IFU MAPS
HexPak	GradPak	SparsePak
WIFOE CAMERA IFU IMAGES
HexPak	GradPak	SparsePak

• About WIFOE
• Aligning The Array - includes rotator offset calculator
• Precision Offsets using WIFOE Camera - includes telescope offset calculator
• Nightly Setup and Operation
• Acquiring The Object
• Drifting Star Across Array -- Using Handpaddle or TkComet
• Returning -- to the same position on consecutive nights

Main concerns:

• Rotator alignment: Is the array rotated to align with N & E on the sky; or aligned according to observers wishes?

  On the first night of an instrument run the array will not necessarily be aligned properly with the telescope/sky. It is desirable to spend a few minutes and determine what rotator offset is needed to align the array. This offset value should be good for the the entire run as long as the instrument is not disturbed on the telescope. But, it should not be trusted from run to run when the instrument has been removed.

• Object positioning on the array using the Pellicle: this is a subtle point. The positioning of the pellicle is not reproducible with successive insertions.

  One unfortunate feature of the WIFOE Pellicle is that it does not return to the exact same position every time it is taken out and brought back in for viewing. The best way to deal with this is to mark the position of the fiber of choice on the TV monitor using the Boekeler Video Image Marker. Then do whatever setup procedures are needed before removing the Pellicle to observe. Every time the Pellicle is brought in the fiber position will need to be re-marked.

ABOUT WIFOE - Summary of GUI Operation

WIFOE has 5 commands, 4 of which are pellicle wheel positions:

• OBSERVE: This takes the pellicle out and sends the light to the spectrograph.
• PELLICLE: This brings in the pellicle and allows the target, along with the fiber array, to be viewed on the monitor
• POS1: A spare position.
• SCREEN: This position brings in a screen used for doing comparisons.
• STOP: This stops WIFOE from moving.

FIRST NIGHT SETUP - Aligning the Array with N/S on the Sky

The alignment of the array should be checked at the start of each night.  If alignment changes dramatically from night to night, the instrument may need to be tightened up on the telescope. Note, that the position of the fiber bundle with respect to the ds9 image will not change after an adjustment—the alignment of the fiber bundle and WIFOE combination with respect to the sky is what changes.

There are two methods available for determining the correct aligment of the fiber array. First: the high resolution of the WIFOE camera allows for precise measurement of fiber positions used to calculate the rotator offset directly. Second: use the handpaddle to drag a star across the array.

METHOD 1 - Direct Calculation of the Rotation Offset

• Using the ds9 display of the WIFOE camera image zoom in so you are viewing just the central array.
• Choose a column of fibers to use for your measurement.
• Place your cursor first on the center of the top fiber of that column and record both the x & y coordinates.
• Now, place your cursor on the bottom fiber of that column and record its x & y coordinates.

  Below is a calculator you can use to determine the rotator offset angle which will align the rotator with north and south on the sky.

  Rotational Alignment Calculator

  X	Y
  		Pick pixel location for top reference fiber.
  		Pick pixel location for bottom reference fiber (on same column of fibers).
  		(degrees)

• Adjust the rotator offset by the value just determined, in the CLI type,
  
  mnir offset set #d
  where # is the value (in degrees) that you just calculated.
  Note, if you use <offset set> as opposed to <offset adj> you will be able to move to other targets throughout the night without having to re-apply the rotator offest each time.
• Make a note of this rotator offset value. This offset will have to be applied at the start of each following night.

