Quick Review

1. Identify Boxes in the afternoon
2. Retrieve DSS images of guider fields in the afternoon
3. Focus the telescope using MIRA: if needed
4. Slew to target and while slewing
• Configure LRIS to image the slitmask
• Update DSS with target coordinates
5. Coarse Alignment
• Grab Guider Image
• Click on guider star
• Offset telescope
6. Fine Alignment:
   • Click on "Start fine alignment" to image the mask
   • Repeat Fine Alignment if necessary.
7. Start Spectroscopic Observations .

Slitmask Alignment

This checklist describes the procedure for aligning multi-object slitmasks on LRIS using the Slitmask Alignment Tool (SAT). Released for use in January 2011, 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. Below are screen shots of the tool for the three primary observing uses:

• Box Identification
• Coarse Alignment
• Fine Alignment

To launch the SAT:

• Navigate to an “analysis” VNC desktop (blue background)
• From the window manager pull-down menu select LRIS Utilities -> Slitmask Alignment Tool

WARNING: The coordinates in the starlist must be the coordinates for the center of the mask, accounting for all relative shifts that may have been applied while designing the masks.

Focus telescope

Focusing the telescope before aligning a slitmask is recommended. The focus is strongly dependent on the LRIS physical rotator position and the telescope elevation. It is generally recommended to re-focus the telescope when the telescope elevation angle has changed by 30° or more, and/or the instrument's physical rotator position (displayed as drive on the FACSUM display) has changed by 40° or more. In practice, this often means that refocusing is done for each slitmask, since each mask may have a different rotator position.

To complete the focus:

1. Highlight the target in the MAGIQ target list using the middle mouse button, and ask the OA to slew to the new highlighted target.
2. Ask to OA to run MIRA in the neighborhood of your target.

Note:

• If you plan to observe the field for two hours (or more), you may ask the OA to run MIRA one hour west of your target field.
• MIRA is always run on the blue side.

Slew to Target

1. While slewing
• Click the Coarse Alignment tab on the SAT.
• If you have not already loaded the starlist, click Load Star List, locate the appropriate directory, and select the appropriate starlist file.
• Select target in the target list, by default this droplist displays "Current DSS."
• If you did not earlier Retrieve all Guider images, Click Update DSS on the slitmask alignment tool to display the DSS image corresponding to the LRIS offset guider FOV.
2. When the OA tells you that your target is on LRIS, check the following information on FACSUM to verify that your position is correct:
   • Target name and coordinates
   • Position angle (skypa)
   • Pointing origin (should be LRIS)

Coarse Alignment

In these steps, we put the stars into the alignment boxes.

1. Ask the OA to set secPer to 5 or less in order to provide frequent "full-frame" offset guider image updates. The SAT needs to read a full-frame guider image and if full-frame images are not updated frequently, this step will take a long time.
2. On the SAT, click the Coarse Alignment tab
3. Click Grab Guider Image, which:
   • triggers MAGIQ to save an image in the nightly directory, and
   • displays the guider image on the right image display.
4. Identify DSS stars in guider image.
   • Compare the Guider field (at right) to the corresponding DSS image (at left). The two images should display a similar stellar field.
   • Adjust the brightness and contrast if necessary by right clicking on the image and dragging the mouse.
   • Click on Overlay DSS Stars to overlay predicted star position.
5. Click on an object in the guider image (at right). The SAT will then:
   • draw a yellow box at the cursor position;
   • draw a corresponding yellow box in the DSS image around the nearest star in the DSS image
   • This star is highlighted yellow in the guide star list
   • The X/Y pixel positions for the GUIDER and DSS images are displayed in the Calculated Offsets Box.
   • The offsets in units of pixels are calculated and displayed.
6. If the highlighted DSS star is not correct, select a different star by either clicking in the DSS image on the appropriate star or selecting the star in the guide star list.
7. Click Move Telescope
   • Offsets the telescope
   • Acquires a new guider image at updated position.
8. Optional: Confirm guider move and repeat above steps if necessary.

