Photometric calibration in AstroWISE For the AstroWISE consortium

Photometric calibration in Astro-WISE For the Astro-WISE consortium: Gijs Verdoes Kleijn Omega. CEN/Kapteyn Groningen University (and Philippe Heraudeau, Johannes Kopppenhoefer, John Mc. Farland, Edwin Valentijn, Ronald Vermeij, etc…)

Overview MSTD =-2. 5 log(countrate)+ ZPT- k. X+ (CT 0*color - CT 1) 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 • DR 5 (in SA fields) with no flags • Preliminary Catalog from ugriz WFC for Omega. CEN secondary standards programme • or your customized standard star catalog

Astro-WISE: photometric calibration chip-by-chip example: WFI@ESO/MPG 2. 2 m ΔZPT chip-to-chip: <=0. 3 mag Δ(ΔZPT) vs time: <=0. 05 mag

Random error in zeropoint ΔZPT=estimated error on ZPT from unweighted scatter (not formal error) ALL instruments and filters WFI@MPG/ESO 2. 2 m <ΔZPT>=0. 045 WFI UBVRI <ΔZPT>=0. 015 0. 009 0. 018 0. 009 0. 017 Typical ΔZPT can be improved. Most ZPTs: • no illumination correction: with illum: <ΔZPT> =0. 01 • no instrumental->standard transformation: with illum+transform: < ΔZPT> =0. 007 Exclusion of “secondary /tertiary standards” does not decrease <ΔZPT>

Monitoring photometric calibration of instrument: • Information sofar obtained with: (and Philippe Heraudeau, Johannes Kopppenhoefer, John Mc. Farland, Edwin Valentijn, Ronald Vermeij etc…. . )

Systematic error in zeropoint • Example: dependence on calibrator set – WFC@INT: DR 5 vs Sloan from Landolt+Jester transformations (2005, AJ, 130, 873) filter Median ΔZPT (DR 5 -Landolt) uncertainty Δu 0. 07 0. 02 Δg 0. 02 0. 01 Δr -0. 03 0. 01 Δi -0. 04 0. 02 Δz 0. 00 0. 04 Verdoes Kleijn et al, 2007, ASP Conf, Series 364, 103

Overall photometric stability 1σ variations photometric scale • Within a photometric night – WFC@INT: u~0. 020, g~0. 015, r~0. 015, i~0. 015, z~0. 020 – WFI@ESO/MPG: R<~0. 03 • Over months (from WFI repeated fields) : – Photom nights only: R~0. 05 in R – All nights (so variation largely atmospheric) : R~0. 1

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 (Omega. CAM calibration plan)

Extinction Curves La Silla measurements 1995 A&AS 112_383 Burki etal Extinction Curve in use in Astro-WISE (La Palma Extinction Curve)

Variation in Extinction Curves La Silla (UBV) CTIO ugriz Burki et al, 1995, A&AS, 112, 383 adapted from Smith et al, 2008, AJ, submitted (variation due to volcanic activity) Wavelength independent shift of extinction coeff (within~0. 025)

Up-coming Southern Sloan Standards • Extension of Sloan standard work via CTIO 0. 9 m telescope • 58 Southern fields (16000 stars) • Smith et al, 2008, AJ (revising for referee comments) In future • Sky. Mapper project (PI Brian Schmidt) • tied to Tycho-2 catalog (BV)+transformations • Omega. CAM secondary standards programme • tied to Landolt ( plus Sloan South? ) • Global photometry

Global photometry • Full data lineage back to raw data for magnitudes of stars in Southern Hemisphere will increase monotonically automatically awe> pp. photcat. get_source_data(columns) awe> pp. photcat. get_content_of_catalog() awe> qsl=(Source. List. ul. DEC<-10. 0 and Source. List. ul. DEC>-20. 0) awe> len(qsl) … 25793

Summary • Chip-by-chip • ZPT accuracy in Astro. WISE – random: ~0. 01 mag – Systematic: no quote: too much instrument/filter dependent • Global photometry conceptually within reach with Astro-WISE

Error estimation on ZPT and extinction • TBD Discuss error estimation and propagation

Photometric quality: zeropoint a test case • Discuss Cen A case: – sd(mag stars)~0. 1 mag – Limited by inter/intra night changes in photometric conditions ultimately (? )

Astro-WISE Standard star program Sloan ugriz standards for Southern hemisphere Astro-WISE ‘STANDARD’ STANDARD SET Field SA 51 SA 57 SA 68 SA 92 SA 93 SA 94 SA 95 SA 98 SA 100 SA 101 SA 102 SA 103 SA 104 SA 105 SA 106 SA 107 SA 108 SA 110 SA 112 SA 113 SA 114 SA 115 (J 2000) (deg) 112. 663 197. 171 4. 146 13. 946 28. 783 44. 033 58. 500 103. 021 133. 529 149. 112 163. 779 178. 779 190. 592 204. 533 220. 533 234. 896 248. 033 280. 679 310. 529 325. 533 340. 529 355. 779 (J 2000) (deg) +29. 828 +29. 384 +15. 844 +0. 949 +0. 824 +0. 571 +0. 000 -0. 328 +0. 546 -0. 386 +0. 866 +0. 556 -0. 553 +0. 676 +0. 427 -0. 252 +0. 369 +0. 348 +0. 524 +0. 493 +0. 689 +0. 888 #Landolt 0 0 0 41 4 7 45 46 6 35 5 2 34 4 2 28 6 39 7 42 9 10 #Stetson #SDSS DR 5 0 214 0 952 0 1302 213 1094 0 1128 0 1099 426 1093 1116 0 1 3343 117 1776 66 1517 0 1507 76 1576 0 2172 15 2864 728 3889 3 6148 589 0 73 12087 483 4046 5 1957 0 1170 #PC 0 0 0 6475 0 0 0 23840 0 5591 0 0 5701 0 0 12006 0 38562 0 13947 0 0 Up-coming steps Southern Sloan photometric standards Omega. CAM 2 ary standards programma Other programs (check with Ivezic)

• Ik weet dat ze van plan zijn met heel korte exposures (4 sec) 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 Ki. DS.

Accuracy UBVRI – ugriz transformations • Discuss Results (systematic+random errors from analysis also presented at Blankenberge

Summary & Conclusions

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

Outline • Chip-by-chip photometric calibration – Content standard star catalog • UBVRI standards only: Stetson, Landolt( R dist , typical errors) • Large ensemble of non-primary standards: SDSS, aw 2 s(fainter, typical errors) – m=-2. 5 log(countrate)+ ZPT- k. X+ (CT_0 * color - CT_1) – Transformations: for which instruments? – Instrumental-Standard: non-diagnonal terms) – UBVRI-SDSS: systematic errors, ( random errors) – Extinction curve: TBD – Calibration procedure • sextractor aperture photometry – Random errors • ZPT repeatability: upper-limit 1: same field, different nights, upperlimit 2: Cen-A observations • TBD: extinction – Systematic errors: • ZPT vs airmass, date-obs, chip, field, origin standards(=WFC results)

Monitoring photometric calibration in Astro-WISE: zeropoint • Calibrating instrument instead of single observations • Stability atmosphere, instrument