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The AO Acquisition Tool User's Guide
- Introduction
- Starting up the acquisition tool
- Grabbing an acquisition image
- Performing the acquisition
- Mode 1 - Setting up a complete AO integration
- Mode 2 - Moving an object to a target position
- Mode 3 - Moving an object onto the pickoff probe
- Finetuning an OASIS Acquisition
- Example acquisition scenarios
- Imaging observations with INGRID/OASIS
- Spectroscopic observations with OASIS
- Further notes
1. Introduction
This page is intended to provide a step-by-step guide to using the AO
Acquisition Tool in conjunction with the NAOMI adaptive optics
system. It also outlines the most efficient techniques for performing
target acquisition, for a variety of observing scenarios with the
INGRID and OASIS instruments.
For more detailed documentation about the tool and its calibration,
as
well as troubleshooting information, you should refer to the WHT
Acquisition Tool User Guide.
There are two major goals when performing an AO acquisition. The
first is to accurately position the science target onto the science
detector (of INGRID or OASIS) at the required position. The second is
to select an appropriate guide star (which may or may not be the
science target), for performing the AO correction, and to send its
light to the wavefront sensor of the AO system. By using the
acquisition tool outlined here, one can simultaneously perform both
these goals, while operating with any sky PA.
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2. Starting up the acquisition
tool
- To start up the acquisition tool:
- Check that the acquisition camera you require (normally AG3)
is configured into the observing system. Note that it must not
be windowed.
- At the SYS> prompt in the pink WHTOCS
window, type acqtool&.
- The image below illustrates the main display page, which should
now appear on the screen.
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3. Grabbing an acquisition image
- To perform the acquisition, you must first grab
an image.
- To bring up the Grab Acquisition Image window, go to
the
menu option Grab and select Grab Acquisition Image.
Alternatively
you can press Ctrl-g on the keyboard, while the mouse is
located over the main display page. The image below illustrates
the appearance of the window that should appear.
- Check that Acquisition Camera is set to AG3.
- Select the exposure time you require in the Duration
box.
- Select the camera field of view(s) (FOVs) to be overlaid on the
acquisition image. By default both INGRID and OASIS are selected (as on
the image above); one can unselect either or both of them by pressing
the appropriate button(s).
- Check that the NCU slide, on the separate observing GUI, is
set to Acquisition.
- Suspend framing on the camera's TV application (or ask the
TO to
do this for you).
- Click on Grab Image.
- Once the exposure has finished and been read out, it should
appear on the main display page with the appropriate overlays, as
illustrated below. (Note that the image is dark as it was taken
during off-sky tests.) The red and green boxes show the field of views
of INGRID and `OASIS imaging' respectively. The green
circle marks the (approximate) position of the centre of the FOV of
OASIS when it in spectroscopy mode, while the red circle shows the
position of the pickoff probe when the latter is set to 0, 0. Finally
there should be a yellow overlay illustrating the directions of north
and east. An on-sky example is
shown here.
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4. Performing the acquisition
- The acquisition tool has three modes of
operation. The most
general mode is for setting up a complete AO integration and this is
recommended for normal observing. The
remaining two modes may be useful for more simple cases of acquisition
and
for commissioning tests. To perform any of these operations one must
first
display the acquisition control window:
- To bring up the Acquisition Control Window, go to
the
menu option View and select Pick Object.
Alternatively
you can press Ctrl-p on the keyboard, while the mouse is
located over the main display page. The image below
illustrates the appearance of the window that should appear. For now
the user should only be concerned with the buttons in the region NAOMI Acquisition
and not those in the OASIS
Acquisition section. Note that
in the following sections, a click on the mouse refers to a
single click with the left hand mouse button.
- Mode 1 - Setting up a
complete AO
integration (recommended for normal observing)
The purpose of this mode is to use the acquisition image to
select
(a) the guide star (b) the science target and (c) the desired position
of the
science target on the science detector, in order to set up an AO
integration. The tool uses this information to simultaneously move the
telescope and Naomi's wavefront sensor pickoff probe.
- Click the Select Science Object button. Click once,
on the
acquisition image, over the science object.
- Click the Pick Science Target Position button.
