Detection and characterization of an ultra-dense sub-Neptunian planet orbiting the Sun-like star K2-292

We present the discovery and characterization of a new transiting planet from Campaign 17 of the Kepler extended mission K2. The planet K2-292 b is a warm sub-Neptune on a 17 day orbit around a bright (V = 9.9 mag) solar-like G3 V star with a mass and radius of M<SUB>⋆</SUB> = 1.00 ± 0.03 M<SUB>☉</SUB> and R<SUB>⋆</SUB> = 1.09 ± 0.03 R<SUB>☉</SUB>, respectively. We modeled simultaneously the K2 photometry and CARMENES spectroscopic data and derived a radius of R<SUB>p</SUB>=2.63<SUB>-0.10</SUB><SUP>+0.12</SUP> R<SUB>⊕</SUB> and mass of M<SUB>p</SUB>=24.5<SUB>-4.4</SUB><SUP>+4.4</SUP> M<SUB>⊕</SUB>, yielding a mean density of ρ<SUB>p</SUB>=7.4<SUB>-1.5</SUB><SUP>+1.6</SUP> g cm<SUP>-3</SUP>, which makes it one of the densest sub-Neptunian planets known to date. We also detected a linear trend in the radial velocities of K2-292 (γ̇<SUB>RV</SUB> = -0.40<SUB>-0.07</SUB><SUP>+0.07</SUP> m s<SUP>-1</SUP> d<SUP>-1</SUP>) that suggests a long-period companion with a minimum mass on the order of 33 M<SUB>⊕</SUB>. If confirmed, it would support a formation scenario of K2-292 b by migration caused by Kozai-Lidov oscillations. The light curve is 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/623/A114'>http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/A114</A>