Directed Follow-Up of Gaia Photometry in Search of Transiting Planets Shay Zucker Yifat Dzigan Tel-Aviv University Dzigan & Zucker, MNRAS, 415, 2513, 2011 Dzigan & Zucker, ApJL, 753, L1, 2012 Dzigan & Zucker,, MNRAS, accepted

Aposteriori Detection of HD209458b in Hipparcos Data Söderhjelm 1999 Robichon & Arenou 2000 Castellano et al. 2000

Why not a real detection? No one believed it was possible Photometry not precise enough Low cadence Can we use the data for detection somehow?

Directed Follow-Up – General Idea Actually sampled transits provide some knowledge about the period, phase, duration and depth of a hypothetical transit, if it exists. Using MCMC we can present this scarce information as a Probability Distribution Function over (P,T c,w,d) (assuming a BLS-like model). For each future time – t, we can use this PDF to calculate an instantaneous transit probability – ITP(t) Each new follow-up observataion is added and the process is repeated.

Could HD209458b have been detected in 2004?

Could HD209458b be detected in 2004?

Lessons from Hipparcos HD Exercise With five sampled transits, low cadence data, augmented by DFU, allow detection. Data become useless after a few years. For completeness – we should mention HD189733b.

Testing DFU on Gaia Simulated Gaia light curves inspired by known transiting planets (period and duration, coordinates) Gaia scanning law Phase chosen to produce required number of sampling transits Photon noise level – 1 mmag. We defined three scenarios of detection.

First Scenario – Gaia data alone Gaia samples enough transits to allow detection of the transit using only Gaia data. 1-mmag precision makes this scenario possible. Simulation inspired by CoRoT-1b (P=1.51 d, w=0.1 d) Assuming five sampled transits (N tot =64) d > mag

First Scenario – Gaia data alone

Second Scenario – one DFU observation Gaia samples enough transits to allow several possible solutions. One DFU observation is enough to constrain the period. Simulation inspired by CoRoT-4b (P=9.20 d, w=0.16 d) Assuming three sampled transits (N tot =63) d > mag

Second Scenario – one DFU observation

Third Scenario – Few DFU Observations Gaia samples enough transits to allow several possible solutions. A few DFU observations are needed to constrain the period. Simulation inspired by WASP-4b (P=1.338 d, w=0.104 d) Assuming four sampled transits (N tot =83) d = mag

Third Scenario – Few DFU Observations

Only Gaia data Gaia data + 1 DFU observation Gaia data + 2 DFU observations

We shouldn’t wait till the last minute ITP deteriorates over time Therefore – we should start observing even before the end of the mission Tres-1b, (P=3.03 d, w=0.104 d) Three sampled tranists (N tot =48) (mid-life of mission) Assume d=0.008 mag

Is it worth it? Observational Window Function 70 Gaia Measurements130 Gaia Measurements

Is it worth it? Assuming 2 hr transit, Galactic model, transiting planet statistics from complete surveys (OGLE) Down to 14 th G magnitude: minimum 7 transits: ~70 transiting HJs and VHJs minimum 5 transits: ~200 minimum 3 transits: ~600 Down to 16 th G magnitude: minimum 7 transits: ~300 transiting HJs and VJHs minimum 5 transits: ~900 minimum 3 transits: ~2600

To do list: Get organized – Dedicated observatory network? – CU7 follow-up network? – Science Alert team? Prescreening scheme (metallicity, brightness, activity etc.) Develop a more efficient computational scheme than MCMC. Objective criteria for applying DFU – Wald statistics – ITP values – ITP skewness Smaller planets (Neptunian and below?) Other low-cadence surveys

Additional slides Contingencies for potential questions

HD – Hipparcos and DFU observations

Sanity checks

Gaia WASP-4b – degradation of ITP over 10 years