PI Applicable Sky Brightness Magnitudes
The PI should base their sky brightness criteria on the actual HET sky
brightness values not the theoretical values.
It is very important that the PI's remember that with slit and
fiber spectroscopy the size of the slit or fiber must be considered.
For example, the 3" slit will have 7"" of area over which to collect sky thus
the affective sky brightness in the fiber aperture will be 2.1 magnitudes
brighter. So if a PI wants only a 1% contamination from sky for a
14th magnitude object with the 3" HRS fibers then the sky must be
14 (object mag) + 5 (1 part in 100) + 2.1 (skyfiber size)
21.1 magnitude per square arcsecond. This means the object would not be
observed in bright time. The PI could reduce the contamination a bit
by using a smaller science fiber 2" has only 3.1"" of collecting area but
also will collect a less flux from the science target.
Also please keep in mind the actual HET sky brightness numbers measured
above are brighter by about a magnitude than the theoretical numbers. Please
do not exceed the default maximum V sky brightness figure of 21.0 in your target
constraints, which HET software employs to signify as fully dark.
NOTE: ALL greyed out text is outdated and should not be trusted. Updated sky brightness information is available on the