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Directed Follow-Up of Gaia Photometry in Search of Transiting Planets

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. Gaia in a Nutshell.

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Directed Follow-Up of Gaia Photometry in Search of Transiting Planets

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

  2. Gaia in a Nutshell • High precision astrometry (~5 μas). • Launch October 2013, five-year mission, L2 orbit. • + spectroscopy, + 1 mmag photometry. • 109stellar targets, On average 70-80 samples per target. • Hipparcos successor

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

  4. Why not a real detection? • No one thought about it… • Photometry not precise enough • Very low cadence Can we somehow use the data for detection?

  5. Directed Follow-Up – General Idea • Actually sampled transits provide some knowledge about P,T,w,d. • MCMC (assuming a box-shaped transit) prvides a pdf over the parameters. • Compute Instantaneous Transit Probability – ITP(t). • Follow-up observation when ITP is large. • Repeat the process (including the new follow-up data). • Stopping criterion.

  6. Could HD209458b have been detected in 2004?

  7. Could HD209458b have been detected in 2004?

  8. Could HD209458b have been detected in 2004?

  9. Lessons from Hipparcos HD209458Exercise • 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.

  10. Testing DFU on Gaia • Simulated Gaia light curves inspired by known transiting planets (period and duration, coordinates) • Gaia scanning law • Photon noise level – 1 mmag. • Phase depends on the simulated situation. • We defined three scenarios of detection.

  11. First Scenario – Detection • 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

  12. First Scenario – Detection

  13. Second Scenario – DFU-assisted detection • 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

  14. Second Scenario – one DFU observation

  15. Third Scenario – DFU Detection • 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

  16. Third Scenario – DFU Detection

  17. Third Scenario – DFU Detection Only Gaia data Gaia data + 1 DFU observation Gaia data + 2 DFU observations

  18. Rapid Response • ITP degrades 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

  19. Is it worth it? Observational Window Function 70 Gaia Measurements 130 Gaia Measurements

  20. Is it worth it? • Assuming 2 hr transit Simplified Galactic model(Bahcall & Soneira 1980) Transiting planet statistics (Gould et al. 2006) • Down to 14th G magnitude: minimum 7 transits: ~70 transiting HJs and VHJs minimum 5 transits: ~200 minimum 3 transits: ~600 • Down to 16thG magnitude: minimum 7 transits: ~300 transiting HJs and VJHs minimum 5 transits: ~900 minimum 3 transits: ~2600

  21. To do list: • Get organized • Dedicated observatory network? • CU7 follow-up network? • Science Alert team? • Prescreening (metallicity, brightness, activity etc.) • Improve on MCMC. • Objective criteria to triggering DFU • Wald statistics • ITP values • ITP skewness • Smaller planets (Neptunian and below?) • Other low-cadence surveys

  22. Additional slides Contingencies for potential questions

  23. HD189733 – Hipparcos and DFU observations

  24. HD189733 – Hipparcos and DFU observations

  25. HD189733 – Hipparcos and DFU observations

  26. HD189733 – Hipparcos and DFU observations

  27. Sanity checks

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

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