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Photometric calibration with Aladin

Method in 4 steps. From an astrometrical calibrated imageThe first step will be to use S-extractor on your image to extract sources and estimate photometryAfter that you will compare this first result with a photometric catalog such GSC2.2And you will adjust S-extractor parameters for fixing unkn

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Photometric calibration with Aladin

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    1. Photometric calibration with Aladin

    2. Method in 4 steps From an astrometrical calibrated image The first step will be to use S-extractor on your image to extract sources and estimate photometry After that you will compare this first result with a photometric catalog such GSC2.2 And you will adjust S-extractor parameters for fixing unknown ones

    3. Requirements.. You have Aladin install on your machine (http://aladin.u-strasbg.fr/AladinJava?frame=downloading) If you have a firewall, you will have to open temporary the port 4128 that Aladin will be using for S-extractor remote usage).

    4. Load your image… Launch Aladin and load your image. Here a SDSS image centered on NGC1087

    5. Use S-extractor… Use the S-extractor tool provided with Aladin for getting a first approximation…

    6. Load a photometric catalog… Load a photometric catalog such as the GSC2.2

    7. X-match the result… Xmatch your result with the GSC to have common objects to compare…

    8. Compare both mags… Compare the 2 mag values in a 2D graph via VOplot.

    9. Adjust the zero point… Extrapolate the zero point -14.5 ? 12.5 ZeroPoint = 27 And refine photometry with this new value

    10. You have it !

    11. Just for the fun Your result compared to the SDSS original catalog

    12. Remarks… S-extractor is developed by E. Bertin from Terapix (Paris) and this version is running on a PC cluster at CDS (Strasbourg). If your calibration requires better tuning that the default Aladin one, download and use S-extractor directly on your machine. NB: Aladin can read directly S-extractor catalog outputs.

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