Photometric Error Definitions

Error

Note: This has also been named Error(E) in some versions of Mira.

This value lists an empirical, or measured estimate of the 1-sigma error based on the noise measured in the background annulus plus the gain, aperture size, and signal level. This value is subject to large statistical fluctuations for faint objects and it may be better to use these values to define a curve that gives a smoother estimate of the random error versus magnitude.

If more than 1 standard star is used, you can choose whether this value is a Root Sum Square error that includes both the internal error of the measurement and the error in the calculated zero point. This is controlled by the Include Zero Point Error checkbox on the Other preferences page.

Error(T)

This value lists a theoretical estimate of the 1-sigma error based on the readout noise, gain, exposure time, aperture size, and signal level. This calculated value is very smoothly changing as a function of magnitude but, since it is not measured, it does not show measurement fluctuations that may indicate a problem with the measurement.

If more than 1 standard star is used, you can choose whether this value is a Root Sum Square error that includes both the internal error of the measurement and the error in the calculated zero point. This is controlled by the Include Zero Point Error checkbox on the Other preferences page.

S/N

This is the Signal to Noise ratio of the object plus background. This is not simply the inverse of Error or Error(T), which refer to the net object signal above the background. Use this quantity to characterize the total amount and "quality" of the signal detected.