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) APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 46 in the apo35-dis archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-dis/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-dis@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO