First-Order Grating G230MB

Description

The G230MB grating mode uses a backup intermediate-resolution grating originally designed for use with the NUV-MAMA which has been repurposed for use with the CCD. It provides R ~ 6000 spectroscopy in the NUV and takes advantage of the CCD's higher throughput longward of λ = 2500 Å. The G230MB grating mode has a spectral range from 1640–3190 Å.

As a single exposure with this grating covers only 150 Å, the grating must be scanned with a series of exposures taken at 11 distinct settings to cover the full spectral range of the grating.

Recommended Uses

The G230MB grating mode is designed for programs needing the highest available sensitivity in the NUV from ~2500 to 3100 Å or more generally to allow observation of sources too bright for the MAMA in the NUV.

Special Considerations

In making the plots for the G230MB grating mode, we assumed that the CCD is subject to a change in the effective quantum yield resulting in the creation of multiple electron-hole pairs per photon for λ < 3400 Å.

Because of the high sensitivity of the CCD to red light, observations of red stars with G230MB are more likely to be affected by scattered light than observations of those stars using the NUV-MAMA G230M (see Section 4.1.6).

G230MB Sensitivities

Table 13.8: G230MB Sensitivities & Throughputs for a Point Source.

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.

G230MB Signal-to-Noise

Note:

The top axis displays constant F_λ values corresponding to the STMAG units (V+STMAG_λ) on the bottom axis. Recall that STMAG=0 is equivalent to F_λ = 3.63E–9 erg/cm²/s^–/Å. The curves are labeled with exposure times in seconds.