6.2 Step-by-step guide to the TTF observing

This guide is intended for the first time observers and as a reference to anybody else.
It is assumed that your project is fairly standard and does not require a specialised support.
There are a few basic steps which should be followed every time while observing with the TTF.

Contents:
                       1. First night checks
                        2. Starting up the Taurus and TTF control software
                        3. Setting up data display and analysis software
                        4. Typical observing routine
                       5. After Observations
                       6. Note on data reduction
 
 

1. First night checks:


                     To keep track of all objects in the wheels, please print out this figure and mark all loaded filters and masks.
                     Whenever you want to rotate a wheel to the specified position you will need to enter numbers
                     of requested filters etc.  in the SMS commands. Therefore it is important to keep this figure as a part of your log file
                     throughout your observing run.
                   More about the masks.
 


2. Starting up the Taurus and TTF control software:

3. Setting up data display and analysis software: 4. Typical observing routine:
  1. Loading setup parameters and housekeeping information
  2. Telescope focus
  3. Twilight flatfields
  4. Wavelength calibration
  5. Target object observations
  6. Standard star for flux calibration
  7. Twilight flatfields again
  8. Dome flatfields
  9. Bias frames

  10.  

     

    Here is a postscript file of a log sheet for your own note taking. Your night assistant will be listing all
    your exposures in a standard log, which will be available on the AAT web page after your observing night.


1. Loading setup parameters and housekeeping information

    Before starting observations one has to input the "housekeeping" information and to specify
    appropriate parameters in the CCD and TAURUS control windows.

    In the CCD control window type the commands:
         data ushort
         ti 1                       (exposure time)
         observer              (enter names)
         instrument           (enter 19 and ignore the !failed to find TAURUS noticeboard error)
         speed normal       (readout speed, choice is: slow, nonastro, fast, xtraslow)

     In the TAURUS_2 control window you need to set up TTF parameters. This is done by loading a setup file,
     which includes etalon settings, camera focus and a command sequence to name all of the slots in all four wheels.
    The example of such file is given here.
    Previously used files are stored on VAX machine in disk$user:[observer.icl_load] directory.
    It is easy to make a copy of such a file and to customize it to your own requirements.
    To load the setup file one has to type a command in TAURUS_2 control window.
    This window can be operated using the previously shown menus or using the command mode.
    Command mode is activated by typing "." (DEL) on the keypad.

    The setup file is loaded with a command:
    load disk$user:[observer.icl_load]startup.icl

    Please use the latest file with the same etalon and possible the same camera setup to one you need.
    The small differences in setup can be adjusted by typing additional commands during the observations.
    Examples:    (bttf_mar01.icl, rttf_mar03.icl)
    load disk$user:[observer.icl_load]bttf_monyr.icl     (for Blue TTF)
    load disk$user:[observer.icl_load]rttf_monyr.icl      (for Red TTF)

    To enter your current camera focus, type in the command mode:
    obeyw taurus camera 425                     (425 is an example number)
     

2. Telescope focus
 

         This part is done under instructions from the night assistant, who will select a suitable star and will ask you
            to take a few exposures with different focus settings each time moving the telescope by a few arcsecond.
            This sequence of exposures will be read out as one image.
            You should display the image in IRAF and to decide, which star in the sequence is best focused by comparing
            the apertures for different settings.

Procedure:

         In the CCD control window type the following commands:
           win mitll_2inch      (this command sets a CCD 2 inch window)  More details about available CCD windows.
            obj focus
            speed normal
            ti 1                      (depending on the magnitude of the star)

         Check positions of the wheels in the TAURUS_2 report window (TTF has to be out of the beam,
            telescope can be focused through the filter).

