Micro-Arcsec mission:

1. Micro-Arcsec mission: implications of the monitoring, diagnostic and calibration of the instrument response in the data reduction chain Deborah Busonero – INAF OATo & the OATo Team Corcione L.,Gai M.,Gardiol D.,Lattanzi M.G.,Loreggia D.,Riva A.,Russo F. D. Busonero - Osservatorio Astronomico di Torino 7 maggio 2009

2. Busonero - 53° Congresso SAIt - Pisa • Instrument monitoring and diagnostic are fundamental to fullfill • the astrometric accuracy goal of the 21° century astrometry space mission • Different approach to perform the instrument monitoring and • diagnostic: SIM - Lite Gaia

3. Busonero - 53° Congresso SAIt - Pisa Gaia SIM - Lite • Scanning mode • Pointing telescope • Spatial correlation among the measurements • No measurements correlation • Self-calibrated system closure condition Instrument health check and monitoring via hardware Measure equations Image location (the observable) as function of several parameters O = f (S, A, C) + n • minimize correlations • hardware cost Huge number of unknowns

4. Busonero - 53° Congresso SAIt - Pisa Astrometric solution for Gaia: Formulation From L. Lindegren

5. Busonero - 53° Congresso SAIt - Pisa The problem: reduction of the numbers of the instrumental calibration parameters • The basic measurement is the "time of observation" for each star's crossing a CCD 10^12 measurements in total • Unknown parameters to estimate: – 5 astrometric parameters per star – attitude (celestial orientation) of instrument as function of time – instrument calibration parameters (basic angle, CCD positions, etc) – possibly additional parameters (incl. PPN-γ) 5×10^9 unknowns in total • Not all stars are suitable for simple modelling (binaries, etc) • – a subset of "primary stars" is used for the astrometric solution: • 100 million primary stars (10% of all) • astrometric solution needs 5×10^8 unknowns

6. Busonero - 53° Congresso SAIt - Pisa Needs procedures and tools for instrument diagnostic and calibration with the goal to decrease the parameter space and solve degenerations. Variation of the instrumental response over the field, with wavelength and in time, are potentially critical. Appropriate modelling of the astrometric response is required for optimal definition of the data reduction and calibration algorithms, in order to ensure high sensitivity to the astrophysical source parameters and in general high accuracy. The measured signal profile is affected by optics, attitude, detector response and operations.

7. Busonero - 53° Congresso SAIt - Pisa From B. Holl

8. Busonero - 53° Congresso SAIt - Pisa Scan width: 0.7° Sky scans (highest accuracy along scan) Data Reduction Principles 1. Object matching in successive scans 2. Attitude and calibrations are updated 3. Objects positions etc. are solved 4. Higher terms are solved 5. More scans are added 6. System is iterated

9. Busonero - 53° Congresso SAIt - Pisa Pre-launch phase (end of 2011) selection of those parameters which have an impact (related to optics, attitude, detector response and operations) on the accuracy performance, analysis of the critical aspects for the formulation of the calibration models; (forward analysis) Commissioning phase, during which the nominal values of the parameters are validated and, if necessary, updated; Operations phase, during which the data will be acquired and processed for the instrument monitoring and for the improvement of the calibration models developed in the previous phases. backward analysis:inverse problem of disentangling both astrophysical and instrumental parameters from the set of science and auxiliary data

10. Busonero - 53° Congresso SAIt - Pisa Focal length common mode variation and CCD displacement . Due to: Temperature variation during a lunar eclipse Something happened difetto to the electronics (irregolar power supply) What to do? Variation of the orbit or new assessment of the alectronics In the case it is a permanent variation we will need to refocus the telescope.

