We present a mass determination for the transiting super-Earth rho 1 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 (Fischer et al.
2008). We obtained 212 RV measurements with the Tull Coude 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 (HET) for the
original discovery of rho 1 Cancri e. Using this large data set we obtain a
5-planet Keplerian orbital solution for the system and measure an RV
semi-amplitude of K = 6.29 +/- 0.21 m/s for rho 1 Cnc e and determine a mass of
8.37 +/- 0.38 M_Earth. The uncertainty in mass is thus less than 5%. This
planet was previously found to transit its parent star (Winn et al. 2011,
Demory et al. 2011), which allowed them to estimate its radius. Combined with
the latest radius estimate from Gillon et al. (2012), we obtain a mean density
of rho = 4.50 +/- 0.20 g/cm^3. The location of rho 1 Cnc e in the mass-radius
diagram suggests that the planet contains a significant amount of volitales,
possibly a water-rich envelope surrounding a rocky core.Comment: 16 pages, 5 figures, accepted for publication in the Astrophysical
Journal (the 300+ RV measurements will be published as online tables or can
be obtained from the author
