  High-precision spectrophotometry is highly desirable in detecting and
characterizing close-in extrasolar planets to learn about their makeup and
temperature. For such a goal, a modest-size telescope with a simple
low-resolution spectroscopic instrument is potentially as good or better than a
complex general purpose spectrograph since calibration and removal of
systematic errors is expected to dominate. We use a transmission grating placed
in front of an imaging CCD camera on Steward Observatory's Kuiper 1.5 m
telescope to provide a high signal-to-noise, low dispersion visible spectrum of
the star HD 209458. We attempt to detect the reflected light signal from the
extra-solar planet HD 209458b by differencing the signal just before and after
secondary occultation. We present a simple data reduction method and explore
the limits of ground based low-dispersion spectrophotometry with a diffraction
grating. Reflected light detection levels of 0.1% are achievable for
5000-7000A, too coarse for useful limits on ESPs but potentially useful for
determining spectra of short-period binary systems with large (Delta m_vis=6)
brightness ratios. Limits on the precison are set by variations in atmospheric
seeing in the low-resolution spectrum. Calibration of this effect can be
carried out by measurement of atmospheric parameters from the observations
themselves, which may allow the precision to be limited by the noise due to
photon statistics and atmospheric scintillation effects.
