A small CCD photometer dedicated to the detection of extrasolar planets has
been developed and put into operation at Mount Hamilton, California. It si
multaneously monitors 6000 stars brighter than 13th magnitude in its 49 deg
(2) field of view. Observations are conducted all night every clear night o
f the year. A single field is monitored at a cadence of eight images per ho
ur for a period of about 3 months. When the data are folded for the purpose
of discovering low-amplitude transits, transit amplitudes of 1% are readil
y detected. This precision is sufficient to find Jovian-size planets orbiti
ng solar-like stars, which have signal amplitudes from 1% to 2% depending o
n the inflation of the planet's atmosphere and the size of the star. An inv
estigation of possible noise sources indicates that neither star field crow
ding, scintillation noise, nor photon shot noise are the major noise source
s for stars brighter than visual magnitude 11.6.
Over one hundred variable stars have been found in each star field. About 5
0 of these stars are eclipsing binary stars, several with transit amplitude
s of only a few percent. Three stars that showed only primary transits were
examined with high-precision spectroscopy. Two were found to be nearly ide
ntical stars in binary pairs orbiting at double the photometric period. Spe
ctroscopic observations showed the third star to be a high mass ratio singl
e-lined binary. On 1999 November 22 the transit of a planet orbiting HD 209
458 was observed and the predicted amplitude and immersion times were confi
rmed. These observations show that the photometer and the data reduction an
d analysis algorithms have the necessary precision to find companions with
the expected area ratio for Jovian-size planets orbiting solar-like stars.