# Summary of K2 Program GO12046

Title: Dynamical masses and additional companions in the TRAPPIST-1 system

PI: Demory, Brice-Olivier (University of Cambridge)
CoIs: Lederer, Susan M.

TITLE. Dynamical masses and additional companions in the TRAPPIST-1 system

SUMMARY. We propose to use K2 to conduct an intensive monitoring of TRAPPIST-1, a nearby ultracool dwarf star around which 3 Earth-size planets have just been detected (Gillon+, Nature, in press). The main aims of this programme are to constrain the masses of these planets and to search for additional companions in the system.

SCIENCE GOALS. Our primary science goal is to measure precise transit timings for the three planets orbiting TRAPPIST-1. We expect minimum transit timing variations (TTV) of the order of 40s for the two inner planets. We require short-cadence observations as to precisely constrain the ingress and egress times, which will provide significantly enhanced accuracy on the transit timings, compared to long-cadence observations. None of these planets will have their masses measured by radial velocities anytime soon, because of the small expected amplitudes (3-5 m/s) and faintness of the host star (Kp=16.9) for RV facilities. TTV therefore represent the only avenue to constrain these planets masses and densities. The secondary goal of our programme is to undertake an unprecedented search for additional bodies in this system, including planets and trojans.

METHODOLOGY. We perform detailed n-body simulations of the 3-planet system TRAPPIST-1. Assuming different planetary masses (pure iron to pure ice), we estimate the amplitude of transit timings variations (TTV) on a 80-day timeframe, corresponding to the length of a K2 campaign. We find amplitudes of about 40s in the conservative case of circular orbits. A modest eccentricity on the c planet (e=0.05) would increase by a factor 3 the TTV amplitudes. Given the target Kp=16.9, we estimate that our proposed programme will yield 1.5 to 6 sigma precision on the planet masses, provided our target is observed in short-cadence mode. Our code is built to invert the TTV problem, ie use a set of transit timings and orbital parameters to derive the planetary masses/eccentricities in a MCMC framework.

RELEVANCE TO NASA. This proposal will dramatically improve our knowledge of the only known exoplanetary system for which atmospheric absorption features in temperate Earth-size exoplanets could be detected with JWST in a reasonable amount of time. Our proposal meets three objectives of the NASAs Origins Program, namely the 1) characterisation of exoplanets, 2) study of planetary formation and 3) the search for cosmic life.

# Targets requested by this program that have been observed (2)
EPIC ID, RA (J2000) [deg], Dec (J2000) [deg], magnitude, Investigation IDs
200164267, , , , GO12022_SC|GO12029_SC|GO12032_SC|GO12039_SC|GO12042_SC|GO12046_SC|GO12123_SC|TRAPPIST
246199087, 346.622013, -5.041274, 12.917, GO12039_LC|GO12042_LC|GO12032_LC|GO12022_LC|GO12123_LC|GO12029_LC|GO12046_LC|GO12046_SC