SDW20051 Vincent Lapeyrère LESIA – Observatoire de Paris Calibration of flight model CCDs for CoRoT mission

SDW20052 Overview 1.The CoRoT mission 2.CCD maps : Defects and pixel capacity 3.CCD sensitivities : to temperature and bias voltages 4.CCD irradiation test 5.Conclusion

SDW20053 The CoRoT mission European mission : –Managed by CNES –In association with 3 French Laboratories (LESIA, LAM, IAS) –Contributions of : Austria, Belgium, Brazil, Germany, Spain, ESA Mission characteristics : –PROTEUS spacecraft –Launch mid 2006 –Polar orbit (896 km) –2,5 years The Corot Mission

SDW20054 Scientific mission Specifications Over 5 days : noise < 0,6 ppm (star m V =5.7) Scientific frequency interval [0,1;10]mHz Frequency resolution 0,1 µHz (150 days runs) Observe 10 stars per field between m V =5,7 and m V =9 Duty cycle 95% Specifications Over 1 hour : noise < (star m V =15,5) Observe stars between m V =11 and m V =15,5 continuously during 150 days If possible chromatic information ASTEROSEISMOLOGY PROGRAM (AS) PLANET FINDING PROGRAM (PF) Measure stellar oscillation frequencies about 2.5 ppm amplitudes Detect exoplanet transits about few 100 ppm aplitudes The CoRoT mission

SDW20055 The instrument Afocal telescope –2 parabolic mirrors off axis Camera : –Dioptric objective –Focal plane with 4 CCDs Electronics : –CCD readout –Thermal control –Data processing Onboard software : –Only light curves are send to the ground PROTEUS spacecraft –Polar orbit (896 km) –5 fields during 2,5 years The CoRoT mission

SDW20056 The CCDs 4 CCDs : 2 for AS and 2 PF program CCDs characteristics: –e2v –Frame transfer –Image area 2048 x 2048 pixels, storage area 2048 x 2052 pixels –Pixel size : 13.5 µm –Back illuminated, thinned –AIMO –Scientific AR coating –Flatness ±10µm Readout modes : –AS channel : 10 windows (50x50) once per sec. 100µs for line transfer 10µs for pixel readout Line and pixel binning –PF channel : Full frame once per 32 sec The CoRoT mission © Sodern

SDW20057 Pixel Response Non Uniformity (PRNU) With narrow bandwidth (10 nm), PRNU is dominated by fringing for wavelength greater than 800 nm No fringing with led (  ~50 nm) Evolution of local PRNU with wavelength (Local PRNU is computed in boxes of 32x32 pixels) Flat fields on the same portion of CCD (300x300 pixels) Line : Local PRNU with monochromator (  ~10 nm) Square : Local PRNU with leds (  ~50 nm) CCD maps

SDW20058 PRNU and jitter A part of photometric noise is produced by the motion of the star on the CCD due to the jitter of the satellite (  jit =0.1 pixels (0.14 arsec)) Knowing : –The instrument PSF –The flat field response of the CCD –A model of jitter  We compute a map of jitter noise This map can be compared to scientific specifications. Jitter noise map of the whole CCD. Unit is r.m.s. noise in ppm CCD maps

SDW20059 Pixel capacity Pixel capacity is determined on flat- field images : Evolution of variance with flash duration Measured on boxes 32x32 pixels in order to map the CCD Variance (X) and Intensity (+) evolution versus flash duration time. The dashed line represents the saturation level. Pixel capacity map of a whole CCD. Unit is e-/pix. Pixel capacity decrease in the centre of the CCD Observation confirmed with spot Due to non established phase Strong differences between CCDs CCD maps

SDW CCD gain sensitivity to temperature The gain is measured on plot variance as function of average  G CCD = 4.3 µV/e- with dispersion of 0.1µV on the ten CCDs The gain is measured at different temperatures   Gccd = ppm/K with a dispersion of 150 ppm/K on the ten CCDs Evolution of gain with temperature CCD sensitivity

SDW CCD QE sensitivity to temp. CCD response measured at different temperature –  ccd =  Gccd +  Qe –  Qe vary with wavelength The impact on photometry depends on the target spectrum With a temperature stability better than 5mK the variation is lower than 2 ppm for principal target stars  CCD = -500 ppm/K ± 50  CCD = -400 ppm/K ± 50  CCD = 2500 ppm/K ± 80  = 470 nm  = 640 nm  = 880 nm Evolution of QE sensitivity to temperature with wavelength Evolution of CCD response with temperature for 3 different wavelengths CCD sensitivity

SDW CCD response sensitivity to bias CCD response is sensitive to 3 bias voltages –V od : Output drain –V rd : Reset drain –V og : Output gate VodVrdVog Gain sensitivity to polarisation (ppm/mV) Bias sensitivity to temperature (mV/K) Total Photometric variation for 1 degree (ppm) This variation is over scientific specifications and must be corrected Evolution of CCD response with bias voltages, dashed lines represent nominal values where sensitivity is computed  V od = -35 ppm/mV  V og = 25 ppm/mV  V rd = -15 ppm/mV CCD sensitivity

SDW CCD irradiation CCDs used for irradiation test : –3 E2V 4210 (2K*512 pixels) –Back thinned –Full frame –The irradiated CCDs were smaller but built with the same technology On each chip different irradiations have been applied: –Three different protons energies : 30, 40, 60MeV –Irradiation dose of 4krad applied in 4 times (flux of 10 7 p.cm -2.s -1 ) –During irradiation CCD were operating with chronograms and bias voltage, 2 at 20°C and 1 at –40°C Parameters measured before and after irradiation : –Dark Current and cosmetics –Gain and operating Point –Quantum efficiency and Pixel Response Non Uniformity –Full Well Capacity and “CTE” CCD Irradiation

SDW Result of irradiation Some performances changed : –Dark current –Cosmetic –CTE No change on : –PRNU and quantum efficiency –Gain and operating point –Full Well capacity Dark current at end of life : (2.5 years, 10 mm shielding, T CCD = -40 °C) 10 e -.pix -1.s -1 (lower than 0.5 e -.pix -1.s -1 at the beginning) CCD Irradiation Pixel with telegraphic noise compared to a normal one

SDW Conclusion The 10 CCDs tested are homogeneous except for: –pixel capacity map (differences between CCDs) –Sensitivity to bias voltage (2 CCDs excluded) According to these results and scientific needs 4 CCDs have been selected (2 for AS channel and 2 for PF channel) With CoRoT characteristics, sensitivity to bias voltages cannot be neglected and must be corrected Conclusion