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

Summary of previous episodes 2 CoRoT SC – 3 july 2012

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

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 R=15.07 –Star R=13.68 CoRoT SC – 3 july

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

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) Transit duration (min) Gain Accuracy (px)10-41,2 x ,6 x ,5 x 10 -4

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

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

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

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

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

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

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

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

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

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

Discussion 17