            In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
            on the keypad) to rotate wheels to the right positions:

            obeyw taurus aperture 1   (big hole)
             obeyw taurus etalon 3       (clear)
             obeyw taurus focal 1         (if 1 is desired filter, otherwise enter an alternative number)
             obeyw taurus pupil 8            (clear)

            Back in the CCD control window type:

             multiple
             exp                    (when prompted by the night assistant)
               exp
               .
               .
               .
              exp
              read           (to read out a multiple exposure)
            single

    Wait until the image is transfer to Unix and display it in IRAF with:

        display /data/ssf/1/obsred/fits/ccd_2/yymmdd.fits 1 1
        imexam

    Move cursor to the centre of the star and press letter 'a' to read the aperture size. Repeat this for all  images
    of the same star and choose the smallest size, which correspond to the best focus settings.
    Your night assistant may want to repeat the procedure for smaller steps in focus values.

3. Twilight flatfields

         The sky flatfields should be taken through all the filters you intend to use to obtain
              the pattern of CCD illumination across the field of view at different wavelengths.
              Three flatfield frames for each filter are usually sufficient.
 

Procedure:

         In the CCD control window type the following commands:

           win mitll_5inch         (choose the size of the window, which corresponds to the TTF field of view you will
                                                                use for your target, if you intend to use shuffle mode, use: mitll_shuffle2 etc. )
             obj flat_sky filter B6  (flat_sky filter B6 - the example of a name for the image frame)
             speed normal
             ti 1                           (exposure time in seconds, the actual exposure time depends on the brightness
                                                                 of twilight sky and needs to be adjusted)
 

               In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
               on the keypad) to rotate wheels to the right positions:

           obeyw taurus aperture 1   (big hole)
             obeyw taurus etalon 3       (clear)
             obeyw taurus focal 1         (if 1 is desired filter, otherwise enter an alternative number)
             obeyw taurus pupil 8            (clear)
 

         Back in the CCD control window type command which starts the exposure:

               sflat 10                   (10 is the exposure time)

            To change the filter type in the TAURUS_2 control window:

                obeyw taurus focal 3      (3 is the number of the position in the filter wheel)

            Then repeat the sflat 10 (or different exposure time) in the CCD control window.

          NOTE: If you intend to tilt any of the filters during your observations, you need to take sky flatfield
              with the tilted filter. In order to do it type an additional command in the TAURUS_2 control window:

              obeyw taurus tilt 15        (15 corresponds to a maximum 15 degrees tilt of the filter)

         More information about the filter tilt and filter transmission range.
 
 

4. Wavelength calibration (making a "sausage cube")

             In this step you will find out how the small change in the etalon gap (z) affects observed wavelength (lambda).
             In other words you will obtain a relationship between z and lambda for the bandwidth you requested.
             The appropriate arc lamp corresponding to your chosen blocking filter should be used. The lamp information and
              lines which can be expected to appear for each filter at given resolution can be found here.
              The following procedures are shown for the one of the most often used intermediate band filter.
              These filters are used to obtain high resolution in wavelength domain.
              If you intend to observe your target with the narrowband filter you should perform  wavelength calibration
              with the intermediate filter which overlaps with the part of the spectrum covered by the narrowband filter.

            More about available filters.

               There are two methods of deriving lambda-z relation. They are described in turn. The second procedure is
                longer but more reliable (therefore preferred) way of wavelength calibration.
                Procedure 1 is often used for quick tests of the TTF performance.

Procedure 1:

               In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
               on the keypad)to rotate wheels to the right positions:

              obeyw taurus aperture 3   (80-shuffle slit)
                obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                obeyw taurus pupil 8           (clear)

               In the CCD control window type the following commands:

               win mitll_shuffle80        (choose the window used for shuffle image )
                obj arc filter B6         (arc filter B6 - an example of the object name)
                speed normal

               At the lamp control console, switch on the appropriate arc lamp and put the "Diffuser Disk" in (red light will flash).
            Don't forget to switch off the lamp and to change the position of the "Diffuser Disk" after calibration is finished.
 

          In the TAURUS_2 control window you should use main menu:
 
startup: setup-  run- operate_ccd-
panic_recovery refresh maintenance- finished

                Expand run-, and select run_ccd option, and subsequently select shuffle_multi option.
                 This will bring up the following menu window. You should highlight the options shown in bold, coloured print.
 
