Revisiting rho 1 Cancri e: A New Mass Determination Of The Transiting super-Earth

TL;DR

This study precisely measures the mass of the transiting super-Earth rho 1 Cancri e using extensive radial velocity data, refining its properties and suggesting a volatile-rich composition.

Contribution

It provides a new, highly precise mass measurement of rho 1 Cancri e based on a large RV data set, improving understanding of its composition.

Findings

Mass of rho 1 Cnc e is 8.37 +/- 0.38 Earth masses.

The planet's density suggests a water-rich envelope.

The data set includes nearly 700 RV measurements from multiple observatories.

Abstract

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.