A vast ground-based programme, in particular to identify real
planets from transit candidates, will be an integral part of the
overall mission, and will be organized should the mission be selected.
Indeed radial velocity observations, as well as ground-based imaging
and photometry observations are required in complement to the space
photometric data, obtained with wide PSFs. The ultra-precise
photometric observations provided by PLATO will also need to be
complemented by ground- and space-based follow-up observations, in
order to complete the characterization of the detected planetary
systems, their central stars, as well as all the stars in the PLATO
programme. One of the main advantages of the approach proposed for
PLATO will be to focus on bright stars, so that this follow-up will be
made easy and efficient.
These follow-up observations will include:
- Radial velocity measurements: by
detecting and measuring the radial velocity modulation due to the
star's wobble as the planet orbits is, these observations will confirm
when needed that the candidate transit was indeed produced by a planet,
and will provide a measurement of the planet mass, taking advantage of
the accurate knowledge of the star's mass derived from seismic
measurement, and the reliable knowledge of the orbital plane
inclination when transits are detected.
- Differential photometry and
spectroscopy: planets around bright stars detected by PLATO will
have a long-lasting legacy for future very precise follow-up
observations to characterize further their nature. In particular,
photometric and spectroscopic observations in the visible and infrared,
taken during primary and secondary eclipses of the planets, will reveal
some details of their atmospheric composition. At the time the first
M-class Cosmic Vision mission will be flown, several very efficient
space- and ground-based facilities will be available for these
purposes, including JWST for infrared photometry and spectroscopy, and
the e-ELT for high resolution spectroscopy in the optical and near IR.
- High resolution spectroscopy:
such observations will be used both in preparation and as follow-up of
PLATO, for deriving all fundamental parameters of stars, such as their
effective temperature, surface gravity, surface chemical composition,
rotation velocity, level of magnetic activity, etc. This will be
essential, in addition to the asteroseismic parameters derived from
PLATO photometry, for refining the modeling of these stars.
- Gaia: the precise
parallaxes derived by Gaia
for all stars observed by PLATO will be used to measure their absolute
luminosities and place them
accurately on the HR diagramme. Also, coupled with
interferometric measurements of stellar angular diameters for the
most nearby of these stars, these precise parallaxes will give us an
independent measurement of the physical diameter of these stars, a very
powerful additional constraint for their modeling.
- Ground-based interferometry: angular
diameters of stars out to several tens of parsecs are within reach of
present and future ground-based interferometers, such as VLTI. In some
cases, these interferometric observations may also be used to directly
detect and characterize giant exoplanets around nearby stars, in
particular those that will have been identified by PLATO.
- Space interferometry:
future interferometric missions can use PLATO results to identify the
best targets for studying terrestrial planets and their atmospheres.
The number of bright and nearby stars monitored by PLATO is high enough
that we can hope to detect a couple of transiting terrestrial
planets around very bright stars, and in any case PLATO will discover a
significant number of giant exoplanets around these nearby stars,
either by the reflected stellar light on the planet atmosphere, or by
the astrometric measurement of the star's reflex motion.