Gaia Photometric Data Analysis Overview

Transcription

1 Gaia Photometric Data Analysis Overview Gaia photometric system Paola Marrese Sterrewacht Leiden Role of photometry in overall Gaia data analysis Photometric data analysis goals Tasks and links to other data processing groups Organisation of the PDA effort Examples of exploratory studies Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.1/30

2 Astro focal plane array Total field: Size cm 170 CCDs CCDs: pixels Sky mapper: detects all objects to 20 mag rejects cosmic-ray events Star motion Astrometric field: pixel size: µm 2 ( mas 2 ) window area: 6 12 pixels Broad-band photometry: five colour Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.2/30

3 Spectro MBP focal plane array Spectro sky mappers red enhanced CCDs blue enhanced CCDs Star motion Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.3/30

4 Designing the photometric systems Objectives: Astrophysical classification and parametrisation of the observed sources Intermediate and broad band photometry Chromaticity correction of the astrometric measurements Broad band photometry Science case demands: Measurement of L, T eff, M, age, composition for the stellar populations in the Galaxy and its neighbours T eff, reddening for OBA stars; T eff, abundance for late giants and dwarfs luminosities for stars with σ ϖ/ϖ > 10% distribution function of abundances to 0.2 dex T eff to 5%; separate determination of [M/H] and [α/fe] Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.4/30

5 Photometric system optimisation Find filter system that maximises separation of stars with different astrophysical parameters in filter flux space gradients of filter fluxes wrt AP changes should be as large as possible (taking the measurement noise into account) gradient vectors should ideally form orthogonal set φ 3 c b d rb α r d rc φ 2 φ 1 Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.5/30

6 Photometric system optimisation Find filter system that maximises separation of stars with different astrophysical parameters in filter flux space gradients of filter fluxes wrt AP changes should be as large as possible (taking the measurement noise into account) gradient vectors should ideally form orthogonal set φ 3 c b d rb α r d rc φ 2 Make use of sensitivity matrix: φ i1 / p 1... φ i1 / p K S i =..... φ ij / p 1... φ ij / p K φ 1 Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.5/30

7 Photometric system optimisation Calculate the posterior errors achievable with PS: C p = (B + S T C 1 φ S) 1, C φ = diag(ɛ 2 j ) The lengths and orthogonality of the AP gradients are contained in C p Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.5/30

8 Evaluating performance Test photometric systems on grid of synthetic spectra Define priority targets from stellar populations in Halo, Bulge, Thick/Thin disk Assign weight to each target Specify precision goals for each of T eff, A V, log g, [M/H], [α/fe] function of magnitude, distance Assign relative priorities to astrophysical parameters For each target compute: Q i = X w k f (σ k /σ k,goal ) Overall figure of merit for PS: Q = X w iq i Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.6/30

9 The baseline photometric systems 1.0 C1B photometric system λ (nm) C1M photometric system λ (nm) Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.7/30

10 Photometry and overall Gaia data analysis Gaia photometric data processing Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.8/30

11 Photometry and overall Gaia data analysis Cross matching plus prompt variability analysis Gaia photometric data processing Broad band photometry Medium band photometry Discrete object classification Astrophysical parametrisation Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.8/30

12 Photometry and overall Gaia data analysis Science alerts Astrometric data processing Chromaticity Cross matching plus prompt variability analysis Gaia photometric data processing Broad band photometry Medium band photometry Discrete object classification Astrophysical parametrisation Reference frame QSOs Global Iterative Solution List of "well behaved" stars RVS data processing Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.8/30

13 Photometry and overall Gaia data analysis Science alerts Astrometric data processing Chromaticity Cross matching plus prompt variability analysis Gaia photometric data processing Broad band photometry Medium band photometry Discrete object classification Astrophysical parametrisation Reference frame QSOs Global Iterative Solution List of "well behaved" stars RVS data processing Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.8/30

