Canada-France-Hawaii Telescope Canada-France-Hawaii Telescope
3 Observing Procedures and User Interface The top Menubar of the Pegasus session will be no different from a normal Pegasus session. In particular a visible imager session will look like a FOCAM Pegasus session with an "AOB" button. Activation of this button opens the following form which, in turn, directs an observer to various adaptive optics options. This form may remain open the whole time. It can be closed by clicking "Done" (no action taken, only the form disappears).
Click the 
button, in the "AOB" main menu to set the parameters of the adaptive correction. Three different type of closed loop control are offered. The most useful is the automatic mode. At regular intervals (2 to 4 minutes) the amplitudes of the control mirror modes versus time are extracted from the real-time computer. A derivative is applied to the phase variance versus the gains for each mode. A noisy mode will receive a small gain (to avoid overshoot because of inaccurate detection of this mode) while a clearly measured and detected mode will be assigned a larger gain and therefore will contribute significantly to the reduction of the phase variance. For this correction type the user needs only to center a guide star and activate AO correction.
The semi-automatic correction is pretty much arbritrary and left to the judgement of the users. It offers the latitude of deciding how many modes will be corrected. A menu proposes the number of low order modes the user wish to use for correction. It is not possible to select arbitrarily any mode number. The choice is restricted to how many high order modes will not be used. For some of PUEO's correction modes, there is an analogy with Zernike modes. When this is the case, this is indicated on the display. Note that the modes "not-corrected" are still applied to the bimorph mirror, but with a very small gain to correct static aberrations.
The Tip-tilt mode is a fast control algorithm using the tip-tilt mirror only. The bimorph is also functional but for the correction of the quasi-static aberrations only. Reference source acquisition is similar to the what was described previously.
To finish with, there are 3 types of aberrations, or modes that can be corrected also by the telescope. This capability insures that the best optical quality images are fed to the AO Bonnette, so that the all the bimorph mirror stroke can be used to correct atmospheric aberrations. These 3 aberrations are tip-tilt, or centering, focus and coma. The systematic low frequency error signals are sent to the TCS for correction. As of this wrinting, only the tip-tilt systematic signals are sent to the TCS. For instance if a constant tip term is detected by the WFS and corrected by the bimorph, after a certain number of cycles it is sent to the TCS, and the telescope moves to cancel this term. Ultimately, we will integrate the f/8 secondary unit to handle residual focus term. The coma correction will be carried out by the motorized defining pads, tipping to the PM and thus cancelling the coma term detected by the WFS. The latter feature is not activated at this time. We need to test and calibrate this option before offering it to users.
The optical gain parameter is a number from 1 to 256, proportional to the amplitude of vibration of the membrane mirror. In order words, it is proportional to the out of focus distance in a curvature wavefront sensing scheme. The value to be entered varies and is somewhat related to seeing. This field might be changed into a sliding bar with a seeing scale. Tests will be carried out in the coming engineering runs to insure this is the best way to optimize this parameter and to offer a user-friendly choice to observers.
A few preliminary steps must have been taken at this stage. You have given to the telescope operator your guide star and objects coordinates (it can also be one of the above and an offset between the two). The telescope is pointed to your guide object. You have also depressed the "AOB" button on the PEGASUS menubar, and have therefore access to the function 
to open another form that requires actions involving the usual Cassegrain bonnette acquisition camera. First, center the guide star in the center of the guide camera (one you have defined as the center of your field) by moving the telescope. Click "Record guide star position". Then center the science source ("Record science object position"). At this point the Pegasus interface has recorded the coordinate offset. Click "Accept" and the telescope is centered on the object, that is it stays where it is (!) and the wavefront sensor is moved to acquire the guide star (the order of acquisition is important; first guide star, second science target, so that in the end the telescope is on the target). We will also implement a field where the user can simply point on the science target, and enter offsets in RA and DEC to where the WFS should be sent.
The acquisition form then appears and allows fine tuning of the centering. Three plots indicate APD measured flux, focus signal, and tip-tilt signal, which is centering. Arrows allow a fine tuning of these parameters before starting correction.
