MII/LDSS3 Observing Procedures

Date of last modification: July 28 2011, 4:40 pm Chilean time
  • Complete instructions on how to operate LDSS3 in longslit mode can be found here selecting 'LDSS3', then 'LDSS-3 Observing Cookbooks' and then 'Long-Slit Spectroscopy'.

  • 1. Accessing Data Acquisition Computer (Guanaco)
  • 2. Start Control Windows in Guanaco
  • 3. Subrasater

  • 4. IRAF ldss3 package

  • 5. Check the slits and calibration lamps

    By choosing, for example, slit coordinates close to (2667, 2127) the objects will be placed on the slit in a clean region between two gaps. Now in the IRAF window edit the parameters for the task 'ltoslit' and fill in the slit coordinates you measured. These coordinates will also be required in order to run 'lcobject'. The slit position will move slightly along the night, thus a new slit image should be taken before each observation (lcobject will stitch that image and let you mark the exact position you want for the object).
  • 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.
  • SLITS: We will use the 1" slit with blue coverage (LS10.2s) as narrow slit, and the 1.5" LS15.2s as wide slit. If the seeing is very good we may want to use the 0.75" slit (Long4_s) instead. Remember to take dome flats for each slit that has to be used.
  • Set the VPH_All grism on and the narrow slit and take a 5s exposure of the He-Ne-Ar lamps.
  • If you plan to use the VPH_Blue grism, put it on 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).
  • Since the VPH_All grism is available, we only occasionally will want to use the VPH_Blue and VPH_Red.
  • HeNeAr lamps should be always observed with the narrow slit.
  • 6. Calibrations
  • 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 -62.0 and HRZ.
    This will set the slit along the parallactic angle.

  • 8. Skyflats

  • 9. Observing