11. Busonero - 53° Congresso SAIt - Pisa Cromatic displacement for Astro 1

12. Busonero - 53° Congresso SAIt - Pisa Cromatic displacement for Astro 2

13. Busonero - 53° Congresso SAIt - Pisa Field distortion (due to optics) See also D.Busonero et al. A&A 2006

14. Busonero - 53° Congresso SAIt - Pisa Field distortion (due to CTIs)

15. Busonero - 53° Congresso SAIt - Pisa Astrometric effects of non-uniform telescope throughput In real telescopes, the optical parameters evolve with time, and the degrada- tion is often not uniform. variations in the image profile photo-centre displacements result in astrometric errors. Need mitigation techniques applicable from design stage to calibrations. GAIA-C3-TN-INAF-MG-008 M.Gai, D. Busonero Remarks: - transmission variation can be minimised by design and construction; - it can be monitored by suitable pupil imaging devices (e.g. WFS); - it cannot be identified by point-to-point measurements

16. Busonero - 53° Congresso SAIt - Pisa Reversing the aberrations and WFE map (specular PSF): Opposite photo-centre displacement for given opacity patch position Patch induced photo-centre displacement Photo-centre displacement: Mean: 0.033 as RMS: 3.341 as PTV: 14.131 as (Potential) astrometric error depending on patch position

17. Busonero - 53° Congresso SAIt - Pisa Remarks on overall instrument Throughput variations independent on each telescope [at least on non-common path, from M1 to M4] Time evolution may be different [e.g. different cross section, due to orientation, to individual solar flares] Transmission distribution could be deduced e.g. from WFS, albeit at low resolution, if read throughout the mission [impact on operations] Global throughput may be monitored by (averaged) photometric information (RBP, BBP, but also AF)

18. Busonero - 53° Congresso SAIt - Pisa PSF/LSF modelling for PSF/LSF calibration The astrometric performance of astronomical instruments is related to the image profile (Point Spread Function - PSF) A complete PSF/LSF analytical modelling is fundamental to reach the accuracy target level • From experiments with “laboratory” CCD data we found: • Bi-quartic spline sufficiently flexible to give good fit everywhere • Residuals fully consistent with expected noise • Tendency to oscillation in wings can be removed by smoothing constraint (difficult) or • adding Lorentzian wings (easy, and gives good extrapolation) • BUT: • – spline representation requires many parameters (~35) • – probably too detailed at ±3-8 samples from centre • – transition from spline to Lorentzian is rather abrupt We need to find a model with (much) reduced dimensionality (work in progress) Preliminary study: GAIA-C3-TN-INAF-MG-007 M. Gai et al.

19. Busonero - 53° Congresso SAIt - Pisa From L. Lindegren

20. Busonero - 53° Congresso SAIt - Pisa What do weneedthisfor? Tobuild the AIM system • AIM is devoted to the monitoring and diagnostics of the astrometric instrument response during in-flight operations. • It is an ensemble of software modules each one dedicated to perform a specific analysis and extract calibration information from the data during in-flight operation.

21. Busonero - 53° Congresso SAIt - Pisa

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24. Busonero - 53° Congresso SAIt - Pisa Simulations Instrument (physical parameters) AIM analysis 1: effects of perturbations Simulated Data Goal: identification of “critical parameters”

25. Busonero - 53° Congresso SAIt - Pisa Simulations Instrument (physical parameters) AIM analysis 2: calibrate instrument model Laboratory Data Calibration procedure

26. Busonero - 53° Congresso SAIt - Pisa Gaia Attittude data AIM - IM Level 0 Attitude simulator module Gaia ASTRO Optical system data Optical nominal and perturbed configurations simulator module Gaia Astrometric Focal Plane Assembly data GAIA raw elementary signal FPA/CCD configurations simulator module Optical PSFs libraries Star spectral energy distribution (SED) Catalogues Effective PSFs libraries Source constructor module Polychromatic Effective PSF/LSFs libraries

27. Busonero - 53° Congresso SAIt - Pisa Simulations Instrument (physical parameters) AIM analysis 3: forward analysis Simulated Data ? Astrometric Instrument Model (effective global parameters)

