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).
Current Progress
- 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.
To Do
- Prioritise targets
- Numerical tests to look at transit timing precision in real lightcurves from Tenagra and FTN.
References
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)