Photodynamical mass determination of the multiplanetary system K2-19

Abstract

K2-19 is the second multi-planetary system discovered with K2 observations.\nThe system is composed of two Neptune size planets close to the 3:2 mean-motion\nresonance. To better characterise the system we obtained two additional transit\nobservations of K2-19b and five additional radial velocity observations. These\nwere combined with K2 data and fitted simultaneously with the system dynamics\n(photo-dynamical model) which increases the precision of the transit time\nmeasurements. The higher transit time precision allows us to detect the\nchopping signal of the dynamic interaction of the planets that in turn permits\nto uniquely characterise the system. Although the reflex motion of the star was\nnot detected, dynamic modelling of the system allowed us to derive planetary\nmasses of $M_b= 44 \\pm 12\\, M_{\\oplus}$ and $M_c = 15.9 \\pm 7.0\\, M_{\\oplus}$\nfor the inner and the outer planets respectively, leading to densities close to\nUranus. We also show that our method allows the derivation of mass ratios using\nonly the 80 days of observations during the first campaign of K2.\n