Report - School of Physics

stars, or large telescopes providing deep exposures to increase the number of targets
monitored. The current transit search surveys therefore group into two classes,
using small or larger (> 70 cm) telescopes. Support for the implicit hypothesis that
the orbits of planetary systems are randomly distributed in the Galaxy comes from
the fact that stellar rotation axes are themselves randomly distributed (obtained
by v sin i distributions, and independently confirmed by magnetic-field orientation
studies).
The wide-angle survey teams follow STARE and Vulcan in using small (10 cm) wideangle
(10 ◦ ) CCD cameras with a pixel size of order 1 arcsec or larger, sacrificing
angular resolution to expand the field of view. The faint limit, at V ∼ 12−13 reaches
to d ∼ 300 − 500 pc, comparable to the disk scale height, so that target fields cover
the entire sky, which may contain some 1000 hot transiting Jupiters to this limit
(Horne, 2003). The deep surveys use (mosaic) cameras on 1–4 m telescopes, reaching
V ∼ 19 − 21 and d ∼ 4 − 5 kpc, so that Galactic plane and open cluster fields are
primary targets. Horne (2003) predicts up to 200 hot Jupiters per month being
discovered by ongoing ground transit surveys in the future (perhaps by the year
2010).
The size of planets detectable from transits with ground-based searches is limited
by the Earth’s atmosphere (Section 1.3). The photometric precision of typical
lightcurves is a little under 1%, which corresponds to about Jupiter-sized planets
for solar-type stars. Ground-based surveys are further limited in their time coverage
of potential transiting planets by daytime and bad weather periods. The small
number of transit surveys operating over more than a few months so far, and the
lack of continuous observations on the target fields, are the most likely reason why
only few planets have been discovered through transit detections so far, somewhat
in contrast with the large number of surveys listed in Table 2. The situation could
be significantly improved by ground-based networks of telescopes spanning a range
of longitudes to ensure continuous observational coverage of target fields.
The discovery of a temporary dimming of the stellar lightcurve alone is not sufficient
to secure the detection of a transiting planet. Grazing eclipsing binary stars,
background binaries, brown dwarfs and stellar spots can cause lightcurves similar to
transiting planets. Follow-up measurements, in particular radial velocity measurements,
and determination of stellar parameters, therefore play an important role in
the detection of planetary transits to exclude other causes of light dimming.
Up to now, five confirmed planets have been discovered by ground-based transit
searches: four using the 1.3 m OGLE telescope, and one with a 10 cm ground-based
system (TrES-1). The OGLE experiment (Optical Gravitational Lensing Experiment)
uses the 1.3 m Warsaw Telescope at Las Campanas Observatory, Chile. It is
equipped with a mosaic of 8 CCDs of 2k×4k each, giving a field of view of 35 arcmin
square with 0.26 arcsec/pixel. The telescope is primarily used to search for
microlensing events by viewing near the Galactic centre, but significant time (more
than three months) was made available for transit searches. It has monitored some
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