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MAIN CONTRIBUTOR NOISES. SPECIFICATION PHILOSOPHY FOR NOISE ASPECTS. For the random noises, the equipments are specified : to have the photon noise as the predominant noise for the Seismology program, and as a result, all other random noises must be negligible for this program
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SPECIFICATION PHILOSOPHY FOR NOISE ASPECTS • For the random noises, the equipments are specified : • to have the photon noise as the predominant noise for the Seismology program, • and as a result, all other random noises must be negligible for this program (1/10 of the photon noise) • the Seismology program gives so the technical specifications, and the Exoplanet program try to use it with a minimum of additional specifications. • For the periodic noises in the frequency range of 0.1 to 10 mHz, • the on board equipments which impact on periodic noises are specified to have spectrum lines amplitude less than 50 ppm, and additional parameters like temperatures are added in the telemetry for ground based corrections, • and any spectrum line must be less than 2 ppm after ground based corrections for the Seismology program, • it is easy to correct the Exoplanets data on ground by the fact that several thousand of stars are observed simultaneously . • The drifts of the parameters are corrected on ground.
NOISE BUDGET FOR EXOPLANETS PROGRAM With chromatic informations, on the blue channel, in one hour :
CONCLUSIONS FOR THE EXOPLANET PROGRAM • In white ligth, the major contributors are : • the photon noise, • the noise due to zodiacal ligth, strayligth and dark current, • the detector and electronics readout noise. • In colors, the major contributors are : • the pointing noise, • the noise due to thermo-mechanical deformations of the telescope.
PERIODIC NOISE BUDGET OF THE SEISMOLOGY PROGRAM This budget gives the performance without any software corrections
HOW TO REACH THE REQUIRED PERFORMANCE • EXAMPLE : GAIN VARIATIONS OF THE READOUT ELECTRONIC "BCC" BOX • THE TEMPERATURE COEFFICIENT (CT) OF THE GAIN IS SPECIFIED AT 100 ppm/°C, • THE TEMPERATURE OF THE ELECTRONIC BOX IS SPECIFIED AT 0.4°C pk pk, • THE CT MUST BE MEASURED WITH A PRECISION OF 3% (3 ppm/°C), • THE TEMPERATURE OF THE ELECTRONIC BOX MUST BE MEASURED WITH A PRECISION OF 0.5% (0.02°C) AND THE VALUE DOWNLOADED, • so : • the spectrum line amplitude without correction is : 100 x 0.4 / 2 = 20 ppm, • it is necesary to have a correction factor of 10 to obtain the specification of 2 ppm • and the possible factor of correction is : 100 / (3 + 0.5) = 28
CONCLUSIONS FOR THE MOST SENSITIVE EQUIPMENTS • THE SCIENTIFIC REQUIREMENT LEAD TO TECHNICAL SPECIFICATIONS OUT OF • THE LIMIT OF TECHNOLOGY, THE SCIENTIFIC REQUIREMENTS ARE REACHED ONLY AFTER GROUND BASED CORRECTIONS : • IT IS NECESSARY TO HAVE VERY PRECISE CALIBRATIONS OF THE CRITICAL PARAMETERS OF THE EQUIPMENTS, • IT IS NECESSARY TO MEASURE ADDITIONAL PARAMETERS (LIKE TEMPERATURES, VOLTAGES) OF THE CRITICAL EQUIPMENTS • IT IS NECESSARY TO DOWNLOAD THESE VALUES, • AND TO MAKE AFTER THE APPROPRIATE CORRECTIONS.