  MAIA, the Mercator Advanced Imager for Asteroseismology, is a new
fast-cadence 3-channel photometric instrument. It is installed on the 1.2-m
Mercator telescope at the Roque de Los Muchachos Observatory in La Palma,
Spain. MAIA comprises 3 cameras that simultaneously observe the same 9.4 x 14.1
arcmin field in 3 different colour bands (u, g and r). Each camera is based on
a very large frame-transfer detector (CCD42-C0) of 2kx6k pixels, specially
designed for rapid time-series photometry. These CCDs were originally developed
by e2v for ESA's cancelled Eddington space mission and are now on permanent
loan to the Institute of Astronomy of the KU Leuven, Belgium. The acquisition
system of MAIA uses a single ARC GEN-III controller, custom programmed to allow
differing exposure times for each of the three CCDs. Predefined sequences
synchronize each read-out with the shortest integration time. Detectors that
are not read-out at the end of an exposure continue integrating and can be
read-out in one of the subsequent cycles. This read method takes full advantage
of the frame-transfer functionality of the CCD42-C0 detectors and allows
optimisation of the exposure times for each wavelength band. This then gives a
similar exposure depth in each of the 3 arms despite the fact that the UV
channel typically sees much less flux. We present the CCD42-C0 detectors, their
characterisation, including a thorough analysis of their non-linearity, and the
MAIA data-acquisition system.
