Users Guide

To the

DBS Autoguider

 

 

Dec 1999

Peter Conroy & Winston Campbell

Front

 


Welcome to the Double Beam Spectrograph Autoguider System. This autoguider system consists of an Apogee direct CCD Camera that views part of the DBS slit via Focal Reducer Optics, and a PC computer running MaxIm CCD Camera Control and Image Processing Software.

To lead users gently into using this guider this manual is arranged as a series of short sections, beginning with the simplest functions and leading on to the complex.

Contents:

  1. Checking the camera.
  2. Taking an exposure.
  3. Setting up a sub frame.
  4. Saving images to WinNT and UNIX Viewing finding charts on screen.
  5. Setting a focus frame. Using the camera as a television.
  6. Inspecting telescope focus.
  7. Setting up for autoguiding. Connecting to the VAX
  8. The Move command. Pulling a star into the slit.
  9. In slit autoguiding.
  10. Offset autoguiding. Jogging the tracking box.
  11. New - Guiding aperture plates.
  12. Freezing the shutter
  13. Daytime testing.
  14. Image processing. Combining images to make colour images
  15. In case of Software, PC or power failure.

1. Checking the camera

When you sit down at the guider control PC called M23guider near the 2.3m console you should find the PC running and MaxIm running. If you cannot find the MaxIm window it may be hidden on the task bar which can usually be found by moving the mouse pointer to the top or bottom of the screen. When you finish observing please leave MaxIm and the camera thermoelectric cooler running, the TE cooler consumes little power and we would like to minimize temperature cycling of the CCD.

There is a button bar near the top of the MaxIm window. Working from the left press the 6,7,8th buttons if they are not already pressed. This will open the Histogram, Information and MaxIm CCD windows. The MaxIm CCD window contains seven tabs that control various camera functions. Press the 7th tab, the Setup tab, and check that the CCD temperature is near 38C and that the CCD and Guider windows are both set to Apogee.

2. Taking an exposure.

The 1st tab in the MaxIm CCD window is the expose tab. Press this tab, set the exposure type to normal and the exposure time to between 0.3 and 1 sec then press expose. An image will appear in the CCD Image window in 3 to 9 seconds depending on sub fame settings. Arrange this image window on the left half of the MaxIm display area. This will leave the right half of the display area for the seperate image display that opens when using the guide tab. If you are setting up in the daytime and there is not enough light to produce an acceptable image of the slit go to the DBS status and control computer, select any arc, insert the arc mirror and take another image. If the image fills the display window grab the lower right corner of the window and stretch the window down and to the right, this will prevent the image from jumping off the edge of the monitor when the zoom function is used

A fully black window may be saturated, use the cursor in the image and the information window to ensure that the maximum values are below 65k. Use the Histogram window to adjust the displayed grey scale, slide the two coloured pointers towards the peak of the graph, or swap them over if you like a negative display. Fast clicking the right mouse button changes the diameter of the sample circle around the cursor. Close the circle around any star in the field and read of the centroid position and FWHM of the star from the Information window. Use the zoom buttons, or better still the + & - keys in the numeric keypad to zoom in the image. If the %400 zoom is to small point in the zoom factor display in the MaxIm button bar and edit this value to between %1000 and %1600. Use the slide bars to pan around the zoomed image or better still place the cursor in the zoomed image, press and hold the right mouse button, move the mouse until a hand appears then drag the zoomed image around in the display window.

3. Setting up a sub frame.

The CCD in the guider camera has 512x512 pixels. The guider uses only one third of the CCD to cover about half of the DBS slit at a scale of 2 pixels/arc sec. Setting a sub frame to the boundaries of the slit will reduce the read time from 9sec to about 3sec. If you take a full frame image with the expose tab then press the settings tab and drag a box in this image the subframe co ordinates will appear under the subframe windows. You can type co ordinates directly into X,Y,W,H windows. The example shown here contains suitable co ordinates for viewing the slit and you can set these up by typing them in the appropriate boxes instead of using click and drag.

4. Saving images to WinNT and UNIX. Viewing finding charts on screen.

MaxIm allows you to save images of star fields, in .fits format, from the slit onto both the WinNT and UNIX platforms, and to read from and save images to your data account on the SUN UNIX system on /data/moist1/cicada/_user_. This is done via samba. The samba share \\murky\data-moist1 will map directly to your directory on /data/moist1/cicada

If you intend saving images on the WinNT platform make yourself a directory on the Explorer D: drive to store data. Please erase this account when you finish observing.