Use the overlays selected in Section 3 to help select the position on
the
acquisition image corresponding to where the science
object should be moved, and click on this position with the mouse.
- Click the Select Guide Object button. Click once, on
the
acquisition image, over the position of the guide star that is to be
used by
NAOMI. Note that this object may or may not be the same as the science
object.
- Click the Setup AO Integration button to
simultaneously
move the telescope and the guide star pickoff probe.
- Once the move has been completed, a new acquisition image
will
automatically be requested.
Note that if you make a mistake during one of the selection steps,
simply
re-click on the relevant button and you can reselect the
object/position.
- Mode 2 - Moving an object to a target
position
The purpose of this mode is to allow the user to
reposition an object to a new position on the acquisition image (and
therefore on the science detector). This mode is useful if one does not
require guiding.
- Click the Select Science Object button. Click once,
on the
acquisition image, over the object to be moved.
- Click the Pick Science Target Position button.
Use the overlays selected in Section 3 to select the position on the
acquisition image corresponding to where the science
object should be moved, and click on this position with the mouse.
- Click the Move Science Object To Target button to
move the telescope.
- Once the move has been completed, a new acquisition image
will automatically be requested.
Note that if you make a mistake during one of the selection steps,
simply
re-click on the relevant button and you can reselect the
object/position.
- Mode 3 - Moving an object onto the pickoff
probe
The purpose of this mode is to allow the user to place an object
onto the
pickoff probe, when the latter is positioned in its nominal position.
- Click the Select Science Object button. Click once,
on
the acquisition image, on the object to be moved to the pickoff probe
nominal position.
- Click the Science Object to Pickoff button to move
the
telescope, so that the object will fall on the pickoff probe
(provided the latter is at its nominal position i.e. 0 0).
- Once the move has been completed, a new acquisition image
will
automatically be requested.
Note that if you make a mistake while selecting the object, simply
re-click on the Select Science Object button and you can
reselect it.
- Remember, after doing the acquisition, that you will only
receive light on the science detector if you move the NCU slide back to
the science position.
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5. Finetuning an OASIS Acquisition
For OASIS observing, one will normally have used Mode 1 (Setup AO Integration) for the
acquisition. In this
instance, the telescope and pickoff probe will have been suitably
positioned and the guide star should appear on the AO wavefront sensor
(once the NCU slide is back in the science
position). The support astronomer should be able to directly close the
AO loop if the acquisition tool is well calibrated; if not, ask the TO
to tweak the telescope position to centre the guide star spots and then
close the loop.
Assuming the observer has selected the science target position to
correspond to the centre of the spectroscopic FOV of OASIS (denoted by
a green circle in the overlay), then in principle one can start to take
science exposures. However, due to the very small FOVs available with
the four spatial enlargers used by OASIS, it is recommended to finetune
the
positioning of the science target whether to (a) centre the target, (b)
offset the target or (c) mosaic a larger field of view. This finetuning
can be performed with the OASIS
Acquisition features of the acquisition tool; these treat the
imaging mode of OASIS as an acquisition camera to correctly position
the science target in the smaller spectroscopic field of view(s). The
tool performs
simultaneous and synchronised moves of the telescope and pickoff probe
so that the guide star will always remain on the wavefront sensor.
- Grabbing an OASIS Acquisition
Frame
- To bring up the Oasis Image Acquisition window, go
to the
menu option Grab and select Grab OASIS Image.
Alternatively
you can press Ctrl-o on the keyboard, while the mouse is
located over the main display page. The image below illustrates
the appearance of the window that should appear.
- Select the exposure time you require in the Duration
box.
- Select the spatial enlarger you will be using with OASIS.
- Confirm that the NCU slide, on the separate observing GUI,
is
set to Science. (It must be if the AO loop has been closed on a
star.)
- Confirm that the OASIS MITLL3 chip has the windowing set
correctly (window oasis 1 "[1:2059,1035:3140]").
- Ensure that OASIS is configured into an imaging
configuration.
- Click on Grab Image.
- Once the exposure has finished and been read out, it should
appear on the main display page with the appropriate enlarger overlay,
as
illustrated below. There should also be arrows indicating the
directions of north
and east.
