Photometric calibration in Astro-WISE

1
Photometric calibration in Astro-WISE

• For the Astro-WISE consortium
• Gijs Verdoes Kleijn
• OmegaCEN/Kapteyn
• Groningen University
• (and Philippe Heraudeau, Johannes Kopppenhoefer,
  John McFarland, Edwin Valentijn, Ronald Vermeij,
  etc)

2
Overview
MSTD -2.5log(countrate) ZPT- kX (CT0color -
CT1)

• To cover full instrument FOV densely
• S/N limited, sigma clipped,
• weighted mean of magnitudes of
• (subset) of stars in 22 SA fields
• Landolt standard stars
• Stetson standard stars
• DR5 (in SA fields) with no flags
• Preliminary Catalog from ugriz WFC for OmegaCEN
  secondary standards programme
• or your customized standard star catalog

3
Astro-WISE photometric calibration
chip-by-chip example WFI_at_ESO/MPG2.2m
?ZPT chip-to-chip lt0.3mag
?(?ZPT) vs time lt0.05mag
4
Random error in zeropoint
?ZPTestimated error on ZPT from unweighted
scatter (not formal error)
ALL instruments and filters
WFI_at_MPG/ESO 2.2m
lt?ZPTgt0.015

• Typical ?ZPT can be improved. Most ZPTs
• no illumination correction with illum
  lt?ZPTgt 0.01
• no instrumental-gtstandard transformation with
  illumtransform lt ?ZPTgt 0.007
• Exclusion of secondary /tertiary standards does
  not decrease lt?ZPTgt

5
Monitoring photometric calibration of instrument

• Information sofar obtained with

(and Philippe Heraudeau, Johannes Kopppenhoefer,
John McFarland, Edwin Valentijn, Ronald Vermeij
etc..)
6
Systematic error in zeropoint

• Example dependence on calibrator set
• WFC_at_INT DR5 vs Sloan from LandoltJester
  transformations (2005, AJ, 130, 873)

filter Median ?ZPT (DR5-Landolt) uncertainty
?u 0.07 0.02
?g 0.02 0.01
?r -0.03 0.01
?i -0.04 0.02
?z 0.00 0.04
Verdoes Kleijn et al, 2007, ASP Conf, Series 364,
103
7
Overall photometric stability1s variations
photometric scale

• Within a photometric night
• WFC_at_INT u0.020, g0.015, r0.015, i0.015,
  z0.020
• WFI_at_ESO/MPG Rlt0.03
• Over months (from WFI repeated fields)
• Photom nights only R0.05 in R
• All nights (so variation largely atmospheric)
  R0.1

8
4 way to model atmospheric extinction in
Astro-WISE
Standard extinctioncurve

1. observations of standard fields at 2 airmasses
2. Standard extinction curve coefficient stored in
   the database
3. standard field plus known zeropoints
4. Combination standard extinction curve and
   extinction report (OmegaCAM calibration plan)

9
Extinction Curves
La Silla measurements 1995AAS112_383 Burki etal
Extinction Curve in use in Astro-WISE (La Palma
Extinction Curve)
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Variation in Extinction Curves
La Silla (UBV) (variation due to volcanic
activity)
CTIO ugriz
adapted from Smith et al, 2008, AJ, submitted
Burki et al, 1995, AAS, 112, 383
Wavelength independent shift of extinction coeff
(within0.025)
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Up-coming Southern Sloan Standards

• Extension of Sloan standard work via CTIO 0.9m
  telescope
• 58 Southern fields (16000 stars)
• Smith et al, 2008, AJ (revising for referee
  comments)

• In future
• SkyMapper project (PI Brian Schmidt)
• tied to Tycho-2 catalog (BV)transformations
• OmegaCAM secondary standards programme
• tied to Landolt ( plus Sloan South?)
• Global photometry

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Global photometry

• Full data lineage back to raw data for magnitudes
  of stars in Southern Hemisphere will increase
  monotonically automatically