 
Csr_Default disk$user:[observer.cs_files]*.csx
Csr_Filename eighty
Preexpose_info 3_1000_100
Cycle_count 1
Bias True     False
Setup_Array True     False
Etalon_Start 0
Etalon_Increment 7

                   Next press PF1 to run this setting.

                   The result of this action should be an image of the narrow slit taken for 80 different spacings of the etalon,
                   when the gap between two plates of the etalon is controlled by the change in z-values starting from z=0 with
                   increment of 7 z-values.
                   How to choose the range of z-values:
                   The TTF response is cyclical over a free spectral range (FSR). The FSR is proportional to wavelengths.
                   By knowing FSR at H-alpha, which is 340 one can find the FSR for any other wavelength. The 80-shuffle image scans
                   the TTF through roughly two FSRs. In this way, there should be at least one set of calibration lines in order of increasing
                   z-values in the spectrum. For the sampling step, use FSR/40, where 40 is the finesse of TTF.
                 More about free spectral Range.

         When the image is transferred to UNIX workstation, you should bin up the columns of the arc in IRAF by typing
         the following commands in xgterm window:

             blkavg  arc  arc_output  10  1    (arc is the name of the input image, arc_output is the output image)
             onedspec
             splot  arc_output[50,*]

          This should bring up a plot of the binned spectrum

          To fit the profiles place the cursor on the flat part on either side of the 4-line group and type "d".
          Mark each peak with "m", or "l" followed by "q", "a", "a", "n".  The fitted line centroids in units of "z"
          are given at the bottom of the plot. Cycle through them forwards using "+" or backwards using "-".
          To exit, keep hitting "q".

          After you identified the lines which you expect in this part of the spectrum, store the z centroids in a file,
          say arc_fit, along with the corresponding wavelengths, e.g.:
     

           6965.431   463.4
           7067.218   589.7
           7147.042   679.9


          and carry out the least-squares fit with  the IRAF command:

              polyfit  arc_fit  1  verbose=yes   listdat=no

         (Alternatively, note that splot writes the fit parameters out to splot.log. Simply use this file after
         inserting the correct wavelengths in the first column and stripping any preamble.)  Notice that in
         the example spectrum  the first strong line falls at y = 275.7 and repeats at y = 589.7 so that FSR_y = 314.
         (Note, here y corresponds to z-values). Another useful quantity used below is the fitted line width,  dy = 11.8.
          The fit yields:
     

              -7853.972      1.194301                                                    y_offset     dy/d(lambda)
              221.5427     0.0313787                                                   +/-error    +/-error

             chi sqr: 16.3168   ftest: 1448.81   correlation: 0.99966    stats
             nr pts:      3.   std dev res: 2.85629

             x(data)     y(calc)     y(data)     sigy(data)                          data vs. fitted points
            6965.43     464.846       463.4          0.
            7067.22      586.41       589.7          0.
            7147.04     681.744       679.9          0.
     

             This fit is used to obtain the z-lambda relation:

                         z = y =  1.1943 * lambda - 7854.0

                (which follows from y=dy/d(lambda)*lambda-y_offset)

    The z-lambda relation can be used to find out a number of instrument properties: For example, if lambda=7100A:
    order of interference m=lambda / { FSR_y *d(lambda)/dy} 27.00 
    plate spacing l_o=m * lambda / 2  9.6 um
    free spectral range FSR_lam=lambda / m 263 A 
    spectral bandpass dlam=dy * FSR_lam / FSR_y 9.8 A
    resolving power R=lambda /  dlam 770
    effective finesse N_eff =FSR_lam / dlam 27
    More about free spectral Range.

