Note:  This chapter is out of date and is scheduled for


                1) TAPE TRANSFER

                i) Transfer your raw data to disk as multiple maps of one

                I2 file :

                                FITS    use MTREAD

                                1DPCA   use PCASAD

                In both cases it is preferable to store your data as multiple

                maps of one file, although there is a hard SAD limit of ~240

                maps per file.

                ii) PCASAD transfers data as 1 row maps. This is OK if you 

                prefer to handle the upper and lower rows seperately. Usually

                it is easier to treat observations as a whole, so use option

                SH (shuffle) to shuffle your data into 2 row maps in a new (I2)

                file :


                        NEW<1>=0.       - create the new file

                        Format=I2       - as I2

                        SIZE=NI,2       - NI is rowlength - same as raw data


                        FILI=OLD        - 1 row maps

                        FILO=NEW        - 2 row maps

                        MAPI=1:N2:2     - 1 to N2 in steps of 2, N2 is no. of

                                          observations x 2 = no of maps in OLD

                        FACM= c/r       - default factors are unity

                        MAPO=1:N        - N is no of observations


                        FACR=1          - (default)

                        ROWO=1          - put odd input maps into first row

                Then :  .SH(MAPI=2:N2:2,ROWO=2)

                This completes the transfer.

                iii) COPY your transferred raw data to a SAVE tape for easy



                i) It is nice to be able to see graphically the instrumental

                movement with time during the night. This is achieved by

                correlating all the central arc rows against the first such row.

                ii) Use SHuffle to shuffle out the central (or top, say for 1DPCA)

                rows into a new file with no. of rows = no. of arc maps NARC.


                        FILI=RAW        - raw data

                                                                Page 2


                        SIZE=NI,NARC    - new file of NI pixels by NARC rows

                        MAPI=1,3,5:21:2,...     - the arc maps

                        FACM= c/r


                        ROWI=1 or 50 or...      - whichever row you select

                        FACR= c/r

                        ROWO=2:,1       - put the first arc central row

                                                  into the last row - the 

                                                  template row.

                iii) Now do :

                FT              on file CENTRE - creating files REAL and COMPLEX

                CR              on REAL and COMPLEX

                BT              "       "       "

                CN              on REAL

                - for rough shifts (which are in any case only an indication

                of instrumental position, essentially the shift of the strongest

                arc line, since the dispersion varies also) - it is not necessary

                to MASK prior to FFT'ing.

                iv) Now do :

                CQ      - produces numeric shifts (at terminal and on REDSHIFT.LOG)

                - which can be stored in a file and plotted (WP).

                3) CREATING AVERAGE ARC FILE

                i) On the basis of the instrumental shifts obtained, and any

                other phenomenological considerations which you wish to include,

                create an average arc map for each observational map to be

                scrunched. Usually this is just a straight average of the 

                before and after arcs, although weights can be included.

                Use AR to do this :




                        AVERAGE=0.4*RAW+0.6*RAW        for example

                The DO loop can not be used with AR (ref: G QUINN), option AD

                can be used, but all input maps must first be copied (CM or AR)

                to the new AVERAGE file before AD (where FILI=FILO) can be used.

                AR is neat but watch your typing.

                                                                Page 3


                i) This is the most difficult part and requires substantial

                user input. LA will not produce good fits regardless, but depends

                on your judgement. 

                Read through the following documentation on LA and skim through

                the detailed documentation in LA.DOC before starting.

                COEF - LAMCOEF                                  (OPTION LA)

                Fits wave coefs to all rows of arc spectra.

                A 1 D fit is used for maps which have each spectral

                row from a different origin (eg - extracted aperature plate

                spectra or many spectra from a single or double row instur-

                ment such as the IDS). A 2-D fit (3rd order in Y, 2nd to

                7th in X (lamda)) is best for true 2D spectra.

                The user is required to carefully fit a selected row (usually

                a sum of several rows from the centre of the map). COEF

                then uses the coefficients so obtained as a first try fit to

                each subsequent row, producing the best fit for each row by

                checking the centres of arc lines found in each row against

                a user selected arc line list. The order in which rows are

                processed is from the STARTROW to the last row, and then from

                STARTROW-1 backwards to the first. STARTROW is defaulted to the

                map centre but can be changed to allow easy re-fitting of

                selected regions.

