Baade/IMACS Observing Procedures
Date of last modification: March 17 2020 (Nidia)

1. Accessing Data Acquisition Computer (Llama)

• Username is obs1; password will be available form the instrument specialist.
• The data will be placed in /Volumes/DATA_BAADE/IMACS
• Check your working directory: it should be something like ut200318_19 that will be created by the instrument specialist before you start.
• In Camera GUI, under Options, "DataPath" should point to this directory.
  
  
• 2. Start Control Windows in Llama
  • The control software is started by typing 'imacs' in a Llama xterm.
  • This will bring up the IMACS GUI and the Camera GUI. Normally, those will be started by the instrument specialist during setup.
  • From the IMACS GUI you will select the SlitMask, Grism (F/2) or Grating (F/4); adjust the tilt if using a grating, select filters for direct imaging, and switch to Centerfield SlitViewer if needed. For most if not all of our observations we will use the F/2 camera with FS_2471 slitmask (four slits mask) and the 300/17.5 (blue) grism.
  • From the Camera Gui you will command the CCD mosaic: exposure time, type of exposure (bias, object, flat), binning (probably only 1x1 will be needed), etc.
  • The filters, gratings/grisms, long slits and FS_2471 mask will be mounted previous to your run according to the instrument setup request, and their names will show up in the GUI pull-down menus.
  • Readout speed should be set to "Fast" unless the target is faint, in which case we may use the "Slow" readout. This will imply switching between "Fast" and "Slow", because the acquisition and calibrations will still be made in "Fast" mode. This can be very tricky and for most of the targets we may want to use just "Fast" readout.
  • If the Quick-Look Tool has not been started (very rare), go to the "Options" pull-down menu of the CamGUI and click there to start it.
  • IMACS will adjust automatically the focus each time you change filter or grating/grism.
  
  
• 3. Subraster
  
  • For the 2020 CSP campaign, we are using FS_2471 mask which provides two slits on chips 5 and 8, respectively, which allow the whole usable range of the spectrum to go into only one chip. No subraster is needed. We save all 8 chips, however, but reductions can be limited to chips 5 and 8, or only one of them.
    
  
  
• 4. IRAF imacs package
  
  IRAF will be also started by the instrument specialist during setup, but in case you need to reinitialize:
  • Open an IRAF window and go to the working directory
  • Load the 'imacs' package (this will automatically set the stdimage parameter to 'imt8192')
  • Open ds9 (if you open the IRAF window from the icon in the toolbar, ds9 will open as well).
  
  
• 5. Check the slits and calibration lamps
  
  • Bring up the flat field/calibrations GUI (if it is not already there) by typing "ffs" in an xterminal of Llama. From there you can put the screen in and out by clicking in "In" and "Out" and turn on/off the comparison and quartz lamps.
  • In IMACS GUI set Hatch to 'open' and 'filter' to the filter in which you plan to do acquisitions (usually r', but it could be other, even the spectroscopic2).
  • Take a short (~5 s) direct image of the slitmask. The field 'Disperser' in the IMACS GUI must say "F/2-Imaging" for the short camera.
    • on Slit-Mask = FS_2471; Disperser = F/2 Imaging; Filter: r (for example).
      
    • Measure on the Quick Look Tool (or using the display task in IRAF) the position on the slit where your objects will be placed. Go to this page and follow the instructions there to calculate the offsets for the 'toslit' task. Edit the parameters of 'toslit' accordingly. The slit position may move slightly along the night, thus a new slit image should be taken before each observation and its position entered under xslit and yslit in 'icobject' (see below) but you generally won't need to update the parameters for 'toslit'. Approximate slit positions for the FS_2471 mask are x=1620 y= 2051 for chip 5, and x=500 y=2056 for chip 8. These numbers are given only for reference, they can vary.
      
