tsys.class

A new Class macro has been written.  It is in the /home/smtsys/macros
directory on Steffens and in /home/smtobs/macros on Jever.  It will compute
the Tsys (and Trec if there's a Cold subscan) for the range of radial
velocities specified.  It's especially useful if bad channels spoil the online
calibration plots or the Chef GAINS plot or make the Chef mean Tsys & Trec
values inaccurate.  To use it, type 

    @"<directory>/tsys" <scan number> <backend> [<min vel> <max vel>]

where <scan number> is the calibration scan number, <backend> is the name of
the backend, <min vel> and <max vel> specify the (optional) velocity range. 
If you omit <min vel> and/or <max vel>, the values used are those from your
last plot.  (Note that when one sets the range with SET MODE X, it won't
transfer the values to USER_XMIN and USER_XMAX until something is actually
plotted.) 

The backend name can be AOSA, AOSB, AOSC, 62.5kHz, 250kHz, 1MHz, CTSA, CTSB,
CTSC or the two digit backend+part number on the end of the TELESCOPE 
parameter in the header.  The names can be upper or lower case, and only the
first 4 characters are needed.  (But the full name given is used in the plot 
title.)

    To compute these values, the value of Tcal must be known.  This is not
recorded in the calibration scan header as it is not computed until the Chef 
CALIBRATE command is done and it is cleared to 1.0 before the calibration 
observation is made.  But it is in the header of all subsequent (normal)
scans.  So the macro looks for an observation following the calibration scan. 
If it can't find one, it uses the Tcal value from a previous observation
(no matter how old!).  (Unless you change frequencies, Tcal doesn't change
much.)  If there is neither, it estimates the Tcal from the opacity and
atmospheric temperatures in the Calibration's scan header (from a previous
calibration, if any!).