ARI contributions to Gaia

Contributions to Gaia management

Gaia Science Team membership:
Consulting ESA on all scientific aspects of Gaia (Ulrich Bastian 2002-2007, Eva Grebel since 2007). The Gaia Science Team is composed of independent scientists with specific scientific and/or technical expertise relevant to Gaia.

DPAC Executive membership:
Leading the Gaia Data Reduction and Analysis Consortium, DPAC (Ulrich Bastian, since 2004). DPAC is the Gaia Data Processing and Analysis Consortium, ESA's official science partner in the Gaia project.

DPAC Project Office:
Supporting the DPAC Executive, controlling the consortium (NN, to start mid 2008). The DPAC Project Office will be located at ESAC (Villafranca, Spain). It will be staffed from several countries contributing to Gaia/DPAC. One member will come from ARI.

CU3 Leadership:
Leading and managing Coordination Unit 3, "Core Processing", one of DPAC's eight subdivisions (Ulrich Bastian, since 2006). CU3 has 73 members, mostly astronomers and software engineers, scattered all over Europe, plus a small group in Brasil. The task of CU3 is to organise and implement the data processing chain all the way from receiving Gaia's raw telemetry down to the core astrometric solution.

First Look Leadership:
Quickly assessing payload and data health, and scientific data quality (Stefan Jordan). First Look (FL) is one of the major building blocks of CU3. Most of the work for this task is done at ARI, but software modules from many other DPAC groups will have to be included into the overall system. The following four FL functions are specifically located at ARI.

First-Look processing framework:
Developing the software needed to run the various FL processes (Stefan Jordan, Michael Biermann, Dirk Dorsch, Wolfgang Löffler), in collaboration with the Gaia Science Operations Centre at ESAC Villafranca, Spain)

One-Day Astrometric Solution, ODAS:
Calibrating Gaia quickly and continuously (Hans Bernstein, Sonja Hirte, Stefan Jordan, Dirk Dorsch). A high-precision astrometric calibration of both the instrument and the observed sky is needed to make an exploration into the data quality at microarcsec level possible. A method to do this on a daily basis is being implemented.

FL Monitor and FL Evaluator:
Diagnosing and assessing the health and quality of the Gaia data (Michael Biermann, Stefan Jordan, Wolfgang Löffler). The FL Monitor software compiles a vast variety of statistics and diagnostics, both from the pre-processed raw data of Gaia and from the results of the ODAS. The FL Evaluator software aids the FL Scientist to inspect and judge the vast Monitor outputs, to verify the proper working of the spacecraft and instruments.

First-Look Scientist:
Executing the First Look (Michael Biermann, NN). The First-Look Scientist will be the human part of the FL Evaluator. He will do the daily assessment of the FL results and decide whether operational consequences should be proposed to the Mission Operations Centre and/or whether special quick investigations into the data be proposed to other DPAC groups.

Auxiliary data management:
Coordinating the acquisition of input data for CU3 that are not produced by Gaia itself (Ulrich Bastian). The astrometric reduction of the Gaia observations needs a broad variety of external input data, including e.g. ground-based astronomical observations of reference and calibration stars as well as industry-derived design and laboratory data, and orbit determination results from ESOC. The following four sets of data are specifically taken care of by ARI.

Initial calibration data:
Planning and surveying the influx of laboratory data from industry and ESA before launch, and of early in-flight calibrations from the commissioning phase after launch (Michael Biermann)

Orbit and time correlation:
Planning and surveying the delivery of orbit determination results and timing information from ESOC (Michael Biermann)

Ecliptic-poles catalogue:
Preparing an important tool for the initial calibration and verification of the Gaia spacecraft and operations (Martin Altmann, Ulrich Bastian). The ecliptic poles are the only sky areas observable by Gaia at any time. Two carefully prepared sky inventories of the order of a square degree will be used both in the commissioning phase after launch and in cases of contingency.

Ground-based optical tracking:
Organizing a 5-year observing campaign to reach the tremendous orbit determination precision needed for Gaia (Martin Altmann, Ulrich Bastian). Gaia's astrometry reduction needs to know the velocity of the spacecraft with respect to the solar-system barycentre to a precision of 0.7 mm/s at all times. An orbit determination to this precision is almost impossible to reach with the usual tracking methods. But using daily astrometric observations of the Gaia spacecraft from the ground will do the job.

Mixed core processing contributions:
Providing conventions and interface softwares to DPAC (Helmut Lenhardt, Ulrich Bastian). Topics covered include softwares for barycentric velocity corrections, for light-travel time corrections, for local coordinates on the sky etc., as well as precise definitions of reference systems and datation schemes to be used throughout the consortium, and the setting of conventional values of Nature's constants.

Public outreach:
Providing public talks, introductory presentations at astronomical institutes, Wikipedia articles, German info materials etc. (Ulrich Bastian, Stefan Jordan, Wilfried Hofmann)

Astrometric binaries:
Deriving "stochastic" astrometric solutions for "nasty" stars (Hans Bernstein). Without doubt there will be a few stars among the 1 billion to be observed by Gaia that will neither move on a single-star straight line through our Galaxy, nor on a double- or multiple-star orbit - if only apparently. This workpackage will attempt to make at least some statistical sense out of their observations.

Off the baseline of DPAC:
Searching for alternative global astrometric solution methods (Hans Bernstein, Alex Bombrun, Stefan Jordan). It would be highly advantageous to have a different, independent method, to either complement or improve or verify DPAC's baseline method (which is called "AGIS", Astrometric Global Iterative Solution).

Gaia Results Database:
Delivering, documenting, presenting the Gaia scientific results to the community. This topic will be treated by a specific DPAC coordination unit, CU9, to be created after a dedicated announcement of opportunity expected from ESA. The true task will be to make the Gaia results as easily understandable, as comfortably accessible and as widely usable as possible.

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