To maximise scientific outputPLATO, the targeted stars must be carefully selected and characterised. This means identifying the optimal observational fields, and examining all possible targets within those fields to create input catalogues. This work is carried out by the Target / Field Characterisation & Selection team.
To maximise the number of targets surveyed, PLATO will continuously monitor two types of stellar fields: "long-duration" fields, and shorter, "step-and-stare" fields. The current observing plan is for two long-duration fields of two-three years each, followed by several step-and-stare fields for up to five months each. Note that this is still under discussion, but since each PLATO FOV will cover ~2000 square degrees, at the end of the mission the surveyed area will easily cover more than 40% of the whole sky.
The bandwidth available for telemetry does not allow us to download complete images of the fields. As a consequence, optimisation of the mission to meet PLATO's scientific goals requires the pre-selection of the most suitable targets for the detection of planets. This is especially true for Earth-size planet detection. The success of the mission is also related to our ability to select fields which maximize the number of optimal targets; namely, dwarf stars of spectral type later than roughly F5, and subgiants for which we can achieve the required photometric S/N. This field selection is closely related to the selection of individual target stars. In other words, a PLATO input catalog (PIC) must be prepared in order to monitor stars appropriate for samples P1-P5, and maximise these samples.
The PIC will help us to assess the nature of the detected transiting bodies: a good knowledge of the central star will help to rule out blends. It will also allow us to get a first estimate of the size of the planet and it will trigger the most appropriate Follow-Up strategy. In summary, the PIC will serve to:
- Select the optimal PLATO Fields.
- Select all the later than F5 dwarf stars and subgiants.
- Characterize target stars as fully as possible, i.e. estimate their temperature, gravity, metallicity, size, variability, atmospheric activity, etc.
- Select the P1-P5 samples.
- Give a first estimate of the size of transiting objects.
- Help to optimise the Follow-Up strategy.
This branch of the PLATO Science Preparation Management features a complex structure, with two of the sub-branches featuring additional levels of organisation. The "Catalogues Analysis" sub-branch (WP131) deals with the analysis and integration of catalogues from external sources, using them to feed into the PIC. In particular, it features strong interaction with the GAIA catalogues. WP131 is structured as shown below (click to enlarge):