    • Set the 300-17.5 grism on and the FS_2471 slitmask. Take a 2-3 s exposure of the He-Ne-Ar turning on 2 He, 2 Ar and 1 Ne lamp in the FFS GUI. Some lines will be saturated but the spectrum will be suitable for wavelength calibration.
    
    
  • 6. Afternoon calibrations
    • Take a bias sequence (5-10 frames): set ExpType= bias; this will automatically set the exposure time to 0s. If using the "Slow" readout you'd want to get some bias frames in this speed as well.
      
      
    • Dome flats for the short camera (F2) with the 300-17.5 grism and FS_2471 mask can be 10s Qh for Fast readout and 5s Qh for Slow readout. Make sure you have the spectroscopic2 filter in.
      In all cases take a test exposure before starting a loop and check that the exposure time is appropriate (quartz lamps get often replaced and do vary with time) giving maximun counts around 20000-25000.
      If you care about good flatfielding in the red region of the spectrum, it is recommended to obtain at least 3 dome flats right after or before the object observation. You can do it after taking the comparison lamp. Otherwise fringing may not remove completely.
      
    • It is a good idea to take some dome flats for the acquisition images (if time allows). For those you need to turn on the variable voltage quartz lamps from the box inside the dome. For the r' filter it may work with 12-15 s exposures and 2.0 Volts (peak around 20000 ADUs); but this has to be checked.
      
    
    
  • 7. Object list
    
    Your telescope operator (TO) 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 -46.15 and HRZ.
    This will set the slit along the parallactic angle.
    
    
  • 8. Observing
    
    • In IMACS GUI set Filter to the filter you want for acquisitions, Dispersr=F2/Imaging (short camera), Slit-Mask: F2/Imaging.
    • Once the TO has slewed the telescope to your target, from the IRAF window execute 'toslit' (return has to be typed twice).
    • In CCD window set ExpType to "object".
    • Take a direct image of the field (10-20s) check that the target is on the same chip as the slit you want to use; otherwise ask the TO to move the telescope a few seconds and try a new exposure of the field (use the compass next to the quick look tool to guess in which direction to move). With the new offsets from the IMACS cookbook this is probably not going to happen.
    • Place the slit in, take a short exposure and confirm the slit position (it may change by 1-2 pixels from what you measured before).
    • Do an epar on 'icobject' and put the name of the direct image of the field and the values of xslit and yslit just measured; then execute the task. You will be presented with the direct image and will be prompted to mark (with the space-bar) the position of the object. If the object is faint you may want to mark its position with 'm' instead. Follow the instructions issued by the 'icobject' task. Once you have marked the target, answer 'yes' in order to offset the telescope and guiders (again, you need to type 'return' twice).
    • If the offsets are a few seconds you don't need to take another image of the field. You can take a short exposure to see the target through the slit, and then place the grating/grism on to start taking the spectrum. If the offsets are larger than a few arcsecs you may need a second direct image and run 'icobject' again.
    • In the IMACS GUI set Filter to Spectroscopic2, slitmask to FS_2471 and Dispersr to 300-17.5 grism.
    • In CCD Camera GUI set the appropriate ExpTime, object to "object name", and click START to begin the exposure
    • To take a comparison ask the TO to stop guiding, move screen into place (wait until the 'wait' sign disappears) click to turn on the He-Ne-Ar lamps, and take the arc exposure.
    • If you decided to take dome flats at the object position, turn the comparison lamps off, turn the Qh lamp on, select ExpType = Flat and take 3 dome flats. Remember to switch ExpType back to Object when flats are done.
    • Turn OFF the lamps, move the screen back to the OFF position, and ask the TO to go to the next object.
    • Take a minimum of 2 flux standards (3 is best. Although a wider slit would work better for standards, with the FS_2471 mask we use the same slit as for science ojbects.
    • Observe one telluric standard if possible. It is desirable to get high s/n in the telluric star.
    • At the end of the night close the IMACS hatch.
    
    
    
    
    nmorrell@lco.cl