FLITECAM Grism Observation Calculator

Web-based input form for FLITECAM Grism Observation Calculator -- beta version


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 instrument configuration (FLITECAM or FLITECAM+HIPO), 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). The choice of slits is either Narrow (1.0 arcsec) or Wide (1.6 arcsec). 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 instrument configuration (FLITECAM or FLITECAM+HIPO), the slit size (Narrow or Wide), the desired signal-to-noise ratio, the integration time for an individual image (in sec), the source flux at the reference wavelength (usually 2.2 microns, K band) or the 2MASS Ks mag of the source (in which case the reference wavelength field will be ignored and a reference wavelength of 2.159 microns will be used), the source spectral shape (blackbody or power law) and either the effective blackbody temperature of the source or the power law index (depending on the shape chosen). The power law index is alpha, and F_lambda ~ lambda^-alpha. 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 instrument configuration (FLITECAM or FLITECAM+HIPO), the slit size (Narrow or Wide), the the source flux at the reference wavelength (usually 2.2 microns, K band) or the 2MASS Ks mag of the source (in which case the reference wavelength field will be ignored and a reference wavelength of 2.159 microns will be used), the source spectral shape (blackbody or power law), either the effective blackbody temperature of the source or the power law index (depending on the shape chosen), the integration time for an individual image (in sec), and the total integration time for the observation (in sec). The power law index is alpha, and F_lambda ~ lambda^-alpha. 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.)

The conversion between the limiting continuum flux and limiting line flux, under the assumption of an unresolved Gaussian line, is given by F_line = 1.06*lambda*F_peak/R = 1.06*lambda*chi_line*F_cont/R where F_line is the line flux in units of W/m2, F_peak is the flux density at the peak of the line and F_cont is the continuum flux density in units of W/m2/micron, lambda is the wavelength of the line in microns, R is the resolving power, and chi_line is the line contrast factor (peak line intensity relative to the continuum intensity). Alternatively, F_line = 3.19e-15*F_peak/(lambda*R) = 3.19e-15*chi_line*F_cont/(lambda*R) for F_peak and F_cont in units of mJy.

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).



Input Observing Parameters

Select the quantity to be estimated:

Choose the instrument configuration:

Choose a slit size (arcsec):

Required Signal-to-Noise ratio:

Single frame integration time (sec):

Total integration time (sec):

Source type:

Source Flux :

at

microns
Source spectral shape:

Source blackbody temperature (K) or Power Law Index:



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