PHOTOMETRIC ZEROPOINT

Kepler's primary mission of precision transit photometry requires differential photometric ability only. Absolute photometric calibration is not essential to the success of the exoplanet mission. A community-led program is underway to flux calibrate the Kepler instrument in-flight for the GO program. Although caveats are created by the broad 4,300−9,000Å spectral response of the Kepler instrument, zeropoint calibrations for standard photometric systems will appear as updates on this page over time.

APPROXIMATE KEPLER MAGNITUDES

Due to downlink and data storage limitations, only a subset of detector pixels are recorded during science observations. Each Kepler target has a defined pixel aperture uploaded to the spacecraft. The brigter a source, the larger the aperture needed to collect the number of photons that meet program requirements. Aperture size is defined by Kepler magnitude which is estimated based upon the Tycho-2 B and V magnitudes using the following scheme:

The Kepler magnitude definition will be detailed further in a paper describing the Kepler Stellar Classification Program once it has been refereed and accepted for journal publication. Kepler magnitudes derived using this rule are presented below for a sample of main-sequence stars. The offset, (m_kep − V) can be applied to stars whose apparent Johnson V magnitude is known.

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