The HARPS search for southern extra-solar planets. XXXIX. HD 175607, the most metal-poor G dwarf with an orbiting sub-Neptune
Context. The presence of a small-mass planet (Mp < 0.1 MJup) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large, dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths.
Aims: In this paper, we present the analysis of
Methods: The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities.
Results: We find evidence for the presence of a small Neptune-mass planet (Mpsini = 8.98 ± 1.10 M⊕) orbiting this star with an orbital period P = 29.01 ± 0.02 days in a slightly eccentric orbit (e = 0.11 ± 0.08). The period of this Neptune is close to the estimated rotational period of the star. However, from a detailed analysis of the radial velocities together with the stellar activity, we conclude that the best explanation of the signal is indeed the presence of a planetary companion rather than stellar related. An additional longer period signal (P ~ 1400 d) is present in the data, for which more measurements are needed to constrain its nature and its properties.
Conclusions: HD 175607 is the most metal-poor FGK dwarf with a detected low-mass planet amongst the currently known planet hosts. This discovery may thus have important consequences for planet formation and evolution theories.
Astronomy and Astrophysics
- Pub Date:
- January 2016
- planetary systems;
- stars: individual: HD 175607;
- techniques: radial velocities;
- stars: solar-type;
- stars: activity;
- stars: abundances;
- Astrophysics - Earth and Planetary Astrophysics
- 12 pages, 9 figures, accepted for publication in Astronomy and Astrophysics