First Observation Field - PLATO

First OBSERVATION Field

The Science Working Team has selected the first PLATO Long-duration Observation phase (LOP) field. The name of the field is LOPS2 and its centre coordinates in the equatorial, galactic, and ecliptic reference frames are given in the Table below.

The LOPS2 sky area is given by the PLATO field of view,​​​​​​ which covers 49° x 49° with the geometry represented in Figure 1. The number of “normal” cameras covering a given line of sight is color-coded. The four blue shades, from dark to light, map regions observed with 24, 18, 12, 6 cameras (corresponding to four, three, two, and one group(s) of six co-pointing telescopes each, respectively). The pink circle marks the contour of the |β| > 63° technical requirement for the centre of the LOP fields (“allowed region”), and the green circle represents the |β| > 70° condition for the centres of fields that are independent on the initial rotation angle of the spacecraft. The yellow circle represents the TESS continuous viewing zone, with the Large Magellanic Cloud indicated as well in red.

The PLATO Input Catalogue for this field contains more than 9000 dwarf and subgiant stars of spectral types from F5 to K7 with m_V < 11 that will be observed with a random noise lower than 50 ppm in one hour, and more than 159,000 dwarf and subgiant stars of spectral types from F5 to K7 with m_V < 13. These values fully meet the science requirements for the PLATO stellar samples for a single field.

Selection process

The first condition that LOP fields must satisfy is the constraint of the satellite orientation with respect to the Sun, which determines that only fields with centres at ecliptic latitutes |β| > 63° can be observed for more than one year, as required for PLATO. Within these two "allowed areas" in the Northern and Southern galactic hemispheres, the refinement of the field selection was driven by scientific optimisation criteria. A metric defined by the Science Working Team was applied that included maximising the stellar counts of the PLATO samples, evaluating the stellar characteristics, the contamination levels, false positive probability, facilities for ground-based radial-velocity follow-up, and synergies with other missions. More details are described in the article "The PLATO field selection process. I. Identification and content of the long pointing fields", by Nascimbeni et al. (2022, A&A 658, A31). In that work, the recommended positions of the baseline LOP fields in the North and the South, respectively LOPN1 and LOPS1, were provided. Since the publication of the paper, the position of the recommended LOP field in the South has moved to LOPS2, to ensure that the selected field is independent of the initial spacecraft rotation angle after launch.

The LOPS2 and LOPN1 fields are very similar for PLATO's core science when comparing their stellar content, characteristics, and selection metric. The Science Working Team has chosen LOPS2 for the first observation field because, at this time, the ground-based facilities available in the Southern hemisphere provide the best capabilities for the mass determination of Earth-size planets in the habitable zone of Sun like stars, which are main targets for PLATO.

Duration of the first observation

Since the nominal operational phase duration of PLATO was established as 4 years, its baseline observing strategy assumes two LOP fields observed for two years each. However, this is conditional to the analysis of the mission performance in the first year of operations. This analysis may lead to a decision to extend the observation duration of the LOPS2 from two to three or even four years to maximise the probability of the detection of Earth-size planets with ~1 year orbital periods, leaving a second long pointing to a potential extension of the PLATO operations. The PLATO spacecraft has been designed to perform scientific operations for at least 8.5 years.