The HARPS search for southern extra-solar planets. XXXIX. HD175607 the most metal-poor G dwarf with an orbiting sub-Neptune
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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 HD 175607, an old G6 star with metallicity [Fe/H] =−0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years. 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.
Mortier , A , Faria , J P , Santos , N C , Rajpaul , V , Figueira , P , Boisse , I , Cameron , A C , Dumusque , X , Lo Curto , G , Lovis , C , Mayor , M , Melo , C , Pepe , F , Queloz , D , Santerne , A , Ségransan , D , Sousa , S G , Sozzetti , A & Udry , S 2016 , ' The HARPS search for southern extra-solar planets. XXXIX. HD175607 the most metal-poor G dwarf with an orbiting sub-Neptune ' Astronomy & Astrophysics , vol 585 , A135 . DOI: 10.1051/0004-6361/201526905
Astronomy & Astrophysics
© ESO, 2016. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at http://dx.doi.org/10.1051/0004-6361/201526905
The research leading to these results received funding from the European Union Seventh Framework Programme (FP7/2007−2013) under grant agreement number 313014 (ETAEARTH). JPF acknowledges support from FCT through grant reference SFRH/BD/93848/2013. This work was supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grant UID/FIS/04434/2013. P.F., N.C.S., and S.G.S. also acknowledge the support from FCT through Investigador FCT contracts of reference IF/01037/2013, IF/00169/2012, and IF/00028/2014, respectively, and POPH/FSE (EC) by FEDER funding through the programme “Programa Operacional de Factores de Competitividade − COMPETE”. This work results within the collaboration of the COST Action TD 1308. A.S. is supported by the European Union under a Marie Curie Intra-European Fellowship for Career Development with reference FP7-PEOPLE-2013-IEF, number 627202.