This page is http://space.mit.edu/HETG/ia/perform_2.html 1998-12-06


AXAF Grating Spectrometer Performance

Resolving Power
"E/dE" 		The ability of the spectrometer to separate closely spaced lines; this depends on the energy, the grating period (amount of diffraction), and the point spread function of the diffracted image.
Effective Area The intensity of the diffracted images; this depends on the HRMA collecting area, the grating diffraction efficiency, and the detector efficiency.


Grating Spectrometer Performance Contributions

HRMA HETG/LETG ACIS/HRC Observatory
Resolving Power = HRMA PSF Grating Period
Grating "dp/p"
Rowland Geometry 		Detector Spatial Resolution
(ACIS: incl. dither rate effect)
Focal Surface Shape 		Aspect Blur
System Focus
Alignments
Effective Area = HRMA Effective Area Grating Facet Efficiency
Vignetting Terms
Grating Alignment 		Detector QE
incl. grade, gain, etc. effects 		Alignments


HETG Calibration: http://space.mit.edu/HETG/xrcf.html perf-2, -->