To connect and make your area on the unix data disk (/data/moist/cicada/_user_) accessible as a drive from the autoguider PC :

1. Open the Windows Explorer, if it is not already open by right clicking on the start button.

2. Choose "Map Network Drive" from the Tools menu. If this share already exists, remove the Mapping.

3. Select a drive letter, "U" for UNIX is a possible choice.

4. Type the share name as: \\murky\data-moist1

5. Put your personal Unix username in the "Connect As" box

6. Turn "Reconnect at Logon" to OFF

7. Enter your personal Unix password when prompted.

8 Use "Disconnect network link" to break the link when you finish observing.

Apogee autoguider users can copy finding charts as .fits files to their private areas on /data/moist/cicada/_user_ before the observing run and view them with MaxIm in a window that can be flipped, rotated and zoomed to simultaneously match data being displayed from the DBS slit. This works best with finding charts up to 1024x1024 pixels. The DBS data can also be viewed in MaxIm once it has been converted to .fits and copied to your Unix directory. Open both red and blue data frames and flip one vertically. Both data panels can be moved around independently and placed end to end to help visually track spectra. I you have both data panels and the appropriate finding chart open you can easially locate the objects that produce "orphan" spectra on the long DBS slit.

Connecting to the UNIX system will work only if you have a Unix account and the directory /data/moist/cicada/_user_ has been created by teldisk. There is no longer an account called "observer" on the UNIX system, all data is stored under personal accounts.

5. Setting a focus frame. Using the camera as a television.

The focus tab in the MaxIm CCD window allows user or auto selection of a subframe for telescope focussing. Press the reset button, then the expose button, then abort the cycle after the first exposure. Now pressing the auto button will place a 64x64 pixel box around the brightest star in field. If the continuous box is checked the focus command will continue until the abort button is pressed.

Use the focus tab to set a sub frame and continuously cycle the camera if you intend to hand guide the telescope. Ensure you have the telescope guide buttons set to slit co ordinates.

6. Inspecting Focus

Once the focus command is running press the inspect tab before you begin focussing the telescope. The inspect tab will display all of the necessary information you need to focus the telescope including the FWHM in pixels and the amplitude. The CCD scale is 2 pixels/arc sec. Focus the telescope for minimum FWHM and maximum amplitude. This MaxIm feature is of little use in poor seeing. The 3D graph of the star image auto scales as the telescope is focussed.

7. Setting up for autoguiding.

At the telescope control computer ensure that the VAX Telescope Control Computer is listening to the autoguider computer by typing <enlist TXA6>

Now at the autoguider computer press the guide tab and the settings button to display the autoguider settings window. Note that the Manual Calibration settings are X=-2.16 and Y=+2.16, these are the guider correction speeds in pixels per arc sec. Do not change these settings or change the sign of the settings or the guider will force the star out of the tracking box. The windows shown here shows typical settings for the autoguider.

You may wish to change the aggressiveness setting on a scale from 1 to 10. This factor inputs to the simplest possible servo filter, a setting of 5 will move the telescope by 5/10 or 1/2 of the calculated error signal, a setting of 10/10 will move the telescope by the full error signal. Our experience thus far is that the better and more stable the seeing the better the guider performs. It is best to set the X,Y,W,H settings to exactly the same values as those shown under the settings tab. From time to time the guide calibrate programme will need to be run and should return speeds near X=-2.16 and Y=+2.16.

8. The Move command. Pulling a star into the slit.

Press the guide tab and check the expose circle inside the guide tab. Do not confuse this expose circle with the expose tab above it. Now press start. MaxIm will display a subframe whose size is set in the autoguider settings box, zoom in on this image. Now press the move command button in the lower right corner of the guide tab. When the move window opens use the mouse in the zoomed image and pick the from star then press the move button in the move window. The to position can be locked to the centre of the slit, or just above the slit, by pointing in the image then checking the lock option, this probably needs to be set only once at the beginning of the observing run. If you intend to use in slit guiding make the to position a few pixels above the slit as MaxIm needs to measure the amplitude of the star before autoguiing it into the slit. If you are using offset guiding make the to position the centre of the slit. The maximum allowable move is 50 arc sec or 100 pixels in x and y./P>

MaxIm will move the telescope and if the auto expose box is checked will take and display another image. There is currently an 8 second delay after a move command to allow time for the telescope to settle before the auto expose occurs. If the star is near or in the slit close the move box. You are now ready to autoguide. The move and guide commands use a separate co ordinate frame system from the expose tab focus commands. Sub frames set under the guide tab will stay set independent of settings under the expose and focus tab.

The manual control buttons are useful for moving the star a discrete amount in x and y directions and are especially useful for Nasmyth aperture calibrations. Set the required manual shift in the manual control entry box in arc sec. The maximum manual shift is 50 arc sec or 100 pixels.

