......................................................................... Description of the GAIA Photometry Tasks based on the discussions in ESTEC 27/28 June and Vilnius 3/5 July 2001 (version 1.0, Sep 3, 2001) Please note the meeting calender of PWG given at the end! ......................................................................... 1- Design of the Photometric System (PS) ======================================== The PS will be designed to account for the scientific goals of GAIA as described in the "Concept and Technology Study Report". The concept "PS" includes the filters (BBP & MBP), the CCDs and the focal plane (disposal of the filters and CCDs, size of samples and patches). The PS (BBP) has to allow the chromaticity effects correction in AF (a must to achieve the aimed astrometric precision). The PS (BBP & MBP) has to allow astrophysical diagnostics of the observed sources down to the limiting G magnitude. GAIA will observe stars (single, multiple), BD, solar system objects, QSO, galaxies, ... The PS has to account for all of them. However, the PS will be optimised for single stars, with special care of those type of stars crucial for the scientific goals (let us call them key photometric targets, KPT). The performance of the PS for other type of stars, multiple systems, solar system objects, etc will be studied and changes in the PS may be introduced accordingly provided that they do not degrade the performance for the KPT. The PS design has to be ready by about mid-2005. 1.1 Identification of the set of KPT (coordinator: M. Grenon) The aim is to provide a list of the KPT and their relevant parameters (Teff, log g, [M/H], [alpha/H], apparent magnitude (or distance), anomalies, peculiarities, ....). [My comment: this is the most urgent task to develop] 1.2 Identification of the existing spectra The aim is to identify the nowadays existing spectra (empirical and synthetic) relevant for the GAIA mission. Priority should be given to identify the existing spectra for the KPT. 1.2.1 Observed spectra, overview (coordinator: A. Brown) 1.2.2 Synthetic spectra, overview (coordinator: C. Jordi) [My comment: Chris, could you provide a report or a list of the empirical spectra you already compiled ?] [My comment: F. Castelli agreed on computing model atmospheres for different [alpha/H] ratios according to our needs] 1.3 Definition of the set of spectra for the KPT (coordinator: M. Grenon+C. Jordi) The goal is to identify (from 1.2.1 and 1.2.2) those spectra representative of the KPT and what KPT lack of spectra now. The design/optimisation of the PS will be based on those representative spectra. 1.4 Spectra acquisition (coordinator: A. Brown) The nowadays available empirical spectra do not cover all the type of sources that GAIA will observe. The atmospheric stellar models do not accurately describe the reality, in some cases. The acquisition of empirical spectra for ALL kind of sources means a huge amount of observing effort not feasible for the PS definition schedule. Thus, the PS definition will be mainly based on synthetic spectra with constraints by the empirical ones. The observational efforts will be focused on those KPT with unaccurate or lacking spectra (empirical/synthetic). For them observing campaigns would start as soon as possible. [My comment: the start of this task is quite urgent since getting observing campaigns takes at least half a year (applications, decisions, ...) as pointed by Anthony. We still have to add time for the reduction of the data. Deadlines for applications to CAHA and Canary's group of telescopes are September 15th and October 1st, respectively. Colleagues of the Tartu Observatory can perform spectrophotometry for GAIA, as they said in Vilnius] 1.5 Design of the filters and focal plane disposal The objective is to improve the existing proposals (or, eventually to make new ones) on the basis on the above items. This includes not only the filters themselves, but also the exposure time devoted to each one. 1.5.1 Progress on the 3G system (coordinator: V. Vansevicius) 1.5.2 Progress on the 2A system (coordinator: U. Munari) 1.5.3 Progress on the 1F system (coordinator: M. Grenon) (1.5.1 and 1.5.2: M. Fiorucci and V. Vansevicius informed us that both teams are ready to integrate the respective PS into a 1H system by next October) The convergence of the present proposals within the next 6-12 months is aimed to concentrate the efforts of the different teams in only one common system. [My comment: It would also simplify the tasks of other WGs (like simulator, imaging capabilities, ...). So, the convergence is desired. However, to reach the convergence at that time is not crucial. The most important is that all teams be convinced of the common system. The PS design has to be frozen at mid-2005. Until then, the PS design can and must benefit from new observed spectra, authomated method of parameterisation, results from other working groups [simulation, data processing prototype, radial velocity spectrometer, etc] and so on. 1.6 PS test/evaluation plan (coordinator: C. Jordi) Design the plan for evaluating the performance of a given PS for each KPT, i.e. what parameters are available from the astrometric instruments and/or by the radial velocity spectrometer and/or from ground and/or other missions, what parameters have to be derived and with which precision, etc. Provide guidelines for the evaluation methods. 1.6.1 Evaluation by minimum distance method (coordinator: V. Vansevicius) 1.6.2 Evaluation by neural networks (coordinator: C. Bailer-Jones) 1.6.3 Evaluation by other methods ???? The PS test by photometric observations from ground was rejected given the schedule for the PS, among other reasons (a report by Ch. Flynn is expected on this subject). [My comment: Please, remember that it was agreed in Vilnius that I collect inputs for everybody on this subject until October 15th.] 1.7 Sampling/patching strategy (coordinator: E. Hoeg) To reconsider the present sampling/patching strategy (as function of magnitude, multiplicity, ... ), yielding to the optimisation of the size of the samples and patches. The budget of the telemetry, the angular resolution and crowding areas have to be considered. 1.8 Assess astrophysical diagnostics of non-KPT To study the performances of the PS for non-KPT and to propose modifications accordingly. The impact of those changes for the astrophysical parameterisation of the KPTs will be evaluated and implementation or not will be decided. Some of the tasks can run in parallel, while others need the result of a previous one. Of course, 1.5-1.8 will iterate to reach an optimal system for GAIA. The item 1.4 will provide new data for that tasks. 2- Technical implementation (coordinator: Ch. Flynn) =========================== To study the feasibility of the designed PS, the manufacturing constraints, etc. 2.1 Realistic filter transmission curves 2.2 Permitted tolerances on filters 2.3 WFE+PSF examples 3- Data analysis ================ This item includes all the steps from the actual GAIA observations to the derivation of calibrated fluxes. The astrophysical parameters determination is done by the Classification Working Group. 3.1 Calibration (coordinator: E. Hoeg) 3.1.1 Calibration of CCD sensitivity variations across the fields of view and with time of the mission, using constant stars. 3.1.2 Calibration of the magnitude scale down to the G limiting magnitude 3.1.4 Sky background determination 3.1.3 Attainable precisions (epoch and end-of-mission photometries) 3.2 Interstellar extinction determination (coordinator: J. Knude) To study the determination of the reddening and the extinction law, from GAIA data and other sources. 3.3 Transformations to ground-based systems (coordinator: U. Munari) [My comment: this point was not really discussed neither in ESTEC nor in Vilnius. From my point of view is not an urgent task] Next meetings ============= A next PWG workshop was agreed to be held in Barcelona at the end of November to analyse the progress since ESTEC & Vilnius meetings, to agree on the subjects needed and to schedule the next tasks. Another PWG workshop is scheduled for July 2002. Thus the calender: Meeting PWG in Barcelona: Wed. 28 Nov. 9:00 to Fri. 30 Nov. 2001 noon Meeting PWG in X-town: Wed. 3 July 9:00 to Fri. 5 July 2002 noon ------------------------===========================--------------------