          Important note: the image taken in this mode is called shuffle image and it changes CCD-control
                  into shuffle mode. (You will notice the shuffle> prompt  in the CCD control window). To return to
                  the single mode you have to request it specifically with the following command typed in the CCD control window:

              method default
 

Procedure 2:

                 This is a bit longer but more reliable (therefore preferred) way of wavelength calibration.
                 A sequence of little 6x3 pixels postage stamp images of the arc lamp over a series of consecutive wavelengths
                 (in fact: z-values) is generated.
                 This cube of images is displayed in iraf in two dimensions: wavelength versus average count number.
                 The emission lines are fitted as in the previous procedure and the z-lambda relation is derived on the basis of this fit.

                 In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
                  on the keypad)to rotate wheels to the required positions:

              obeyw taurus aperture 1   (big hole)
                obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                obeyw taurus pupil 8           (clear)

                  In the CCD control window type the following commands:

                  method default         (just to make sure that the CCD controller is in the single mode)
                   win mitll_on_off       (choose the window for sausage images, if the lamp is faint, esp. in U and B bands,
                                                                   use mitll_on_off_large window which has a size of 60x30 pixels )
                 obj B6 sausage          (B6 sausage- an example of the object name)
                 ti 1                      (very important to set the exposure time here)
                 speed normal

                 At the lamp control console, switch on the appropriate arc lamp and put the "Diffuser Disk" in (red light will flash).
              Don't forget to switch off the lamp and to change the position of the "Diffuser Disk" after calibration is finished.

        In the TAURUS_2 control window you should use main menu:
     
    startup: setup-  run- operate_ccd-
    panic_recovery refresh maintenance- finished

        Expand run-, and select run_ccd option, and subsequently select run_step option.
        This will bring up the menu window, which asks you to enter the first and last z-value, and the step increment .
        How the run_step z-values are chosen?  Try to scan the TTF over two FSRs and choose the step as FSR/40
        (in a similar way as for Procedure 1).
        If e.g.  first = 0, increment = 10, last =790. The 80 images will be created:

                        /data/ssf/1/obsred/iraf/ccd_1/yymmdd/ddmon0007.fits
                                                                      :
                                                                      :
                    /data/ssf/1/obsred/iraf/ccd_1/yymmdd/ddmon0087.fits

       Pay attention to the numbers of the first and last image, because these numbers will be used as the  parameters
       of the Perl Script, which his used to transform these images into a spectrum. This Perl Script is called sausage.pl
       and it should be copied from the ~ttf/Scripts directory on aatssf. Corresponding script for the images taken with
      mitll_on_off_large window is called sausage_large.pl and it can be found in the same directory.
      The line: $dir = "/data/ssf/1/obsred/fits/ccd_1/000211/"; of the script has to be updated every night to
       the current date,  where  000211/ is yymmdd/.
       This script stacks the images into a cube structure, and bin up the left hand and right hand 3x3 regions
        into separate spectra for fitting by use of the following IRAF and Unix commands:

             !ls  -1  /data/ssf/1/obsred/iraf/ccd_1/980825/   >  cube1 (the script selects only images which belong to the calibration cube)
             imstack  @cube1  cube1
             blkavg  cube1[1:3,*,*]  spec1o  3  3 1
             blkavg  cube1[4:6,*,*]  spec1    3  3  1
     

        To run the script type the following command under Unix

        sausage.pl   1   ddmon  7   87  (1 is the id of the list of the names of selected images, ddmon is a first

                                                             part of the image names, 7 and 87 is a number range of selected images)
        Sausage.pl  creates a file called LIST1 and reports back about any missing files.
         It also returns the exact command sequence you need to run within IRAF, i.e.
       
             imstack @LIST1 cube1
             blkavg cube1[4:6,*] spec1
             splot spec1

