Quick Review

1. Launch the SAT
2. Load the starlist
3. Retrieve DSS images of guider fields in the afternoon
4. Focus the telescope using MIRA if needed
5. Slew to target and, while slewing, configure MOSFIRE to image the alignment slitmask
6. Complete Coarse Alignment :
   • Select the Target
   • Grab Guider Image
   • Click on guider star
   • Offset telescope
7. Complete Fine Alignment:
   • Start fine alignment to image the mask
   • Send moves
   • Repeat Fine Alignment as necessary until moves are small
8. Start spectroscopic observations

The Tips and Tricks section covers topics such as alignment of crowded fields, alignment check for targets requiring very long (more than 2 hours) integrations and manually loading old alignment images.

Slitmask Alignment

This checklist describes the procedure for aligning multi-object slitmasks on MOSFIRE using the Slitmask Alignment Tool (SAT). Released for use in June 2012 during MOSFIRE commissioning, the SAT provides a complete set of tools for aligning slitmasks. Given a properly-formatted starlist, the SAT predicts guide star locations which may be used to coarse-align a slitmask. When fine-tuning mask alignment, the SAT displays graphical fits to objects/boxes in an all-in-one display and makes recommendations for telescope offsets and rotation. Mask alignment with the SAT is more efficient than the traditional command-line and IRAF-based scripts.

Launch the SAT

To launch the SAT:

1. Navigate to an “analysis” VNC desktop (blue background)
2. From the window manager background menu select MOSFIRE Utilities -> Slitmask Alignment Tool

Load the starlist

Click on the "Load Star List" button immediately below the left-hand image the SAT.

WARNING! The target coordinates in the starlist must correspond to the center of the mask, accounting for all relative shifts that may have been applied while designing the masks. To ensure that the proper coordinates are entered into your starlist file, generate your starlist using our custom script for MOSFIRE.

Focus Telescope (Optional)

Focusing the telescope before aligning a slitmask should be done periodically during the night but is not necessary to do before every mask alignment. We generally recommended re-focusing the telescope when the telescope elevation angle has changed by 30° or more since the previous focus.

To complete the focus:

1. Select target on MAGIQ. On the MAGIQ Observer UI, locate the line listing your next target in the target list at the bottom of the window. (Note: this can be done while you have an exposure in progress) Click the middle mouse button on that line to highlight it, thus indicating to the OA which target you plan to observe.
2. Select focus star. Ask the OA to locate a suitable star to run MIRA in the neighborhood of your next target. The process can take the OA several minutes.
3. Queue align mask. Pre-configure the CSU for your alignment. On the MAGMA UI, click on the name of the next mask to observe in the Mask Configurations area, then click on Setup Alignment Mask to queue the moves in the controller. (Note: this can also be done while the exposure is in progress)
4. Wait for exposure. Wait for your current exposure to complete.
5. Protect detector. On the MOSFIRE Desktop Observing Mode UI, click on DARK-IMAG mode to protect the detector from exposure to bright light during your reconfiguration and telescope slew.
6. Slew to focus star. Ask the OA to slew the telescope to the focus star and run MIRA in the neighborhood of your new target.
7. Confirm safe drive angle. Check the drive angle shown on FACSUM. If it is within ±10° of either 0° or 180° (or any multiple of 180°) then moving the CSU may trigger a CSU fatal error. To avoid this, have the OA rotate MOSFIRE to a safe drive angle and execute your CSU move at that rotator position.
8. Execute CSU move. On the MAGMA UI, click on Execute Mask to perform the moves you queued above.
9. Wait for mask. Be sure to tell the OA to wait until your CSU move is completed before launching the telescope focus routine (MIRA).
10. Launch MIRA. Once the mask move is done, ask the OA to complete MIRA. Wait while the OA completes the focus routine.

Notes

• If you plan to observe the field for two hours (or more), consider asking the OA to run MIRA one hour west of your target field in order to represent the midpoint of the exposure.
• MIRA is always run using the J band filter.

