Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 14

First-Order Grating G230L

Description

The G230L grating is used with the NUV-MAMA and has a relatively high throughput and a resolving power of ~500.

Recommended Uses

G230L is designed for observations where high spectral resolution is not required, but efficient, spatially resolved spectroscopy with full spectral coverage in the near-ultraviolet is desired.

Special Considerations

Notice that the CCD G230LB grating mode also covers the near-ultraviolet with comparable resolution; see Comparison of G230LB and G230L for a detailed comparison of these two grating modes in that wavelength regime.

Grating
Spectral Range
Average Dispersion (Å per Pixel) Plate Scale (arcsec / pixel)
Tilts
Central Wavelengths

Complete Per Tilt

G230L 1570-3180
1610

1.58

0.025
Prime
2376

Figure 13.30: Wavelength Range for the G230L Grating Settings

G230L Sensitivities

Table 13.9: G230L Throughputs and Sensitivities for a Point Source

Sensitivity

% Throughput

1600

2.5E12

0.0

1700

2.4E13

0.4

1800

4.4E13

0.7

1900

6.4E13

0.9

2000

8.6E13

1.2

2100

1.2E14

1.5

2200

1.4E14

1.8

2300

1.6E14

1.9

2400

1.8E14

2.0

2500

1.9E14

2.0

2600

1.9E14

2.0

2700

1.8E14

1.9

2800

1.7E14

1.7

2900

1.5E14

1.4

3000

1.1E14

1.0

3100

6.4E13

0.6

Figure 13.31: G230L 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.

G230L 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 13.32: Diffuse Source Signal-to-Noise as a function of STMAG for G230L

Figure 13.33: Point Source Signal-to-Noise as a Function of STMAG for G230L

Grating	Spectral Range	Average Dispersion (Å per Pixel)	Plate Scale (arcsec / pixel)	Tilts	Central Wavelengths
Complete	Per Tilt
G230L	1570-3180	1610	1.58	0.025	Prime	2376

	Sensitivity	% Throughput
1600	2.5E12	0.0
1700	2.4E13	0.4
1800	4.4E13	0.7
1900	6.4E13	0.9
2000	8.6E13	1.2
2100	1.2E14	1.5
2200	1.4E14	1.8
2300	1.6E14	1.9
2400	1.8E14	2.0
2500	1.9E14	2.0
2600	1.9E14	2.0
2700	1.8E14	1.9
2800	1.7E14	1.7
2900	1.5E14	1.4
3000	1.1E14	1.0
3100	6.4E13	0.6

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