OBSERVING PROCEDURES

Contents :

• Overview of the observing process

• Opening/closing the OASIS session

• Taking an exposure

• Controlling OASIS/TIGER via the PEGASUS interface

• Observing Assistant
• AOB
• F/8 Mode
• Oasis
• Offset
• IQE
• Engineering
• Files
• Image
• Graph
• Tools
• Suggestions
• News
• Aloha



• Saving data on disk or tape

• Have the instrument setup fulfilling the observer's needs; this means installing grisms, filters, CCD, and controlling the relative orientations of the lens array, the grism dispersion, and the CCD columns. The OASIS configuration files are then updated using the Engineering mode. This is done by the CFHT staff in accordance to the pre-run preparation form sent by the observers prior to their missions.



• Using the OASIS PEGASUS interface, define the scenarios to be used to observe the astrophysical targets scheduled.



• Prepare a list of the exposures to be obtained, containing at least the minimal set of exposures which is mandatory for data reduction.



• Plan carefully your observations to minimize the number of AOB beamsplitter changes. At best, 15 minutes will lost on the sky for each change.
  
  
• If you are not already familiar with these tools, practice the Image, IQE and Graph functions. They are extremely useful aids for TIGER observations.



• Become familiar with the AOB control windows when working with the f/20 mode.



• Control OASIS during the rest of the run through the Observing Assistant function of the PEGASUS interface.



• Use the Offset command when working at f/8 for centering on astronomical targets.



• Save data on DAT tape, and bring the tape home, using the Save Data function.

• Go to the Observer's console, the one with the triple display system in the telescope control room, and log in on Neptune as oasis, using the password given by the Support Astronomer. The PEGASUS interface should pop up.



• To quit, just click on the aloha button at the upper extreme right of the main menu bar. This should be done after putting the AOB system to sleep (from the AOB control window) and closing down the OASIS shutter (function found under the oasis button)

• To take an astrophysical object exposure, a sky flat exposure, a dome flat exposure, or a GUMBALL flat or calibration exposure, you must open the Observing Assistant, then click on Take a Scenario Exposure. You will first be prompted to select a scenario, then to give the exposure identification and the exposure time. See the Take a Scenario Exposure section for details.



• To take a bias or a dark exposure, you may also open the Observing Assistant, then click on Take a CCD Service Exposure. You will first be prompted to choose between bias, dark and test exposure, then to give the exposure identification and the exposure time. See the Take a CCD Service Exposure section for details. Note that such exposures are also accessible from the Take a scenario exposure function.

• Take a Scenario Exposure
  
  When selected, a menu pops up to allow the user to choose a scenario among the list that he/she has already defined. Once this is done, the left window displays information depending on the type of scenario (i.e. imaging or spectroscopy) selected :
  
  
  • For a spectrography scenario :
    
    
    
    You may then select one of the following possibilities :
    
    
    • Object Spectroscopy Exposure
      
      This is used to take the "science exposures" of the astrophysical target which once justified the observing time allocation...
      
      
      
      In the new window which pops up after you click Accept :
      
      
      • The first (red) line reminds the name of the currently selected scenario.
      • The second (blue) line remind you that you are on the way to take a spectrography exposure on your favorite astrophysical target.
      • The third and fourth (black italic) remind the optical characteristics of the selected scenario.
      • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields. The values entered here will be recorded as keywords in the final data file header.
        It is good practice to use very informative alphanumeric strings for the identifier field. For instance NGC 1068 .04 .5 HR1 is better than NGC 1068 as it gives immediate information regarding the samplings and the wavelength range. All the information about the optical configuration is recorded as keywords anyway and the short form is also acceptable; you may just have to check several file keywords.
    
    
    • Field Check Exposure
      
      This is used to verify the centering of the target on the CCD before starting a long spectrography exposure. For that, OASIS is switched to the imagery configuration defined in the current spectrography scenario, that is a classical imagery mode, but using the same filter as the one used for the spectrography exposure. It may eventually lead to the use of the Offset function to fix a mis-centering (Note: if you are already guiding with the AOB, the offsets have to be apply from the Offset function available under the "Special Functions" button for AOB). The IQE and Image functions maybe helpful at this point.
      
