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32.10 PSF/LSF

32.10.1 Point Spread Functions

Pre-COSTAR:

FOS ISR 104 presents a comprehensive series of TIM modeled monochromatic FOS point spread functions. Default values for dust and mirror micro-roughness were included in the PSF models as was pointing jitter with an rms of 7 milliarcsec. FOS/BL PSFs were calculated every 200 Å. throughout the range 1200-5400 Å. FOS/RD PSFs were calculated every 200 Å. throughout the range 1600-8400 Å.

Observational white light PSFs for the 4.3 aperture are described in FOS ISR 148. These PSFs were formed by superposition of numerous ACQ images of the same point source located at different positions in the 4.3 aperture.

The model PSFs were used to produce theoretical aperture throughputs and aperture throughput ratios relative to the 4.3 aperture (see FOS ISR 105). Theoretical aperture throughputs for miscentered targets were also derived from the model PSFs (see FOS ISR 107).

Post-COSTAR:

Post-COSTAR observational white light PSFs for the 4.3 aperture are described in FOS ISR 148. These PSFs were formed by superposition of numerous ACQ images of the same point source located at different positions in the 4.3 aperture.


The pre-COSTAR PSFs are available from the STScI anonymous FTP site, ftp.stsci.edu. See the FOS WWW Calibration Products and Tools page for further information.

32.10.2 Line Spread Functions

Pre-COSTAR:

Both FOS/BL and FOS/RD monochromatic LSFs for each non-occulting FOS aperture were derived from the pre-COSTAR model PSFs (see FOS ISR 104). The LSFs were computed for a point source perfectly centered in each aperture. FOS/BL LSFs were calculated every 200 Å. throughout the range 1200-5400 Å. FOS/RD LSFs were calculated every 200 Å. throughout the range 1600-8400 Å.

Observational white light LSFs for the 4.3 aperture are described in FOS ISR 148. These LSFs were formed by integration of the pre-COSTAR white light PSFs described above.

Post-COSTAR:

Observational white light LSFs for the 4.3 aperture are described in FOS ISR 148. These LSFs were formed by integration of the post-COSTAR white light PSFs described above.

Observational line profiles of unresolved spectrum lines (observational dispersed light LSFs) are available in ASCII format from the FOS WWW page for FOS/BL G130H, G190H, and G270H, and FOS/RD G190H, G270H, and G400H and the 4.3, 1.0, and 0.3 apertures.

These LSFs, which are the subject of forthcoming FOS ISR 155, clearly display typical Voigt profiles with both a Gaussian core and Lorentzian wings. For S/N < 10 only the Gaussian core is evident. At higher S/N through the two larger apertures, the Lorentzian wings develop at approximately 20% of peak intensity. The width of the LSF is determined by the width of the response of the FOS detector element, a nominal 1 diode FWHM Gaussian profile (FOS ISR 061).

The FOS/RD G270H has the narrowest core (FWHM~1 diode), whereas the FOS/BL G270H has the widest core (FWHM~1.25 diodes). All FOS/BL profiles have broader wings than those in the FOS/RD spectra. The different profiles are attributable to different magnetic and optical focus quality for the two detector assemblies as well as possible grating alignment differences in the optical paths inside the FOS.

The FOS/RD G270H profile most nearly matches the FOS/RD white light profile, while the FOS/RD G130H comes closest to the FOS/BL white light profile.


You can download the post-COSTAR ASCII LSF listings from the FOS WWW Calibration Products and Tools page. The pre-COSTAR LSFs are available from the STScI anonymous FTP site, ftp.stsci.edu. See the FOS WWW Calibration Products and Tools page for further information.



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