Prepare for Alignment

In this phase, we prepare the instrument for mask alignment during the telescope slew to the science field.

1. Click Quick Dark on the MOSFIRE Desktop Observing Mode GUI.
   This will protect the detector from exposure to bright light during your slew to the science field. (Note: if you just ran MIRA, then it should have done this for you).
2. Setup Alignment Mask
   • Select the new mask in MAGMA
   • Click SetupAligment Mask
3. Wait for Filter to move to the Dark
4. Confirm safe drive angle.
   Once the telescope has reached your target field, check the drive angle shown on FACSUM. If it is within ±10° of either 0° or 180° (or any multiple of 180°) then moving the CSU may trigger a CSU fatal error. To avoid this, have the OA rotate MOSFIRE to a safe drive angle and execute your CSU move at that rotator position, then rotate back to your mask PA to complete the mask alignment process.
5. Execute Mask.
   Use the MAGMA UI to execute your alignment mask pattern for the target.
6. Optional: Click Dark Imaging: J . This configures the spectrograph efficiently for J-band imaging, which is the filter used for imaging the mask.
7. Load coarse align. Click the Coarse Align tab on the SAT.
8. Verify pointing. When the OA tells you that your target is on MOSFIRE, check the following information on FACSUM to verify that your position is correct:
   • Target name and coordinates
   • Position angle (skypa)
   • Pointing origin (should be MOSFIRE)

Coarse Alignment

In this phase, we put the stars into the alignment boxes using the SAT Guider Coarse Align tab.

1. Select target. Click the target list selector on the SAT Guider Coarse Align tab and select the target to observe. By default, this drop-list displays Current DSS, but you should select the desired target to trigger SAT to verify your pointing. This will:
   • Download a DSS image of the guider field corresponding to the science target (unless you did so earlier) and display the image left side of the pane.
   • Overlay red boxes on the six brightest objects cataloged in the field.
   • Populate the table at the bottom of the pane with object names, celestial coordinates, and predicted guider positions.
   • Erase any existing telescope offsets shown under Calculated Offsets as a visual cue that offsets are not calculated, and disable the Move Telescope button.
2. Wait for OA to turn Guiding on
3. Grab guider image. Click the Grab Guider Image button once the telescope is in position. This will:
   • Trigger MAGIQ to save an image of the guider field
   • Display the guider image on the right image display
   • Overlay RED boxes on the predicted positions of the alignment objects
   • Overlays WHITE boxes on the actual guider image after analyzing the image using a find asterism algorythm. White boxes are usually offset from the red boxes.
   • Analyze the image to locate the actual images of the six alignment objects and draw white boxes around them
   • Erase any existing offsets from the screen as a visual cue that offsets are not calculated
   • Disable the Move Telescope button
   Observers may adjust the brightness and contrast (if necessary) by right-clicking on the image and dragging the mouse.
4. Click On Star in Guider image on the right hand side Select an object which is visible in both the predicted DSS guider image at left and the actual guider image at right. The SAT will then:
   • Measure the position of the object
   • Overlay a yellow box on the star to indicate the selection and centering
   • Locate the corresponding image of the object in the DSS image and toggle the surrounding square yellow
   • Toggle the selection indicator from red to yellow in the table at the bottom of the pane
   • Calculate the telescope offsets required to put the star at the predicted location and display them in the offsets table below the image
   • Enable the Move Telescope button as a visual cue that moves can be sent
   If the SAT highlights the incorrect star in the DSS image, select a different star either by clicking in the DSS image or selecting the star in the guide star table.
5. Click Move Telescope. This will cause SAT to:
   • Offset the telescope
   • Acquire and display a new guider image at the updated position
6. Verify move. Wait for the guider image on SAT to update and verify that the stars are in the RED boxes on the right-hand side guider image now agree. If necessary, click on a new star and send another telescope move to improve the centering.

Fine Alignment

In this phase, we refine the positions of the stars within their respective alignment boxes to achieve optimal centering of the slitmask using the SAT Fine Align tab.

