The G230LB grating mode uses a low resolution grating originally designed for use with the
STIS/NUV-MAMA which has been re-directed for use with the
STIS/CCD to enable R~700 spectroscopy in the near-ultraviolet (NUV) which takes advantage of the CCD’s higher throughput and dynamic range longward of
λ=2500 Å.
The G230LB 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.
In making the plots for the G230LB 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.
Also be aware that because of the high sensitivity of the CCD to red light, observations of red stars with
G230LB are more likely to be affected by scatter than observations of red stars using the MAMA
G230L mode.
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.
The top axis displays constant Fλ values corresponding to the STMAG units (V+STMAG
λ) on the bottom axis. Recall that STMAG=0 is equivalent to
Fλ = 3.63E-9 erg/cm
2/s/Å. The curves are labeled with exposure times in seconds.