Fine Alignment

In this step, we refine the positions of the stars within their respective alignment boxes to achieve optimal centering of the slitmask.

1. On the SAT, click on the Fine Align tab.
2. Confirm that LRIS is configured for imaging:
   • Appropriate slitmask selected
   • Correct dichroic in beam
3. Click Start Fine Alignment button. The software will then:
   • If the grism is still in beam, removes the grism from the optical path.
   • Set up instrument according to "inst config" tab.
   • Acquire a 20 second blue side image.
   • Wait for the image to read out.
   • Read and analyze image.
   • Display object and box profile fits.
   • Calculate offsets in translation and rotation.
   • Suggest telescope moves by preselecting Y/N for X/Y-inst and Rotation.
4. Review Object and Box fits, calculated offsets, and move recommendations. For each star the SAT graphs:
   • X fit to the stellar and box profile
   • Y fit to the stellar and box profile
   • Residual fit to the object position in the box on the Fit Residuals plot on the right.

   XYFIT codes

   Graphic	Description
   white solid line	star and box profile
   vertical white dotted line	fitted object peak intensity
   green box	shows centering of the fitted box
   blue dashed line	estimated sky level

5. If necessary, remove a star from the fitting process by de-selecting the star. Click the button to the left of the offending star's graphs. Some possible reasons to remove a star from the fit are:
   • The white dotted line is not at the stellar peak.
   • The object is not visible in the box.
   • The residual is much greater than the other targets, indicating bad astrometry for the alignment star.
   If you exclude a star from the fit, the offsets will be recalculated with that object ignored. Please see the example image of a star excluded from the fit.
6. If you want to change a move recommendation, select the Y or N button next to the offset.
7. Send the Moves
   • Click Send Moves and Retake Image if moves are large and a second image is needed to further fine tune the position.
   • OR click Send Moves and Stop/Reconfigure - This does not yet reconfigure the instrument, so you need to reconfigure by hand.
   • If conditions are variable, it may not be possible to converge below the threshold limits.

Spectroscopy

1. Reconfigure the instrument for spectroscopy:
   • Set dichroic and grism to the appropriate position for spectroscopy
   • Set blue filter to clear position
   • Set blue camera focus as appropriate for the clear position.
2. Set exposure time as desired for spectroscopy.
3. Expose...phew!

Retrieve all Guider Images

• Click the Coarse Alignment tab on the SAT.
• If you have not already loaded the starlist, click Load Star List, locate the appropriate directory, and select the appropriate starlist file.
• 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"
• To preview the guider fields, select a target in the target dropdown list. By default the list shows "Current DSS" as the target.

If you adjust the coordinates in your target list, you will need to reclick on Retrieve all Guider Images to ensure your guider images are up to date.

Identify Boxes

Follow these steps to generate the “box files” that record the locations of your alignment boxes. Please note that this procedure is typically completed in the afternoon.

1. Acquire a set of direct slitmask images via the LRIS Slitmask Imaging Tool, as described here.
2. Launch the Slitmask Alignment Tool.
3. Click on the ID Boxes tab on the Slitmask Alignment Tool. Please see the example image of the identify boxes tab.
4. Click Load Image and select one of your slitmask images. The image will be read from disk and displayed in the GUI.
5. Locate one of your square alignment boxes on the image. Move the mouse cursor to the center middle of the box.
6. Press the m key to mark the box. The tool will draw a red square around the box, and will automatically add the new box coordinates to the box file on disk.
7. Repeat the above step for each box on the mask.
8. If you need to delete a box, press the d key to remove the box nearest to the cursor position. Again, the software automatically updates the box file stored on disk.
9. If desired, verify that the box file was written to disk by listing the contents of your data directory and verifying that box files (with a .box suffix) exist.
10. Repeat the above steps for additional slitmasks.