9. In slit autoguiding.

Leave the Declination setting set to zero, the Telescope TCS will automatically take care of this. As noted in Section 9 in slit autoguiding should begin with the star a few pixels above or below the slit as MaxIm needs to measure the peak value of the star before autoguiding it into the slit. Maxim will report "Guide Star Fade" once the star is in the slit and the peak value falls by about 50% and will not transmit tracking commands until the peak value lifts above 50% of the original value. If the star is in the slit at the beginning of the guide sequence then MaxIm may attempt to move a relatively faint star that is inside the tracking box into the slit.

Once the star is in near the slit check the track circle in the guide tab and press start. MaxIm will now read up a 32x32 pixel tracking box and begin transmitting correction commands to the telescope control computer. MaxIm will pull the star to the RELATIVE co ordinates shown in the guide star box on the lower section of the guide tab window. This position can be set by simply pointing at the centre of the slit and pressing the left mouse button. When the 32x32 pixel guide window opens zoom into this window and leave the cursor over the guide star in the Autoguider Image window. MaxIm will then show the current guide error in arc seconds or pixels in the lower left of the guide tab window and the centroid and FWHM in pixels in the information window. There is currently about 1.8 seconds of dead time in the autoguiding cycle.

10. Offset autoguiding, Jogging the tracking box

Setup the MaxIm desktop to show two image windows, place the CCD image window on the left and the guide/expose window on the right. Grab each image window and stretch it a little so that the image does not jump off the screen when the zoom functions are used. Get used to using the left image window with the expose tab and the right image window with the guide tab.

Having used the track or move command to drag the star into the slit now press the auto button near the guide star co ordinates, MaxIm will now automatically find the brightest object in the field and place its co ordinates in the guide star box. Now check the track circle and press start. Maxim will begin autoguiding on the offset object. The in slit object will not be shown in the 32x32 pixel tracking box, only the offset guide star. The tacking box should be displayed in the right side image window. Zoom on this image.

To periodically check that the object is still in the slit, stop the tracking, press the expose tab and take an image, this image will appear in the left image window. It is normal to use a longer exposure time for this image than for the guide exposure. Zoom on the object in the slit. If the object is out of the slit use the cursor and information window to estimate the Y error. Now return to the guide tab and jog the guide star Y position up or down by the necessary number of pixels. You can use the small up-down buttons to do this or type directly into the Y window. Now press start and the autoguiding cycles will continue. The guider tracking box will continue to be displayed in the right image window. For long exposures check that he object is still in the slit every 10 minutes or so.

NOTE For successful in slit and offset autoguiding the telescope instrument rotator MUST be configured with the aperture at the rotator centre. If the aperture centre is not at the rotator centre the field will rotate about the offset guide star and move the object out of the slit. See pages 8.5 and 8.6 of the 2.3m Telescope Observers Manual.

11. New - Guiding aperture plates.

This feature relies on back scattered light from the telescope side of the aperture plate and is only useful in dark time, scattered moonlight swamps the star images and makes guiding aperture plates impossible. Aperture plates give the DBS a multiplex gain of up to 20 for compact sources (Up to 6 arc min) and are well worth the extra effort involved in cutting the plates. The DBS slithead turret will carry five aperture plates at a time and these should be loaded early in the afternooon. See the DBS manual for instructions, ensure that you follow the safety instruction and use the black velvet board as plates and bezel rings can easially be dropped onto the blue grating. Our current best estimiate for the telescope focal plane scale at the aperture plate is 0.20143mm/arc sec. The current mask cutting machine covers a circle 72mm in diameter in the centre of the 86mm diameter plate.

The aperture plate shown here has a mix of 2 arc sec holes and slots for sky background subtraction. Ensure that your plates are labled with your object, your name and that the viewing side is marked. There are three reflections in the telescope so the aperture pattern is flipped with respect to the sky. Note the key slot at the top of the plate, the dispersion direction is vertical from the key slot through the centre of the plate. Aperture plates have the viewing side lightly polished parallel to the slit with fine sandpaper to enhance scatter into the guider optics. The plates are viewed from the telescope side of the DBS. i.e. The polished viewing side is inserted into the the slithed turret facing the telescope.

At dusk, after focusing the telescope, begin observing at the DBS control computer by inserting and aperture plate and switching on the back illuminator. Now take exposures with the MaxIm expose tab and set suitable sub frames, set identical sub frame values under the expose and guide tabs. This sub frame is usually taller than that used for slit guiding as the aperture plates extend vertically beyond the slit field. The holes slowly go out of focus as they depart vertically from the slit line, this effect is due to focal reducer viewing the plate at an oblique angle (20 degrees), the plate is normal to the telescope axis and does not see any degradation of the aperture plate performance.

