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Properties of the Echelle Gratings

Reference Information on Instrument Performance

Properties of the Echelle Gratings

Wavelength Coverage, Bandpass, and Sensitivity

The following tables summarize basic properties of the two echelle gratings. The dispersion in each order has not been listed but does not change if it is computed in velocity units. At the center of each order, the dispersion is 3.0 km s-1 per diode, at the long-wavelength end of each order it is 2.9 km s-1 per diode, and at the short-wavelength end of each order it is 3.1 km s-1 per diode.

Figure 8.3: Properties of Grating Echelle-A

Figure 8.4: Properties of Grating Echelle-B

Echelle Wavelength Formats

The illustrations below provide a means of estimating where particular wavelengths fall within the echelle formats and where they lie relative to the blaze peak. Note that these layouts are purely schematic; the actual length of the free spectral range changes from order to order. The center of each order is at ml = 56200.

Figure 8.5: Schematic format of wavelengths for Echelle-B.

Figure 8.6: Schematic format of wavelengths for Echelle-A.

Echelle Blaze Function

The figure below shows the echelle blaze function (also known as the "Ripple Function") in the form of sensitivity relative to the peak of the blaze as the product of wavelength and order number.

Figure 8.7: Normalized blaze function for the GHRS echelle gratings.

Wavelength Coverage, Bandpass, and Sensitivity
Figure 8.3: - Properties of Grating Echelle-A
Figure 8.4: - Properties of Grating Echelle-B
Echelle Wavelength Formats
Figure 8.5: - Schematic format of wavelengths for Echelle-B.
Figure 8.6: - Schematic format of wavelengths for Echelle-A.
Echelle Blaze Function
Figure 8.7: - Normalized blaze function for the GHRS echelle gratings.