Report - School of Physics

time will be required. Existing transit measurement facilities and amateur networks
could contribute, although some new dedicated provision for follow-up is probably
needed, in particular enlarging networks in longitude to significantly improve the
efficiency of ground-based transit observations.
Radial velocity follow-up will be needed for all high-mass candidates, of which Gaia
will generate a very large number. Thousands of the more massive planets could be
observed by ground-based radial velocity instruments, assisting the determination of
multiple planets, relative orbital inclinations, etc. ESO could consider a coordinated
large-scale follow-up of such radial velocity observations, and whether additional
facilities will be needed. An assessment of telescope time/aperture needed for these
projects has not been made — probably a combination of existing facilities and
larger dedicated instruments would be needed.
4.2.2 Low-Mass Planets
Low-mass (of order 1 M ⊕ ) planets will hopefully be detected by Kepler and Eddington,
perhaps in moderately large numbers (some hundreds).
They will typically be too low-amplitude for ground-based photometric follow-up,
which in any case are unlikely to improve on the S/N of weak transit events detected
by Kepler or Eddington – these missions will have years of lightcurves on a star,
and if the signal is still weak after phasing and adding all data, it will be difficult
to improve from the ground in a reasonable time. This is a potential problem,
since such follow-up observations will be needed: (i) to confirm the reality of the
lower S/N detections; (ii) to search for planetary periods for candidates for which
only one transit is detected; (iii) to confirm candidate detections for which two or
possibly more transits were detected (since periods and transit times are known,
ground-based follow-up may be more feasible); (iv) to search for period changes due
to planetary moons etc.; (v) to characterise the transit systems in terms of chemical
abundances. Probably the only prospect is follow up with HST and/or JWST (see
Section 2.2.1) for transits, and possibly SIM for astrometry, although many of the
transit candidates will be too distant even for these instruments.
Radial velocity measurements are again needed in principle to supplement the orbital
information. Improvements in radial velocity precision for transits may be achieved
by the stacking of repeated observations at the known planet period, as described
in Section 1.3. If Eddington is approved (or for the study of Kepler candidates), the
development of new telescope facilities should be considered, such as a high-precision
spectrograph (like HARPS) based on an 8-m (or larger) telescope. Given the low
expected surface density of accessible candidates, it is unlikely that a multi-object
instrument would be effective and so a highly-optimised single object instrument
offering a precision of ∼ 1 m s −1 would be preferred. The HARPS detection of a
14 M ⊕ planet demonstrates that it may be possible to characterise all the exo-planets
detected by COROT (massive Earths with short periods) in this way.
62