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The secondary standards programme for OmegaCAM at the VST

The secondary standards programme for OmegaCAM at the VST. Gijs Verdoes Kleijn, Ronald Vermeij & Edwin Valentijn For the Astro-Wise consortium OmegaCEN at Kapteyn Astronomical Institute, Groningen, The Netherlands. The two teams. OmegaCAM team = wide-field imager

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The secondary standards programme for OmegaCAM at the VST

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  1. The secondary standards programme for OmegaCAM atthe VST Gijs Verdoes Kleijn, Ronald Vermeij & Edwin Valentijn For the Astro-Wise consortium OmegaCEN at Kapteyn Astronomical Institute, Groningen, The Netherlands

  2. The two teams OmegaCAM team= wide-field imager USM (Munich), ESO, Padova, OmegaCEN(Groningen)/NOVA(NL): Astro-Wise team =software environment for OmegaCAM (but being used also for data from various other wide-field imagers) USM/MPE, Terapix (IAP), OAC Naples, ESO, OmegaCEN Astro-Wise team • OmegaCEN: Edwin Valentijn (PI) • Munich, USM/MPE: Ralf Bender local PI • Paris, Terapix: Yannick Mellier local PI • Naples, OAC: Massimo Cappacioli local PI • Munich, ESO: Peter Quinn local PI Groningen: Kor Begeman Michael Pohlen Danny Boxhoorn Michiel Tempelaar Ewout Helmich Gijs Verdoes Kleijn Philippe Heraudeau Ronald Vermeij John MacFarland Willem Jan Vriend Edwin Valentijn (PI) Leiden: Konrad Kuijken (OmegaCAM-PI) Erik Deul

  3. Outline • VST, OmegaCAM and filter specs • The calibration challenges for OmegaCAM • Secondary standards programme Goal of this talk: introduce the instrument and its’s analysis system to you; discuss our scheme for photometric calibration. All discussion welcomed.

  4. OmegaCAM@VST, Paranal

  5. VLT Survey Telescope-VST • Alt-AZ • aperture 2.610 m • corrected FOV 1.47 degree • f/5.5 • Single instrument: OmegaCAM Artist’s impression

  6. 1deg 1deg The OmegaCAM panoramic camera • Successor at Paranal of WFI from LaSilla • Cassegrain focus at VST • 16k x 16k mosaic of 32 CCDS: 2k x4k thin CCDs • pixel size 0.21 arcsec / 15μm. • 330 to 1000 nm • filter system contains: ugriz (core) + more • Retractable Atmospheric Dispersion Compensator for u’ and large air mass • Only Service Mode observations. USM Padova

  7. filter g’, r’, i’, z’ have been measured Filter+ccd Sagem: u’g’r’I’z’, 4-segmented around Hα (10nm) 4-segmented narrow-band at 850nm Strömgren v Barr: B,V 4-segmented u’g’r’I’ Filters in production

  8. The challenges using ΩCAM Vast amount of data • Single image 550 Mbyte (~200 screens for full resolution) • Sole instrument: OmegaCAM observes equivalent of Southern sky in ~3 years (30 min exp, 300 nights/year) • Many filters & programs (75% public surveys, 25% GTO) • Of order 10 Tbyte of raw data/year with time-varying atmosphere, instrument & telescope performance • The Calibration (& Science) Wishes • Good calibration/monitoring every location on each chip: (e.g., flatfield illumination correction, fringing zeropoints) • Easy re-calibration as insight in instrument/telescope improves • All raw and reduced data at finger tips: needle in the hay stack searches, subtle statistics • Flexibility for various reductions/analyses on large data sets (quick ‘n dirty or thorough)

  9. The chosen solution:“The 2 central ingredients of the Astro-Wise system” • Make strict & ‘fully-handshaking’ procedures from scheduling through calibration/reduction Photometric calibration: every night identical procedures for a monitoring field (3x/night) and standard star field (≥1x/night) • Put everything in ‘smart’ database • All raw data & derived products resident in single database system • Information how a product was derived also resident: all bits are traceable • Both calibration and analysis software in database system • Database is smarter than filing system of fits tables and images with headers: internet vs library • As time goes on newly/better/differently derived products are added Photometric calibration: easy (re-)calibration & trend analysis It’s the database that is special: ‘smart’ database vs filing system == internet vs library

  10. 1deg 1deg OmegaCAM photometric calibration in Astro-Wise • 1 (atmosphere) monitoring field near south equatorial pole • 8 equatorial standard star Landolt fields Photometric calibration / monitoring per chip: • Landolt (1992) • Stetson (CADC) Full FOV coverage by standards needed

  11. Intermediate step Secondary Standards Preparatory Programme WFC/INT @ La Palma Final situation (after ~1 year of OmegaCAM operation) • Secondary Standards calibrated to ugriz system from OmegaCAM observations covering ~1.1x1.1 deg2 ΩCAM secondary photometric standards Current situation: 8 Landolt fields with • Landolt catalog converted to ugriz (Smith+02) • Stetson catalog converted to ugriz (Smith+02) • (SDSS non-standard stars)

  12. WFC/INT La Palma Observations • WFC/INT: • D=2.5m; • FOV=0.5deg x 0.5 deg, • four CCDs, pixel size 0.333arcsec; • Observations: • Jun 2002 and Feb 2003; • 7/8 fields observed (not SA95) • 5-dither (1.1deg x 1.1deg); • Ugriz filters; short (~10s) and long (~300s) exposure • Goal: secondary standards from 14th-19th mag stars…..work in progress…..data reduced, tests and full error analysis in progress

  13. Stable nights Monitoringthe quality of the night Standard extinction coefficients adopted : u' = 0.47 r' = 0.09 g' = 0.19 i' = 0.05

  14. Color terms for WFC→ugriz system u' : none detected g' : 0.14 +/- 0.01 r' : none detected i' : 0.07 +/- 0.01

  15. The preliminary catalogue of secondary standards

  16. Illustrative test: WFC (aperture)-SDSS3 (modelmag) magnitude residuals SA92 SA101 SA104 SA107 SA113

  17. SA101

  18. Conclusions • OmegaCAM= wide-field 1sq degree imager operational early 2007 • Astro-Wise: specifically developed analysis environment: ‘smart database’ (‘internet vs library’) concept • 1.1.x1.1deg2 fields of secondary standards in u’g’r’i’z’ system in construction centered on 8 Landolt equatorial standard fields • Final outcome: deep public imaging surveys of significant (>10,000deg2) part of Southern Sky and more….

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