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MegaPrime Detrended Photometric Data Query Help


General Description

This form can be used by registered CFHTLS users to browse the photometric data for processed science images. The basic relevant photometric equations are:
where m is the instrumental magnitude, DN are counts in digital units, EXPTIME is the exposure time in seconds, M is the calibrated magnitude, Zp_obs is the observed zeropoint, C_airmass is the airmass term, C_color is the color term, FILTER1 is the magnitude measured in the filter specified by FILTER1, and FILTER2 is the magnitude measured in the filter specified by FILTER2.

Queries can be executed based upon specified exposure number(s).

Search Constraints

Field Name Description
Exposure Number The unique identifying "odometer" number for a CFHT exposure.


Detrended Image Photometric Data Query Tabular Output

Field Name Description
Observed Image Quality Observed image quality (FWHM in arcseconds). The IQ statistics are derived from the Elixir processing based on SExtractor analysis of each of the MegaPrime CCDs. The five IQ statistics provide several views of the global image quality in a MegaPrime image.
  1. IQ_REFCCD gives the image quality measured for the single reference CCD (currently ccd13). This measurement is used by the QSO team during the observations and the validation stage to assess if the image meets the requested image quality.
  2. IQ_CENTER is derived from the central 10 detectors. The 10 values are clipped for > 3 sigma outliers before the remaining detector IQ values are averaged.
  3. IQ_R_RATIO provides the ratio between the central 10 detectors and the outer 26 detectors. Both lists are clipped by 3 sigma as above.
  4. IQ_X_RATIO provides the ratio between the left (east) 8 detectors and the right (west) 8 detectors. Both lists are clipped by 3 sigma as above.
  5. IQ_Y_RATIO provides the ratio between the top (north) 9 detectors and the bottom (south) 9 detectors. Both lists are clipped by 3 sigma as above.
Observed Sky Background Value Observed sky background value in counts per pixel.
Nightly zeropoint - Actual Actual value for image photometric zeropoint.
Nightly zeropoint - Nominal Nominal value of photometric zeropoint. This is the zeropoint value for perfectly transparent conditions.
Nightly zeropoint - Scatter RMS scatter of image zeropoint value. The scatter is computed from all standard star observations taken on the same night as the image.
Nightly zeropoint - Color Term Color term of photometric solution for the night the image was taken. See equation (2) above.
Nightly zeropoint - Airmass Term Airmass term of photometric solution for the night the image was taken. See equation (2) above.
Nightly zeropoint - Filter 1 Name of first filter used for photometric solution for the night the image was taken.
Nightly zeropoint - Filter 2 Name of second filter used for photometric solution for the night the image was taken..
Nightly zeropoint - N images Number of MegaPrime images used to compute photometric solution for the night the image was taken.
Nightly zeropoint - N stars Number of standard stars used to compute photometric solution for the night the image was taken.
Saturation Magnitude Magnitude of objects saturating the MegaPrime image.
Limiting Magnitude Magnitude corresponding to 5-sigma, point-source detection on MegaPrime image.