        These can be typed or copied and pasted and executed within IRAF. The result is a plot of the spectrum,
          which should appear on your xgterm.
        To fit the profiles specify the range of z-values you stepped through (e.g. 0 to 790). Do it by typing "p" and
          the start and end z- values. Next place the cursor on the flat part on either side of the line group and type "d"
          to mark the continuum level. Mark each peak with  "l" for Lorenzian fit followed by "q", "a", "a", "n".
          The fitted line centroids in units of "z" are given at the bottom of the plot. To exit, keep hitting "q".
          The splot package writes the line wavelengths and centres to a file splot.log. This file should be edit by stripping
          the first two lines, and inserting the correct wavelengths in the first column. After that the least-squares fit is
          performed with a command:

                 polyfit   splot.log  1  verbose=yes  listdat=no

          This could return something like:

             -3604.095        0.4716382                                                     z_offset     dz/d(lambda)
                18.951       0.0022202                                                       +/-error    +/-error

         chi sqr: 0.15791   ftest: 45220.6   correlation: 0.99999     stats
         nr pts:      3.   std dev res: 0.280992

         x(data)     y(calc)     y(data)     sigy(data)                           data points vs. fitted points
           8416.      365.212       365.3          0.
           8521.4    414.923       414.7          0.
           8668.      484.065       484.4          0.

     This fit is used to obtain the z-lambda relation:

                         z = y =  0.472 * lambda - 3604.1

                (which follows from y=dy/d(lambda)*lambda-y_offset)

    Write this equation into the observing log, because the choice of z-value for the imaging of your target
    will be based on this relation.
    The wavelength calibration procedure should be done once at the beginning of each night,
    after changing a filter or spectral resolution, and after a system crash.
     

5. Target object observations

         The objective is to obtain the image of the target source in the specified bandwidth around your wavelength
             of interest. You can calculate z-value from the z-lambda relation, and use it to specify the gap between
             the plates of the TTF etalon.
             After that you can offset the z-value from your target wavelength to obtain off band images used for
             sky subtraction. Alternatively  you can accomplish this purpose better if you use shuffle mode,
             where your images on and off band are shuffled in cycles between two positions on the CCD.
             Charge shuffling is used mainly to correct for variations in seeing and atmospheric transparency.
             As a working principle, we find that 20 shuffles every 30 sec works well enough for a 10 min
              exposure in each of two bands. The conditions do not need to be photometric if the relative calibration
              is sufficient.
             Charge shuffling builds up a CCD exposure comprising several on-chip charge movements made, generally, into
             and out of an aperture of a masked CCD. The state of an external device (etalon, filter wheel, polariser, telescope
             position, chopping secondary, etc.) may be synchronised to these movements (shuffles) as can the opening and
             closing of a shutter.  Charge-shuffled exposures range in complexity from the simplest two-image shuffle comprising
             only 2 phases per cycle, through to a large number of image phases each comprising
              a chopping between two conditions. A very fast flash facility which fills the CCD in a single burst over a short
              interval is also available to, for example, sample transient phenomena, e.g. occultations at rates almost down to 1 ms,
              if required.
           Currently it is not possible to shuffle images with the change of blocking filters at the same time.
 

           The following three examples describe a procedure of taking :
a single image at a given wavelength,
2 shuffle image and
2-straddle shuffle image, which is a most complex shuffle.
 

More modes of TTF observing.
           Make sure the calibration lamps are off and the "Diffuser disk" is out.

Single image

        E.g. You may want to build a cube of images stepping in wavelength or you just need a continuum image taken
               with a broadband filter.
 

Procedure:

               In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
                on the keypad) to rotate wheels to the right positions:

              obeyw taurus aperture 1   (big hole)
                obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                obeyw taurus pupil 8           (clear)
              obeyw taurus zset 116      (set your z-value calculated from z-lambda relation)
              obeyw taurus tilt 0                 (check if you need to tilt your filter, if the answer is yes enter
                                                                             the appropriate number of degrees)

               In the CCD control window type the following commands:

              win mitll_5inch            (choose the window: 5inch covers full Taurus field of view)
                obj NGC1068 z=116 B6   (NGC1068 z=116 B6 - an example of the object name)
                speed normal               (decide on the speed of readout)
              ti  1800                         (set the exposure time in seconds)
                run                               (start the exposure)