      
      
      In the new window which pops up after you click Accept :
      
      
      • The first (red) line reminds the name of the currently selected scenario.
      • The second (blue) line remind you that you are on the way to check the centering of your favorite astrophysical target into the CCD frame.
      • The third and fourth (black italic) remind the optical characteristics of the selected scenario.
      • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields; The values entered here will be recorded as keywords in the final data file header.
        It is good practice to use very informative alphanumeric strings for the identifier field. For instance NGC 1068 .04 .5 HR1 is better than NGC 1068 as it gives immediate information regarding the samplings and the wavelength range. All the information about the optical configuration is recorded as keywords anyway and the short form is also acceptable; you may just have to check several file keywords.
    
    
    • Wavelength Calibration Exposure
      
      This function is used to obtain the calibration spectra from the GUMBALL spectral line illumination system. This is a crucial step since the resultant data cube of calibration spectra will be used to reduce a nearby spectroscopy frame. Each spectroscopy exposure must have an associated wavelength calibration exposure, taken as much as possible immediately before or after it, with the telescope in the same position, and no scenario change between the two (to avoid any possible repositionning errors). See section Minimal Set of Exposures for a list of all wavelength calibration frames needed. The new window looks like this:
      
      
      
      This form presents the following elements:
      
      • The first (red) line reminds the name of the currently selected scenario.
      • The second (blue) line remind you that you are on the way to take a GUMBALL wavelength calibration exposure.
      • The third (black italic) reminds the spectral sampling and the filter used.
      • The user is invited to choose one or more Illumination source(s) which will be turned ON in the GUMBALL during the exposure. When selected, you must enter an exposure time for the respective lamps. Different lamps with different exposure times can be used for the same calibration frame. The lamps must be selected by checking the appropriate source(s) in the window. There are eight such usable units :
        
        • Neon 1 : Bright Neon lamp
        • Neon 660/22 : Idem through a 660nm/22nm filter.
        • Argon 1 : Bright Argon
        • Argon 2 : Idem
        • Mercury 1 : Bright Mercury lamp
        • Mercury 2 : Idem
        • Blue FP (360-500nm) : Fixed Fabry-Perot etalon for channelspectra between 360nm and 500nm
        • Red FP (500-869) : Fixed Fabry-Perot etalon for channelspectra between 500nm and 869nm
        Exposure times vary according to the resolution requested and the spectral range used. Calibration spectra obtained with the FP etalons must be combined with a normal spectral lamp source to make sure that a line can be used as a reference for the channel spectra.
      • The user is invited to enter an identifier for the frame which will be obtained (only twenty alphanumeric characters are allowed here; this field is not scrollable). The values entered here will be recorded as keywords in the final data file header.
        It is good practice to employ very informative alphanumeric strings for the identifier field. For instance Neon 0.5 HR1 is better than Neon as it gives immediate information regarding the sampling and the wavelength range. But all the optical informations are recorded as keywords, anyway, and the short form is OK; you may just have to check several file keywords.
    
    
    • Other Service Exposures
      
      This is used to obtain every type of service exposure which is not a wavelength calibration exposure; this covers flat fields, micropupils and continuum source spectra, which are all mandatory for future data reduction. See the Minimal Set of Exposures for details.
      
      
      
      In the new window which pops up after you click Accept :
      
      
      • The first (red) line reminds the name of the currently selected scenario.
      • The second (blue) line remind you that you are on the way to take a calibration exposure other thant a wavelength calibration one.
      • The third and fourth (black italic) remind the optical characteristics of the selected scenario.
      • There are four pre-defined service exposures :
        
