Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 17

First-Order Grating G430L

---

Description

G430L, used with the CCD, is a low resolution grating (R~500) with a relatively high throughput. The grating has only a single setting.

Recommended Uses

This grating is designed for observations where high spectral resolution is not required, but efficient spectral coverage in the blue portion of the optical is desired.

Special Considerations

Notice, that by taking two observations, one with G750L and one with G430L, the full spectral region, from the near-IR at 10000 Å through the optical at 3000 Å can be efficiently observed at an R~500.

Grating	Spectral Range		Average Dispersion (Å per Pixel)	Plate Scale (arcsec / pixel)	Tilts	Central Wavelengths
	Complete	Per Tilt
G430L	2900-5700	2800	2.73	0.05	Prime	4300

Figure 13.10: Wavelength Ranges for the G430L Grating Settings


 

G430L Sensitivities

Table 13.5: G430L Sensitivities & Throughputs for a Point Source

	Sensitivity	% Throughput
3000	2.7E14	1.4
3250	6.8E14	3.4
3500	9.5E14	4.4
3750	1.3E15	5.7
4000	2.0E15	8.1
4250	2.5E15	9.2
4500	2.7E15	9.9
4750	2.8E15	9.6
5000	3.0E15	9.7
5250	3.1E15	9.5
5500	2.9E15	8.6

Figure 13.11: G430L 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.

G430L 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 13.12: Diffuse Source Signal-to-Noise as a Function of STMAG for G430L


 
Figure 13.13: Point Source Signal-to-Noise as a Function of STMAG for G430L