When these steps have been carried out, it is important to swiftly activate the AO correction before the centering degrades (because of telescope tracking errors) Use the 
button to do this. Three real-time displays allow the observer:
to choose the appropriate neutral density filter in the WFS path,
to move the telescope to center the reference source,
to change focus if a focus term is detected.
Note tha that as of 05/04/96 the TCS does not control the focus unit of the Cassegrain upper end. This means that the observer should cancel the focus term using the usual focussing handpaddle. When all functions are completed, click "Accept" and the loop will be closed. When the loop is closed, this window appears on the screen, and allows the observer to stop AO corrections (or open the loop).
The button 
simply puts the AO bonnette into a safe sleep mode. Use it when you leave the summit in the morning for instance.
There can be 4 different focii matching when observing with PUEO: telescope f/8, wavefront sensor vibrating membrane, AO bonnette output f/20, and if present, focal reducer camera on CCD detector. This section aims at explaining which one is accessible for adjustment and how to proceed. However, the AO Bonnette and instrument will be set up in advance by CFHT's technical staff. In other words, it may well be the first instrument you have ever used which does not require focussing. So you're better get used to the idea...
During observation, the WFS detects the focus error signal, or defocussing, and the bimorph mirror corrects this aberration. If the focus signal persists for more than a few seconds, the systematic focus error is sent to the telescope to zero the focus error signal on the WFS, thus allowing the bimorph mirror full stroke to be dedicated to the correction of the atmospheric aberrations (not implemented as of May 1996. This will requires TCSIV).
The following description is essentially all the user needs to know to focus the AO bonnette. However, if you wish to learn more, click here to read a more complete description.
If at any time the observer suspects the focus to be inadequate, a simple
CAF (Computer Aided Focus) procedure is required. The observer selects the 8 micron artificial star, and activates the AO correction. Then a CAF is carried out, which is done by depressing 
button. Then use the 
. This button activates a simple CAF moving the WFS Z axis until the image on the detector is at its sharpest. This may put a small focus term on the bimorph mirror, but it will later be cancelled by updating the telescope focus. This might change the collimation within the AO bonnette but not by a large amount.
The calibration lamps are inside the GUMBALL on the Cassegrain bonnette. This means that the adaptive optics must be stopped before a calibration can be performed. The reason being that the calibration hardware needs to be moved into place, which then prevent star light from feeding the wavefront sensor.
There are obviously more calibration procedures related to the use of PUEO. It involves WFS measurements for a given bimorph electrode displacement. This is called the interaction matrix. The control matrix used during closed loop control, is the inverse of the interaction matrix. This particular calibration takes approximately 45 minutes, and requires a certain knowledge of the system. This is why it is envisioned that CFHT staff will carry this task out during the instrument setup, before an observing run. Our experience shows that it is very stable. As an anecdote, we have used at the summit of Mauna Kea the command matrices that were taken in Meudon during the
integration phase. This means that temperature and pressure changes, shocks, travelling etc, had negligible effect on the quality of the correction. Nevertheless, we believe it is proper to acquire an interaction matrice regularly. If need be, the process is simple enough that an observer could be guided through the procedure over the phone. The acquisition of interaction matrices is done with the help of the MUI (Maintenance User Interface) developed by CILAS. It is accessed under the menu button. There, access the 
. The menu "Calibration" takes the proper actions.
An item related to calibration is the calculation of the offset voltages for the bimorph mirror. The bimorph deformable mirror optical figure is not optimal when no voltages are applied. A far better optical quality (flat) can be obtained when a set of low voltages are applied to make it perfectly flat. The button 
opens a form that measures these voltages, apply them or apply a set of 0 voltages to all electrodes of the bimorph mirror.
In the lower part of the main AOB menu are 2 options called "Special Functions" and "Displays". Some of the functionalities of the first one have been discussed already, we will explain the others below.
