Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 14

First-Order Grating G140L

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Description

The G140L grating mode is used with the FUV-MAMA, has a resolving power R~1000, and covers a spectral range from 1150 to 1700 Å in a single exposure.

Notice, that with two observations, one with G140L and one with G230L, the full spectral region, from 1150 to 3100 Å can be efficiently observed at an R~1000.

Recommended Uses

The G140L grating mode is designed for observations where high spectral resolution is not required, but efficient, spatially resolved spectroscopy providing wide spectral coverage in the ultraviolet is desired.

Grating	Spectral Range		Average Dispersion (Å per Pixel)	Plate Scale (arcsec / pixel)	Tilts	Central Wavelengths
	Complete	Per Tilt
G140L	1150-1730	610	0.6	0.025	Prime	1425

Figure 13.38: Wavelength Range for the G140L Grating Setting


 

G140L Sensitivity

Table 13.11: G140L Throughputs & Sensitivities for a Point Source

	Sensitivity	% Throughput
1200	3.6E13	2.2
1250	5.8E13	3.4
1300	6.3E13	3.5
1350	5.7E13	3.1
1400	4.8E13	2.5
1450	3.9E13	2.0
1500	3.1E13	1.5
1550	2.3E13	1.1
1600	1.5E13	0.7
1650	1.1E13	0.5
1700	8.2E12	0.4

Figure 13.39: G140L Point Source (left axis) and Diffuse Source (right axis) Sensitivities.


 

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 plate scale in units of arcseconds per pixel and by the width of the desired slit in units of arcseconds.

G140L 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 13.40: Diffuse Source Signal-to-Noise as a Function of STMAG for G140L


 
Figure 13.41: Point Source Signal-to-Noise as a Function of STMAG for G140L


 

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