        • Dome Flat field
          This is not recommended as the exposure times are very long. If you want to do these flats, you must check that no other lamp than the top ring lamps located on the telescope is ON in the dome, and that no optical element remains in the beam, such as the Cassegrain bonnette guiding probe.
        • Sky Flat Field
          This is usually done on the bright twilight sky to get enough light.
        • Continuum source
          This exposure will constitute the basic spectra pattern template for the reduction software; one continuum exposure is mandatory for each scenario. The GUMBALL continuum light is used for that, giving a set of continuum spectra. See the Minimal Set of Exposures for details.
        • Micro Pupils
          This exposure will constitute one of the basic references allowing the reduction software to find the spectra into the CCD frame, and precalibrate them. One micro-pupil exposure is mandatory for each scenario. See the Minimal Set of Exposures for details.
      • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields; The values entered here will be recorded as keywords in the final data file header.
        It is good practice to use very informative identifiers. For instance Microp .04 HR1 is better than Micropupils as it gives immediate information regarding the sampling and the wavelength range. All the optical information are recorded as keywords anyway so the short form is also OK; you may just have to check several file keywords.
      • The exposure time must be entered for the dome or sky flats. This field is not available when other exposure types are selected.
        
      • The user gives the number of exposures, either a single one, or some number; in the last case, he may ask for an automatic computation of the median of the frames; only the median frame file will eventually be kept on disk. This is good practice, as it produces an essentially noise-free frame.
      • Illumination source
        For the continuum source or the micro-pupils exposures, the Halogen Spectral, Halogen Imaging or both lamps at the same time can be selected. The first lamp is significantly brighter than the second one. The exposure time must be entered here.
        
    
    
    • Test Exposure
      
      This is used to obtain quickly sub-rastered binned frames allowing to evaluate the correct integration time to be used for the full frame hour-long science exposure. The observer may also obtain bias, darks, or Field Check exposures from this window :
      
      
      
      These options are available:
      
      
      • The first (red) line gives the name of the currently selected scenario.
      • The second (blue) line reminds you that you are on the way to take a test spectrography exposure, maybe on your favorite astrophysical target.
      • The third and fourth (black italic) remind the optical characteristics of the selected scenario.
      • For Dark, Object Spectro. and Field Check exposures, the user is invited to give the exposure time. For all the other cases (except of course for the Bias exposures), the exposure time is defined in the spectral lamp menu.
        
      • The user specifies the sub-raster he wants to use for this exposure; default is full frame. Usually, one makes an exposure with the chip raster limited to a few tens of spectra (300x300 pixels in the center of the CCD), binned 4x4 to obtain some readable signal in a reasonable time, exposed for a few minutes for a faint object. The resulting frame is then displayed with the Image function, and the mean pixel value in the spectra evaluated from the continuous reading at the cursor location, or by using the IQE function. The background of the image is evaluated in the same way, and subtracted. If an object signal of N has been obtained in S seconds with a 4x4 binning, and if the sky transparency does not change significantly, an object signal of N * 3600 / (S * 16) is to be expected in one hour.
      • Six exposure types are available and the user has to select one type among them. Depending of his/her choice, a different menus will appear for the Gumball lamps. In case the Other services exp. is selected , the user is also invited to select a continuum source or a micro-pupil exposure.
  
  
  • For an imagery scenario :
    
    
    
    You may then select one of the following possibilities :
    
    
    • Object Imagery Exposure
      
      
      
      In the new window which pops up after you click Accept :
      
      
      • The first (red) line reminds the name of the currently selected scenario.
      • The second (blue) line reminds you that you are on the way to obtain an image of your favorite astrophysical target.
      • The third and fourth (black italic) remind the optical characteristics of the selected scenario.
      • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields; The values entered here will be recorded as keywords in the final data file header.
        It is good practice to chose something informative the identifier alphanumeric strings. For instance NGC 1068 .06 ima HR1 is better than NGC 1068 as it gives immediate information regarding the samplings and the wavelength range. But all the optical informations are recorded as keywords, anyway, and the short form is OK; you may just have to check several file keywords.
    
    
    • Calibration Exposure
      
      
      
      In the new window which pops up after you click Accept :
      
