Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 14

First-Order Grating G430M

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Description

Like the G430L grating, the G430M grating is used with the CCD and has a spectral range from 3020-5600 Å.

Since a single exposure taken with this grating covers only 286 Å the grating must be scanned, with a series of exposures taken at 10 distinct settings, to cover the full spectral range of the grating.

Recommended Uses

The G430M grating mode is designed for observations where spatially resolved, long slit spectroscopy is desired at relatively high spectral resolution (R~6000) over a limited region of the near-ultraviolet or optical spectrum.

Grating	Spectral Range		Average Dispersion (Å per Pixel)	Plate Scale (arcsec / pixel)	Tilts	Central Wavelengths
	Complete	Per Tilt
G430M	3020-5610	286	0.28	0.05	Prime	3165, 3423, 3680, 3936, 4194, 4451, 4706, 4961, 5216, 5471
					Secondary	3305, 3843, 4781, 5093

Figure 13.14: Wavelength Ranges for the G430M Grating Settings


 

G430M Sensitivities

Table 13.6: G430M Sensitivities & Throughputs for a Point Source

	Sensitivity	% Throughput
3100	8.3E13	4.2
3300	1.0E14	4.9
3500	1.1E14	4.8
3700	1.5E14	6.3
3900	2.2E14	9.0
4100	2.6E14	9.9
4300	2.8E14	10.4
4500	3.1E14	10.8
4700	3.0E14	10.1
4900	3.3E14	10.7
5100	3.8E14	11.6
5300	3.6E14	10.7
5500	3.3E14	9.3

Figure 13.15: G430M 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.

G430M 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 13.16: Diffuse Source Signal-to-Noise as a Function of STMAG for G430M


 
Figure 13.17: Point Source Signal-to-Noise as a Function of STMAG for G430M


 

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