stellar surface inhomogeneities. Finally, we find our survey sensitive to few Earth-mass planets for periods up to several hundred days. We derive a first estimate of the occurrence of M-dwarf planets as a function of their minimum mass and orbital period. In particular, we find that giant planets (m sin i = 100 - 1,000 M) have a low frequency (e.g. ƒ ≲ 1% for P = 1-10 d and ƒ = 0.02+0.03-0.01 for P = 10-100 d), whereas super-Earths (m sin i = 1-10 M) are likely very abundant ( ƒ = 0.36+0.25-0.10 for P = 1 - 10 d and ƒ = 0.35+0.45-0.11 for P = 10 - 100 d). We also obtained η = 0.41+0.54-0.13, the frequency of habitable planets orbiting M dwarfs (1 ≤ m sin i ≤ 10 M). For the first time, η is a direct measure and not a number extrapolated from the statistic of more massive and/or shorter-period planets.

Palavras chave
planetary systems – techniques: radial velocities – methods: data analysis

Notas
Based on observations made with the HARPS instrument on the ESO 3.6-m telescope at La Silla Observatory under programme ID 072.C-0488(E)
Figures 3, 13–19, Tables 3–9, and Appendix A are available in electronic form at http://www.aanda.org
Radial velocity data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A109

Astronomy and Astrophysics
Volume 549, Página A109_1
janeiro 2013

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Instituto de Astrofísica e Ciências do Espaço

O Instituto de Astrofísica e Ciências do Espaço (IA) é uma nova, mas muito aguardada, estrutura de investigação com uma dimensão nacional. Ele concretiza uma visão ousada, mas realizável para o desenvolvimento da Astronomia, Astrofísica e Ciências Espaciais em Portugal, aproveitando ao máximo e realizando plenamente o potencial criado pela participação nacional na Agência Espacial Europeia (ESA) e no Observatório Europeu do Sul (ESO). O IA é o resultado da fusão entre as duas unidades de investigação mais proeminentes no campo em Portugal: o Centro de Astrofísica da Universidade do Porto (CAUP) e o Centro de Astronomia e Astrofísica da Universidade de Lisboa (CAAUL). Atualmente, engloba mais de dois terços de todos os investigadores ativos em Ciências Espaciais em Portugal, e é responsável por uma fração ainda maior da produtividade nacional em revistas internacionais ISI na área de Ciências Espaciais. Esta é a área científica com maior fator de impacto relativo (1,65 vezes acima da média internacional) e o campo com o maior número médio de citações por artigo para Portugal.

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