      
      • The first (red) line reminds the name of the currently selected scenario.
      • The second (blue) line reminds you that you are on the way to obtain an image calibration exposure.
      • The third (black italic) reminds the optical characteristics of the selected scenario.
      • The user is invited to choose between dome and sky flat. Dome looks more comfortable, but is not recommanded, as the exposure times are very long.If you want to do it, you must check that no other lamp than the top ring lamps is ON in the dome, and that no optical element remains in the beam, such as the Cassegrain bonnette guiding probe. Sky flat is best obtained on the bright twilight sky.
      • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields; The values entered here will be recorded as keywords in the final data file header.
        It is good practice to use informative alphanumeric strings for the identifier field. For instance Flatima .06 HR1 is better than Flat as it gives immediate information regarding the sampling and the wavelength range. But all the optical informations are recorded as keywords, anyway, and the short form is OK; you may just have to check several file keywords.
      • Number of exposures allows the user to perform automatically a series of N exposures; one may even choose to keep only the median of the series, to obtain an essentially noise-free flat.
      • Important : do not be afraid by the number of "defects" which appear on OASIS/TIGER imagery flat frames; they come from the unavoidable tiny dust specs on optical parts, which may look as almost in focus due to the very narrow beams of the TIGER mode. All these strucutres will disappear from the science/calibration frames after flat correction.
    
    
    • Test Exposure
      
      
      
      This is used to obtain quickly sub-rastered and/or binned frames allowing to evaluate the correct integration time to be used for the full frame deep imagery exposure decribed above. The observer may also obtain bias or dark exposures from this window.
      In this window, the possibilities are :
      
      
      • The first (red) line gives the name of the currently selected scenario.
      • The second (blue) line reminds that you are on the way to take a test imagery exposure, maybe on your favorite astrophysical target.
      • The third and fourth (black italic) remind the optical characteristics of the selected scenario.
      • The user is invited to give the exposure time, useless of course if the Bias button is checked (see below).
      • The user specifies the sub-raster he wants to use for this exposure; default is full frame. Usually, one makes a full-raster exposure, binned 4x4 to obtain some readable signal in a reasonable time. The resulting frame is then displayed with the Image function, and the mean pixel value in the region of interest evaluated from the continuous reading at the cursor location, or by using the IQE function; the pixel location of this region is read with the cursor, and if necessary the Offset function is used to move the field to where it should be on the CCD. The background of the image is evaluated in the same way, and subtracted. If an object signal of N has been obtained in S seconds with a 4x4 binning, and if the sky transparency does not change significantly, an object signal of N * 60 / (S * 16) is to be expected in one minute with no binning.
      • Three check buttons are provided to specify the exposure type: Bias,Dark, or Object (i.e. imaging test on your astronomical target).


• Take a CCD Service Exposure
  
  This function is used to obtain bias and darks, either full frame or sub-rastered for test purposes :
  
  
  
  
  From this window, these secondary-level windows can be brought up according to your needs :
  
  
  • Bias
    
    
    
    These options are available :
    
    
    • The first (red) line reminds the name of the function currently used.
    • The second (blue) line reminds you that you are on the way to obtain a Bias exposure.
    • The CCD raster and binning may be selected from a pull-down menu which appears when one clicks on the CCD raster button. At the moment, only one choice is available :
      
      • Full frame, no binning : bias suitable for any spectroscopy scenario.
    • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields; The values entered here will be recorded as keywords in the final data file header.
      It is good practice to use informative alphanumeric string for the identifier field. For instance Bias 1x1 12/25/98 is better than Bias as it gives immediate information regarding the date of the bias, which may be important is some CCD troubles, ending in controller resettings, chip temperature variation, etc..., are encountered (never happens, of course). All the optical information is recorded as keywords anyway so the short form is also acceptable; you may just have to check several file keywords.
    • Number of exposures allows the user to perform automatically a series of N exposures; it is very important at this point to be able to calculate the median of all these biases (and you may choose here to have it done automatically just after the end of the series of exposures, keeping on disk only the median of the series), to obtain an essentially noise-free bias.
  
  
  • Dark
    
    
    
    These options are available :
    
    
    • The first (red) line reminds the name of the function currently used.
    • The second (blue) line reminds you that you are on the way to obtain a Dark exposure.
    • The CCD raster and binning may be choosed from a pull-down menu which appears when one clicks on the CCD raster button. At the moment, only one choice is available :
      
      • Full frame, no binning : dark suitable for any spectroscopy scenario.
    • The user is invited to fill in the exposure identifier (only twenty alphanumeric characters are allowed here; this field is not scrollable) and the exposure time fields; The values entered here will be recorded as keywords in the final data file header.
      It is good practice to use informative alphanumeric string for the identifier field. For instance Dark 1x1 12/25/98 is better than Dark as it gives immediate information regarding the date of the dark, which may be important in case of some CCD troubles, chip temperature variations, etc..., are encountered. All the optical information is recorded as keywords anyway so the short form is also acceptable; you may just have to check several file keywords.
    • Number of exposures allows the user to perform automatically a series of N exposures; it is interesting at this point to be able to calculate the median of all these darks (and you may choose here to have it done automatically just after the end of the series of exposures, keeping on disk only the median of the series), to obtain an essentially noise-free dark.
  
