Mortier, A.A.MortierFaria, J. P.J. P.FariaSantos, N. C.N. C.SantosRajpaul, V.V.RajpaulFigueira, P.P.FigueiraBoisse, I.I.BoisseCollier Cameron, A.A.Collier CameronDumusque, X.X.DumusqueLo Curto, G.G.Lo CurtoLovis, C.C.LovisMayor, M.M.MayorMelo, C.C.MeloPepe, F.F.PepeQueloz, D.D.QuelozSanterne, A.A.SanterneSégransan, D.D.SégransanSousa, S. G.S. G.SousaSOZZETTI, AlessandroAlessandroSOZZETTIUdry, S.S.Udry2020-07-202020-07-2020160004-6361http://hdl.handle.net/20.500.12386/26501Context. The presence of a small-mass planet (M<SUB>p</SUB> < 0.1 M<SUB>Jup</SUB>) 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. <BR /> Aims: In this paper, we present the analysis of <ASTROBJ>HD 175607</ASTROBJ>, 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. <BR /> 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. <BR /> Results: We find evidence for the presence of a small Neptune-mass planet (M<SUB>p</SUB>sini = 8.98 ± 1.10 M<SUB>⊕</SUB>) 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. <BR /> 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. <P />Based on observations taken with the HARPS spectrograph (ESO 3.6-m telescope at La Silla) under programmes 072.C-0488(E), 082.C-0212(B), 085.C-0063(A), 086.C-0284(A), and 190.C-0027(A).Radial velocity and stellar activity data are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A135">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A135</A>STAMPAenArticle10.1051/0004-6361/2015269052-s2.0-84954271077000369710300142https://www.aanda.org/articles/aa/abs/2016/01/aa26905-15/aa26905-15.html2016A&A...585A.135MFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation