MJD of Observation: Enter the Modified Julian Date of the observation's start time. This is the header keyword EXPSTART. The expected format is 5#####.####...
Measured Source Counts: Enter your measured counts, in electrons, for the source you wish to estimate CTE effects.
X-Position on CCD: Enter the X-position of the source on the CCD. The expected range is from 1 - 800.
Y-Position on CCD: Enter the Y-position of the source on the CCD. The expected range is from 1 - 800.
Background Counts: Enter your measured background for the observation, in electrons.
Stellar Magnitude: Enter your stellar magnitude.
The CTE Correction Formulae:
1. Calculate the following variable values:
LCT0 = ln (CT) - 7 BG = sqrt (background2+1) - 10 LBG = ln( sqrt(background2+1) ) - 1 YR = (MJD - 50193) / 365.25
2. Calculate XCTE, the CTE loss (in magnitudes) in the X readout:
XCTE = 0.0202 * e - (0.00083 * BG) * (X/800.0)
3. Recalculate LCT using:
LCT = LCT0 + 0.921*XCTE
4. Calculate YCTE, the CTE loss (in magnitudes) in the Y readout:
c1 = 0.01785 * (0.655 * e - (0.402 * LBG) + 0.345 * e - (0.0156 * BG)) * (1.0 + 0.253 * YR + 0.0082 * YR2) * (Y/800.0) c2 = 2.35 * e - (0.517 * LCT) - (0.476 * XCTE) YCTE = ( ln (ec1 * 1.0 + c2) - c2) / 0.476
5. The corrected magnitude for the star is then given by:
MAGcorr = MAG - XCTE - YCTE
CT = Number of counts in electrons for the point source. XCTE = CTE loss in percent over 800 pixels in the X-direction. YCTE = CTE loss in percent over 800 pixels in the Y-direction. X, Y = X, Y source position in pixels. background = Mean number of counts in electrons for a blank region of the background. BG = sqrt (background2+1) - 10 LBG = ln( sqrt(background2+1) ) - 1 MJD = Modified Julian Date for the observation. YR = (MJD - 50193) / 365.25 MAG = uncorrected stellar magnitude. MAGcorr = CTE corrected stellar magnitude.
Note 1: Small uncertainties in the bias level can lead to the measurement of negative values for background when the background is very low (about 4 DN in a 14 sec exposure).