  
  • Test
    
    
    
    This is a kind of do-as-you-want CCD exposure menu... These options are available :
    
    
    • The first (red) line reminds the name of the function currently used.
    • The second (blue) line reminds that you are on the way to obtain a Test exposure.
    • The integration time is to be specified if a dark exposure is required.
    • The CCD raster and binning may be specified; the default is full-frame, no binning.
    • The user is invited to choose between Bias and Dark.


• Display the Log Book
  
  This very useful function allows the observer to manage the lot of FITS files produced by the TIGER mode from an electronic logbook :
  
  
  
  
  The windows presents first some display options :
  
  • Scenarios: allows the user to display...
    • All the files, regardless of the scenario they come from.
    • Only the files from a given scenario, chosen in a pull-down menu among the currently defined ones.
  
  
  • Exposure types : allows the user to display all or only one or several of the following types available in the pull-down menu :
    
    • Field Acquisition
    • Object
    • Test
    • Dark
    • Bias
    • Dome flat fields
    • Sky flat Fields
  
  The next zone presents the files from the category selected, and short information about each one, as recorded in the file header keywords. Two actions are possible in the list :
  
  • A single left click on one line higligths the file, and displays in the Comment for the current exposure zone the commentary which may have been associated with this file. This zone can be freely edited, and the text entered is saved as a keyword in the file header.
  • A double left click on one line displays the file with the SAOimage package. This is similar to the use of the Image function
  
  The buttons in the bottom part allow the user to display the last exposure, rebuild the logbook or print it.
  
  
• Display Scenario Info
  
  This function is used to get a general look at the optical configuration of a specific scenario. In the popping-up window, things are self-explanatory once you have gone through the Create a new scenario process :
  



It is strongly recommended to use this function after defining a new scenario to check for any mistakes!



• Create a New Scenario
  
  
  
  This function is fully descibed in the Scenarios section of the On-Site Preparation chapter of this manual.
  


• Give the Observer Name
  
  This is the first thing to verify and modify (if necessary) after starting the Pegasus session :
  
  
  
  
• Delete scenario
  
  In the pull-down menu, just select the scenario you want to delete. A warning windows pops up, asking for confirmation :
  
  
  
  

• Start AO correction
  
  This button controls the adaptive optics (AO) correction and is very frequently used during an observing night, as the servo-loop must be closed (for sky observation) or open (for wavelength calibration, telescope slewing, etc). The window looks like this :
  
  
  
  This is the main control window for the AOB. When a guide star has been found at the location of the wavefront sensor (see below), the AO correction can be started. These possibilities are offered :
  
  
  • Automatic correction : This is the optimal configuration for a full AO correction using both the tip/tilt and bimorph (i.e. deformable) mirrors. If the object is bright enough, punctual enough or if the seeing is very good, this is the mode to use.
  
  
  • Dim guide star : If the object is faint but the seeing is still good, you can use this correction. In this mode, the bimorph is not doing any tip/tilt correction so the frequency of the correction is slower. Image quality will be improved but this mode should not be used if the seeing degrades too much. It is then better to go back to the Automatic correction.
  
  
  • Semi-automatic correction : In this mode, you can select the orders used for the AO correction. See PUEO manual for details.
  
  
  • Tip/tilt mirror only : This modes used a fast algorithm applied to the tip/tilt mirror. The bimorph mirror is used to correct the quasi-static aberrations.
  
  
  • Optical Gain : A number between 50 and 128, it is proportional to the amplitude of vibration of the membrane mirror. The value to enter varies and is related somewhat to the seeing or if the guiding object is punctual or not. For galaxy nuclei, tests suggested that a gain around 80 is preferable to the optimal value normally used for star-like objects (128).
  
