2012ApJ...759...19E

We present a mass determination for the transiting super-Earth ρ¹ Cancri e based on nearly 700 precise radial velocity (RV) measurements. This extensive RV data set consists of data collected by the McDonald Observatory planet search and published data from Lick and Keck observatories. We obtained 212 RV measurements with the Tull Coudé Spectrograph at the Harlan J. Smith 2.7 m Telescope and combined them with a new Doppler reduction of the 131 spectra that we have taken in 2003-2004 with the High-Resolution Spectrograph (HRS) at the Hobby-Eberly Telescope for the original discovery of ρ¹ Cancri e. Using this large data set we obtain a five-planet Keplerian orbital solution for the system and measure an RV semi-amplitude of K = 6.29±0.21 m/s for ρ¹ Cnc e and determine a mass of 8.37±0.38 M_⊕. The uncertainty in mass is thus less than 5%. This planet was previously found to transit its parent star, which allowed them to estimate its radius. Combined with the latest radius estimate from Gillon et al., we obtain a mean density of ρ = 4.50±0.20 g/cm3. The location of ρ¹ Cnc e in the mass-radius diagram suggests that the planet contains a significant amount of volatiles, possibly a water-rich envelope surrounding a rocky core.