Toward 1% Photometry: End‐to‐End Calibration of Astronomical Telescopes and Detectors

We review the systematic uncertainties that have plagued attempts to obtainhigh precision and high accuracy from ground-based photometric measurementsusing CCDs. We identify two main challenges in breaking through the 1%precision barrier: 1) fully characterizing atmospheric transmission, along theinstrument's line of sight, and 2) properly identifying, measuring and removinginstrumental artifacts. We discuss approximations and limitations inherent inthe present methodology, and we estimate their contributions to systematicphotometric uncertainties. We propose an alternative conceptual scheme for therelative calibration of astronomical apparatus: the availability of calibrateddetectors whose relative spectral sensitivity is known to better than one partin $10^3$ opens up the possibility of in situ relative throughput measurements,normalized to a precision calibrated detector, using a stable but uncalibratednarrowband light source. An implementation scheme is outlined, which exploitsthe availability of tunable lasers to map out the relative wavelength responseof an imaging system, using a flatfield screen and a calibrated referencephotodiode. The merits and limitations of this scheme are discussed. In tandemwith careful measurements of atmospheric transmission, this approach couldpotentially lead to reliable ground-based photometry with fractionaluncertainties below the percent level.Comment: 25 pages, no figures. To be published in Ap