METHOD 2 - Dragging the star across the array with the handpaddle:

1. Slew to a nearby star of about 9th. or 10th. magnitude (GSC star perhaps).
2. Bring in the Pellicle and turn on the Back Illuminator
3. Adjust the focus by eye using a very faint star (if there is one in the field) and the TV gain down very low. The offset from the focus that was determined by a wavefront is around -200 microns.
4. Try to balance the Illuminator intensity with the star's brightness so that the star can be centered reliably on a fiber (less than 8 on the slider is recommended).
5. Set the telescope handpaddle to equatorial mode (Sky MOUNT on handpaddle)
6. Align the star at the top or bottom of a column of fibers and run the star vertically. Check that the star runs straight up and down relative to the fibers.
7. If the array is not aligned you will need to offset the mos rotator and repeat step (7) above until it is aligned. In the CLI type:
   mnir offset set #d
   where # is the number of degrees by which you wish to offset rotator. A positive offset will cause the star to move counter clock-wise with respect to the array.
   Note, if you use <offset set> as opposed to <offset adj> you will be able to move to other targets throughout the night without having to re-apply the rotator offest each time.
8. Refer to the Rotators page for explaination of rotator commands.
9. Repeat step 7 until satisfied with the alignment.  Make a note of the final rotator offset.  This offset will have to be applied at the start of each following night.
10. GOTCHA!: Don't forget to set the handpaddle back to AZ/EL mode.
11. Turn off the Back Illuminator

An Important Point: If the observer needs the rotator set to different Position Angles you will need to apply a rotator offset adjustment to accomodate this. That is, in the CLI type:

• mnir offset adj #d. This offset will not persist when you slew to a new target. However, the alignment offset you applied using, mnir offset set #d will persist from slew to slew until you set the offset to 0d.

MAKING PRECISION OFFSETS Using the WIFOE Camera

Precision offsets are especially needed and useful when faced with aligning an "invisible" science target with a fiber of choice (fiducial). They are very impotant when trying move a star or science target from one of HexPak's central fibers to another, or doing the same with GradPak and SparsPak. HexPak's and GradPak's small fibers are especially tough to align a target on visually. As a comparison, all of SparsePak's fibers 5 arcsecs on the sky. GradPak has fibers less than 2 arcsecs up to 5 arcses, and HexPak has fibers of both 2.8 and 0.94 arcsecs on the sky. WIFOE's camera allows accurate measurement, using the ds9 image display, of both fiber and check star positions. It's pixel scale is accurately known in several different binning modes.

Use the calculator below to determine the telescope offset from check star to science target, or from fiber to fiber.

Formula for calculating offsets from well X/Y pixel coordinates.

• RA offset = (X₁ - X₂) * (pixel scale, ie., binning factor)
• DEC offset = (Y₂ - Y₁) * (pixel scale, ie., binning factor)
• Note, that the RA offset has X₁ and X₂ swapped. This is because East & West are flipped as seen (measured) on the WIFOE image.

NIGHTLY SETUP AND OPERATION

1. Set the determined rotator offset and apply any desired rotator offset adjustments provided by the observer.
2. Turn on and start integrating with the WIFOE camera
3. Adjust focus: Slew to a nearby star of about 9th. or 10th. magnitude (GSC star perhaps).
   • Bring in the Pellicle and turn on the Back Illuminator
   • Adjust the focus by eye using the GSC star (or a fainter one if there is one in the field) - best if integration time is low (0.1 to 0.05 second).
     Note, the focus offset from that determined by a wavefront is around -200 microns.
4. Mark (with a circle) the fiber of choice on the ds9 display - simply clicking on the fiber should suffice.
   Note, if you click within the circle after creating it you can move it either with your mouse or, more precisely with the keyboard arrow keys.
5. Dim or turn off back Illuminator.
6. Perform a "quick pointing check", ie., quickly, roughly center star on TV mark.
   Don't spend any time centering - precise alignment with the fiducial will follow in next section.
7. DO NOT REMOVE PELLICLE YET - you still need it for target acquisition.

ACQUIRING THE OBJECT

In general, there are two scenarios under which the target can be acquired. Either the target is visible and can be placed on the fiducial by eye, or the target is not visible and a check star is needed.

