|STIS Instrument Handbook for Cycle 25|
The E140H grating is used with the FUV-MAMA and provides echelle spectra at a resolving power of ~114,0001 from ~1140 to 1700 ÅA single E140H echellogram covers ~210 Å over ~50 orders. The order separation is ~16 pixels (0.47 arcseconds) at 1150 Å and ~36 pixels (1.05 arcseconds) at 1700 Å. The grating must be scanned, with exposures taken at three distinct settings to cover the full spectral range of the grating.Note that while the spectral format of the 1234 Å setting extends down to 1133 Å, the throughput becomes vanishingly small below about 1140 Å.
λ/228,000 Figure 13.58: Wavelength Ranges for the E140H Grating SettingsTable 13.16: E140H Throughputs & Sensitivities for a Point Source
Figure 13.59: E140H Point Source (left axis), and Diffuse Source (right axis) Sensitivities. Throughput curve traces the peaks of the blaze function for each order.Point source sensitivity assumes full transmission (zero slit losses). Diffuse source sensitivity assumes a 0.1” wide slit. To convert point source sensitivities to diffuse source sensitivities multiply the point source values by the grating spatial (cross dispersion) plate scale in units of arcseconds per pixel and by the width of the desired slit in units of arcseconds.The top axis displays constant Fλ values corresponding to the STMAG units (V+STMAGλ) on the bottom axis. Recall that STMAG=0 is equivalent to Fλ = 3.63E-9 erg/cm2/s/Å. The curves are labeled with exposure times in seconds.