MOS for the experienced

This sub-page is designed to provide a cookbook-style 9-step observing program for MOS observing. This page assumes that everything is on and working and that you have had experience using Prospero and OSMOS (multi-slit) before (as well as the guider and TCS).

1. Slew to nearest bright star to focus/send RA DEC encoder

   • Need to do this first thing at night,  and before you slew away to the next cluster after step 9.

     • Switch to call ROI1k for the central part of the CCD. Move to a nearby bright star using "Get Coords-> Nearby Bright"

     • set exp = 1 and take an exposure with filename 'focus1'. use imexam with the open IRAF window to check the FWHM displayed as the rightmost number in the lower panel. Fiddle with the focus (using the handpaddle) to get the smallest FWHM possible. Moving in increments of +/- 10 seem to be good.

     • Once focused, turn on "movie" mode.

     • Use paddle to get the bright star in the center of the CCD (where the 4 amplifiers meet). Note that the rotation of the instrument plays a role in how the cardinal directions of the paddle work.

     • Click "Setup ->Set Encoders RA/DEC" on the TCS wants the star is centered.

2. Slew to your target

   • • • You target field should be loaded correctly. Type the name and then "Get Coord -> Named Target". If not, simply type coordinates in.

3. Rotator

   • • • Make sure the mirror covers are open

       • If your mask has rotation, go out into the dome, turn on the TCS monitor and rotate the instrument using the paddle control (attached to the fork). You need only get to within a few tenths of the correct rotation, which you can read on the monitor.

       • Turn off the monitor when you are done

       • If the rotator stops working, cycle the power (with patience). The power box hangs up above and you will need a ladder (which you will want to remove afterwords).

       • Come back inside and use the ROTATOR GUI to finely adjust to the correct rotation.

4. Guide

   • • • In the JSkyCalc guide star tool, enter the Rotator Angle and make sure the coordinates are correct.

       • Find Guide Stars (click "Guide Stars"). Pick one that is 10-14 magnitude outside (or at edge) of the large OSMOS FOV (the circle).

       • Move the guide probe

       • In the Guide Star Camera monitor, take an exposure ("Exposure tab" and a single) to see the star.

     • In "Guide " tab, click "calibrate" and push start. 

       • When finished, start "tracking". Wait to make sure the tracking takes (if not, try again. If not again, try a new star).

5. Flats/Arcs/Direct Masks

   • • • Get your lamps out of the way now.

       • Bring the "Retrocam" mirror in.

       • For flats, turn on "Flats" and take 3x30s. Use 1x1 binning (normal) and the full CCD. Make sure the mask is in as well as the disperser. No filters. Name = "mask# flat"

       • For arcs, turn on "Argon" (and off "flats") and take 3x60s (same as above). Name = "mask# arc"

       • Take a 1s direct mask image. Use the "flat" lamp and the SDSS g filter. Keep the mask in but remove the disperser. Name = "mask# direct mask". Switch to ccdbin xbin=2 ybin=2 AKA 2x2 binning.  You could also take these images during the day to save time here.

       • Switch back to 1x1 binning.

       • Turn all lamps off and move "Retrocam" out.

6. Align

   • • • Set 2x2 binning (ccdbin xbin=2 ybin=2).

       • Set full field (call ROI4k)

       • Take a 5s exposure with mask out, disperser out, no filter. Name = "mask# alignment"

       • Run oalign_bin2.py against the mask (.oms file), the direct mask image (binned 2x2) and the sky (image you just took).

       • If dPa which is the rotator angle is >+/-0.1, enter the dPa into the ROTATOR GUI, and quickly stop guiding (on guider comp) while you send the rotation correction. Immediately press START on guiding and hopefully the star has not moved out of the field. Max rotation for this to work is ~0.3. Wait for star to return to center of the small guiding box and take another alignment image.

       • Run oalign_bin2.py again with you new alignment image, and the dPa should be small. Enter the negative of the given gdx into the dx box and hit enter. Then enter the gdy into the dy box and hit enter. Take another exposure.

       • Another run of the program and the stars should now be in the boxes and the dPa, gdx, and gdy should be small. Repeat until gdx and gdy <~ 7.0. Be careful to click on the center of the boxes and stars.

       • ALWAYS wait for the guider to get back to center before adjusting or taking a new image.

       • When done, switch back to 1x1 binning.

7. Science

   • • • Put mask in. Put disperser in. Make sure filters are open.

       • Take 2x1800s or 3x1200s or 4x900s  (Name = "mask# science")

       • Follow the two science exposures with an offset sky (if needed). Offset by 10' in declination and stop guiding.  900s (Name = "mask# offset sky")

8. Flat/Arcs

   • • • Follow-up with a single arc ("Retrocam" in and argon on). Make sure mask is still in and the disperser as well.

       • If you took (or are taking) twilight flats, no need for flats afterwords

9. Take a deep image for slit comparison later

   • Same setup as the alignment. x/ybin=2, full field, no filters, no slit no disperser. Set exposure to 15s and name 'mask#_deep'.

   • This exposure will be deep enough to see most of our galaxies, and we can use this to see if our slits are lined up correctly.

10. See step 1