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OmegaCAM: The 16k x 16k Survey Camera for the VST

OmegaCAM: The 16k x 16k Survey Camera for the VST. Observing and data reduction a Virtual Survey System. Edwin A. Valentijn. Paranal . July 2004. VLT Survey Telescope-VST. Alt-AZ - Cassegrain aperture 2.610 m corrected FOV 1.47 degree lens corrector: U - z

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OmegaCAM: The 16k x 16k Survey Camera for the VST

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  1. OmegaCAM: The 16k x 16k Survey Camera for the VST Observing and data reduction a Virtual Survey System Edwin A. Valentijn

  2. Paranal July 2004

  3. VLT Survey Telescope-VST • Alt-AZ - Cassegrain • aperture 2.610 m • corrected FOV 1.47 degree • lens corrector: U - z • Atmospheric disp. correct.: B -z • f/5.5 • scale 14.266 arcsec/mm • CCD pixel size: 15 um • 0.214 arcsec/pixel • image quality: 80% EE • two-lens: 1.70 pixel • ADC: 1.77 - 2.18 pixel

  4. VST factory - Napoli

  5. Detectors • Science array 1 x 1 degree, 32 CCDs • 15 mm pixels – 0.21 arcsec/pixel • Marconi (former EEV) 2k x 4k • 16k x 16k pixels • Auxiliary CCD’s – 4 CCDs • For guiding • Image analysis

  6. Filters • Primary set: Sloan u’, g’, r’, i’, z’ high throughput interference • Johnson B, V, Stromgren-v • Segm Ha up to ~12000 km/s 658.8 665.5 672.2 678.9/ 10.7 nm • 1100, 4200, 7300, 10400km/sec / 4900 km/sec • Composite u’, g’, r’ ,i’ in four quadrants • Segm Ly alpha z=2-3 372, 400, 450, 507nm / 8 nm • Night sky leak CWL=851.8nm - 877.8nm /13nm

  7. Wide Field Imaging Science • Provide targets for VLT • ~60% of time through ESO’s OPC • Individual programs • Supernovae, Lensing, Kuiper belt objects, Gamma ray, bursts, Microlensing, Brown dwarfs, High proper motion objects, Galactic halo objects, Quasars, AGNs • Sky Surveys • Long term archival research (10 yr mission) • Science Cases • Finding exceptional single, rare objects • Statistics on large samples of objects

  8. Handling of the data is non-trivial • Pipeline data reduction • Calibration and re-calibration • Image comparisons and combinations • Working with source lists • Visualization } ESO compliant Large Data Volume • Wide-field imaging instruments, vast amounts of data • E.g.: VST = Southern sky (30 min exp, 300 nights/y) in 3 years. Large amount of data! 100 Tbyte of image data and Tbytes of source list data • Science can only be archive-based

  9. Concepts for solutionVirtual Survey System • Environment that provides systematic and controlled • Access to all raw and calibration data • Execution and modification reduction/calibration pipelines • Execution of source extraction algorithms • Archiving reduced data and source lists, or regenerates these dynamically • Can be federated to link different data centers • Dynamical archive continuously grows, can be used for • small or large science projects • generating and checking calibration data • exchanging methods, scripts and configuration • Key functionality • Link back from source data to the original raw pixel data and calibration files

  10. How to use this • Deep multi-color fields • No need to take all data in one campaign • Combine data of particular quality, assess results • Select sources, visualize interesting ones, … • 1-in-1,000,000 events spurious or not? • Large homogeneous surveys • E.g. weak lensing maps, cluster searches, star counts • Variability (source list- or pixel based) • Proper motions (asteroids, nearby stars) • Flux variations • Monitor instrument (calibration files) • Planning observations • View quality of existing data • Build on what already exists, add more filters, more exposure time, better seeing, …

  11. Keys -Solution • Procedurizing • Data taking at telescope for both science and calibration data • Full integration with data reduction • Design • Data model (classes) defined for data reduction and calibration • View pipeline as an administrative problem

  12. Observing Modes Dither • Dithermatching max. gap between arrays ~400 pixels • N pointings (N=5 is standard) • nearly cover all gaps in focal plane and maximizes sky coverage • Very complex context map • couple the photometry among individual CCDs. Dither with N = 5

  13. Observing Modes Jitter • Jittermatching the smallest gaps in CCDs ~5 pixels • optimizes for maximumhomogeneity of the context map • observationsfor which the wide CCD gaps are not critical • all data from single sky pixel originates from single chip

  14. Observing ModesStare and SSO • Stare reobserving fixed pointing positions multiple times • main workhorse monitoring instrumentand optical transients. • SSO observing Solar System objects • non-siderial tracking and the auto guiding switched off.

  15. Strategiesscheduling observing modes • Standard • Single observations (one observing block) • Deep • Long, multiple integrations • Selected atmospheric conditions • Several nights • Frequent • Monitors same field • Timescales from minutes to months (overriding) • Mosaïc • Maps areas of sky > 1o

  16. Calibration procedures Sanity checks Image pipeline Source pipeline Calibration procedures Quality control

  17. Bias pipeline Source pipeline Flatfield pipeline Photometric pipeline Image pipeline Science Observations

  18. Share the loadAstroWise Survey System • Processing • Hardware • Beowulf processors – 32 (most cases) • Multi Terabyte disks (10 – 100) • Data reduction • Derive calibration • Run image pipeline (1 Mpx/s) • Archiving • Storage • Images (100’s Tbyte), Calibration files (10 Tbyte) • Source parameters (1-10 Tbyte) • Federate (network speed) • 5 Mb/s (24 hours/day) full replication • 200 Mb/s no replication, on-the-fly retrieval

  19. Concepts of federation • Federation maintained by a single database- Oracle9i • Full history tracking • of all input that went into result • providing on-the fly reprocessing • Dynamical archive - Context as object attributes • Project: Calibration, Science, Survey, Personal • Owner: Pipeline, Developer, User • Strategy: Standard, Deep, Freq (monitoring), Mosaïc • Mode: Stare, Jitter, Dither, SSO • Time: Time stamping VO interface • Software standards • Classes/data model/procedures • 00 – inheritance/ persistency • Python scripts/ c-libraries USER Python

  20. Observing proposals • Garanteed time NOVA 10% • Call – 25 April--- see www.omegacam • Super clusters- distant clusters • Galactic structure • Weak shear, microlensing • Bulge • 2dF, 100 Sq Degree, 10000 Sq Deg • Deep field • Lorentz center July 2003 • Fall 2004

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