Hubble Space Telescope Why doesn't the Exposure Time Calculator work?
Q.: Why doesn't the Exposure Time Calculator work?
A.: NICMOS has three independent Cameras, and it is necessary to select
the desired Camera (click on the button to the left of the Camera
number) for the Exposure Time Calculator to work. After that, the
filter requested for the observation should be selected from the
pull-down menu. CLEAR is not a filter.
Q.: When using the WWW Exposure Time Calculator for polarimetry,
what is the source flux I have to input?
A.: The TOTAL source flux can be input in the Exposure Time
Calculator. The Calculator takes care of using only half of the input
flux for estimates of the exposure time with the polarizers, which is
correct for an unpolarized source. For a strongly polarized source, of
course, the detected flux will be larger or smaller than this for a
strongly polarized source, depending on the polarization angle of the
source relative to each of the three polarizers.
Q.: How do I convert a line strength into a flux in Jy?
A.: If you have a total line flux in W/m2 you can convert it into an
equivalent continuum flux in Jy for one of the NICMOS filters by dividing
it by the filter bandwidth in Hz and then multiplying by 1.0E+26. This
will give you a flux that you can use in the Exposure Time Calculator
as though it were a continuum source. If you have a ground-based
spectrum calibrated in Jy, you should integrate the spectrum across
the filter bandwidth in order to determine the total flux, and then
convert back to an equivalent continuum flux as above. If your source
is entirely dominated by very strong line emission inside the filter
bandpass, you can use the `emission line source' option in the Exposure
Time Calculator, and enter the relevant line flux.