Subject: slew standard star across slit

From: Xiaohui Fan

Submitted: Wed, 25 Mar 1998 08:09:41 -0500 (EST)

Message number: 46 (previous: 45, next: 47 up: Index)

How to slew a standard star across the slit:

 When doing accurate spectroscopy of galaxies, one wants
the standard star to have a uniform illumination on
the slit, by trailing the star across the slit at a fixed
rate. We found the procedures below work quite well for DIS.

 1) Keep your slit viewer (ST6) on all the time.
 2) slew to the standard;
 3) normally the star won't be on the slit, but that's fine.
    try to SLEW the telescope (not offset, slew, i.e., type
    in different coords) to move the star 10-20" below the slit.
 4) if you want the total effective exposure time to be, say 1.5sec
     on the 1.5" slit, set the expoure time to be 30 sec.
 5) separately, on the tcc window, type 
       	"offset inst/pabs 0,0,0,0.000278"
    (0.000278=1./3600, the last number is the slewing rate in deg/sec)
    BUT DON'T HIT RETURN YET
 6) start the exposure
 7) when the shutter opens, hit return in the tcc window. 
   the offset command will drive the telescope on a constant
   rate of 1"/sec towards the slit, and it will take 1.5 sec to
   go across the slit
 8) when exposure is over, in tcc windwon
      "offset inst/pabs", this will stop the slew.
 9) check the result to see if the star really goes across the slit.
-- 
Xiaohui Fan
Princeton University Observatory
Peyton Hall
Princeton, NJ 08544

email : fan@astro.princeton.edu
tel   : (609) 258-5153 (O)
        (609) 716-0480 (H)

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