First-Order Grating G230M

Description

Like the G230L grating, the G230M grating is used with the NUV-MAMA. It has a spectral range from 1650–3100 Å; however, with a resolving power R ~ 10,000 a single exposure with the G230M grating covers only 90 Å. The grating must be scanned with a series of exposures taken at 18 distinct settings to cover the full spectral range.

Recommended Uses

The G230M grating mode is designed for observations where spatially resolved, long slit, spectroscopy is desired at relatively high spectral resolution covering a limited region of the NUV spectrum.

Special Considerations

Notice that the CCD G230MB grating mode also covers the NUV with comparable resolution. See Comparison of G230MB and G230M for a detailed comparison of these two grating modes in that wavelength regime.


GratingSpectral Range

Average
Dispersion

(Å/Pixel)

Plate Scale
(arcsec/pixel)

Tilts

Central Wavelengths

CompletePer Tilt

G230M

1640–3100

90

0.09

0.029

Prime

1687, 1769, 1851, 1933, 2014, 2095, 2176, 2257, 2338, 2419, 2499, 2579, 2659, 2739, 2818, 2898, 2977, 3055


 

 

 

 

 

Secondary

1884, 2600, 2800, 2828

Figure 13.34: Wavelength Ranges for the G230M Grating Settings.


G230M Sensitivities


Table 13.10: G230M Sensitivities & Throughputs for a Point Source.

λ

Sensitivity

% Throughput

1700

4.8E11

0.1

1800

9.1E11

0.2

1900

1.5E12

0.4

2000

2.0E12

0.5

2100

2.9E12

0.7

2200

3.9E12

0.9

2300

4.2E12

0.9

2400

4.4E12

0.9

2500

4.6E12

0.9

2600

4.6E12

0.9

2700

4.6E12

0.8

2800

4.8E12

0.8

2900

4.2E12

0.7

3000

3.2E12

0.5

3100

1.2E12

0.2

Figure 13.35: G230M 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 (cross dispersion) plate scale in units of arcseconds per pixel and by the width of the desired slit in units of arcseconds.

G230M 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 13.36: Diffuse Source Signal-to-Noise as a Function of STMAG for G230M.


Figure 13.37: Point Source Signal-to-Noise as a Function of STMAG for G230M.