CAIN-III: quick observing guide

  • Open session in cir. Username and password are in the screen of cir
  • Open a xterm in the directory  /scratch/cir/aammmdd>
  • Run > iac username (use your own username)
  • Automatically open the 3 panels of the User interface
 

Localizing the target field
 
            A. Check the telescope pointing
 
  • Pointing to a bright star (FK) near the target field
  • Select open, object, Fowler, 500 ms, 100, 8, 2 y save images NO
  • Locate and center if neccesary the FK within the upper right quadrant of the camera by moving the telescope.
  • Change the telescope focus if neccesary
  • Adjust telescope coordinates ((this must be done by the night assistant, please phone him/her if necessary))
  • Center the FK in the FOVIA field varying the x and Y parameters with the bottons int he control panel
  • Point ot another FK to double check that the coordinate adjustment was correctly done

B.  Focusing the telescope

  • Focusing the telescope using the J filter (the focus offsets are calculated with respect to J)
  • Pointing to object of magnitude J 8-10 and view the display image. It is convenient to use a x10 zoom centered central pixel of the object.
  • Change the focus of the telescope as if the elongation of the object is horizontal or vertical
  • Determine the ellipticity of the selected object with the final focus (using the IRAF task imexamine)
  • Select autofocus yes in order to use the focus offsets already determined for different filters
        

C. Pointing to the scientific field of interest

 

Taking images

A. Dithering using the autoguiding system*

  • Search for an object suitable for guiding in FOVIA
  • Place marks for dithering patern (up to 4 marks).
  • Activate autoguiding
      
B.Dithering using telescope offset.
  • A macro using telescope offsets is recommended. (Typical macros are shown in D.)
* The advantage of using telescope autoguiding against telescope offsets is that, in the first case, the object remains within the same detector area for each dithering point. This is very important to reduce pixle-to-pixel variations and to optimize the photometry. The downside is that it may take up to 15 secounds to activate the autoguiding for each dithering point. If the astronomer is looking for fast photometry, is ready to recenter the telescope pointing after compleating a dithering patern, a macro including telescope offsets and not including autoguiding may be advisable.
 
C. Observing manually
  • Select filter, camera, object and exposure time (tipically 1-10 seconds), readout mode fowler and saving mode diff 

D. Creating and executing macros

  • This is the complete command list.   
  • Macros are executed from the control panel. A macro is selected introducing the complete path. Please save your macros in the folder Users_Macros
  • Examples of available macros that can be used or adapted are here:
         Example 1: 4-points dithering with autoguiding marks
         Example 2: 9-points dithering with telescope offsets
Useful recommendations: 
  • The Narrow camera needs 6.2 times more integration time than the Wide camera
  • A bright object may be observed by closing some of the four telescope mirror covers
  • A weak field can be more easily identified by taking two images, the secound one with a slight difference of focus or a small telescope offset relative to the first one, and displaying the subtraction of the two of them. For this, the first image should be selected as sky image in the image display, and the option rest skyshould be selected.
  • It is convenient to use the fowler, # cicle, 8, 2 mode. For each cicle: at t0, 5 readings of each pixel are done, the first reading is discarded, the remaining 4 are averaged, then an exposition of each pixel is taken, and again, at t1, 5 readings are done, the first is discarded and the remaining 4 are averaged – (This process was revised to cain-III).
  • If save in the  diff mode has been selected, the difference between the second and the first average is saved (these images are BIAS CORRECTED). If Save in all mode have been selected the two averages are saved separatelly.
  

Taking dome flats:

  • J and H require just bright flats red light to a minimum (see mark on the dome switch)
  • Other filters require bright flats (low red light) and dark flats (no lights)
  • Procedure:
      
    1. Close mirror covers, close lower and upper hatchs, and park the telescope to the zenith. Place the dome to the south (azimuth 180)
    2. Open telescope mirror covers. Regulate the red light intensity rotating the dome switch according to the mark and turn off all other dome  lights.
    3. Choose exposure time (the table below is only indicative) taking about 20-50 bright flats and verifing the number of counts (note: use always the display in diff mode!)
    4. Turn off the dome light switch in the control room panel
    5. Take dark flat fields with exposure time equal to the previous bright flats     

 

Band
Exposure time (ms)

Count Numbers
 Bright Flats
Count numbers
 Dark Flats
J
500
10.000
–
H
600
10.000
–
K
900
10.000
3.500
Ks
1500
10.500
3.500

 

Table 1. Relationship between exposure time and number of counts for the dome flats with the most used filters. The values are for the W camera. Note that the number of counts varies depending on outside temperature so the values shown are only approximate

 

Taking sky flats:

Procedure:

        1. In the evening, park the telescope to the east and take first bright flats following the order: CO, Brγ, K continuo, K short, K, H and J
        2. Estimating the exposure times with images of proof for the flats are between 10000 and 15000 counts in diff mode.
        3. The dark flats will be taken during the night using the same integration time than for the bright flats