Background values listed below are the count rate in DNs per square pixel per second. The conversion to electrons is NOT done here (or in the zero point calculation).
Zero point is the amount to be added to the instrumental magnitude (-2.5*log(DN/sec)) of a source to obtain the intrinsic magnitude of the source. It is calculated at an airmass of 1.0. To get the magntiude at an airmass of 0.0, add the extinction coefficient listed below. Note that the instrumental magnitude is calculated with DNs, NOT electrons.
The plate scale is 0.25 arcsec/pixel.
The gain (NOT used here) is 14.2 electrons per DN.
The dark current is 13 electrons per second per pixel.
The read noise is 46 electrons per pixel.
The signal is linear to better than 5% up to count levels of 5500 DN.
| Filter |
Background
(DN/sec/pixel) |
Background
(mag/sq arcsec) |
Zero point
magnitude |
Extinction
coefficient [IRTF values] |
Max exp time (minutes)
for sky linearity |
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| J | 3.8 | 15.67 | 20.13 | TBD [0.102] | 24 | ||||||||||||
| H | 12.6 | 14.02 | 19.78 | TBD [0.059] | 7 | ||||||||||||
| K | 40.7 | 12.48 | 19.51 | TBD [0.088] | 2 |