Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 17

Echelle Grating E230M

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Description

The E230M grating is used with the NUV-MAMA and provides echelle spectra at a resolving power of 30,000 from 1570 to 3100 Å.

Special Considerations

A single exposure with this grating covers 800 Å over ~20-40 orders. The interorder separation is ~18 pixels (0.52 arcseconds) at 1650 Å and 62.5 pixels (~1.8 arcseconds) at 3100 Å. The grating must be scanned, with exposures taken at two distinct settings to cover the full spectral range of the grating.

Grating	Spectral Range		Average Dispersion (Å per Pixel)	Dispersion, Cross Dispersion Plate Scales (arcsec / pixel)	Tilts	Central Wavelengths
	Complete	Per Tilt
E230M	1570-3110	~800	/60,000	0.035,0.029	Prime	1978, 2707
					Secondary	2124, 2269, 2415, 2561

Figure 13.46: Wavelength Ranges for the E230M Grating Settings


 

E230M Sensitivities

Table 13.13: E230M Throughputs & Sensitivities for a Point Source

	Sensitivity	% Throughput
1700	1.2E11	0.1
1800	2.5E11	0.2
1900	3.7E11	0.2
2000	5.1E11	0.3
2100	7.6E11	0.4
2200	1.0E12	0.6
2300	1.3E12	0.7
2400	1.4E12	0.7
2500	1.6E12	0.7
2600	1.7E12	0.7
2700	1.7E12	0.7
2800	1.7E12	0.7
2900	1.4E12	0.5
3000	1.1E12	0.4
3100	4.5E11	0.2

Figure 13.47: E230M 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.

E230M 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 13.48: Diffuse Source Signal-to-Noise as a function of STMAG for E230M


 
Figure 13.49: Point Source Signal-to-Noise as a Function of STMAG for E230M