MII/LDSS3 Observing Procedures

1. Accessing Data Acquisition Computer (Guanaco)

• Username: obsmag2a or obsmag2b (check with the staff)
• Password: check with the staff
• Open an xterm window
• cd /home/obsmag2b/data (e.g.)
• mkdir 20020914_15 (e.g.); in CCD Camera GUI "DataPath" should point to this directory (see below).

2. Start Control Windows in Guanaco

• The control software is started by typing 'ldss2gui' in a Guanaco xterm (you will ususally not need to do this because the instrument specialist will have the system initialized for you).
• This will bring up the LDSS GUI from which the aperture, filter and grim wheels are moved by holding the left mouse button on the circle to the right of the wheel's name.
• By holding the right button of the mouse in the same circles, a second window will appear, in which the names of the filters, apertures and grisms can be edited. The filters and grisms are always mounted in the instrument and their names should not be changed.
• The CCD startup window is started by a script called "ldss3" (again, it will usually be ready for you to start working). The "observer" field there will be updated with your name. Clicking OK there, will start the CCD Camera GUI.
• In the CCD Camera GUI make sure that the "DataPath" found in the "Options" pull-down menu points to the directory where you want the data to be stored.
• Readout speed should be left to "fast".
• In the LDSS GUI you can adjust the focus (enter lDsS3 as password) to the nominal value for the r' filter at the current temperature in order to fit the list fixed on the wall (if in doubt, check with the staff).
• Check that the long4_s (0.75", blue coverage) and the LS15.2S (1.5", blue coverage) slits are in the aperture list.
• If the Quick-Look Tool has not been started, go to the "Options" pull-down menu of the CamGUI and click there to start it.

3. Subrasater

• The chip is read in a 2-amplifier mode, so each exposure will be stored in a 2 different files: ccd????c1.fits and ccd????c2.fits. In order to set the subraster in the CCD Camera GUI you have to enter, for each of the two files (c1 and c2) the Xc Yc (X and Y of the center) the width (W) and height (H) of the subraster. The subraster menu calls them: chip 1 and chip2.
  
  You should enter:
  • chip1 1017 2100 2032 1801
  • chip2 1017 2100 2032 1801
  • Then click apply and save.
  This will set the subraster to 1:2032; 1200:3000.
• Keep the "save mode" to "full" which will fill with zeroes the areas outside the subraster.

4. IRAF ldss2 package

• Open an IRAF window and go to the working directory (20020914_15)
• Load the 'ldss2' package
• Open XImtool
• Do an epar to "ltoslit" and set the xoff and yoff parameters to 653 and -220, respectively.
  This task will offset the telescope so that your object falls near the slit position which lies in chip 1 for the chosen slits.

5. Check the slits and calibration lamps

• Take a short (5s) exposure of each of the two slits and measure the position where the targets will be placed. We found that adopting (1401.0, 2290) as slit coordinates, would put the objects on the slit in the clear region between two gaps. The slit position will move slightly along the night and should be measured before each observation.
• Bring up the flat field/calibrations GUI (if it is not already there) by typing "ffs" in an xterminal of Guanaco. There you can put the screen in and out by clicking in "go in" and "go out" and turn on/off the comparison and quartz lamps.
• Set the VPH_Blue grism on and the narrow (0.75") slit and take a 20s exposure of the He-Ne-Ar lamps.
• Do the same with the VPH_Red grism plus OG590 filter using an exposure time of 1s (some of the lines will be saturated but the spectrum will be suitable for wavelength calibration).

6. Calibrations

The dome is not dark enough at daytime to take good dome flats, so VPH_Blue dome flats cannot be obtained before twilight. As for VPH_Red grism, in order to properly get rid of fringing, they should be acquired right after each object exposure (a short sequence of 3 dome flats 8s each will be enough).
• Use the Qf quartz lamp for all the dome flat exposures.
• Dome flat VPH_Blue: Flat field screen should be in; ExpType=flat, ExpTime=40s, aperture=0.75" slit, loops=7 (during twilights). Take anohter sequence with the 1.5" slit, with ExpTime=20s.
• Dome flat VPH_Red + OG590 filter: Flat field screen should be in; ExpType=flat, ExpTime=8s (4s for the 1.5" slit), loops = 3; after each VPH_Red comparison lamp.
• Take a 10 bias sequence (ExpTime= 0.; ExpType= zero). This can be done during the afternoon.

7. Object list

Your telescope operator will need a catalog with the selected objects for the night (to which you can add new targets at any time).
You should edit it following the instrucions given here
In that file, fields #8 (instrument rotator offset angle) and #9 (instrument rotator offset mode) should be set to 133.85 and HRZ.
This will set the slit along the parallactic angle.

8. Skyflats

At sunset you must take sky flats for direct imaging:

• SLEW telescope to the East
• In CCD Camera GUI set ExpTime to 5 (minimum), object to "Dome Flat", Filter=i' Aperture=Open, Grism=Open
• In CCD Camera GUI set ExpType to "flat"
• Start exposure with START botton
• After completing the exposure slew telescope by 20 arcsec (in any direction)
• Take 5 frames per filter (i', r', g') with exposures longer than 5 sec and never exceeding 28000 adu

9. Observing

• Execute the task 'ltoslit' and answer yes to its question (this will set the object near the slit position).
• In LDSS GUI set Filter=g' Aperture=Open, Grism=Open
• In CCD window set ExpType to "object"
• Take direct image of the field
• Take a short exposure of the slit and measure (xs,ys; which should be close to 1401, 2290 in chip 1)
• Edit parameters for 'lcobject' and enter xs,ys and the name of the direct image of the field.
• Run 'lcobject'. You will have to mark object (space bar or 'm') and answer 'yes' in order to offset the telescope
• This is an iterative process; but normally the second time you run lcobject the object will lie in the slit.
  To make sure that this is the case you can take an exposure to see the object through the slit.
• In LDSS GUI set Filter=Open/OG590, Aperture=the appropriate slit, Grism=VPH_Blue/VPH_Red
• In CCD Camera GUI set ExpTime, object to "object name", and click START to begin exposure
• To a comparison move screen into place, click to turn on the He-Ne-Ar lamps, and take the arc exposure (20s for VPH_Blue and 1s for VPH_Red) (don't forget to remind the NA to disable guider)
• If you will tak a spectrum with the VPH_Red grism you must have the OG590 filter in, and you will need 3 dome flat exposures after the comparison lamp, 8s each, with the Qf lamp on.
• Move screen back, turn OFF the lamps; and ask the telescope operator to go to the next object.
• Take a minimum of 2 flux standards (3 is best) with the wide slit and don't take comparison spectra for those.
• Observe one telluric standard with narrow slit and take a comparison lamp after it. Make sure you get high s/n in this data without reaching the saturation.

nmorrell@lco.cl