Now use the guide/expose tab to take a bias frame, save this image as bias then slide the frame to one corner of the screen but do not close it, you will re use this frame with each new observation. Again use the guide/expose tab to take an image of the back illuminated aperture plate, save this image as plate, leave this image on the screen. Now set the telescope to the object and the instrument rotator to the correct position angle and use the Maxim expose tab and take a deep image. The object is imaged in scattered light from the polished surface of the aperture plate so exposures are normally long, typically 60-90 seconds. Once this exposure is complete and shown on the screen pull down the Colour menu in MaxIm and select Combine Tricolour. Make the bias frame blue, the back illuminated aperture plate red and the deep sky image green. Now select autocombine with no shift or rotation. Once the colour image appears pull down the colour menu and use adjust colour balance, only the background colours normally need adjusting. Now use the move command to move the green stars into the red holes. Take another deep image, if the stars are in the holes a halo may be seen around the some of the brighter stars as shown in this thumbnail image. Now in the guide tab, reduce the exposure time, press auto then track then start and MaxIm will begin guiding on the brightest object in the field. Peroidically interupt the guiding and take a deep exposure with the expose tab to ensure that the stars are still in the holes. It is wise to save some of the images of the aperture plates, the colour images can be saved as .jpg or .tif format.

Once the DBS exposures are complete and the data has been converted to .fits and moved to /data/misty/you, the data and aperture plate images can be viewed simultaneously on the PC screen. Open both red and blue images together and flip one image vertically so that the spectra have the same end of the slit at the top. Then open an image of the aperture plate, rotate the image by 90 degrees, then slide it over the spectra and zoom it to fit. The image shown here is a small section of the red arm spectra, note the Ha emission and absorption near the left edge of the spectra. Only one of the aperture plate holes has not delivered spectra.

12. Freezing the shutter

The mechanical shutter in the Apogee camera has an expected life of about 1 400 000 operations. In autoguide mode we would reach this limit in about 1 1/2 years. We can extend the life of the shutter considerably by freezing the shutter open during normal autoguiding operations. To freeze the shutter press the setup tab then the CCD button. A window will open, check the freeze shutter option and close the window, then return to the guide tab. For the very shortest exposures the images will show vertical downward tails on each image but his does not seem to effect normal autoguiding operation.

Under normal conditions use the shutter for setting up, focussing and for taking presentation images then switch to freeze shutter mode for normal autoguiding.

13. Daytime testing.

To test the autoguider functions during the daytime and practice autoguiding go to the DBS control computer, then to the slit turret control and insert the row of holes aperture plate. Then switch on the back illuminator. This will insert an aperture plate and back illuminate it to create a row of fake stars for the autoguider to work with.

At the VAX telescope control computer, start the telescope control computer, type <enlist TXA6> then start the telescope tracking by typing <track/here>.

Now at the autoguider computer start the Apogee camera and work down through sections 1 to 11 of this manual. When the autoguider sends move or guide commands to the telescope control computer the offsets are updated in the VAX co ordinate display window. The DEC offsets are in arc seconds, the RA offsets are in sidereal seconds where one sidereal second equals 15 arc seconds. Jog the tracking box to one side of a fake star and start autoguiding. The star will remain off centre of the tracking box and the offset co ordinates will increment with each tracking cycle. Jog the tracking box to the other side of the star and the offsets will decrement with each tracking cycle.

14. Image processing. Combining images to make colour images.

MaxIm has excellent features for combining tricolour images. The programme knows about centroids, rotation and XY shift, allows colour adjustment of both foreground and background and has a colour pickup feature for repairing hot colums and pixels. See the Maxim help files for description of these features. Observers using this feature should copy their source files to their personal areas on /data/misty then access them, and save the resulting colour images from the M23Guider PC back to /data/misty.

 

15. In case of Software, PC or power failure.

Both the M23Guider PC and the Apogee boost box are connected to no break power supplies and should not normally fail even during extended mains power failures. The MaxIm programme can be closed down at any time and re started by double clicking on the MaxIm icon on the Win NTdesktop.

The M23Guider PC runs Microsoft WinNT4 operating system and should, like UNIX, never need power cycling of the PC. The NT4 kernel normally continues even when an application programme freezes. To stop a frozen programme press Ctrl+Alt+Delete and select task manager. Under the task manager press the applications tab button, locate and highlight the programme that is not responding and press the end task button. You can then re start the application. MaxIm stores all settings during use and will normally re start with your selected settings intact.