1. Check that the CSU has finished moving. Wait for the CSU to finish the alignment mask configuration.
2. Optional: Verify the exposure options. The instrument configuration options set on the SAT Options tab are appropriate. Unless set to current, these override the current instrument settings.
3. Click Start Fine Alignment button on SAT to start the fine alignment process. The software will then:
   • Reconfigure the spectrograph as needed to image the mask
   • Acquire an image of the sky a few arcseconds away to serve as background subtration.
   • Acquire an image of the target.
   • Subtract the sky image from the target image and display the resulting difference image
   • Compute and display object and box profile fits
   • Calculate offsets in translation and rotation
   • Suggest telescope moves by preselecting Y/N for X/Y offset and rotation moves
4. Review fits. For each star the SAT graphs:
   • X fit to the stellar and box profiles
   • Y fit to the stellar and box profiles
   • Residual fit to the object position in the box on the Fit Residuals plot on the right.
   Review the object and box fits, calculated offsets, and move recommendations.

   XYFIT codes Graphic Description White solid line Star profile (sky subtracted) White dotted vertical line Star center Red solid vertical line Predicted star position Green box Shows centering of the fitted box Yellow dashed line Box profile (object +sky)

5. Remove outliers. If necessary, exclude a star from the fit by clicking the button to the left of the offending star's graphs. Possible reasons to remove a star from the fit are:
   • No object is visible in the box
   • The white dotted line (centroid) is not at the stellar peak
   • The residual displayed in the residual plot is much greater for one star than for the other targets, indicating bad astrometry for that star
   If you exclude a star from the fit, SAT will recalculate the moves ignoring that object. Please see the example image showing a star excluded from the fit.
6. Review moves. In the Offsets area, the SAT displays the recommended moves in X, Y, and rotation. Moves which are significant are enabled by default, while small moves are disabled. If you want to override the default move recommendation, click the Y or N button next to the offset.
7. Send moves.
   Two options:
   • Send moves and Retake Image
     If a rotation is required, or if X/Y moves are larger than 0.1 arcsec, an additional iteration is needed to further refine the pointing; click Send Moves and Retake Image.
   • If no rotation is required and X/Y moves are under 0.1 arcsec, no additional iteration is needed; click Send Moves Only.
   • Repeat acquisiton and send moves until all moves default to "N" indicating no moves are needed.

     Note: If seeing conditions are variable, it may not be possible to converge below the threshold limits.

Spectroscopy

Reconfigure MOSFIRE for spectroscopy:

1. Click Setup Science Mask:

   On MAGMA, click Setup Science Mask to prepare the CSU for moving the alignment bars to the science position.

2. Click Quick Dark mode:

   On the MOSFIRE desktop Observing Mode GUI, select Quick Dark mode (to prevent persistence)

3. Wait for filter. Filter should say DARK. The graing may continue to move.
4. click EXECUTE Mask:

   On MAGMA, click Execute Science Mask to prepare the CSU for moving

5. Click on the desired Dark spectroscopic mode:(e.g. H )

   On the MOSFIRE desktop Observing Mode GUI, select Dark Spectroscopy: band (e.g. H) for the spectroscopic mode for your science. This efficiently configures the filter, grating, and pupil for your science setup.

6. Configure detector.

   On the MOSFIRE desktop Exposure Control GUI, set the exposure and nod parameters:

   • Set Integration Time as appropriate (see recommended exposure times)
   • Set Coadditions to desired value
   • Set Sampling mode to MCDS
   • Set Repeats as appropriate
   • Set Dither Pattern to Mask Nod
   • Click Edit Params and set nod size to the appropriate value for the mask
7. Wait for CSU mask.

   Wait for the CSU move to complete the move.

8. Set grating/filter.

   On the MOSFIRE desktop Observing Mode GUI, select the appropriate spectroscopy mode.

