The telescope's pointing origin is the physical position within the focal plane corresponding to the currently selected right ascension and declination. Having different pointing origins allows you to specify that a certain object should be placed in the center of the LRIS detector field-of-view rather than within the field-of-view of the offset guider, for example. The name of the current pointing origin is always displayed in the lower right corner of the Facilities Summary (FACSUM) window. The pointing origin can only be changed by the OA. Below is a list of the current pointing origins (XIM YIM). Last updated: 28 April 2010-MK

name Description XIM (mm) YIM (mm) Xpix Ypix Usage
REF Slit-viewing guider, slightly offset from center of the field-of-view 11.85 -267.08 485 520 longslit observations, pointing checks. Pix location on guider detector.
REFO Center of the Offset guider FOV. -84.45 59.29 512 512 pointing checks, imaging of field on offset guider, IQM measurements. Pix location on guider detector.
LRIS Center of the LRIS detector 3.97 -309.82 in gap in gap Multi-object slitmasks where the field is specified by the center of the mask. Also used to image large fields when we don't care what falls in the detector gap.
slitb Long slit location to move object out of the blue side detector gap. -14.41 -263.74 ? ? longslit spectroscopy
slitc Long slit location to move object out of the blue side detector gap on the other side of the mosaic 31.85 -262.58 ? ? longslit spectroscopy
POL Center of the polarimetry module's field-of-view 3.91 -273.12 ? ? Polarimetry mode
LRISB Location to move object out of the blue side detector gap. -53.11 -320.54 ? ? Imaging of a point source. Ensures that the point source does not fall in the detector gap.
Pickoff Center of the pickoff mirror used on certain LRIS slitmasks 27.95 -260.63 ? ? Multi-object slitmasks where the field coordinates are specified by a guide star that should land on a pickoff mirror.
MIRA Center of the FOV for the MIRA sub window 3.67 -300.34 ? ? Not Used.

Defining a new pointing origin

  1. Get Hand Paddle: If you are not an OA, ask the OA to send a handpaddle to a desired display.
  2. Stationary Mode w/ PA=0: Put the rotator in stationary mode at some easily remembered P.A
  3. Center star on REF:
  4. Send to instr PO:
    5. if an instrument PO will be updated instead of REF.
  5. Record center: Find the star's center, and call this coordinate x0, y0. For the slit viewing guider, the center should be very close to 192.0, 144.0.
  6. Rotate to PA=180:
  7. Record center: Again, find the star's center, and call this coordinate x1, y1.
  8. Determin current PO: Average the x- and y-values, and call this (<x>,<y>). The average value is the current PO.
  9. Move Star to current PO: Using the handpaddle in TV coordinates (instr for instance), move the star to the current PO (<x>,<y>). The star is now on the current REF P.O.
  10. Shift PO to desired location: Using the (XIM,YIM) coordinate system on the handpaddle, steer the star to the position of the new P.O.
  11. Double Check: Record the star's current (x,y), and rotate back 180 degrees to the initial PA. If the star does not show up at the same (x,y), calculate the average value as before, and repeat steps 9-11 until it has converged to your tolerances (e.g. one arcsec on LRIS).
  12. Confirm PO with OA: Inform the OA that the PO has been redefined. Ask OA for PO XIM and YIM values and record them. This will update *Porg* files in the qfix directory of the k1obs account.
  13. Update Information: Update the Information and recalculate values for differential guiding if necessary.

qfix file location

All LRIS pointing origins are located in a file called k1dcsPorgLris.par. To access the file, you will need to login as K1obs on the primary server at the summit for K1 observing. After logging in, cd qfix to move into the directory that contains the qfix file for LRIS. The file contains the most up-to-date pointing origin values. If the file is corrupted, try using the values listed in the table at the top of the page. If the pointing origin is not correct you will have to define a new pointing origin.

MAGIQ

MAGIQ will automatically re-read the qfix file without having to restart. By overlaying the POs in MAGIQ, you should see the updated positions. Please see the MAGIQ manual for overlaying POs MAGIQ home page.