Caveats

The defaults for das-merge work well for most purposes; that is, taking the default number of channels for removal, then refusing the vertical adjustment between subbands. Long integrations suggest that it is correct not to take the vertical subband adjustment. The intrinsic flatness of the DAS response is excellent, and applying the subband adjustment actually can introduce low-level offsets between subbands, which, particularly for wide weak lines, could result in spurious detections. Hence one should use the default command, equivalent to

$\gt\!\gt$ das-merge$\backslash$#$\backslash$n$\backslash$

for almost all cases.

One particular case which can readily introduce baselevel offsets if one applies the vertical subband adjustment is when one has a bright line in the central overlap region. One such example is shown in Figure . In such case one should most definitely use the default `n' option.
 

Possibly the only time the `n' option may introduce artificial effects is when observing a planet. Even then the effect is likely to be small. See Figure .