1. Measurement of the photocentre position variations with CoRoT - further investigations M. Ollivier (IAS)

2. Summary of previous episodes 2 CoRoT SC – 3 july 2012

3. Why measuring the photocentre position ? 3 CoRoT SC – 3 july 2012

4. Accuracy of the photocentre position determination Realistic approach : “realistic case” : Estimation of the photocenter position using the imagettes –Determination of the optimal mask for the exo target –Estimation of the photocentre position using the pixel within the mask as it is done for the sismo stars (white light) –Determination of the residual jitter thanks to the sismo stars –Correction of the jitter in the photocentre curve for the exo target –Estimation of the photocentre stability (rms of the photocentre position curve) –“clever” filtering : gain by a factor of 2 in the rms value ? Work done for 2 targets –Star 101062850 R=15.07 –Star 102797300 R=13.68 CoRoT SC – 3 july 2012 4

5. Accuracy of the photocentre position determination Star 102797300 R=13.68 : rms=0.015 px -> 0.0075 px CoRoT SC – 3 july 2012 5

6. Photocentre position averaging If we average over the transit duration + several transits: If à 80 day run 6 CoRoT SC – 3 july 2012 Orbital period (d)241080 Transit duration (min)136170230460 Gain100806040 Accuracy (px)10-41,2 x 10 -4 1,6 x 10 -4 2,5 x 10 -4

7. Amplitude of the photocentre position variations (ΔmV=3) CoRoT SC – 3 july 2012 7 ΔF/F 0.6 % 2 % 3 %

8. Amplitude of the photocentre position variations (ΔmV=5) CoRoT SC – 3 july 2012 8

9. Open question 1: implementation of the photocentre computation A modification of the onboard software is costly (time, manpower, money) Computation thanks to the imagettes –Performance of the imagettes pipeline (cf. S.B’ presentation) –Need for operations modifications : ability to change the target status during a run : (cf. S.C. O.V presentations) How, when, how many times per run ? How to handle different types of data for the same target –Need for the alarm mode –All the alarm in imagettes Need to be tested before generalized CoRoT SC – 3 july 2012 9

10. Open question 2: Is there an alternative method ? The use of colored photometry (about 2000 targets/run) Differentiel effect of a contaminant eclipsing binary on the colored photometry. Simulation : a CEB in the field : Δm=3, Δx entre +/- 10 arcsec Utilisation du simulateur de contamination (cas idéal, bruit de photon stellaire CoRoT SC – 3 july 2012 10

11. Open question 2: colored photometry? CoRoT SC – 3 july 2012 11

12. Open question 2: colored photometry? CoRoT SC – 3 july 2012 12 ΔmV=3, eclipse depth : 10%

13. Open question 2: colored photometry? CoRoT SC – 3 july 2012 13

14. Open question 2: colored photometry? CoRoT SC – 3 july 2012 14 ΔmV=3, eclipse depth : 10%

15. Open question 2: colored photometry? CoRoT SC – 3 july 2012 15 Ability to detect a CEB with Δx> +/- 2 arcsec (1 pixel) Can be performed on the colored photometry if sufficient S/N Can be considered for mV<15 Works only along the dispersion direction

16. Proposed strategy Evaluation of operational impact of photocentre calculation Test on 2 or 3 targets with photometric variations Comparison with actual colored photometry. 16 CoRoT SC – 3 july 2012

17. Discussion 17