- Finetuning the Acquisition
- To finetune the acquisition one uses the same Pick Object dialogue as was used
for the main acquisition (see illustration in section 4). The relevant
portion of the GUI is shown below. In order to be as versatile as
possible, there are three ways in which
one can finetune the acquisition: "Move Object to Centre with Offset",
"Apply Offset" and "Move Object to Target Position". The GUI has three
corresponding columns to lead the user through the acquisition - the
user should select the type of move they require and work down the
corresponding column. More details are given below.
- Use the "Refresh OASIS Image" tickbox to specify whether or
not the
OASIS image should be refreshed after the move. It is advantageous to
ensure that the finetuning has been successful before taking science
exposures, however refreshing the image will increase the acquisition
overheads.
- The acquisition tool will always ensure that the AO loop is open during the telescope and
pickoff probe movements. However by default it will return the loop
status to that in which it found the system. So if the loop were open
it will always remain so, whereas if it were closed it would be opened
for the move and closed again afterwards. One can override this
behaviour with the "Never Close Loop" tickbox to ensure that the loop
is always left open after the move.
- One can now perform the finetuning using one of the three
available options. Option 1 should be used to (a) centre an object or
(b) move an object to a position with a well defined offset relative to the centre of the field of view.
Option 2 allows one to make a offset relative
to the current position. Option 3 allows one to click on the
position to which an object should be moved.
- Option 1 - Move Object to
Centre with Offset
- Click
on the Select Object button.
Click once, on the OASIS acquisition image, over the science object.
- Type in the offsets, if required, and select the
coordinate system to be used for the offset (see discussion below) in the first column of the GUI. To
simply centre the object, ensure that the offsets are both set to 0.
- Click on the Move Object
to Centre with Offset button to make the move.
- Option 2 - Apply Offset
- Type in the offsets required (see discussion below) and
select the
coordinate system to be used for the offset in the second column of the GUI.
- Click on the Apply Offset
button to make the move.
- Option 3 - Move Object to Target
Position
- Click on the Select Object
button. Click once, on the acquisition image, over the science object.
- Click on the Select
Target Position button. Select the pixel on the acquisition
image corresponding to where the object should be moved, by clicking on
it with the mouse.
- Click on the Move Object
to Target Position button to make the move.
- The offsets (x, y) should be specified in
arcseconds, separated by white space. Three different coordinate
systems are available for the
offsets. The NE coordinate system will move the telescope x arcsec north and y arcsec east. The remaining
coordinate systems will move the object
x right and y up in the frame of reference of
either (a) the pickoff probe (and OASIS imaging) or (b) OASIS
spectroscopy.
- If the move is successful then one can start to take science
exposures. First one must remember to reconfigure OASIS from imaging
mode into the correct spectroscopic configuration!
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6. Example acquisition scenarios
This section is intended to record efficient techniques
for performing
the acquisition under different scenarios of targets and science
modes. It is currently under construction and will be updated with
more information in the future.
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7. Further notes
This tool will only work if it is correctly calibrated
with the
correct data in the Grab Acquisition Image window. These values
will be
monitored and updated by the AO team - any problems should be reported
to them. If it is necessary to recalibrate the Nominal WFS Offset Pixels (eg. if
the camera
has been moved or if the dichroic has caused an offset):
- Ask the TO to move the telescope to a bright star.
- Use the acquisition tool to grab an acquisition image. (Make
sure the NCU slide is set to acquisition.)
- Use the acquisition tool to move "Science Target to Pickoff"
(with the bright star selected as the science target).
- Check the new acquisition image.
- Move the NCU slide to science
and the pickoff probe to 0, 0.
- Ask the TO to tweak the telescope position to centre the guide
star spots on the wavefront sensor.
- Move the NCU slide to acquisition,
take a new acquisition image, and measure the coordinates of the star
on this image.
- On the Grab Image
window, replace the values of Nominal
WFS X/Y Offset Pixel with the coordinates you have just measured.
- Click on Save Data on
the same window.
For more details on the acquisition tool please refer
to the WHT
Acquisition Tool User Guide
by Craige
Bevil.
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