J/AJ/155/257ivo://CDS.VizieR/J/AJ/155/257doi:10.26093/cds/vizier.51550257CDSSarkis P.Henning T.Kurster M.Trifonov T.Zechmeister M.Tal-Or L.,Anglada-Escude G.Hatzes A.P.Lafarga M.Dreizler S.Ribas I.,Caballero J.A.Reiners A.Mallonn M.Morales J.C.Kaminski A.,Aceituno J.Amado P.J.Bejar V.J.S.Hagen H.-J.Jeffers S.,Quirrenbach A.Launhardt R.Marvin C.Montes D.2019-02-01T10:48:30Z2019-01-15T08:48:27ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frdwarf-starsm-starsinfrared-photometryvisible-astronomybroad-band-photometryradial-velocityspectroscopyexoplanetsK2-18 is a nearby M2.5 dwarf, located at 34 pc and hosting a transiting planet that was first discovered by the K2 mission and later confirmed with Spitzer Space Telescope observations. With a radius of ~2 R_{Earth}_ and an orbital period of ~33 days, the planet lies in the temperate zone of its host star and receives stellar irradiation similar to that of Earth. Here we perform radial velocity follow-up observations with the visual channel of CARMENES with the goal of determining the mass and density of the planet. We measure a planetary semi-amplitude of K_b_~3.5 m/s and a mass of M_b_~9 M_{Earth}_, yielding a bulk density around {rho}_b_~4 g/cm^3^. This indicates a low-mass planet with a composition consistent with a solid core and a volatile-rich envelope. A signal at 9 days was recently reported using radial velocity measurements taken with the HARPS spectrograph. This was interpreted as being due to a second planet. We see a weaker, time- and wavelength-dependent signal in the CARMENES data set and thus favor stellar activity for its origin. K2-18 b joins the growing group of low-mass planets detected in the temperate zone of M dwarfs. The brightness of the host star in the near-infrared makes the system a good target for detailed atmospheric studies with the James Webb Space Telescope.2018AJ....155..257Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/155/257CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/608/A35 : K2-18 HARPS time-series (Cloutier+, 2017)J/A+A/609/A117 : CARMENES radial velocity curves of 7 M-dwarf (Trifonov+, 2018)J/A+A/612/A49 : 324 CARMENES M dwarfs velocities (Reiners+, 2018)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/155/257https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/155/257http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/155/257https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/155/257https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/155/257http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/155/257GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapInfraredOpticaldefaultJ/AJ/155/257/table5WiFSIP photometry in the Cousins R filterrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[7812.628906/7921.41] Barycentric Julian Date (BJD-2450000)dtime.epochdoubleDRmag[0.9904/1.0115] Differential Cousins R band magnitudemagphot.mag;em.opt.R;arith.difffloate_DRmag[0.0018/0.0057] Uncertainty in DRmagmagstat.error;phot.magfloatJ/AJ/155/257/table4WiFSIP photometry in the Johnson B filterrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[7812.628906/7921.402344] Barycentric Julian Date (BJD-2450000)dtime.epochdoubleDBmag[0.9855/1.0153] Differential Johnson B band magnitudemagphot.mag;em.opt.B;arith.difffloate_DBmag[0.0019/0.0062] Uncertainty in DBmagmagstat.error;phot.magfloatJ/AJ/155/257/table6Radial velocities obtained with CARMENES and the spectroscopic activity indicatorsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJD[7735.61786/7924.3808] Barycentric Julian Date (BJD-2450000)dtime.epochdoubleRV[-13.49/9.82] Radial velocitym/sphys.veloc;pos.heliocentricfloate_RV[1.61/11.91] Uncertainty in RVm/sstat.errorfloatRV(blue)[-30.21/16.88] The blue order radial velocity (1)m/sphys.veloc;pos.heliocentricfloate_RV(blue)[2.08/15.66] Uncertainty in RV(blue) (1)m/sstat.errorfloatRV(red)[-14.18/12.35] The red order radial velocity (1)m/sphys.veloc;pos.heliocentricfloate_RV(red)[1.69/10.86] Uncertainty in RV(red) (1)m/sstat.errorfloatCaII(IRT1)[0.567/0.6074] The Ca II H and K, calcium infrared triplet activity indicator (8498.02{AA}) (dex)phot.flux;arith.ratiofloate_CaII(IRT1)[0.0021/0.0105] Uncertainty in CaII(IRT1) (dex)stat.errorfloatCaII(IRT2)[0.4228/0.474] The Ca II H and K, calcium infrared triplet activity indicator (8542.09{AA}) (dex)phot.flux;arith.ratiofloate_CaII(IRT2)[0.0022/0.0132] Uncertainty in CaII(IRT2) (dex)stat.errorfloatCaII(IRT3)[0.4004/0.4449] The Ca II H and K, calcium infrared triplet activity indicator (8662.14{AA}) (dex)phot.flux;arith.ratiofloate_CaII(IRT3)[0.002/0.0123] Uncertainty in CaII(IRT3) (dex)stat.errorfloatHalpha[0.93/0.9715] H{alpha} activity index (6562.81{AA}) (dex)spect.index;em.line.Halphafloate_Halpha[0.0021/0.0121] Uncertainty in Halpha (dex)stat.errorfloat