Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-Poor K Dwarf
Abstract
Using radial velocity measurements from four instruments, we report the mass and density of a 2.0430.069 ~R sub-Neptune orbiting the quiet K-dwarf Wolf 503 (HIP 67285). In addition, we present improved orbital and transit parameters by analyzing previously unused short-cadence K2 campaign 17 photometry and conduct a joint radial velocity-transit fit to constrain the eccentricity at 0.410.05. The addition of a transit observation by Spitzer also allows us to refine the orbital ephemeris in anticipation of further follow-up. Our mass determination, 6.26+0.69-0.70~M, in combination with the updated radius measurements, gives Wolf 503 b a bulk density of = 2.92 +0.50-0.44 g~cm-3. Using interior composition models, we find this density is consistent with an Earth-like core with either a substantial H2O mass fraction (45+19.12-16.15\%) or a modest H/He envelope (0.50.28\%). The low H/He mass fraction, along with the old age of Wolf 503 (112 Gyrs), makes this sub-Neptune an opportune subject for testing theories of XUV-driven mass loss while the brightness of its host (J=8.3 mag) makes it an attractive target for transmission spectroscopy.