[evlatests] Line detection at 18.1 GHz

[Mark Claussen]

Last evening I used 1/2 hour with EVLA antennas to see if I
could detect the SiS (1->0) line at 18.154 GHz.  Earlier attempts
to see if we could do this were unsuccessful, and we think it was
do to the where the old method of setting up the LOs placed the 
line in the 64 MHz sub-band. The executor update of 4/9/2008, 
allows us to do a better job in the lower end of K band (see K.
Sowinski post of April 8).  

This line (and several other rotational transitions) have been detected
many years ago with single dish observations toward the well-known
two micron source IRC+10216.  In the ground-state rotational transition
it is a maser.  This transition has never been detected with an interferometer,
and was indeed the subject of a successful proposal for the last A
configuration by Al Wootten and me (we failed to detect it, probably because
of the tuning business).

Last night I was able to detect this line.   Attached is a pdf of the
spectrum, made with ISPEC, after imaging.  The absolute flux calibration
is probably good to a factor of 2 or so, since I didn't observe a flux calibrator.
It is certainly gratifying to see that things actually work pretty well at 18.15
GHz.

Mark
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