The Astro-Wise standard stars

(with a focus on OmegaCAM)Gijs Verdoes Kleijn & Ronald Vermeij

For the Astro-Wise consortium

Aim: sampling complete FOV with photometric calibrators

OmegaCAM FOV

Aim: sampling complete FOV with photometric calibrators

OmegaCAM FOV

Aim: sampling complete FOV with photometric calibrators

OmegaCAM FOV

•Accurate photometric calibration ( per chip)•Quantifying sky concentration effects

Photometric accuracies

• Instrumental requirement: 5% accuracy in photometry with usual data reduction

• Our estimate: with Astro-Wise infrastructure 2-3% achievable with bit extra work on top usual data reduction

OmegaCAM calibration plan

All-year round monitoring field near South Equatorial Pole

Candidate field:(ra,dec)=(51.429,89.04)deg (l,b)=(302.29 -27.82)deg

Purpose: monitor instrument performance and atmospheric conditions through night

Standard star catalog in Astro-Wise

• 8 equatorial fields• Final catalog will be produced from

OmegaCAM observations of fields in first year.

• Currently a preliminary version in place – to be used during commissioning.– derived from WFC/INT La Palma data – WFC data was calibrated using Landolt

standards (transformed to Sloan system)

The standard star fields

The content of a fieldField SA92

● = Landolt stars published data (transformed to ugriz)

+ = Sloan published data●= “AW2S”, our secondary standards obtained from WFC/INT La Palma data

Deriving a Zeropoint

•Reduce standard starfield

•Associate stars with entries in•standard star catalog.

•Sigma clip to discard outliers

•Estimate zeropoint for each remaining star

•Zeropoint= weighted mean of estimates

Work in progress

• Good determination random and systematic errors of standard star– magnitude in the catalog– measured flux

• Propagation of these errors to ZPT

SA92 SA101

SA104 SA107 SA113

Aw2S-SDSS3 magnitude residuals

SA92

SA101

SA104

SA107

SA113

Independent photometry checks

• Galaxy number counts

Stellar locus in color-color space

Izevic et al 2004

In conclusion

• First version of standard star catalog in Astro-Wise in place: accuracy/systematics analysis in progress.

• Additional independent photometry checks being considered.