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The Fan Mountain Observatory 40-inch Astrometric Reflector


THE FAN MOUNTAIN 40-INCH TELESCOPE

(Rev. August 15, 2011)

Introduction

Figure 1: The Fan Mountain 40-inch Telescope.
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This manual gives general instructions for operating the Fan Mountain 40-inch telescope, the filter control system, and the autoguider.

Fan Mountain Observatory is a research facility of the University of Virginia Department of Astronomy. The instruments are being used for graduate student teaching and the research programs of faculty and their students. You should conduct your work with the utmost care, patience, and forethought, keeping in mind that the equipment is delicate, complex, and expensive to maintain.

To minimize the potential for accidents, you should have a clear idea of your observing plan for the night, including the optimal observing times of your target and calibration objects, lists of coordinates and finder charts, and an efficient plan for minimal changing of filters. Do not neglect to obtain the necessary set of bias frames and flat fields for calibration, or the rest of your data will be worthless.

If anything in this manual is unclear, consult the TA or appropriate faculty member for clarification. As with all delicate equipment, NEVER force any moving part beyond reasonable and expected resistance. Always keep track of the telescope position in relation to the sky, dome, and objects within the dome. NEVER touch any optical element. Oils from your skin will permanently embed into glass surfaces and optical coatings. It is better to leave small amounts of dust on optical surfaces than to risk scratching or marring them with attempts at cleaning. If dust is a serious problem, ask the TA, Jim Barr, Charles Lam, or a faculty member to remove it with dry nitrogen. If, while in the control room, you hear any peculiar noises or have any uncertainty about the location of the telescope or dome, you should make the trek up one flight of stairs to check the dome in person. If you are uncertain about any aspect of operating the telescope, or any other piece of instrumentation, STOP and ask someone. THINK BEFORE DOING.

Home phone numbers: Fan Mountain caretaker Nick Nichols (979-0684), David McDavid (434-985-4378), Jim Barr (540-832-5304), Steve Majewski (434-975-6435). In case of emergency don't hesitate to call, but please try not to call unless it is absolutely necessary.

Description

The Fan Mountain 40-inch telescope has an f/13.5 Schmidt-Cassegrain optical system with a 40-in (1-m) aperture, a focal plane image scale of 15.3 $^{\prime\prime}$mm$^{-1}$, and a corrected photographic field of 50$^{\prime}$. It has a computerized telescope control system (TCS) developed by DFM Engineering, Inc. and described in detail in the TCS486 Operations Manual on the bookshelf in the control room.

A pair of fans inside the telescope tube near the corrector plate can be turned on with the toggle switch on the west side of the telescope tailpiece. Power to the toggle switch is on only when the CCD switch on the bottom rack panel (Fig. 2) in the control room is on. Running these fans helps to improve tube seeing under some conditions.

Startup Procedure

  1. Begin filling out a new log form in the blue Observing Log notebook which is kept on the bookshelf in the control room.

  2. The CCD switch on the Rack Panel (Fig. 2) controls a large uninterruptible power supply (UPS) and is normally left ON all the time. If it is not already on, turn it on and leave it on.

  3. Power up the autoguider PC if it is not already on. It will boot to a Windows 7 logon prompt. Turn on the telescope control PC (the one in the electronics rack on the far right side of the table). It will boot to a DOS prompt. This PC shares the large monitor and keyboard in the middle of the table with the autoguider PC (which must be powered up first) through a pushbutton toggle switch with LEDs indicating which system is selected.

    Figure 2: The Rack Panel.
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  4. At the telescope control PC DOS prompt, enter tcs to start up the DFM Telescope Control System. Set the date and the universal time, referring to the clock in the electronics rack for the local time. To do this:

  5. Set the switches on the DFM panel (Fig. 3) to Track, Track Off, Drives Off, Auto Dome Off, External Computer On, and Dome Home, then turn on the Motor Drive Chassis, Motors On, and Drives switches.

    Figure 3: The DFM Panel.
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  6. At the telescope control PC DOS prompt, enter tcs to start up the DFM Telescope Control System. Set the date and universal time, referring to the clock in the electronics rack for the local time. (Start from the Main Menu (press ESC if it is not displayed), enter 1 (Initialization menu), enter 1 (Set date and time), then fill in the blanks.) The TCS will assume the telescope is pointed at the zenith and will approximately initialize the coordinates based on the latitude, longitude, and local sidereal time.