         To change z-value for the next exposure you need only type the command:

                 obeyw taurus zset 120
 

2-shuffle image

          E.g.  you care for a superb sky subtraction. In 2-shuffle image you will shuffle the CCD output between two bands.
                 One band is typically your target band, e.g. Halpha, OIII line. The other band is off-line continuum.
                 To ensure that there are no atmospheric features in your continuum check the following information on the
                 OH night-sky lines, solar spectrum etc.
                The 2-shuffle exposure produce two images of the line and continuum placed in the same frame next to each other.
 

Procedure:
 

                   In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
                   on the keypad) to rotate wheels to the right positions:

                obeyw taurus aperture 1   (big hole)
                 obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                 obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                 obeyw taurus pupil 8           (clear)
                obeyw taurus tilt 0                 (check if you need to tilt your filter, if the answer is yes enter
                                                                              the appropriate number of degrees)

                   In the CCD control window type the following commands:

                 win mitll_shuffle2        (this is a correct window)
                  obj NGC1068 R0 Halpha (NGC1068 R0 Halpha - an example of the object name with additional information)
                  speed normal            (decide on the speed of readout)

                  In the TAURUS_2 control window you should use main menu:
 
startup: setup-  run- operate_ccd-
panic_recovery refresh maintenance- finished

                 Expand run-, and select run_ccd option, and subsequently select shuffle_multi option.
                  This will bring up the following menu window. You should highlight or type in the options
                   shown in bold, coloured print.
 
 
Csr_Default disk$user:[observer.cs_files]*.csx
Csr_Filename twostep60m
Preexpose_info 3_1000_100
Cycle_count 10
Bias True     False
Setup_Array True     False
Etalon_Start 68
Etalon_Increment 30

                Next press PF1 to run this setting.

         The file twostep60m.csx is explicitly for 2-shuffles, with a minute at each band.
                Here we have requested 10 cycles,
                therefore the total exposure time is (a little more than) 20 minutes.
                There exists a few other twostep files called twostep3m, twostep10m, twostep30m.
                The OH power spectrum has no preferred timescale so the recommended time is 1 minute
                per band.  The example z-values will be switched between z=68 and z=98.
 

2-straddle shuffle image

  This mode is used to obtain even better estimate of a continuum level in your image.
    In straddle mode one shuffles between the  target  image, and off-band images on
    both sides of the target line image.   To ensure that there are no atmospheric
    features in your continuum check the following information on the OH night-sky lines,
    solar spectrum etc.
   The 2-straddle shuffle exposure produce two images of the line and continuum placed in
    the same frame next to each other. The line image gives a total exposure twice longer than
    each off-band continuum image. However the displayed image of  continuum is an averaged exposure
    of both off-band, red and blue side images.
 

Procedure:

               In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
                on the keypad)   to rotate wheels to the right positions:

               obeyw taurus aperture 1   (big hole)
                obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                obeyw taurus pupil 8           (clear)
              obeyw taurus tilt 0                 (check if you need to tilt your filter, if the answer is yes enter the appropriate
                                                                            number of degrees)

              In the CCD control window type the following commands:

               win mitll_shuffle2        (this is a correct window)
                obj NGC1068 R0 Halpha  (NGC1068 R0 Halpha - an example of the object name with additional information)
                speed normal              (decide on the speed of readout)

              In the TAURUS_2 control window you should use main menu:

 
startup: setup-  run- operate_ccd-
panic_recovery refresh maintenance- finished
            Expand run-, and select run_ccd option, and subsequently select shuffle_multi option.
             This will bring up the following menu window. You should highlight or type in the options shown
             in bold, coloured print.
 
