If Point Source is selected, the FWHM of the point-spread-function (PSF) is used to calculate the point source sensitivity. The point source sensitivity is calculated from the surface brightness noise in a diameter given by the root-square-sum of the Airy disk and a seeing disk, assuming half the source flux is within this diameter. The observed image FWHM is determined by diffraction plus the following three effects: telescope aberration, chopper distortion, and seeing (these latter three are combined in a single user-specified parameter below called 'seeing'). At the IRTF, the three combined effects are typically .5 arcsec. Alternatively, you canuse the 'User-entered PSF' option to directly specify the FWHM of the PSF. If Extended is selected instead of point source, the sensitivity for an extended source is calculated, in Jy/arcsec^2.
Note that the results present the total on-source time required; standard star and gain calibration observations must also be done.
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