28. Busonero - 53° Congresso SAIt - Pisa AIM - IM Instrument angular rate Level 0-bis Scanning law Attitude Operations mirrors position & orientation CCD position & orientation Geometry contributions Perturbed Nominal WFE maps for each SM/AF CCD no-uniformity AC FWC Shaping errors map for each field sensitivity variation polishing errors map for each field fringing aging effects Degradation reflecting surface inter-intra CCD vart. PRNU Mirror Coating radiation effects,CTI Trasmissivity saturation non linearity QE, MTF, gain, RON Polarization effects Detectors Reflectivity Straylight Optics Perturbed Nominal Perturbed Nominal

29. Busonero - 53° Congresso SAIt - Pisa AIM analysis 4: backward analysis Satellite Data Astrometric Instrument Model (effective global parameters) Calibration procedure Instrument Monitoring

30. Busonero - 53° Congresso SAIt - Pisa Backward Analysis Merit statistics to process raw data and performed data analysis (methods, algorithms) Forward Analysis Image characterization analysis Telescope characterization analysis CCD characterization analysis

31. Busonero - 53° Congresso SAIt - Pisa Backward Analysis Modello di risposta strumentale per la riduzione dati di Gaia Si individuano tre modelli I tre modelli sono collegati e in generale dipendentidal tempo Gerarchia: 1) Risposta locale => forma della PSF/LSF effettiva 2) Variazione distribuita sul campo => FPSM o varianti 3) Legame campo-campo => base angle generalizzato Sviluppo: analisi e identificazione parametri/forme funzionali convenienti; definizione algoritmi. Progresso documentato da pubblicazioni e note tecniche Applicazioni: monitoraggio e analisi dati Gaia – identificazione di correlazioni, eventi critici, …

32. Busonero - 53° Congresso SAIt - Pisa Optics Risposta locale Forma della PSF/LSF policromatica effettiva Detectors Geometry contributions Variazione distribuita sul campo CCD-Field transformation modeling and estimation A) Operations Base Angle Legame campo-campo CCD-Field transformation

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34. Busonero - 53° Congresso SAIt - Pisa Gaia: Complete, Faint, Accurate

35. Busonero - 53° Congresso SAIt - Pisa Payload and Telescope Basic angle monitoring system Rotation axis (6 h) Two SiC primary mirrors 1.45  0.50 m2 at 106.5° SiC toroidal structure (optical bench) Combined focal plane (CCDs) Superposition of two Fields of View (FoV) Figure courtesy EADS-Astrium

36. Busonero - 53° Congresso SAIt - Pisa Figure courtesy Alex Short Focal Plane 104.26cm Blue Photometer CCDs Red Photometer CCDs Wave Front Sensor 42.35cm Wave Front Sensor Radial-Velocity Spectrometer CCDs Basic Angle Monitor Basic Angle Monitor Star motion in 10 s Sky Mapper CCDs Astrometric Field CCDs Sky mapper: - detects all objects to 20 mag - rejects cosmic-ray events - FoV discrimination Astrometry: - total detection noise: ~6e- Total field: - active area: 0.75 deg2 - CCDs: 14 + 62 + 14 + 12 - 4500 x 1966 pixels (TDI) - pixel size = 10 µm x 30 µm = 59 mas x 177 mas Photometry: - spectro-photometer - blue and red CCDs Spectroscopy: - high-resolution spectra - red CCDs

37. Busonero - 53° Congresso SAIt - Pisa In fase operativa le misure stesse saranno utilizzabili per estrarre l’informazione sui parametri strumentali. La media sulle diverse osservazioni sul transito ci permettera’ di raggiungere precisioni del μas sulla stima dei parametri. Basti pensare che gli oggetti piu’ brillanti di V=15 disponibili sono 40 milioni e il numero medio di oggetti simultaneamente osservati nei due campi di Gaia e’ dell’ordine di 1000.

38. Busonero - 53° Congresso SAIt - Pisa From L. Lindegren