  
  • Neutral Density Filter : This is to protect the avalanche photo-diodes (APDs) of the AOB against too high a flux. The flux on the APDs should always be less than 15000 counts; linearity is good for flux less than 8000. Use a very opaque density filter (position 3) if you do sky-flats during the day. A neutral density filter is automatically moved into the beam when taking a calibration with the Gumball. Always check this parameter before starting the AO correction!
  
  
  • ADC : This button allows the user to move the atmospheric dispersion corrector (ADC) into the beam. This is important for OASIS due to the high spatial resolution and the spectral ranges in the visible light. Unless you are observing an object at one airmass with a low spatial resolution mode in a red spectral range, always use the ADC!
  
  
  
• System Sleep


This button put the AOB is a safe sleep mode and should be used at the end of night before leaving the summit.


• Special Functions ...


This is the second most important button for the control of the AOB. It opens this window :



This window offer the following possibilities :


• Recenter the Hot Spot : This allows to define the position where the wavefront sensor (WFS) should be put to have your object of interest where you want on the CCD. Normally, it was defined by the CFHT staff using the AOB artificial star and should be close to the center of the CCD. This hotspot is marked on the TV camera by the Observing Assistant and is used after for accurate and rapid pointing. Avoid changing the hotspot as much as possible unless you know exactly what you are doing!


• Go to Observe Configuration : This bring the WFS at the location of the hotspot. Should always be executed if an offset was applied at some point and a new acquisition is needed. This is also the first thing to do with the AOB at the beginning of the night.
  
• Offset : This button is used to apply small offsets using the WFS in guiding mode (i.e. when the AO correction is active). It opens a new window :
  
  
  
  The following actions can be performed :
  
  
  • Offset in pixels : From your image, you enter the (X,Y) coordinates from where our object is, taken from SAOimage, to where you want it on the detector. You must enter the coordinates first and then hit the "Offset in pixels" button on the left.
  
  
  • RA/DEC offset with correction: This is used to move the telescope by a certain amount using the WFS. You must first enter the offsets required for RA and DEC in the small windows and then click on "RA/DEC offset with correction".
  
  
  • Sky Offsets : These buttons are not used for OASIS.
  
  
  
• ADC Control ...
  
  This offers another way to control the ADC, similar to the entry field available in the Start AO Correction window :
  
  
  
  
• Beamsplitter Change
  
  It is possible to change the AOB beamsplitters to optimize the efficiency of your observations. This is done by the observing assistant (the real person pushing the telescope buttons, not the OASIS one!) after bringing the telescope back to zenith. The beampslitter holder has to be move twice: first, to have access to it for the change and, second, to bring it back in the light path. This is done with two buttons in the AOB "Setup functions" window:
  
  
  
  The "Move Beam Splitter In" button moves the beamsplitter in the light beam after the change and the "Move Beam Splitter Out" must be applied before the change up procedure. It takes about 2 minutes for the splitter holder to move to the desired position. The beamsplitter is identified automatically while mounted. Any attempt to use a scenario requesting a splitter different from the one that is actually mounted will fail.
  
  

• Mode switching


The mode switching consists to remove the central mirror of the AO bonnette so the light goes directly to the instrument. This is done easily from the AOB menu by opening the "Setup Functions" window:



By cliking on "Switch to F/20 AOB mode" or "Switch to F/8 no AOB mode", the central mirror is moved and the desired focus becomes available.


• Focussing


Focussing in the F/8 mode is similar to what is done for instance with MOS. The most important things to know are: 1) There is a difference of about 40 telescope focus units between the AOB mode and the F/8 imaging mode; 2) There is a difference of 25 units between the imaging and TIGER modes with the F/8 focus. The focus in the F/8 mode for a given imaging scenario can be determined manually through a focus sequence on a star, started by selecting the "Focus" window:



The entries are straigthforward: the exposure time in seconds, the number of frames (generally around 7-9), and the area used for calculating the statistics. Please, note that the star should be close to the center of the CCD field. The focus steps, applied manually with the secondary movement handset, should be around 10-20 focus units. Before starting the sequence, bring the telescope focus to the first value of the sequence. During the sequence, a window will pop up and ask you to move the focus to the next value. At the end, the focus curve is plotted and the best focus value can be established.

