Echelle Grating E140H

Description

The E140H grating is used with the FUV-MAMA and provides echelle spectra at a resolving power of ~114,000¹ 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.

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.

 

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	λ/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

λ	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 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.

 

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

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1

R ~ 200,000 possible with the 0.1x0.03 aperture; see page 249.