Mass bias in TTV systems

Wednesday 4 July, 10:10

Most of the known exoplanets have been discovered by the transit method. For these systems, followup observations are often not feasible and Transit Timing Variations (TTVs) are one of the few ways to measure the planets' masses. We investigate TTV signals for systems with low signal to noise ratio and find that there is a systematic bias, over-estimating the masses. This can be understood in the limiting case where there are no perturbing planets and the TTV signal is zero. We add any finite amount of noise to the transit times and then try to recover the mass of the perturbing object (which should be zero). However, to do that we have to take into account that the mass is positive definite. As a result, any fit or MCMC will converge on a finite positive mass. We quantify this effect and discuss if it could help to explain some of the discrepancies seen between masses obtain by TTVs and radial velocity.

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