The Astro-Wise standard stars (with a focus on OmegaCAM)
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Transcript of The Astro-Wise standard stars (with a focus on OmegaCAM)
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.