  7. Upstairs in the dome, use the ladder to connect the shutter power cord from the electrical outlet to the shutter motor box and turn the knob on the motor box counterclockwise. The shutter will open and automatically stop when it is done. Unplug the power cord from the motor box. If you don't, you'll destroy the cord or the connectors when the dome moves and you will be in serious trouble when you need to close the dome.

  8. Turn on the TCS monitor on the desk in the dome. This monitor and keyboard will function even when the shared monitor and keyboard in the control room are being used by the autoguider PC. Adjust the brightness and contrast as desired. When working in the control room and taking data, you will usually want to have this screen dim.

  9. Use the control paddle (Fig. 4) to slew the telescope to the North (towards the horizon in the direction of the desk in the dome room) just far enough so you can reach and remove the telescope lens cover by climbing up the ladder to the upper level. Strap the lens cover to its stand on the upper level so the wind won't blow it away.

    Figure 4: The Dome, Focus, and Telescope Control Paddle.
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  10. Horizon Limit: You may find that you have passed the TCS horizon safety limit in slewing the telescope to the North to get to the lens cover, and the telescope will no longer move by motor control. If this happens, go back to the control room, turn off the Drives and Motors On switches on the DFM panel, then go back to the dome and push up on the telescope tube by hand while standing on the upper platform to move it in declination until it points well above the horizon. Then go back to the control room and turn the Motors On and Drives switches back on. For the safety of the telescope, go back to the dome and use the paddle to verify that normal motor operation is restored.

  11. Use the paddle to slew the telescope back to the zenith.

  12. With the dome slit facing South (AZIMUTH 180.0), which is the HOME position, turn on the Dome Track and Auto Dome switches on the DFM control panel so the dome will automatically follow the telescope.

  13. In the TCS Main Menu enter 4 (Miscellaneous menu), enter 1 (Set switches), then turn on RATE CORRECTION, which will enable automatic track rate correction derived from the mount model parameters currently compiled into TCS, and DOME, which must be consistent with the setting of the Auto Dome switch on the DFM control panel.

  14. In the TCS Main Menu enter 3 (Rates Menu), enter 1 (Set Track Rates), then input 14.980 for the RA rate and leave the rest of the fields blank. Press Enter for the changes to take effect.

  15. Turn on the Track switch on the DFM control panel to start the telescope tracking.

Initializing the Coordinates

  1. For the safety of the telescope, always do this operation in the dome.

  2. Pick a star near the zenith from the BRIGHT STAR LIST in the Astronomical Almanac. In the TCS Main Menu enter 2 (Movement menu), enter 1 (Set slew position), then enter the coordinates and their associated equinox. When TCS asks ``Any Changes?'' respond with a RETURN.

  3. In TCS, enter 7 (Start slew). Be prepared to stop the telescope if it should wander off to extreme angles. You can do that by entering 8 (Stop slew).

  4. Center the star in the finder scope eyepiece, assuming it is aligned with the main scope. If you aren't sure you have the right star, check it in Norton's Star Atlas on the desk in the dome.

  5. From the TCS Main Menu, enter 1 (Initialization menu), enter 2 (Set telescope position), then enter once again the coordinates and equinox for the star you just centered. This will update the telescope position in TCS to the correct coordinates.

  6. To set the TCS coordinate display to any desired equinox, start from the Main Menu, enter 4 (Miscellaneous menu), enter 2 (Set display equinox), then enter a decimal year.

Shutdown Procedure

  1. Set the DFM panel switch to Dome Home to send the dome to the home position (AZIMUTH 180.0). Wait for the dome to go home, then switch Auto Dome Off.

  2. Using the paddle, point the telescope low to the North over the upper dome platform and replace the lens cover.

  3. Plug in the shutter power cord, and turn the knob clockwise to close the shutter. Unplug the power cord from the motor box after the shutter has closed.

  4. Turn off the DFM Panel Track switch, then slew the telescope to the zenith with the paddle.

  5. Turn off the Drives, Motors, and Motor Drive Chassis switches on the DFM Panel.

  6. Do NOT turn off the CCD switch on the Rack Panel. Leave it on.

  7. Turn off the telescope control PC power switch.

  8. Finish filling out the Observing Log notebook and return it to the bookshelf in the control room.

The Filter Control System

The filter wheels inside the telescope tailpiece above the CCD camera shutter can be operated from the filter control panel on the south face of the tailpiece when the switches are set to LOCAL or from a computer in the control room when the switches are set to REMOTE. When used with the GenI CCD camera the filter wheels can also be operated from the camera control program through a popup window, and filter information is recorded automatically in the image FITS headers (see documentation for the GenI camera).