Important:

• Pellicle: Once you've brought in the pellicle for setting up do not remove it until the setup is complete and you are ready to observe the object. Pellicle position is not exactly repeatable.
• Guiding: Get in the practice of always using the cur button—guide at current location—when initiating guiding. This will ensure the guider does not drag the object off the fiducial.
• Probes GUI: The –Pak– field of view is small so make sure that the guide overlay has PAK selected to maximize guide star options.
• Guided vs. Non-guided Offsets: Due to WIYN's poor open-loop tracking unguided offsets are more repeatable than guided offsets. If doing offsets of more than 3 arcminutes guided offsets can have errors in X/Y (ie., N.S.E.W.) due to poor alignment, plus errors in rotation angle.
• G-Probes GUI: Use the PAK "field vignette" overlay to ensure largest guide FOV available. PAK size on ds9=2000x2000 (IAS gprobe units) — 10 gprobe units = 1 arcsec.

The following procedure assumes that either the slew from the last target was short, or a local pointing check has just been made (that is, a pointing star has been quickly placed near the fiducial but no exact positioning has been done).

If Target IS Visible - No Check Star Needed:

1. Slew to target
2. Perform quick pointing check - don't worry about precise centering just yet.
3. Find guide star
4. Warp to star
5. Guide at current location (initiate guiding with cur button)

   This is advised so there is no possibility of the guider dragging the target object off the fiber.

6. Precise centering on fiducial: tweak position of target using guided offsets (select Follow offsets on Probes GUI - note, handpaddle must be in AZ/EL mode).
7. Or, use WIFOE camera image to measure pixel position of fiber center and object position to calculate exact offsets
   
   • 5x5 binning: scale=0.258 arcsec/pixel
   • 2x2 binning: scale=0.103 arcsec/pixel
   • 1x1 binning: scale=0.0515 arcsec/pixel
8. NOW YOU CAN REMOVE THE PELLICLE (set WIFOE to Observe).

If target is NOT visible and a check star IS needed (three scenarios):

1. Observer provides a check star AND check star is within field of view of target (ie., check star is within 2.5 arcmin of target)

1. Slew to check star - roughly, quickly center on fiducial.
2. Find guide star.
3. Precisely center check star on fiducial using handpaddle.
4. Warp to star.
5. Guide at current location (initiate guiding with cur button)
6. Offset to science target: do guided offset of telescope (using Follow offsets on Probes GUI) to target using offsets you or your observer have calculated.
   
   CAUTION: After offset - Ensure that guide probe does not vignett "PAK" field of view (PAK size=100x100 arcseconds) and, that probe does not hit limit at the edge of the FOV.
7. NOW YOU CAN REMOVE THE PELLICLE (set WIFOE to Observe).

Use the calculator above, in the Making Precision Offset Using the WIFOE Camera section to determine the telescope offset from check star to science target.

One can also use the handpaddle, if the guide star has been acquired and guiding is off, to do the final tweak of the check star's position on the fiducial. Remeber, after slewing back to target, and after doing Warp to star YOU MUST USE THE CUR BUTTON AND GUIDE AT THE CURRENT LOCATION.




2. OA finds check star using NOMAD:

In this scenario it is important that the OA know well in advace of slewing to a target that he or she needs to search for a check star. The NOMAD catalogue provides highly accurate star coordinates appropriate for use as check stars.

1. OA uses NOMAD to obtain a check star
2. Same as a through g in scenario (1) above



3. OA uses PPM or SAO star to zero pointing > 2.5 arcmin from target:

1. Slew to target
2. Find guide star and quickly place near center of screen
3. Slew to check star
4. Carefully center star on fiber of choice
5. Slew back to target
6. Quickly Warp to star
7. Guide at current location (initiate guiding with cur button)
8. Remove pellicle and observe

Notes:

• Each time the pellicle is brought in, its position as viewed on the monitor may change slightly.  The back illuminator must be brought in every time the pellicle is moved, and the fiber positions remarked.
• Check that the field is optimally centered about once an hour.  The probes guider does not provide any corrections for rotational guiding, so rotational tracking errors can accumulate.  Although, if the rotational alignment is OK there shouldn't be much drift.
  
• The header information is written at the end of readout.  To ensure positional information is correct, do not move the telescope until readout is complete.
• Never move the back illuminator while exposing or reading out.  Added noise.
  

