directed follow-up of gaia photometry in search of transiting planets shay zucker yifat dzigan...
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Directed Follow-Up of Gaia Photometry in Search of Transiting Planets
Shay ZuckerYifat Dzigan
Tel-Aviv University
• Dzigan & Zucker, MNRAS, 415, 2513, 2011• Dzigan & Zucker, ApJL, 753, L1, 2012• Dzigan & Zucker,, MNRAS, accepted
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Aposteriori Detection of HD209458b in Hipparcos Data
Söderhjelm 1999Robichon & Arenou 2000
Castellano et al. 2000
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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?
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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,Tc,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.
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Could HD209458b have been detected in 2004?
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Could HD209458b be detected in 2004?
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Could HD209458b be detected in 2004?
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Lessons from Hipparcos HD209458 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.
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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.
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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 (Ntot=64)• d > 0.005 mag
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First Scenario – Gaia data alone
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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 (Ntot=63)• d > 0.001 mag
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Second Scenario – one DFU observation
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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 (Ntot=83)• d = 0.005 mag
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Third Scenario – Few DFU Observations
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Third Scenario – Few DFU Observations
Only Gaia data
Gaia data + 1 DFU observation
Gaia data + 2 DFU observations
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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 (Ntot=48) (mid-life of mission)
• Assume d=0.008 mag
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Is it worth it?
Observational Window Function
70 Gaia Measurements 130 Gaia Measurements
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Is it worth it?
• Assuming 2 hr transit, Galactic model,
transiting planet statistics from complete surveys (OGLE)
• Down to 14th G magnitude:
minimum 7 transits: ~70 transiting HJs and VHJs
minimum 5 transits: ~200
minimum 3 transits: ~600
• Down to 16th G magnitude:
minimum 7 transits: ~300 transiting HJs and VJHs
minimum 5 transits: ~900
minimum 3 transits: ~2600
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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
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Additional slides Contingencies for potential questions
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HD189733 – Hipparcos and DFU observations
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HD189733 – Hipparcos and DFU observations
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HD189733 – Hipparcos and DFU observations
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HD189733 – Hipparcos and DFU observations
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Sanity checks
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Gaia WASP-4b – degradation of ITP over 10 years