14 Photometric data analysis goals Science: Mission-averaged fluxes and magnitudes for each object and each filter Object classification Astrophysical parametrisation Epoch photometry for each object Variability database Science alerts during the mission Calibration: Standard fluxes CCD parameters PSF and LSF Photometric pass-band reconstruction Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.9/30

15 Complications Focal plane array motion across focal plane array (along scan direction) Data transmitted to ground GAIA image pixel sample Window numerical binning flux position electronic binning Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.10/30

16 Complications TDI operation across very large focal planes Complex calibration task Windows may contain in addition to single star: binary components, background sources spikes from PSFs of nearby stars Overlapping fields of view in Astro Windows mostly 1-dimensional Line-spread function (LSF) instead of Point-spread function Mapping of surroundings of observed objects required Very different resolution scales Astro and Spectro Specific treatment crowded regions Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.10/30

17 Scale of the effort Star density Average , typical , worst stars/deg 2 Number of CCDs Astro: 110 AF and 40 BBP; Spectro 32 MBP Number of Filters BBP: 5, MBP: 14 Number of images per second per FOV Astro AF: Astro BBP: Spectro MBP: Total (2 Astro+Spectro): Realistic FOV projections on sky and Spectro windowing limits: = maximum of images/sec to be processed. Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.11/30

18 Photometric data analysis tasks MBP Astrophysical information G, GS band Variability Sky image BBP Colour info for Astrometry Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.12/30

19 Photometric data analysis tasks Calibration Passband reconstruction CCD spectral response large/small scale Different colour response core/wings PSF CTE effects Flux outside window Bright stars (wings, gates) Magnitude scale MBP Astrophysical information G, GS band Variability Sky image BBP Colour info for Astrometry PSF/LSF TDI, AC/AL motion MTF, Charge diff Gates Filter/mirror ageing Sky background Trend monitoring Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.12/30

20 Photometric data analysis tasks Astrophysical parametrisation Automatic classification Crowded areas Solar System Imaging analysis Double star treatment Science Alerts Calibration MBP Astrophysical information G, GS band Variability Sky image BBP Colour info for Astrometry Variable stars Provide standard fluxes Provide calibration parameters (CCD, LSF, PSF, etc) Provide calibrated fluxes to other parts Gaia data analysis Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.12/30

21 Photometric data analysis tasks see document PWG AB 001 Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.12/30

22 G-band photometry Links separating true from false images (11 successive AF CCDs) instantaneous image of sky for BBP and MBP prime source for variability analysis run in combination with or on output from astrometric processing Task details image verification; CCD calibrations development of photometric calibration model sky-background (overlapping FOVs!) and CCD zero-level calibration of spectral response variations between CCDs statistical tests on formal errors bright star treatment calibration trend monitoring software magnitude scale calibration Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.13/30

23 Broad-band photometry Links supply colour information to astrometric processing provide (limited) astrophysical information especially in crowded regions spectral response based science alerts detection of specific types of binaries with astrometry in BBP Task details see G-band tasks wavelength dependent sky-background model Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.14/30

24 Medium-band photometry Links detailed photometric information for astrophysical parametrization of sources maintenance clean list of GIS sources high-resolution information from AF and BBP will enable treatment of crowded areas spectral response based science alerts input for RVS data analysis (priors on stellar parameters) link between astrometric, spectroscopic and photometric parameters Task details see G-band and BBP tasks Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.15/30

25 Imaging analysis Links detection of disturbing faint background sources near Gaia targets important for proper photometric data reduction (background treatment) identification of faint components of binaries and multiples identify possible spurious variability Task details properly stack AF11, BBP, ASM and SSM windows and construct a sky image around each Gaia source Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.16/30

26 Accumulation of data and variability Links check on source variability without examining individual measurements variability based science alerts checks on the effects of accidental superpositions from other FOV maintenance clean list of GIS sources Task details accumulate parameters for each star and each successful observation in a general database input parameters for statistical tests histograms of normalized residuals see variable star working group Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.17/30

