An example of STIS E230H echelle spectroscopy (both the echelle spectrum and a few sample extracted orders) of star CPD-59D2603 showing the interstellar absorption from the Carina Nebula is given in
Figure 15.3. (See also Walborn et al. 1998,
ApJ,
492, L169.)
There are four echelle grating modes which provide spectroscopic coverage from ~1145 е to 3100 е at resolving powers from R ~ 30,000 to
R ~ 114,000 (or even
R ~ 200,000 with the
0.1x0.03 aperture and specialized data reduction; see
Section 12.6). Through simultaneous observation of multiple orders, they are designed to maximize the spectral coverage achieved in a single exposure of a point source.
Figure 4.10 below summarizes the wavelength coverage and kinematic resolutions of the echelle gratings. In short:
Although we do not recommend routine use, the echelle gratings can be used with a long slit (the 6X0.2 slit) to obtain echelle spectroscopy of extended objects with weak continua. Long-slit echelle data, however, will not be calibrated by the STScI pipeline, and they will require more extensive post-observation processing by the user since ambiguous overlap of wavelengths from different parts of sources will occur in the image (see
Section 12.2 if you are considering such observations). In addition to the spectral purity considerations in the dispersion direction mentioned above for the first-order gratings, echelle observations are subject to contamination in the cross-dispersion direction by scattered light. This effect is aggravated toward shorter wavelengths as the orders become more crowded. Continuum sources should not normally be observed with slit lengths greater than 0.2 arcsecond, and even then special data analysis may be required to optimize the accuracy of the results. See
Section 13.7.