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The Kepler mission showed us that planets with sizes between that of Earthand Neptune appear to be the most common type in our Galaxy. These"super-Earths" continue to be of great interest for exoplanet formation,evolution, and composition studies. However, the number of super-Earths withwell-constrained mass and radius measurements remains small (40 planets with$\sigma_{\rm{mass}}<$ 25\%), due in part to the faintness of their host starscausing ground-based mass measurements to be challenging. Recently, threetransiting super-Earth planets were detected by the K2 mission around thenearby star GJ 9827/HIP 115752, at only 30 pc away. The radii of the planetsspan the "radius gap"' detected by Fulton et al. (2017), and all orbit within~6.5 days, easing follow-up observations. Here we report radial velocity (RV)observations of GJ 9827, taken between 2010 and 2016 with the Planet FinderSpectrograph on the Magellan II Telescope. We employ two different RV analysispackages, SYSTEMIC and RadVel, to derive masses and thus densities of the GJ9827 planets. We also test a Gaussian Process regression analysis, but find thecorrelated stellar noise is not well constrained by the PFS data, and that theGP tends to over fit the RV semi-amplitudes resulting in a lower K value. OurRV observations are not able to place strong mass constraints on the two outerplanets (c & d) but do indicate that planet b, at 1.64 R$_{\oplus}$ and ~8M$_{\oplus}$, is one of the most massive (and dense) super-Earth planetsdetected to date.

Magellan/PFS Radial Velocities of GJ 9827, a late K dwarf at 30 pc with Three Transiting Super-Earths