3.5.1 Special Functions The button calls a few other functions of interest for the user. During setup, the CFHT technical staff will define a center field position for the artificial star stage and WFS stage, and opto-mechanical bench state for observation and setup. The two buttons 
and 
set the bench in the proper configurations. The observer himself might wish to change the WFS and artificial star positions for his particular program. This is done with the help of the buttons 
and 
to define the positions of the WFS and artificial star, for observing and setup configurations respectively. This means that a specific position has been defined on your detector. Let's call it your detector "HotSpot". Once it has been found, ask the Telescope Operator to bring the Cassegrain bonnette central mirror in. Clearly indentify your HotSpot location on the TV monitor. This will make subsequent pointings much more efficient. You (or CFHT staff) have found the WFS stage coordinates that brings the WFS at the corresponding position of your "HotSpot" (using "Define Observe Configuration"). Click the button 
to record this position.
Click the 
button to gain manual control of the Atmospheric Dispersion Compensator. There you can select 2 angles of rotation for the counter rotating prisms, or define a dispersion power and position angle. Note that in normal operation the ADC settings are updated at each new telescope slews.
Click the 
button to optimize centering of the reference source in the WFS. This tool might look identical to the one open with the button. The only difference is that here the WFS stage is moved to center the reference source instead of the telescope.
As said before, the CILAS is accessible from this menu. This interface is somewhat specialized and won't be described here. It is envisioned that specialized staff at CFHT will use it. However, an on-line help is available in each form. We recommend the observer to contact its support astronomer before to make use of the Maintenance User Interface.
The 
button opens a menu that offers a choice of displays. This is where one gets access to the control of indivicual components in the opto-mechanical bench. This is a DataViews input/output form. Selecting the "Visible" option under the label "Optical Mechanical Bench Assembly" and clicking 
opens the following form. The observer might wish to keep the form open for the whole duration of the run. Within this form a set of control buttons (command panel) can be made visible or iconified. If on, it allows the observer complete control of the mechanical bench. When off, the window displays the status of the bench. A question mark displayed instead of the device means that for this device, the last commanded motion failed and left it in an unknown state. The Shutter can be operated, the atmospheric dispersion compensator, the WFS TV viewing system, the artificial stars position and WFS position and finally the uncorrected f/8 beam or f/20 AO corrected.
The ADC can be set to any position the user wishes, but an automatic mode is also offered and recommended. In this mode the ADC dispersion amount and dispersion direction is set after each slew of the telescope. For IR work the ADC can be removed from the beam.
Other options under the "Displays" menu are real-time and non real-time displays. The real-time display takes many flavors. Again select the option "visible" and "Accept". The last selected real-time display will appear and a choice of five different displays are offfered:
for APD counts display,
for wavefront sensor signals and membrane stroke display,
for a display of the voltages on bimorph electrodes and tip-tilt mirror,
for a displays of the 19 modes measured,
for a display of ro, to, strehl ratio and phase variance.
The APD counts display is extremely useful (if not necessary!) to insure that your reference source is being "seen" by the WFS. All four other displays show the user something slightly different whether AO correction is on or off (close loop or open loop respectively). The WFS signals in open loop are representative of the atmospheric or real wavefront. In close loop, the signals indicate the residual wavefront after correction by the AO system. The Voltages display shows the offset voltages (or zeros) in open loop, but give a excellent representation of the input or real wavefront in close loop. This is what the observer should look at in order, for instance, to see if the centering is good, or whether a strong focus term is applied on the bimorph or again if a strong coma or astigmatism is present as a static aberration. The modes display, as for the WFS display, shows real wavefront modes, or residual wavefront modes whether the loop is opened or closed. The monitoring parameters, again give different readings whether the loop is opened or closed.
The non real-time displays are used to visualize the power spectra of various modes either in opened or closed loop. It assumes that a circular buffer has been acquired.
A non-sidereal tracking option will be implemented in the User's interface although it is not know at this time in what window. The "tos" guide star selecting program will be made available on the Pegasus interface. This tool will ease enormously the search for guide stars. For observation of non-sidereal rate objects (planets, asteroids, comets etc.) the WFS module can be moved at a constant rate in any direction in the field of view. However, the duration of a single exposure will be limited by the 90" field of view divided by the differential rate. Keep in mind that the PSF on your science object keeps degrading as your guiding source gets further away.
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