Csr_Default disk$user:[observer.cs_files]*.csx
Csr_Filename straddle60m
Preexpose_info 3_1000_100
Cycle_count <integer:see below>
Bias True     False
Setup_Array True   False
Etalon_Start 0
Etalon_Increment 7


             Before running this selection one has to decide on the cycle_count and to provide the array of z-values
              which will be used in the straddle  mode. Setting "Setup_Array" to false means that "Etalon_Start" and
              "Etalon_Increment" are ignored.
              Instead, the z-array look-up table has to be provided explicitly. This is done by a set of commands like these:

      obeyw taurus sfill 1 52
     obeyw taurus sfill 2 38
     obeyw taurus sfill 3 52
     obeyw taurus sfill 4 76
     obeyw taurus sfill 5 52
                     :
                     :
     obeyw taurus sfill 40 76

These commands are included in an ICL file, which has to be loaded into Taurus control system by typing
 the following command in the TAURUS_2 control window (command mode is activated by typing "." (DEL)
 on the keypad):

       load disk$user:[observer.icl_load]file.icl.

(The name of the file can be more informative but it should have the extension .icl)

             The example shown above fills the z-array with 40 values in the order shown. "52" is the on-band,
               "38" is the blue off-band an "76" is the red off-band.
               The number of cycles <integer> associated with file.icl is found as follows:
               since straddle60m performs four actions for every cycle and it takes a 60 sec exposure
               for each  z-value, each cycle corresponds to 4 mins. If you wish to obtain a  20-minutes exposure image
               in the target line, than you need to specify the number of cycles as 10.
               The file "file.icl"  will take a total exposure of 40 mins where a single cycle steps through "52 38 52 76"
               generating a double image on the screen. The on-band is a total exposure of 20 mins at z=52 as required, and
               the off-band is an averaged exposure of 20 mins at z=38 and z=76.

               If you decide to shuffle through fewer cycles, say for a flux standard, that's fine because the remaining z-values
              will be ignored. There are 200 entries in the z-array, which can be filled in by the repetition of your straddle
                sequence. The number of actual repeats for your exposure is specified by the number of cycles typed into
                the straddle menu in the TAURUS_2 control window.

                The straddle file .icl is generated by use of a perl script: shuffle_cycle.pl

                The script should be downloaded to your local directory and to made executable by a Unix command:

                           chmod +x shuffle_cycle.pl

                To create the file.icl file, which fills the z-array with 200 values in the order shown. "52" is the on-band,
                "38" is the blue off-band an "76" is the red off-band, type

                            shuffle_cycle.pl  52 38 52 76  >  file.icl

                The  file.icl is then transferred by FTP to VAX  (it needs to be sent as ASCII). This is done by use of a shell
                 script FTPtoVAX, which should be downloaded to your local directory. To transfer  file.icl type:

                            FTPtoVAX file.icl password

                It will prompt you for the password, which you can find out from your support astronomer or the night assistant.
                You can check to see that your file was transferred with

                             ls -tl /vaxuser/observer/icl_load

                The last step is to load the file into Taurus control system by typing the following command
                 in the TAURUS_2 control window (command mode is activated by typing "." (DEL) on the keypad):

                               load disk$user:[observer.icl_load]file.icl

         To activate the straddle shuffle press PF1 key.
 
 

6. Standard star for flux calibration

         The list and atlas of spectro-photometric standard stars is kept by the night assistant and you can choose the best
               object for a given time on a spot. You usually would like to image your standard in the same configuration as your
                target data. Therefore choose appropriate etalon and filters. You need to take and repeat exposures for all z-values
                and tilts of the filters you used.
 

