This form can be used to estimate (1) the limiting fluxes of objects that can be
observed with FLITECAM for a given signal-to-noise and exposure time; (2) the integration time needed
to reach a requested signal-to-noise for an input source flux and temperature; or (3) the
signal-to-noise resulting from an input source flux and temperature and integration time.
The output data file generated by this routine (flitecam.plt...dat) can be saved to your machine from
your browser window once the program has been run.
When estimating (1) the limiting flux, the user should specify the slit size, the desired signal-to-noise
ratio (per resolution element), the integration time for an individual image (in sec), and the total
integration time for the observation (in sec). At each wavelength point over the observed range,
the limiting flux is calculated for the input parameters. Magnitude limits are given for the nominal
centers of each broadband filter covered (e.g., at 2.2 microns for the K band). Saturation will occur
if the single frame integration time is too long. This can be seen in the plot as a red background for
those wavelengths that are saturated.
When estimating (2) the integration time needed to reach a specified signal-to-noise ratio (per resolution
element), the user should specify the slit size, the desired signal-to-noise ratio, the integration time
for an individual image (in sec), the source flux at 2.2 microns (K band), and the effective blackbody
temperature of the source. It should be noted that 0.3 sec is the shortest frame time allowable for a
full array readout. For long wavelengths single frame times of 0.3 sec are typical in order to
prevent saturation,
while for the mid wavelengths 3 sec is a typical value. For the shortest wavelengths, 300 sec is common.
(Note that Vega has a mag of 0.03 and a flux of approximately 4.14e-10 W/m2/micron, or 655 Jy,
in the K band.)
When estimating (3) the signal-to-noise ratio per resolution element, the user should specify the slit size, the the source flux at 2.2 microns (K band), the effective blackbody temperature of the source, the integration time for an individual image (in sec), and the total integration time for the observation (in sec). Saturation will occur if the single frame integration time is too long. This can be seen in the plot as a red background for those wavelengths that are saturated. (Note that Vega has a mag of 0.03 and a flux of approximately 4.14e-10 W/m2/micron, or 655 Jy, in the K band.)
This form and the program to estimate the desired quantities was written by Bill Vacca based
on the expected performance of FLITECAM. No guarantees regarding actual performance are
claimed or implied. The program uses a model of the atmospheric transmission
and emission as a function of wavelength for an altitude of 41000 ft, an elevation angle of 45 deg
(airmass of 1.4), and a zenith water vapor content of 7.3 microns. The model is smoothed to the
requested resolution (which depends on the slit size). The calculations assume perfect flat-fielding
and telluric division, and nominal instrument behavior. Note that the plate scale for FLITECAM is
0.475 arcsec/pixel.
Questions about FLITECAM and its expected performance should be directed to the SOFIA Help Desk. If you have problems with this form, please contact the SOFIA Help desk (sofia_help@sofia.usra.edu).