GAIA Photometry tasks ===================== E. Hoeg 17 July 2001 CONTENT: Guidelines for the Photometry Working Group (PWG): - GAIA Photometry Tasks from June 29 plan, corrected - actions PWG July 2001 - example of task description: Photometry calibration ========================================================================== ***** GAIA Photometry Tasks from the June 29 plan, ESA/GAIA-SMP/WP. Note however that interstellar extinction has been included at NEW, and that classification should be taken out as separate task in MPs next edition. Also further changes are marked and agreed with Jordi. .............. this part is updated .................................... Objective: To design the photometric system to reach the scientific goals, i.e. to account for the chromatic effects and the astrophysical diagnostics across the broadest range of sources. To study the detection, selection, sampling and patching strategy and their implication in compression and telemetry. To study the data analysis (sky background determination, calibration, accuracies). ......................................................................... * Optimise BBP, including: * chromaticity assessment * astrophysics assessment (ADDED) * number and details of bands, feasibility, tolerances (UPDATED) * sampling/patching strategy (patching ADDED) * angular resolution * accuracy versus crowding, magnitude, etc * Optimise MBP, including: * astrophysics assessment (ADDED) * number and details of bands, feasibility, tolerances (UPDATED) * detection/selection strategy (ADDED) * sampling/patching strategy (patching ADDED) * angular resolution * accuracy versus crowding, magnitude, etc * Assess astrophysical diagnostics of: * stars (wrt redd., lumin., Teff, log g, metals, alpha elem, etc.) * solar system objects * quasars * galaxies * extra-solar planets * diffuse sky background (* Optimise photometric system(s) with respect to a library of stellar spectra SUBSTITUTE BY:) * Compile/identify available synthetic and empirical spectrophotometry and determine spectrophotometric observations to be performed for the optimization of the BBP and MBP * Interstellar extinction determination/mapping NEW We propose to joint some of the items under the concept of the "data analysis": * Data analysis, including: * Study the calibration of photometry (sky background determination, PSF versus aperture photometry, CCD calibration) (ENLARGED) * Evaluate analysis requirements for single and multiple stars as well as extended objects (ENLARGED, the extended objects may be left for the "imaging capabilities" ?) * Assess the colour information in the width of the astrometric image (UPDATED) * Transformation to ground-based systems *** Separate task group: Classification *** Separate task group: Imaging Capabilities - --------------------------------------------------------------------- ***** A list of actions/tasks based on the discussions in ESTEC 27/28 June and Vilnius 3/5 July 2001. It has been updated with Jordi. Only one person is usually listed as responsible, but more persons may be contributing. ***** Actions PWG July 2001 Responsible Report exp'd *** Define photometric system (PS) Observed spectra, overview Brown Synthetic spectra, overview Jordi List of objects to be observed, about 50? Grenon Define set of spectra for PS design Jordi+Grenon 15 Sep Define a test/evaluation plan for PS Jordi 1 Nov Define 2F system Geneve+UB Oct Define 1H system Padova/Vilnius Oct Define one common system, 1C PWG Nov/Dec 2001 Photometric system evaluation (MDM) Vansevicius Photometric system evaluation (NN) Bailer-Jones Ground-based test of filters ? Report on this question Flynn Specification of filters and tolerances Flynn 1 Oct *** Organization Update the letters of interest to Perryman all Collect task descriptions Jordi 15 Aug Collect inputs for the test/evaluation plan Jordi Meeting PWG in Barcelona: Wed. 28 Nov. 9:00 to Fri. 30 Nov noon Meeting PWG in X-town: Wed. 3 July 9:00 to Fri. 5 July 2002 noon *** Special objects Requirements for asteroid photometry Dotto (+Hestroffer?) 15 Oct Emission line stars Grenon 1 Nov Binary and multiple stars Soederhjelm Galaxy photometry Chiosi ? *** Other tasks Transformations between *all* systems Munari Calibration of photometry Hoeg 15 Oct Extinction law determination Knude Data analysis, sampling, imaging (Gilmore) Separate task group: Classification Bailer-Jones Separate task group: Imaging Capabilities who? - ---------------------------------------------------------------- Photometry calibration ====================== A brief task description E. Hoeg 17 July 2001 Principles of GAIA photometric calibration will be outlined in a report expected 15 Oct. 2001. - Calibration of CCD sensitivity variations across the fields of view and with time of the mission, using constant stars. - Calibration of the magnitude scale over the range V=3-23 mag, using the cross-scan spikes of the diffraction images, and based on the calculated diffraction image. - The required sampling as function of magnitude, and the (small) impact on the telemetry rate. - Required sampling of bright stars for the purposes of millimagnitude accuracy, and for the measurement of double stars. Limitations: - CCDs assumed to be non-linear, but otherwise ideal, ie. eg. no CTI, or cosmic damage. - No simulations of actual calibrations. - No discussion of possible other supplementary methods of calibration. -----------------------------------------------------------------