Procedure:

               In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
                on the keypad) to rotate wheels to the right positions:

              obeyw taurus aperture 1   (big hole)
                obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                obeyw taurus pupil 8           (clear)
              obeyw taurus zset 116      (set your z-value calculated from z-lambda relation)
               obeyw taurus tilt 0                 (check if you need to tilt your filter, if the answer is yes enter the appropriate number of degrees)

               In the CCD control window type the following commands:

                 win mitll_2inch           (you can choose smaller window than you used for your target to save on readout time)
                  obj LLT 4364 z=116 B6   (LLT 4364 z=116 B6 - an example of the object name and additional information)
                  speed normal              (decide on the speed of readout)
                ti  10                            (set the exposure time in seconds, typically it will be a short exposure)
                  run                              (start the exposure)

       To change z-value for the next exposure you need only type the command in the TAURUS_2 control window:

                obeyw taurus zset 120
 
 

7. More twilight flatfields

         The sky flatfields should be taken through all the filters you  used to obtain
              the pattern of CCD illumination across the field of view at different wavelengths.
              Three flatfield frames for each filter are usually sufficient. For the procedure check point 3. Twilight flatfields.
 
 

8. Dome flatfields

         Dome flats are taken for all z-values used and all the tilts with the appropriate etalon in.
              The procedure is similar as for the single imaging.

Procedure:

              Ask your night assistant to switch on the dome light. You can regulate the illumination intensity with a dial
                on the lamp panel.

                In the TAURUS_2 control window type commands in the command mode (activated by typing "." (DEL)
                on the keypad) to rotate wheels to the right positions:

              obeyw taurus aperture 1   (big hole)
                obeyw taurus etalon 1      (choose the right TTF: 1 or 2 )
                obeyw taurus focal 1        (if 1 is desired filter, otherwise enter an alternative number)
                obeyw taurus pupil 8           (clear)
               obeyw taurus zset 116      (set your z-value calculated from z-lambda relation)
               obeyw taurus tilt 0                 (check if you need to tilt your filter,
                                                                              if the answer is yes enter the appropriate number of degrees)

               In the CCD control window type the following commands:

               win mitll_5inch           (use the same window as for your target images, e.g. mitll_shuffle2, mitll_5inch)
                obj domeflat z=116 B6   (LLT 4364 z=116 B6 - an example of the object name and additional information)
                speed normal              (decide on the speed of readout)
               ti  10                            (set the exposure time in seconds, typically it will be a short exposure)
                dflat                            (start the exposure)

        To change z-value for the next exposure you need only type the command in the TAURUS_2 control window:

           obeyw taurus zset 120
 

9. Bias frames

            Biases can be taken any time during your observations.
                    In the CCD control window type the following commands:
 

 Procedure:

               win mitll_5inch           (use the same window as for your target images, e.g. mitll_shuffle2, mitll_5inch)
                obj bias                       (bias - an example of the object name and additional information)
                speed normal              (decide on the speed of readout)
               ti  10                            (exposure time is irrelevant)
               repeat10                      (this will change mode to multiple exposures, 10 in this case)
                bias                            (start 10 bias frames)
 

5. After Observations:
 

         After observations are finished it is recommended to logout from the TAURUS_2.  With a cursor in the TAURUS_2
           control window press PF4 key until you see the question: Do you want to exit (yes/no)? Answer: yes.
              This will shut down TAURUS_2 controls. Next click on the CCD control window  and type:
                   exit
         This will return the aat40a> cursor. To logout from remaining windows type:
                    logout
               in each window.

              If this is your first night of observing you can leave the Unix aatssf machine running. If you finished logout from all the
              packages and windows used, and shut down the workstation. Ask your support astronomer for the instructions on data
              saving procedure. This is your responsibility to backup your data.

              If you are coming back on the next night you will start up the TAURUS_2 and CCD control as you did on the first night.
              Things to remember:

check the available data space, which is shown on the  UNIX_SERVER window
change the date to the current date in your sausage.pl and sausage_large.pl scripts
ask  your support astronomer or technical support about any daily  maintenance, which could
        change or affect your  system setup
you may repeat wavelength calibration during the day to check for any drifts of the instrument
make sure that you find time to go for a bush walk before the night time
 

6. Note on data reduction:

       This is not a part of observing guide, but we recommend to read the paper by
          D. Jones, P. Shopbell and J. Bland-Hawthorn on 'Detection and Measurement from Narrowband Tunable
          Filter Scans' (postscript version) submitted to MNRAS.