Filter wheel A (the lower one, also known as filter wheel 1) has 4 openings spaced at 90$^{\circ}$ intervals and holds 6-in square filters. Filter wheel B (the upper one, also known as filter wheel 2) has 6 openings spaced at 60$^{\circ}$ intervals and holds 4-in square filters.

To load a filter into a filter wheel, first open the filter wheel access door (the rectangular panel above the filter control panel held shut by clamps) so you can see the filter wheels inside the tailpiece. Switch the filter wheel to LOCAL and use the SLEW button on the filter control panel to rotate it. Open the lock at the edge of the filter opening you select, slide the filter into the slot, then close and gently screw down the lock with your fingers. The filter opening in the telescope light path is the one diametrically opposite the one at the access door.

  1. To control the filter wheels remotely, begin by turning on the filter PC (white tower) underneath the table in the control room. It shares the monitor and keyboard in the middle of the table with the autoguider PC through a splitter switch. The filter PC boots to a DOS prompt.

  2. Enter cd c700$\backslash$motion at the DOS prompt to get to the correct directory. If the default filters.txt file does not correspond to your arrangement of filters in the filter wheels, make a new file in the same format which does. Then enter motion to start the filter control program. Ignore error messages about No blank found.

  3. When the program asks Hit Return when wheels are homed?, go upstairs to the dome and HOME both filter wheels under LOCAL control if you have not already done so. Then switch both wheels back to REMOTE and go back down to the control room.

  4. Now enter a RETURN in response to the Hit Return when wheels are homed? prompt on the filter PC. Enter ? to get a list of commands. The command goto filtername should place the filter you specify in front of the detector. Experiment with issuing commands and going upstairs to verify the actual filter wheel positions until you are sure the system is set up correctly.

  5. After this point, if you move the filter wheel under LOCAL control and wish to go back to REMOTE, exit and restart the motion program on the filter PC as described earlier. Otherwise the program may not indicate correctly which filter is in the beam at any time.

Available filters include standard 4-in square UBVRI and 6-in square Washington filter sets, a 4-in square H-alpha/red continuum interference filter pair, 4-in square H-beta, OIII, NII, and SII interference filters, and a small collection of other assorted interference filters, including a DDO51 filter. The filters are stored away from moisture, dust, and extremes of temperature in wooden boxes on the table below the bookshelf in the control room and should be kept there except for periods of active use when conditions are not potentially harmful.

Filter observations can be calibrated with observations of Landolt standard stars listed in the catalog on the bookshelf in the control room. See other references on the bookshelf for details of the filter characteristics, instructions on using IRAF to reduce CCD photometry data, and methods for the transformation of CCD photometry data to standard systems. Some useful references are:

The Telescope AutoGuider

Figure 5: The Autoguider mounted on the 40-inch.
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Almost all research facility telescopes are equipped with an auxiliary autoguider, a device that assists the main telescope in tracking a target for a longer time than the telescope alone is capable of. The 40-inch Fan Mountain telescope can track a star unaided for approximately 3 minutes (when pointed within $\approx 20^\circ$ of the zenith). With the autoguider, exposures of up to 30 min have been tested, and longer ones are possible. The autoguider was built during the summer of 2001 by Jim Barr, Jeff Crane, Charles Lam, Eugene Lauria, and Kiriaki Xilouris.

The autoguider consists of a CCD video camera (SBIG STV) connected to an 8-inch Meade LX Schmidt-Cassegrain telescope that is mounted on the main telescope tube, supported by a pivot stage. This structure enables limited but independent motion of the Meade with respect to the main telescope tube, increasing the possibility of finding a guide star close to the target area. Between the Meade and the STV there is a focal reducer to optimize the image scale for autoguiding and a JMI motorized focusing stage to enable remote focusing of the guider from the control room. The manual focus knob on the Meade telescope has been disabled and should not be used. Characteristics of the autoguider system are given in Table 1.

The autoguider can be controlled from its controller box, which is mounted on the west side of the telescope tailpiece, or remotely from the control room using the autoguider PC and the SBIG STVRemote application software. The pivot and the focusing stages are normally operated from the control room. A special cable is available to operate them from the dome room.