DRIFTING STAR ACROSS ARRAY -- Using the Handpaddle or TkComet

There are two good methods for drifting a star across the array. It depends on the star's magnitude and what speed is needed for it to move across the array and still get adequate counts in each fiber.

DRIFT METHOD 1 -- Very Bright Stars → Using the Handpaddle

With this method you will likely need to change the paddle rates to suit the observer's needs for drifting a star across the array. You can use either the XTCS inspector, or the CLI to accomplish this. Remember to change the rates back afterward.

Changing rates using the Paddle inspector:

1. Center the star as normal.
2. On the XTCS Pallet, select the handpaddle icon (bottom row).  This will bring up the Handpaddle/Rates Inspector.
3. In the Handpaddle Inspector, change the handpaddle mode by selecting from the menu button labeled, SKY1.
   • For Up/Down drifts - select RA (menu button becomes SKY2).
   • For Left/Right drifts - select DEC (menu button becomes SKY1).
4. Change the guide rates for either (guide, set, or search).  Rates should be provided by the observer.
5. Hit Apply,  (this will change the rate for the corresponding speed on the handpaddle).
6. Bring in the pellicle and back illuminator, and turn up the illumination.
7. Mark, on the ds9 display, the ends of the row or coloumn of fibers that you will be drifting across.
8. Put handpaddle into to equatorial mode (Sky MOUNT), and set speed to "SLOW","MED" or "FAST", whichever corresponds to the rate you've changed.
9. Move the star to the start fiducial position and run a timed test through the desired fibers. 
10. When satisfied, center the star on the start fiducial position. 
11. Remove the Back Illuminator and the Pellicle (move WIFOE wheel to the Observe position). When the shutter opens immediately press the appropriate "Jog Arrow" and move the star across the array.

Changing rates with the CLI:

1. First check the 'p' WIYN-page for the current SKY1 or SKY2 default speeds. You will need to set the rates back to this configuration when done.
2. Choose which direction you want to drift (SKY1 (RA) for across the array, SKY2 (DEC) for up and down the array).
3. Say you want to drift up and down the array at 2 arcsecond per second of time. In the CLI type:

   paddle speed sky2 set 2", 10", 60" 60"

   and use the SLOW speed on the handpaddle.

4. Follow the above listed steps for drifting the star across the array
5. Return paddle rates to normal as record from the 'p' WIYN Page using default values in the above CLI command.

DRIFT METHOD 2 -- Faint Stars (Spectophotometric stars) → Using TKComet

This method is prefered for very slow drift rates (on the order of 0.5 ″/sec). You can use the handpaddle and adjust the rate, but the squeal will last a long time. It is recomended that you use TkComet for this. Documentation for the TkComet GUI contains instructions on how to use it as a drift tool for any IFU. Please look at that page for futher information.

RETURNING TO THE SAME POSITION on Consecutive Nights

There are occasions when the observer will need to return to exactly the same position from night to night. Hopefully you will be informed of this before you even begin the setup procedure (the setup person should have already acquired this information and informed you).

There are three good ways to accompish this task.

METHOD 1

If the observer has a Mosaic or other image of the field they can compute accurate offets from stars with known coordinates. These should be sufficient from night to night. However, Method 2, below, could also be used as a double check.

METHOD 2

Once the position has been determined and the Observer is satisfied you can simply record the G-Probe's X and Y values along with the Guide Box's X and Y values. There is a small disadvantage to this method; the particular guiding position within the Guide Box itself may not be exactly the same from observation to observation.

METHOD 3

This method works if you can see the object.

1. Slew to the object coordinates.
2. Locate a guide star near by (use the XTCS's New next GSC search feature to find a guide star near your current position).
3. You can calculate (roughly) the offsets from the coordinate of the object and the G-star. Make this rough offset back to the object using Non-Guided offsets.
4. Continue to use small Non-Guided offsets to center the object on the TV mark.
5. Record both the G-Star name and its coordinates.

Note: For all methods, the observer will probably want to record positions and X/Y values for future reference.

Last modified: 03-Apr-2020 16:08:52 MST