                A large scale plot of an arc row, with lines correctly identified,

                is necessary for the first, careful fit. COEF tells you the

                centres of the found lines, and you set up the first, linear

                fit by typing in some channel, lambda pairs. The value of WIDE

                is used as a test for valid correspondences between found line

                centres (and their wavelengths calculated from the linear fit)

                and the wavelengths given in the library of arc line wavelengths

                (stored in SCANLAM.DAT).

                You are then required to carefully prune out mismatches and

                faulty lines - where faults may be due to the line being blended,

                or saturated (arc lines counted at rates > 5 Hz on the IPCS are

                susceptible to beam bending, and should not be used).

                It is usual to fit coefficients to summed (ie. before obsn. and

                after) arcs, since these most closely represent the instrumental

                position midway during the observation. You can check the arc

                drift by SHuffling out the central rows of all arc maps into 

                a single map, and correlating them against the first row.

                                                        (see 2 above)

                ii) Files used

                                                                Page 4

                SCANLAM.DAT     - a comprehensive list of arc line wavelengths

                                  for arcs used at MSSSO and AAO.

                                  COPY from [develop.spt] onto your area.

                                  Select a list from here, and prune out blends

                                  or saturated lines to obtain your

                REDLIST.DAT     - a reduced list of lines which you want to use

                                  for a particular observing run. SAVE this when

                                  asked in LA during setup, and thereafter say NO

                                  otherwise you will get repeated versions, each

                                  being the last used lines.


                5) LA - AUTOMATIC

                i) After setting up and obtaining coefficients in a file (COEF

                say), LA is designed to allow fairly automatic fitting to all

                other arc maps. Use :

                        a) REDLIST - say YES to reduced list ?

                        b) OPTION 3 - read old coeffs from file - this is OK

                                      for a first try provided that the instrument

                                      has not FLOPPED.

                        c) SAVE - say NO - use the initial reduced list for all

                                  subsequent maps.

                It is best to go through a second map, setting up the answers

                for auto fitting in the .SVE file, and then try :

                DO($=3:N,&=3:N) .LA(MAPI=$,MAPCO=$,DEL=,DLINES=)

                In most cases the output coef map (MAPCO) numbers are in 1:1

                correspondence with the input arc map (MAPI) mapnumbers, but

                this is not essential.

                Leaving DEL and DLINES blank allows you to examine each fit

                at the first proper attempt (press c/r after first fit which

                is merely the fit to the input coefficients) and delete any

                spurious matches which may arise.

                PLEASE NOTE:

                1)  Small sigmas can always be obtained by deleting all lines which

                fit poorly, however good (accurate) fits really require 20-30

                lines to be considered valid.

                         Never delete lines on the basis of a linear fit to

                           a few chosen lambda-channel pairs. Let the program

                           try a polynomial fit first.

                2) Be wary of deleting bad matches at the edges, these lines tie

                down the polynomial fits at the edges, and ensure good fits in

                the central regions : if you delete them, the range of validity

                will merely be narrowed.

                                                                Page 5

                3) Don't use high order fits if you have few lines.

                4) Each row is initially fitted with the previous best fit, and

                arc lines accepted or rejected according to the value of WIDE2

                (in channels) : this needs to be large for 1DPCA data where the

                shift between rows can be large.

                5) In the automatic fit, lines are automatically rejected if

                their wavelength difference (between calculated and true) is

                > 2 * MAX( TOL, SIGMA), therefore allow a reasonable tolerance

                so as not to invariably delete lines at the edge of the fit,

                where differences can be high (~ 1 channel).

                6) Reasonable sigmas are of order 0.2 - 0.5 channels, where

                the high values are tolerable if large differences occur only

                at the edges.

                7) Check fits by scrunching your arc, and displaying both it

                and the raw arc on the TV (or in the absence of a TV

                by crosscorrelating one row with the rest - see redshifts for

                a discription of the crosscorrelation routines.)

                If a blow up occurs, this is usually due to the shift being

                too great for the auto fit to work, and you will have to set up