The interface has been modified to take into account the different focus values between the different modes (F20,F/8 (imaging vs TIGER). Windows will appear while these changes are necessary.


• Offsetting


Offsets can be applied in the F/8 mode using the "Offset" tool:



This form can be used as such only in the imaging mode. To use it in the TIGER mode, the pixel scale has to be taken into account (that is, 1 lens=56 pixels). The entries in the form are straigthforward: the start X and Y are the coordinates of the object seen in the field, the end coordinates are where the object should go.

• Display Oasis status


This window presents the actual optical configuration of OASIS:



The status (lock-unlock, wheel position and optical element) of all nine OASIS modules is displayed. The Update button forces an update of the display.


• Display Oasis setup


This window offers the possibility to move individually the different optical elements in OASIS :



By pulling down a selected menu, the optical element can be moved into the beam.

IMPORTANT : To avoid creating any unrealistic optical configurations, this form should NEVER be used by the observers unless assisted directly by the Support Astronomer!


• Close Oasis shutter


This open a dialog window to close the OASIS shutter after each observing night:

• Put an object unvisible on the TV monitor but whose position relative to a visible object is well known in the center of the CCD frame.
• Move the field image on the CCD between an imagery and a spectroscopy exposure to compensate for slightly different centerings of these two TIGER modes.
• Move the field image on the CCD between two spectroscopy exposures to master spatial sampling effects.

• CCD coordinates
  The start (where is the object) and the end (where the object should go after the offset) positions are given in terms of CCD pixels. The values are given as real numbers, and do not need to stay within the real physical range of the CCD map, but their differences Xend-Xstart and Yend-Ystart, once converted into bonnette displacement using the calibration value, should give valid figures. Ask the Support Astronomer or a local bonnette guru for details.
  If the above positions are wisely chosen to be the ones of an easily identified object, like a field star, the start position can be obtained easily with the Saoimage cursor or IQE. The values shown at the bottom represent the calibration between the Cassegrain bonnette displacement and the actual offset on the CCD. This calibration has been done for one mode by the CFHT staff prior to the observing run. The Pegasus session for OASIS has been modified so that the Offset function can be operated with all the spatial samplings available without need for manual calculation; switching from a configuration to the other will not affect the way to use Offset.
  
  However, it might be interesting to know the CCD pixel scale (i.e. arcsecond/pixel) for each mode. This value is derived from the spatial sampling which has been selected in the scenario definition (available in the display info on scenario window). Spatial samplings are defined for both imagery and spectroscopy modes and have different values.
  
  • In imagery mode, the spatial sampling is done by the CCD pixels; so, it IS the arcsecond-per-CCD pixel value. This is the value to be used to offset the imagery field a given amount.
  • In spectrography mode, the spatial sampling is performed by the lens array, and the arcsecond-per-CCD pixel value is given by the formula :
    [arcsec-per-CCD pixel] = [scenario spatial sampling] / 55
    This is the value to be used to move the spectrography field a given amount.
  The magic number "55" is the diameter, expressed in CCD pixels, of the CCD plane image of a micro-lens opening; this is an OASIS/TIGER constant.
  
  
• Accept
  Starts the actual offset operation. The Cassegrain bonnette moves OASIS to the new position requested. Before that, in the f/20 mode, the AOB bonnette servo loop must has been opened to stop the continuous automatic position correction.



• Save values
  Allows the user to keep the (x,y) start and (x,y) end values for the next offset usage. As the difference between the two position is the only significant figure, this defines a vector which will remain the offset displacement as long as no change is made in the four input windows.



• Defaults
  Reset all the above values to some "standard" ones.