9. Start exposure.

   On the MOSFIRE desktop Exposure Control GUI, click on Wait & Go button to begin the exposure.

Phew!

Appendices

Retrieve all Guider Images

Do this step in the afternoon to save time at night:

1. Click the Coarse Alignment tab on the SAT.
2. If you have not already loaded the starlist, click Load Star List, locate the appropriate directory, and select the appropriate starlist file.
3. Click, Retrieve all Guider Images. This will store FITS images in the data directory for each target in the list. The FITS data will have names target.fits
4. To preview the guider fields, select a target in the target dropdown list. By default the list shows Current DSS as the target.

Note: If you modify the coordinates in your target list, you will need to re-click on Retrieve all Guider Images to update your guider images.

Tips and Tricks

To specify the sky frame to use for background subtraction

1. Select Actions -> Load MOSFIRE Sky Image
2. Set all moves to N
3. Click Send Moves and Retake Image to trigger a new image at the current position. It will use the selected sky image as the sky.

To load an alignment image manually

1. Click Actions -> Load Fine Alignment Image.
2. If necessary, use the Actions -> Load MOSFIRE Sky Image to set the sky image to match.

Alignment check

When observations require very long integrations it is recommendable to perform an alignment check every 2 to 2.5 hours to make sure targets are still well centered in the slits. This can be done easily and efficiently with the option Check Alignment in SAT's Fine Alignment tab. The procedure to perform an alignment check is as follows:

• Once the current science exposure is close to be completed, click on Check Alignment. Note it is not necessary to wait until the last science exposure is completed. Check Alignment will standby until the current science exposure is finished.
• Once the science exposure is completed, Check Alignment will automatically:
  1. Setup and execute the corresponding alingment mask in CSU.
  2. Change the observing mode to J-imaging mode.
  3. Take an alignment image. Note that no sky image will be taken. Check Alignment uses the sky image from the previous alignment.
  4. Display the results from the alignment algorithm.
• If you are happy with the alignment, then click on Done: Check Align.
• If the alignment does not look good enough, then you can start an iterative process using the commands Send Moves and Retake Image or Send Moves Only, until the mask is well aligned again. Once you are happy with the alignment, click on Done: Check Align.
• If the alignment stars residuals are too big, this is likely due to a bad sky subtraction caused by a strong change in the sky background since the last alignment. In this case it is recommendable to Start Fine Alignment, which will take a new sky image.
• The command Done: Check Align will automatically:
  1. Setup and execute the corresponding science mask in the CSU.
  2. Reconfigure the observing mode to the science observing mode previous to the alignmemt check.
• At this point you can continue with your science observations.

Crowded Field Fine Alignment

For some fields it may be necessary to use guile to fine align a slitmask due to the density of objects in the field. Below are some tips and tricks that may be used to manipulate the software and align a mask.

• When the field is crowded, you may need to acquire a sky frame manually at a location far away from the field, and then acquire an on-target alignment image.
  1. Slew the telescope to a relatively blank field
  2. Review the options tab to see the current exposure parameters (typically: CDS mode, 10s, and 2 coadds)
  3. Acquire a sky frame using MOSFIRE's exposure control gui
  4. On SAT select: Actions->Load Mosfire Sky Image, and select the appropriate sky frame
  5. Slew to the target and coarse align the mask
  6. Acquire a science frame by either:
     • Acquiring an image using the MOSFIRE exposure control gui and then click Actions -> Load Fine Alignment Image. to initiate the analysis.
     • Or set all the moves to "N" and click Send Moves and Retake Image. This will take an image at the current location and analyze the data.
• Another option is to simply change the sky nod parameters using the script nod # #. The default is to take an initial sky image 10 arcsec east, but you can change the nod throw by updating the nod parameters. This is helpful if one of the boxes has a bright star at the "sky" position.
• If necessary, use the Actions -> Load MOSFIRE Sky Image to set the desired sky image, and then set all moves to "N" and then click Send Moves and Retake Image. This will take an image at the current location and analyze the data.