What is the Kepler magnitude?
The “Kepler magnitude” is a magnitude synthesized from Sloan-filter colors observed in the SCP program. For late type stars it has an equivalent wavelength of about 6000 Angstroms (discounting color effects in hot and cool stars). Note that the Kepler magnitude has nothing to do with fluxes observed by the unfiltered Kepler instrumental system. The SCP documentation on the KIC, and the FITS keyword in the light curve headers use the word KEPMAG. MAST has followed this nomenclature. • What is the Spectral Classification Program (SCP)? Early on, the Kepler Project realized the need for homogeneous ground-based observations that would provide information about all the stars in its detector’s field of view. The SCP, a project commissioned to the Harvard-Smithsonian Center for Astrophysics (led by Dr. D. Latham), realized the solution to this need by providing colors from copies of the filters used for the Sloan survey (plus an additional “metallicity” filter). A copy of the SCP plan is ava
The “Kepler magnitude” is not to be confused with satellite flux measurements from the satellite. It is a magnitude computed according to a hierarchial scheme and depends on what pre-existing catalog source is available, SCP, Tycho 2, or photographic photometry, in order of preferred selection. For SCP objects (see next FAQ) the Kepler magnitude is usually synthesized from the Sloan-like g and r magnitudes according to the following prescription: if one defines “color” as g – r, then for color ≤ 0.8 one defines kepmag = 0.8r + 0.2g, while for color > 0.8 one defines kepmag = 0.9r + 0.1g. Empirical measurements for presumed constant stars suggest that the r.m.s. for this quantity is slightly larger 0.02 mags. (R. Gilliland, priv. comm.). except for very faint and bright stars. We note that for the small fraction of objects for which Sloan photometry is not available the Kepler magnitude is taken from photographic catalogs. The errors in these cases are typically +/-0.2 to 0.3 mags. • Wh
