J/MNRAS/529/3323ivo://CDS.VizieR/J/MNRAS/529/3323doi:10.26093/cds/vizier.75293323CDSPalethorpe L.Anna John A.Mortier A.Davoult J.Wilson T. G.Rice K.,Cameron A. C.Alibert Y.Buchhave L.Malavolta L.Cadman J.,Lopez-Morales M.Dumusque X.Silva A. M.Quinn S. N.Van Eylen V.,Vissapragada S.Affer L.Charbonneau D.Cosentino R.Ghedina A.,Haywood R. D.Latham D. W.Lienhard F.Martinez Fiorenzano A. F.,Pedani M.Pepe F.Pinamonti M.Sozzetti A.Stalport M.Udry S.,Vanderburg A.2024-11-06T20:35:18Z2024-06-05T08:43:31ZCDS support team

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

cds-question@unistra.frmultiple-starsexoplanetsradial-velocityvisible-astronomyWe report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 (M*=1.17M_{sun}_, R*=1.31R_{sun}_) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and radial velocity observations, and find that the planet, HD 77946 b, orbits with period Pb=6.527282_-0.000020_^+0.000015^d, has a mass of Mb=8.38+/-1.32M_{Earth}_, and a radius of Rb=2.705_-0.081_^+0.086^R_{Earth}_. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a ~1 per cent H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with Teq= 1248^+40^_-38_K, water may be in a supercritical state. The characterization of HD 77946 b, adding to the small sample of well-characterized sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.2024MNRAS.529.3323Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/529/3323CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/529/3323https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/529/3323http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/529/3323https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/529/3323https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/529/3323http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/529/3323GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/MNRAS/529/3323/table1HARPS-N RV DRS reduced datarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian datedtime.epochdoubleRVRadial velocitym/sphys.veloc;pos.heliocentricdoublee_RVError in radial velocitym/sstat.errorfloatBISBisector inverse spanm/sphys.velocfloate_BISError in bisector inverse spanm/sstat.errorfloatFWHMFull-width-at-half-maximum of the CCFkm/sspect.line.widthdoublee_FWHMError in Full-width-at-half-maximum of the CCFkm/sstat.error;phys.angSizedoubleHalphaHalpha indexspect.indexdoublee_HalphaError in Halpha indexstat.error;spect.linedoublelogRHKRHK activity indexspect.indexdoublee_logRHKError in RHK activity indexstat.errordoubleJ/MNRAS/529/3323/table2HARPS-N RV s-BART reduced datarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBarycentric Julian datedtime.epochdoubleRVRadial velocitym/sphys.veloc;pos.heliocentricdoublee_RVError in radial velocitym/sstat.errorfloat