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