• awegt pp.photcat.get_source_data(columns)
• awegt pp.photcat.get_content_of_catalog()
• awegt qsl(SourceList.ulDEClt-10.0 and
  SourceList.ulDECgt-20.0)
• awegt len(qsl)
• 25793

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Summary

• Chip-by-chip
• ZPT accuracy in AstroWISE
• random 0.01mag
• Systematic no quote too much instrument/filter
  dependent
• Global photometry conceptually within reach with
  Astro-WISE

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Error estimation on ZPT and extinction

• TBD Discuss error estimation and propagation

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Photometric quality zeropointa test case

• Discuss Cen A case
• sd(mag stars)0.1mag
• Limited by inter/intra night changes in
  photometric conditions ultimately (?)

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Astro-WISE Standard star programSloan ugriz
standards for Southern hemisphere
Astro-WISE STANDARD STANDARD SET
Up-coming steps Southern Sloan photometric
standards OmegaCAM 2ary standards
programma Other programs (check with Ivezic)
             
Field (J2000) (J2000) Landolt Stetson SDSS DR5 PC
(deg) (deg)        
             
             
SA51 112.663 29.828 0 0 214 0
SA57 197.171 29.384 0 0 952 0
SA68 4.146 15.844 0 0 1302 0
SA92 13.946 0.949 41 213 1094 6475
SA93 28.783 0.824 4 0 1128 0
SA94 44.033 0.571 7 0 1099 0
SA95 58.500 0.000 45 426 1093 0
SA98 103.021 -0.328 46 1116 0 23840
SA100 133.529 0.546 6 1 3343 0
SA101 149.112 -0.386 35 117 1776 5591
SA102 163.779 0.866 5 66 1517 0
SA103 178.779 0.556 2 0 1507 0
SA104 190.592 -0.553 34 76 1576 5701
SA105 204.533 0.676 4 0 2172 0
SA106 220.533 0.427 2 15 2864 0
SA107 234.896 -0.252 28 728 3889 12006
SA108 248.033 0.369 6 3 6148 0
SA110 280.679 0.348 39 589 0 38562
SA112 310.529 0.524 7 73 12087 0
SA113 325.533 0.493 42 483 4046 13947
SA114 340.529 0.689 9 5 1957 0
SA115 355.779 0.888 10 0 1170 0
             
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• Ik weet dat ze van plan zijn met heel korte
  exposures (4sec) hun calibratie op te hangen aan
  de tycho catalogus. Maar dan wel met de SDSS
  filters, dus daar zit wel een transformatie in.
  Meer heb ik niet kunnen ontdekken. Voordeel van
  skymapper is wel dat ze een flink groter veld
  hebben, dus zeropoint fluctuaties gebeuren op een
  andere schaal dan in KiDS.

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Accuracy UBVRI ugriz transformations

• Discuss Results (systematicrandom errors from
  analysis also presented at Blankenberge

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Summary Conclusions
20
Overview

• Photometric quality random and systematic errors
• Zeropoint
• Atmospheric Extinction
• Color transformation?
• Developments in Southern standard stars

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Outline

• Chip-by-chip photometric calibration
• Content standard star catalog
• UBVRI standards only Stetson, Landolt( R dist ,
  typical errors)
• Large ensemble of non-primary standardsSDSS,aw2s(
  fainter, typical errors)
• m-2.5log(countrate) ZPT- kX (CT_0 color -
  CT_1)
• Transformations for which instruments?
• Instrumental-Standardnon-diagnonal terms)
• UBVRI-SDSSsystematic errors,( random errors)
• Extinction curve TBD
• Calibration procedure
• sextractor aperture photometry
• Random errors
• ZPT repeatability upper-limit1 same field,
  different nights, upperlimit2 Cen-A observations
• TBD extinction
• Systematic errors
• ZPT vs airmass, date-obs, chip, field, origin
  standards(WFC results)
• Systematics in
• Issues
• atmospheric cut-off

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Monitoring photometric calibration in Astro-WISE
zeropoint

• Calibrating instrument instead of single
  observations
• Stability atmosphere, instrument