The transits of a planet in a Keplarian orbit around its host star are exactly periodic. However, if a third body is present in the system, the orbits are not Keplarian, and the time between consecutive transits varies (Holman & Murray 2005, Agol et al. 2005). This offers the possibility of detecting non-transiting planets via photometry.
The timing variations depend on the masses of the bodies and the exact geometry of their orbits. In a transiting hot-Jupiter system, there are cases where an additional terrestrial-mass planet in a resonant orbit will cause timing variations of order 0.1-1 minute. This can be detected in high-precision photometry from ground-based telescopes.
The LCOGT network will allow routine monitoring of transits of known exoplanets. Many of these planets have bright hosts (V=7-12), so even the 0.4m telescopes will obtain photometry useful for this project. The Faulkes Telescopes will allow searching for TTVs of the planets around fainter stars (mainly those detected by OGLE).
- Several transit observations have been scheduled on FTN. Tenagara will also observe some.
- A simple test on Tenagra lightcurves suggest that we can achieve a timing precision of ~1 minute down to R=12-13. This should really be redone more rigorously, to look at the effects of systematics, and repeated for FTN data. The equation given in Steffen et al. 2007 gives a precision of 0.5min.
- Prioritise targets
- Numerical tests to look at transit timing precision in real lightcurves from Tenagra and FTN.
Agol et al. 2005 On detecting terrestrial planets with timing of giant planet transits
Holman & Murray 2005 The Use of Transit Timing to Detect Terrestrial-Mass Extrasolar Planets
Steffen et al. 2007 Detecting and Characterizing Planetary Systems with Transit Timing (white paper)