27 Passband reconstruction Links essential for scientific exploitation of data science alerts automatic classification Task details identify or create suitable calibration data for Gaia modelling and monitoring of filter transmission ageing modelling and monitoring of mirror reflectivity ageing in-flight passband calibration from differences between predicted and measured responses for stars of varying spectra types Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.18/30

28 Science alerts Links Identify outstanding events that warrant immediate ground-based follow-up Task details accumulate sky-history variability based events from comparison of new and accumulated photometric data spectral response based events from sources that do not fit automatic classification schemes design robust detection filters with very low false detection probability see science alerts working group Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.19/30

29 Automatic classification Links astrophysical parametrization of sources input (priors) for RVS/MBP data reduction and maintenance clean list of GIS sources science alerts post-mission data preparation Task details see classification working group Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.20/30

30 Double and multiple stars Links double and multiple star processing Task details identify resolved double and multiple stars in data stream and pass to appropriate reduction pipeline this pipeline has to be fully integrated into photometric processing in practice! take into account scan orientation effects design mechanisms to detect poorly resolved multiplicity Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.21/30

31 Solar system objects Links solar system objects processing Task details develop early identification mechanism and filter out for a separate pipeline develop a posteriori recognition methods in the accumulated data (avoiding confusion in science alerts) see solar system working group Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.22/30

32 CCD calibrations Links all CCDs need to calibrated and monitored in a coordinated effort glue between all astrometric and photometric data processing Task details define calibration data base structures and manipulation software pay attention at early stage to speed and efficiency interfaces for access and iterative updating of calibration parameters develop calibration monitoring and visualization tools Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.23/30

33 PSF and LSF calibration Links removal of diffraction pattern effects from data correction for the effects of TDI operation Task details effect of charge transfer losses micro variations scan rate localized pixel inhomogeneities study use of TDI gates details of PSF wings; differences in response between core and wings Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.24/30

34 General tasks identify the core and shell tasks within the photometric processing validation and optimisation of windowing scheme optimization of database interfaces for photometric data processing development of trend-monitoring tools for all calibration tasks coordinate with astrometric and radial velocity processing develop efficient interactive display tools implement software documentation package ensure proper version tracking (CVS) Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.25/30

35 Simulation needs simulated data for various processing stages are needed telemetry (for GDAAS core processing) window level data (photometric data reduction studies) pixel level data (PSF modelling, window simulations) intermediate photometric data products (e.g., variability studies) identify shortcuts for modelling parts of the data processing that precede intermediate or final data products detailed PSF models (wings) sky-background (overlapping FOVs, faint stars, zodiacal light) realistic simulations of CCD properties and TDI operation simulations for studying photometric processing of binary and variable star data Available now telemetry and window level data from GASS pixel and window level data from GIBIS CCD model under development Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.26/30

36 Organisation Working group Exploratory studies Ideas for algorithms Simulations High level pipeline design Integration with overall data analysis Data processing group Implementation Preparation of reliable and efficient software for the mission Setup of actual pipeline GDAAS Laboratory studies and detailed modelling of CCDs TDI operation CTE Radiation damage Calibration Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.27/30

37 To Do update work-packages in PWG AB 001 add packages focused on implementation identify who will do what Priority tasks this year end-to-end simulation of photometric processing chain, starting from relatively simple AF case calibration related efforts, such as PSF, LSF, response functions develop more sophisticated sky background treatment (overlapping FOVs, crowding) bright star (gates, PSF wings), binary, and variable star photometry corresponding simulations (gates already available in GIBIS) Please coordinate your interests with Anthony Brown: Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.28/30

38 Crowded regions with MBP Result obtained by Dafydd Evans Performance limited by: detection, windowing, spatial resolution Use position information from astrometry to carry out PSF fitting From data analysis point of view MBP can handle regions up to stars/deg 2 Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.29/30

39 Images from AF11 Result obtained by Pasi Nurmi Proper photometric data reduction requires knowledge of contaminating background sources Windows from last AF column will be larger Surroundings of stars can be mapped to V 24 for V < 8 Photometric system Role of photometry Goals Tasks/links Organisation Exploratory studies Bologna p.30/30