Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 14

Echelle Grating E230H

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Description

The E230H grating is used with the NUV-MAMA and provides echelle spectra at a resolving power of ~110,000 from 1620 to 3100 Å.

Special Considerations

A single E230H echellogram covers ~267 Å, over ~20-70 orders. The orders are spaced by only ~ 12.7 pixels (0.37 arcseconds) at 1650 Å and 47.2 pixels (~1.38 arcseconds) at 3100 Å. The grating must be scanned, with exposures taken at six distinct settings to cover the full spectral range of the grating.

The secondary central wavelength at 2812 Å has had direct sensitivity calibrations performed during Cycle 7 to support the large number of observations using that position.

Grating	Spectral Range		Average Dispersion (Å per Pixel)	Dispersion, Cross Dispersion Plate Scale (arcsec / pixel)	Tilts	Central Wavelengths
	Complete	Per Tilt
E230H	1620-3150	~267	/228,000	0.047,0.029	Prime	1763, 2013, 2263, 2513, 2762, 3012
					Secondary	1813, 1863, 1913, 1963, 2063, 2113, 2163, 2213, 2313, 2363, 2413, 2463, 2563, 2613, 2663, 2713, 2812, 2862, 2912, 2962

Figure 13.50: Wavelength Ranges for the E230H Grating Settings


 

E230H Sensitivities

Table 13.14: E230H Throughputs and Sensitivities for a Point Source

	Sensitivity	% Throughput
1700	4.5E10	0.2
1800	8.3E10	0.3
1900	1.1E11	0.4
2000	1.5E11	0.4
2100	1.9E11	0.5
2200	2.4E11	0.6
2300	2.7E11	0.7
2400	2.8E11	0.7
2500	2.9E11	0.7
2600	2.9E11	0.6
2700	2.8E11	0.6
2800	2.5E11	0.5
2900	2.2E11	0.4
3000	1.6E11	0.3

Figure 13.51: E230H 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.

E230H 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 13.52: Diffuse Source Signal-to-Noise as a Function of STMAG for E230H


 
Figure 13.53: Point Source Signal-to-Noise as a Function of STMAG for E230H


 

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