• Fits file name
  Allows the user to set the name of the file which is the data source for IQE; current.fits designate the last CCD frame obtained.
• Area for statistics
  Allows the user to specify the area which will used : either the full CCD frame (entire raster) or a partial area, designated by its center (Xc,Yc) and its X,Y size (Xs,Ys).
• Values computed
  The button labels are self explanatory. For instance, on an image frame, one is usually interested in the image size, and shall check Fwhm/Centroid..., plus Maximum pixel to check for a possible CCD saturation. On a bias frame, Mean and Standard Deviation are of interest, etc...
• Accept
  Starts the computation.
• Save values
  Allows the user to keep the "Fits file name", "Entire raster" or (Xc,Yc,Xs,Ys), and "Values to be computed" until the next IQE usage.
• Defaults
  Reset all the above values to some "standard" ones.

• File name
  Allows the user to set the name of the file which is the data source for SAOimage; current.fits designate the last CCD frame obtained.
• Contrast
  Allows the user to select either linear color coding, or histogram equalization to enhance low-contrast details.
• Level setting
  Used to set the low and high cuts of the dislayed image.
• Accept
  Display the image with the above options taken into account.
• Save values
  Allows the user to keep the "File name", "Contrast", and "Level setting" until the next SAOimage usage.
• Defaults
  Reset all the above values to some "standard" ones.

• Playing with the color table and image contrast/luminosity to detect on TIGER images the faint extensions which are the usual 3D spectroscopy targets. It is usually better to chose scale log or histeq for such a purpose.
• Displaying the CCD coordinates of various object details, for example to prepare offsets.
• Roughly evaluating the flux level for different sources or spectral lines with the cursor.
• Zoom on certain regions to look for details (under pan).
• Examining rapidly the whole frame by deplacing the small green box in the panner section.
• Print a hardcopy of the display (under etc).

• The axis for the cut (X= along the rows; Y=along the columns).
• The file names used for the cut. When more than one file is checked, the cuts will be superimposed.
• The position of the cut (CCD row or column)
• The number or rows or column to average for the cut
• The cut and the number of rows or columns to average is we want to subtract it from the previous cut (e.g. subtract a sky spectrum from a science spectrum).

• Plots : pop-up menu accessible with the left mouse button and allowing to reconfigure each plot (file name, cut location, subtraction)
• Options : allows to modify the line type, compute statistics on the graph and add labels
• Print : allows to print the displayed graph to the summit or Waimea printers
• Zoom : zooming by a factor between 1/4 and 4.
• Show plot : by selecting on the appropriate boxex, you can enable or disable one of the 4 plots allowed simultaneously.
• Scaling in X an Y : automatically adjust the X and Y scales
• Pan : by moving the long horizontal bar at the bottom, you can pan the plotted line or column.
• Area statistics : You can select an area on the cut by selecting the lower and upper limits with the left mouse button. By clicking in the background with the right button, you can select the "area statistics" option. Statistics of the selected region will appear in the OASIS feedback window.

• Calculator


This opens a scientific Hewlett-Packard programmable calculator:




• Pointer


This tool offers the possibility to mark positions or directions on the workstation:

• Closed OASIS upper shutter (see Oasis)


• Put the AOB in SLEEP mode.


• Save your data ?
  

• Like all CFHT data, OASIS/TIGER data are automatically saved into an archive system which holds in Waimea all the CCD frames obtained at the telescope. See the CFHT Data Archive@ for more details.



• One usually wants to get a copy of the run data at the end of the last night. This can be done on both DAT or EXABYTE tapes. The recorders are located in the computer room at the summit. Ask the Telescope Operator for a tape (if necessary) and insert it in the unit. You have now two options to save your data: 1) from the Files window or, 2) by opening a Neptune window. For the latter, go to the data file directory (ask the Support Astronomer for details), and issue some backup command, like " tar cvf /dev/rmt/3mn * ". To save time, you can compress your data (gunzip *.fits or compress *.fits).



• The TIGER mode, like any 3D spectroscopy system, produces huge amounts of data. Be prepared to spend up to several hours saving on tape. It may seem a good idea to perform some clean-up before saving, removing "useless" files, test exposures, and so on... But years of experience showed that this may drive into severe problems if a critical service file is thus inadvertently removed; it is so strongly suggested to save ALL the run files, even at the expense of a reduced sleeping time...



• It is strongly recommended to perform data saving in several batches, for instance at the end of each night. This costs more tapes but shortens significantly the data saving processus after the last night...

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