Table 1: Characteristics of the autoguider system.
Aperture 200 mm
Resolution Limit 0.69 arcsec
Focal Length 2000 mm (EFL 1190 mm w/focal reducer)
Focal Ratio f/10 (f/5.95 w/focal reducer)
Image scale 103 arcsec/mm (173 arcsec/mm w/focal reducer)
STV pixel size 7.4 microns (640x480 pix)
STV pixel scale 0.76 arcsec/pix (1.28 arcsec/pix w/focal reducer)
STV Field of View $\sim$6x8 arcmin ($\sim$10x13 arcmin w/focal reducer)


To operate the Autoguider make sure that:

  1. There is power to the tailpiece of the telescope.

  2. The STV controller box in the dome is turned on.

  3. The parallel cable from the camera head is connected to the controller box.

  4. The video cable is connected to the controller RCS port marked Video Out via an RCA to BNC adapter and is routed through the dome floor to the control room.

  5. The Serial I/O (RS232) cable is connected to the controller and is routed through the dome floor to the control room.

  6. The video monitor cube on the computer table in the control room is turned on and is connected to the video cable from the controller box in the dome.

  7. The Serial I/O cable from the dome is connected to a serial port of the autoguider PC in the control room.

  8. The autoguider PC in the control room has Window 98 up and running. It shares the large monitor and keyboard in the middle of the table with the TCS PC through a splitter switch.

Figure 6: The STV virtual control panel window on the autoguider PC.
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On the autoguider PC click on the STVRemote icon to start the remote control software (See Fig. 6.) You will normally see ``Link Established'' in the PC Message window as the serial link to the controller box is automatically established. If you do not, you may need to select either COM1 or COM2 (whichever works) from the Link pulldown menu to establish the link.

Setup Procedure

Click Setup, then click Parameter to cycle through the Setup menu. Click Value to adjust a parameter. Most of the Setup parameters should be correct by default, but you can easily cycle through the choices and select any options you want. You can dismiss the Setup menu by clicking Setup again. All the buttons on the STV Remote virtual control panel work according to this model.

Internal Filter Wheel

A filter wheel inside the STV camera head allows selection of an R, G, B, or Clear filter to approximate the passband being used by the imager on the main telescope in order to reduce autoguiding error due to differential atmospheric refraction. The filter position is changed from the Setup procedure described above, where it appears as one of the adjustable parameters.

Sometimes a commanded change of filter or the function of ``Covering the CCD'' in Tracking or Calibration mode will stall, but this is easily remedied. Click Setup and advance to ``Adj Filter'' in the Setup menu sequence by clicking Parameter a few times. If the display reads ``Fail'', click Value repeatedly to adjust the displayed voltage until the ``Shtr'' position is as close as possible to the optimum value of 7.5%. The display will then begin to read ``Pass'' and the malfunction will be corrected.

Image Procedure

To begin taking images click Image, then click Parameter repeatedly to see the adjustable parameters, then set each one by clicking Value. Choose a likely exposure time (say 5-10 s), set Continuous, then click Image again to start a continuous video stream on the monitor cube.

Focus and Finding Procedure

Focus the 8-inch Meade by pushing the buttons on the focus hand paddle on the control room table while watching the video monitor. You can adjust the focusing speed with the rotary button between the IN and OUT focus buttons. Move the Meade about its zero point position with the small hand paddle on the table to find a star if none appears on the monitor.

When you have the 40-inch pointed at an object and are ready to set up for autoguiding, use the same procedures to find a bright guide star and an appropriate exposure time and to adjust the focus for the filter you have selected.

Calibrate Procedure

Click Calibrate and set AUTO Mode. Click Calibrate again to start the STV automatically learning how far and in what directions its four relays move the telescope for guiding, by exercising the relays and measuring the resulting displacements of the selected guide star. If the calibration sequence is successful, the Message window will show ``Passed'' and the monitor cube will display four arrows showing the motions produced by the relays.

Track Procedure

To start tracking click Track, set AUTO Mode, and click Track again. The tracking status will be displayed on the monitor cube and in the Message window.

Monitor Procedure

The Monitor functions include monitoring the seeing, checking the optical quality of the Meade, and measuring the periodic errors in the drives.

Many More Features

If the STV doesn't behave the way you expect it to, consult the Operating Manual STV for much more detailed information on its operation. You will also find many more functions which are not mentioned here, as well as complete instructions for running the AUTO Mode procedures manually with a great variety of interactive options.

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