1.2.2 Structure

DPAC is composed of nine Coordination Units (the CUs), each in charge of a specific aspect of the data processing, with clearly defined responsibilities and interfaces. Each CU is composed of several dozen members, spread around various (academic) institutes in various, mostly European countries (see https://www.cosmos.esa.int/web/gaia/dpac/institutes). The details of the various DPAC data processing systems are provided in Gaia Collaboration et al. (2016). In Table 1.3, the DPAC Coordination Units are listed by number, together with the data processing (sub)systems that the CU in question is responsible for. Although this is not of direct interest to the reader of this documentation, the CUs are sometimes referred to in the text and this table provides the means to understand the context of such references.

The actual processing of the Gaia data takes place at six data-processing centres (DPCs) in Europe, located at / in ESAC (DPCE, Section 1.3.4), Barcelona (DPCB, Section 1.3.4), CNES Toulouse (DPCC, Section 1.3.4), the Institute of Astronomy (IoA) in Cambridge (DPCI, Section 1.3.4), Geneva (DPCG, Section 1.3.4), and Turin (DPCT, Section 1.3.4). More details are provided in Gaia Collaboration et al. (2016).

DPAC is managed by an executive body (the DPAC Executive, DPACE) consisting of a chair, a deputy chair, and the scientific leaders of the coordination units (Section 1.2.2) plus representatives from the DPCC and DPCE data-processing centres. See https://www.cosmos.esa.int/web/gaia/gaia-dpac-executive for the composition of DPACE.

The DPAC Executive (Section 1.2.2) is supported in its tasks by the DPAC project office (PO). See Gaia Collaboration et al. (2016) and https://www.cosmos.esa.int/web/gaia/project-office for more details.

A Payload Experts group is dedicated to (discussing the findings of the) monitoring of the health of the Gaia payload, which is routinely done by First Look (Section 2.5.2), and is formed primarily by DPAC members who are directly involved with processing the Gaia’raw’ data stream on a daily or semi-daily basis (Section 1.2.3), as well as members of the Project Office (Section 1.2.2), Gaia’s Mission Manager and Project Scientist (see https://www.cosmos.esa.int/web/gaia/esa-team), and members of ESA’s Science Operations Centre (Section 1.1.5). During Gaia’s Commissioning phase, the Payload Experts played a critical and intensive role in verifying the operational health of the payload, assisting in the adjustment of payload calibration and configuration parameters (such as the spin rate and focussing), and in the early identification of various instrument anomalies and investigation into their root causes, including a variable, and higher-than-expected, background and the periodic variation of Gaia’s basic angle. During the routine science operations phase, the Payload Experts continue to monitor the instrument status (such as optical throughput and quality) and of various, known instrument issues that (may) impact the quality of the science data. The Payload Experts propose adjustments in the payload operating parameters as well as signal the need for decontamination and refocussing campaigns. The description of the current instrument status in Section 1.3.3 gives some concrete examples of their efforts.