WIYN Observatory

OBSERVING WITH WIFOE - TECHNICAL INFORMATION

IFU MAPS

HexPak

GradPak

SparsePak

WIFOE CAMERA IFU IMAGES

HexPak

GradPak

SparsePak


Main concerns:

ABOUT WIFOE - Summary of GUI Operation

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

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

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:

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.

Telescope Offset Calculator
Select bin mode:Bin 5x5 (default) Bin 2x2 Bin 1x1
X     Y(pixels)
Pick pixel location for check star, or initial fiber.
Pick pixel location of science target, or next fiber.
RA offsetDEC offset(arcseconds)
      

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

 

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:


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:

  3. 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

  4. 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:

 

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.

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