Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 17

Echelle Grating E140H

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Description

The E140H grating is used with the FUV-MAMA and provides echelle spectra at a resolving power of ~110,000 from 1140 to 1700 Å

Special Considerations

A 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.

The secondary central wavelength at 1271 Å has had direct sensitivity and wavelength calibrations performed during Cycle 7 to support the large number of observations using these positions.

Grating	Spectral Range		Average Dispersion (Å per Pixel)	Dispersion, Cross Dispersion Plate Scale (arcsec / pixel)	Tilts	Central Wavelengths
	Complete	Per Tilt
E140H	1140-1700	~210	/228,000	0.047,0.029	Prime	1234, 1416, 1598
					Secondary	1271, 1307, 1343, 1380, 1453, 1489, 1526, 1562

Figure 13.58: Wavelength Ranges for the E140H Grating Settings


 

E140H Sensitivity

Table 13.16: E140H Throughputs & Sensitivities for a Point Source

	Sensitivity	% Throughput
1200	5.0E10	0.4
1250	9.4E10	0.6
1300	1.1E11	0.7
1350	1.0E11	0.6
1400	8.9E10	0.5
1450	7.3E10	0.4
1500	5.7E10	0.3
1550	4.2E10	0.2
1600	2.9E10	0.1
1650	2.2E10	0.1

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.


 

Note

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.

E140H Signal-to-Noise

Note:

The top axis displays constant F values corresponding to the STMAG units (V+STMAG) on the bottom axis. Recall that STMAG=0 is equivalent to F = 3.63E-9 erg cm^-2 s^-1 Å^-1. The curves are labeled with exposure times in seconds.

Figure 13.60: Diffuse Source Signal-to-Noise as a Function of STMAG for E140H


 
Figure 13.61: Point Source Signal-to-Noise as a Function of STMAG for E140H