C100/WFCCD Observing Procedures

Date of last modification: July 6, 2015 (Nidia)

1. Accessing Data Acquisition Computer (clarity)

• Check with the staff for username (either obs1, obs2 or obs3) and password
• Most probably the following steps will have been accomplished by the technincal staff; so please check before proceeding.
• From any terminal in clarity type ccd
• A dialog window will pop up, in which you must fill some fields:
• Observer: your name, or just CSP
• CCD: WF4K-1
• Instrument: WFCCD
• Leave the 'Overscan' and 'Biaslines' to the defalutls (128).
• Clicking ok will launch the WFCCD GUI.

2. WFCCD Graphical User Interface (GUI)

• In the 'Options' menu select 'Datapath' end enter the name of the directory where data will be stored; for example:
  /Volumes/Data_Clarity/obs1/20101128_29
  If the chosen directory does not exist, it will be then created.
• Click on the 'Edit' button next to the 'Aperture' box and enter the following aperture names
  • 150u
  • 750u
  • open
  • Pinhole
• Click on the 'Edit' button next to the 'Filter' box and enter the following:
  • B
  • V
  • I
  • grism_blue
  You can use different names in those files, but if you use the above, the reduction process will be smoother.
• Set Binning to 1 in both X and Y
• Set 'Speed' to 'Fast'
• From the "Modules" pull-down menu in the CCD Camera GUI, bring up the quick look tool (QL-Tool), where exposures will be automatically displayed.
• Click on the 'Full' label on the right side of the GUI: this will start the subraster window.
  • Click on the 'CoordMode' button and chose X1X2Y1Y2 and write the following values for 'Subraster #1'
  • 1 4064 1400 2650
  • SaveMode: Full (needed! otherwise the alignment tasks won't run)
  • Apply
  • Done
  • A yellow rectangle will mark the selected region on the QL-Tool.
• Make sure that the 'wfccd' package is loaded into your IRAF session (it must have been loaded during setup).

3. Check Masks and Arc lamps

• Take short (2-sec) exposures of both masks using dome lights. Note than 'ExpType' should be 'Object' for all exposures other than bias and dome-flats.
• In the IRAF window type 'wflip imagename'. This will produce an image called ccd????f.fits
• Make sure that the image is not saturated and measure the slit coordinates with imexam --> (xs,ys) (should be ~2670,2050 or ~2628, 2050, in the flipped image, depending on which of the two available narrow long-slits is mounted). Zoom in the image in an appropriate way; then place the cursor on the location you will want for your objects at night: choose an ys coordinate (in this example is 2050, and it is a good idea to keep it the same for all the objects), then type the j key which will display in the irafterm a cut along one line across the slit and will give you the xs coordinate. Write down this coordinates in order to use them for the first run of cobject.
• Turn ON He and Ne arc lamps and take a short (10-15 sec) exposure.
• Check that wavelength range is correct and that lines are in focus (~4 pixels wide)
• Check that spectral lines are duly aligned with CCD columns (within 2-4 pixels)
• Please keep this first lamp image because it will be used in the reduction process.

4. Dome Flats and Bias

• Turn OFF platform lights
• Turn ON quartz light and adjust voltage to values given below
• In CCD GUI set Filter, Aperture=open, Loops=7, ExpTime, ExpType=Flat, and object="DomeFlat". With the following values you should obtain ~20000 cts/px on each filter.
  • B: 20 sec (voltage=395)
  • V: 20 sec (voltage=325)
  • I: 15 sec (voltage=255)
  • R: 20 sec (voltage=275) you may happen to want it instead of I
• In WFCCD GUI set Filter=grism_blue, Aperture=150u/750u, Loops=7, ExpTime, ExpType=Flat, and Object="DomeFlat" (maximum flat value will be ~20000 cts/px).
  • 1.65" slit (150u): 40 sec (voltage=470)
  • 8.25" slit (750u): 10 sec (voltage=470)
• Start sequence with START button
• When the sequence of flats is complete turn OFF quartz lamp
• Set ExpType=bias (ExpTime will automatically be set to 0s), Loops=10, Object: Bias and take a sequence of bias frames.

5. Telescope Pointing

• Point to a bright star
• Take a short direct image
• Compute telescope offsets to place star at center of rotation which is near x=1828 y=1993 in the flipped image (== x=2236, y=1993 in the unflipped image). In the flipped image, North is up and East is right (for CR =180); in the quick look tool, North is down and East is left; the detector scale is 0.484 arcsecs/pixel.
• After performing these offsets, take a short confirmation image, and ask the NA to CSET the telescope.

6. Telescope Focus

• Ask the NA to move the telescope a bit away from the bright star used for poinging.
• In CCD GUI set ExpType: Focus (this will set the Loops=7) set filter=V, ExpTime=5-10, and press START. A dialog window will prompt you to 'continue' once the focus has been changed to the next position. The focus sequence will be writtn to a regular image name, i.e. ccd????.fits
• Imexamine the image (the NA has the value for the last time the instrument was used; it shoud be close to that).

7. Observing

• Set ExpType=Object
• Ask NA to point the telescope to object
• Use 'pangle' to determine paralactic angle and ask the NA to set the rotator angle (Cass. Ring. P.A.). Example: if your object is 2hs20m West from Meridian, type 02:20 in the 'ha' field; if it is 2hs20m East, you should type: -02:20 instead.
• Edit parameters for 'toslit', enter Cassegrain Ring angle, coordinates of rotation center (xcen,ycen), and slit (xs,ys)
• Run 'toslit' and ask the NA to offset the telescope (a big offset which should bring the object close to the slit)
• In CCD GUI set Aperture=Open, Filter=V, and take direct image of the field
• Edit parameters for 'cobject', set mark=yes, last coordinates measured for the slit, coordinates of guider box, and the object's CCD frame
• Run 'wflip' on the direct image.
• Run 'cobject', mark object (space bar), use the CAMERA offset yielded by 'cobject', and ask the NA to move the telescope accordingly
• In CCD GUI set Filter=B or I, and take another direct image of the field
• In CCD GUI set Aperture="150u" and take 5-sec exposure of narrow slit mask, display it using imexam and measure (xs,ys)
• Edit parameters for 'cobject', and enter your new values (xs,ys) normally only xs will change , and the new flipped image name
• Run 'cobject', mark object (space bar), use the CAMERA offset yielded by 'cobject', and ask the NA to move the telescope accordingly (or the guider box, if the offsets are small, ~1").
• If in doubt, you can take another image to check that the object is on the slit.
• In CCD GUI set Filter="grism_blue", Aperture="150u", exposure time, object to "object name", and click START to begin exposure
• Turn ON He and Ne lamps, ask the NA to close dome shutter, and take 10-sec exposure (don't forget to remind the NA to disable guider) (DON'T BOTHER TO TAKE LAMPS FOR FLUX STANDARDS)
• Turn OFF He and Ne lamps, and ask the NA to open dome shutter

nmorrell@lco.cl