[daip] ISPEC question

[Eric Greisen]

I suggest a closer look at the actual data - perhaps smoothed to lower
resolution if needed for S/N reasons.  ISPEC conceals too much
although it can be illuminating.

I have certainly seen negative spectral stuff in the case of a
rotating galaxy where the short-spacing flux has not been fully
accounted for.  If I sum over the right half and the left half
separately, i see emission in one at low frequency and emission in the
other at high.  But I see what looks like absorption at high frequency
in the first and low frquency in the second.  The absorption more or
less mirrors the emission in the other.  This is the negative bowl
that surrounds a region of emssion when the short and zero spacing
data are missing - the sum of the flux must be zero so there must be
areas of negative that integrate to the same as the positive - and
ISPEC does that integration.

I would not expect negative at a frequency that shows no emission.
Negative at frequencies in the interfering source is possible but that
negative should not surround the other source alone but cover a wider
region.

Eric Greisen