Report - School of Physics

chemical composition of the primordial molecular cloud. To add new constraints
to the link between star chemical composition and frequency (or properties) of exoplanets,
two programmes are being carried out. The first is a search for exo-planets
orbiting solar-type stars with notable metal deficiency (for most of them [Fe/H]
between −0.5 and −1.0). Among the existing detections of exo-planets only two or
three have been found with metallicity in that range. The aim is to estimate the
frequency of exo-planets in that domain of metallicity and, if possible, to compare
their characteristics (masses, orbits) to planets orbiting metal-rich stars;
(e) the second ‘abundance-related’ programme aims at exploring the link between
stellar metallicity and properties of exo-planets. Visual binaries with solar-type stars
of almost identical magnitudes have been selected. For those including giant planets
a detailed chemical analysis will be done for both stellar components to search for
possible differences in their chemical compositions;
(f) follow-up radial velocity measurements for stars with planetary transits detected
by COROT will be made with HARPS (where the photometric transit provides an
estimate of the radius of the transiting planet as well as the orbital period and
phase). Complementary ground-based spectroscopic measurements with HARPS
will constrain the planetary mass and thus the planet mean density. The main
scientific return for the planetary programme of the COROT mission will come
from this combination of photometric and radial velocity data.
2.1.2 Transit Searches
The transit method aims at detecting the dimming of the stellar light by occultation
due to an orbiting planet. Transit experiments offer a number of very important contributions:
(i) searches can be conducted over wide fields over long periods (5 years
or more), and are therefore potentially efficient at detecting previously unknown
systems; (ii) from the ground they are able to detect massive transiting planets,
especially the ‘hot Jupiters’, while from space planets down to Earth-mass or below
can be detected; (iii) spectroscopy during the planet transit can yield physical
diagnostics of the transiting planets. A summary of ongoing or planned transit experiments
is given in Table 2; see also the recent review by Horne (2003). Again,
Table 5 summarises predictions of the numbers of planets that might be detected
by this method out to 2008–12.
Transit measurements can only detect planets with a favourable orientation of their
orbital plane, implying that only a small fraction of planets can ever be detected
or monitored using this technique. In particular a nearby census can only reveal a
small fraction of existing systems. The probability of viewing a planetary system
edge-on depends on the distance of the planet to the central star. For close-in orbits
it is about 10%, decreasing for more distant planets. Transit searches therefore
try to maximise the number of stars they can observe simultaneously. This can be
reached by either small telescopes with wide field of view observing relatively bright
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