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 − 9,000 Å
spectral response of the Kepler instrument, zeropoint calibrations for standard photometric systems will
appear as updates on this page over time.
Each Kepler target has a pre-set observing aperture
uploaded to the spacecraft. These apertures are defined in terms of the number of pixels and shape of the
array. The brigter a source, the larger the aperture needed to collect the photons for an optimal detection
of that source. Aperture size is primarily defined by the source's Kepler magnitude (Kp), a
measure of the source intensity as observed through the wide Kepler
- The Kepler Science Team conducted an extensive observing program prior to launch in order
to classify stars in the FOV. The fundamental goal was to develope a list of FGKM dwarf stars as the primary
source list for exoplanet detection. Objects were observed in the SDSS griz bands. This photometry,
along with 2MASS data form the basis of the
Kepler Input Catalog.
- No observations were obtained
from the ground using a pseudo-Kepler band filter. The Project constructed a set of stellar spectral
synthesis models covering a range of effective temperature, gravity and mean abundance, and derived
g,r,i,Kp magnitudes by convolving the filter response functions with the models. Using correlations
between these values, Kepler magnitudes are estimated from the observed SDSS magnitudes using empirical
- Most proposers will adopt the Kp values directly from the KIC. Exceptions are strongly variable stars,
in which a magnitude range should be provided as described on the
Target Checks page, and sources lacking a Kepler
magnitude. For the latter, an approximate esimate of Kp can be derived using the following
exxpression, which is based on the empirical relations used by the Kepler Stellar Classifiction
If only B,V magnitudes are available, the user can convert B,V into SDSS g,r using
the transformation derived by Smith etal (ApJ 123, 2121, 2002, Table 7). The expression below uses this
transformation equation. If SDSS g,r values are available, just use the conditional statements
in line 3 and 4 below.