Untitled - Laboratoire d'Astrophysique de l'Observatoire de Grenoble

With this new tool at hands, searches for low mass companions around A-F type stars are performed since
2003, in a collaboration between the LAOG and Geneva Observatory teams: radial velocity observations are
obtained with ELODIE (Northern hemisphere) and HARPS (Southern hemisphere). Studies based on such
observations lead to the conclusion that this new RV measurement method can be applied to A-F type stars in
the frame of planet/BD searches (Galland et al., 2005a, A&A, submitted): with ELODIE, the planetary domain
can be reached for A type Main-Sequence stars with v sin i up to 100 km/s and orbital periods less than 10
days. For late A type stars, the accessible range is v sin i up to 80 km/s and orbital periods up to 100 days.
Planetary masses can be detected for all F type Main-Sequence stars. With HARPS, RV uncertainties are lower
(by a factor of 5 to 7), and the planetary domain is accessible for all A and F type stars, even with large v sin i.
100 stars have now been observed with ELODIE at least twice, and 65 at least four times, leading to the
detection of RV variations in 17 cases. Seven of them have a probable planetary origin. A first planet, around
an F6V star has already been characterized (Galland et al., 2005b, A&A, submitted), see Fig. 6.12.
Complementary adaptive optics imaging observations of the same sample has been started with PUE’O at
CFHT (Northern hemisphere), in order to search for companions with large periods, and to test the correlation
between binarity and the presence and properties of planets found by radial velocity.
In 2006, we plan to increase (up to 300 objects) the size of our A-F Main Sequence stars sample for radial
velocity observations with SOPHIE. The sample of stars observed with HARPS will also be increased to 300
objects.
6.5.3 Low-mass companions and planets in nearby associations
The field of extrasolar planet detection and characterization has been limited, so far, to the domain of indirect
detection measurements, either by radial velocity or photometric transit surveys. However, this exploration is
presently intrinsically limited to the close circumstellar environment, typically within ∼4 AU of the central star.
With the development of high contrast and high angular resolution instrumentation, the situation is changing
and the exploration of planets with large semi-major axes becomes achievable.
Figure 6.13: Offset positions in terms of separation (Top) and position angle (Bottom) of 2M1207 b from A,
on 27 April 2004, 5 February 2005 and 31 March 2005 (full circles with uncertainties). The expected variation
of offset positions, if b is a background object, is shown (solid line), based on a distance of 70 pc, a proper
motion of (µα, µδ) = (−78, −24) mas yr-1 for A and the initial offset position of b from A. Also reported are the
associated uncertainties (shaded region) and the different contributions (distance, proper motion, initial offset
position) in dotted lines.
Young and nearby open clusters are ideal targets for such programmes since lower mass objects such as
brown dwarfs and giant planets are brighter when they are young and can thus be more easily detected. It is
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