Mees Observatory telescope and camera checklist

Transcription

1 Mees Observatory telescope and camera checklist Last revised 1 September 2011 DMW Telescope startup...1 Telescope shutdown...6 CCD camera startup...7 Taking data CCD camera shutdown Telescope startup 1. Turn on all circuit breakers in the breaker box by the front door. (The breakers marked with yellow tape are always on.) For tours, make sure that the solar lights are placed near the bottom stair. 2. Plug in computer console in the control room (Figure 1). CCD UIC TCS TCS UIC Figure 1: computer console in control room. Computers, left to right on the console: the (downstairs) user interface computer (UIC), telescope control system (TCS). Further right, on the lab table, is the CCD camera s laptop computer. 1

2 Initial switch settings: In U-D-U-U-D-U U U-off-off Figure 2: the Telescope Control System (TCS) front panel, and the settings that the switches should have before the system power is turned on. U = up, D = down. 3. Check switches on telescope control system (TCS) front panel (Figure 2). The HALT MOTORS button should be pushed in, TRACK/OFF and EXTERNAL COMPUTER/OFF should be set to OFF (switch down). All other switches on the upper row (TRACK/AUXILIARY TRACK, DRIVES, AUTO DOME, DOME TRACK), and the MTR DRIVER CHASSIS switch (locking toggle switch between the fuses) should be in the UP position. The lowest row of switches should have the EAST/WEST switch on EAST, and the HARD LIMIT OVERRIDE switch OFF. Important note: Always be sure that the TCS computer operator does not inadvertently hit the switches with his/her knees. 4. Turn on system power (middle switch in the lower row). 5. Turn on telescope control computer, which is behind the door that hangs from that hinge visible on the front panel. 6. Let the TCS computer boot. Check the date and time (type DATE or TIME <RETURN>, at the DOS prompt), and correct them if they re off by more than a few seconds. Note that it is universal time (UT) and date that the TCS computer requires (5 hours ahead of standard time, 4 ahead of daylight savings time; summer = daylight savings time). If your watch is not synchronized to UT, and you didn t bring a cell phone or a GPS receiver (both of which give you time synchronized to UT), then pick up the phone and call a friend to help you find out. If your friend happens to be sitting by a 2

3 networked computer, he or she can look up UT for you on the US Naval Observatory website, Make sure you enter times either in 24-hour format, or with a P for PM or A for AM. 7. Make sure the EXTERNAL COMPUTER switch is still OFF and type TCS <RETURN>. The telescope operating system will take a few minutes to initialize, the longest step being the finding of the focus reference point (fiducial). You ll have to wait until it s done initializing the focus before proceeding with instructions to the TCS computer. 8. Push the HALT MOTORS button, so that it is in its out position; this un-halts the motors. Immediately check upstairs to make sure the telescope isn t moving; push HALT MOTORS in again if it is. (This rarely happens, but usually indicates a serious problem. Consider contacting Dan (cell phone ) for further instructions, if this happens to you.) 9. Check the TCS computer s UT, on its monitor display, and set if necessary. (It should be correct, if step 6 succeeded.) Now check it again. Setting the time wrong has been the most frequent error in telescope setup, by far. Mirror lever (as shown, the CCD camera is selected) Eyepiece SBIG ST-9E CCD camera Figure 3: the back of the telescope, showing a CCD camera, the eyepiece, and the diagonalmirror lever that switches the telescope between the two. 10. You will be using the user interface computer (UIC) in the control room to the left of the TCS computer. The cable switch that sits to the left of the TCS computer s monitor must be set to Downstairs for the UIC to talk to the TCS. (Note that it is possible to run a laptop up in the dome as the UIC, and if doing so, you would set the cable switch to Upstairs.) Turn on the UIC and let it boot into Windows while you re upstairs working on the next steps. 3

4 11. The necessary focal plane equipment should already be installed. On the back of the telescope you will find the 2-inch-aperture eyepiece and one of several CCD cameras, both mounted on a metal box (Figure 3). The box contains a mirror that can direct light from the telescope either to the camera or the eyepiece by moving the lever on its northeast side. Swing the mirror s-lever all the way in the direction of the eyepiece, since you are about to use the eyepiece to initialize the telescope pointing. If you will be using the CCD camera, see the separate camera startup instructions. Telescope setup precedes camera setup. 12. Unlatch both of the locks on the gears of the dome-door mechanism, remove the hooked rubber strap on the doors, and open the dome. Make sure that whatever may fall in (leaves, snow, tourists ) gets cleaned up and doesn t get all over the telescope or instruments. 13. Slew telescope to the south using the telescope paddle (push SLEW and S simultaneously) until the top is in reach on the large ladder, and remove tarp and covers. 14. Put the telescope at zenith according to the dials on the telescope base, visible in Figure 4. The hourangle dial (the smaller of the three) should read precisely zero. The declination (right-hand) dial should read the observatory latitude: 42 degrees, 42 arcminutes, 1 arcsecond. Make sure you re reading the dial and tick-marks correctly: at our northern latitude the declination increases when the needle moves counterclockwise, and each degree is subdivided on the dial into ten-minute major intervals and two-minute minor intervals. The correct reading is just past 40 on the coarse (small, inner) scale, and 2 42 on the fine (large, outer), counterclockwise scale. This latter setting is illustrated in Figure Figure 4: Correct settings for zenith on the hour angle (small, center), and declination (larger, right) dials, and a schematic diagram of the outer, high-resolution circle on the declination dial, with an angle of 2 42 indicated. Never mind the right ascension (larger, left) dial. 15. Return to the control room and set the telescope position to RA = ST (found on TCS display, underneath the UT), Dec = latitude ( ) in the Initialization menu of TCS. When the TCS computer asks for EPOCH, enter the current decimal year: for example, for mid-september, and for mid-october. 4

5 16. Check the date and time on the UIC by double-clicking on the time shown in the lower right corner of the screen, and correct them if they re wrong. Note that the UIC should be set to local time, not UT. 17. Run TheSky, using the icon on the UIC s desktop. (Be sure not to run it twice.) 18. In the Data menu of TheSky, check the Site Information item to make sure the observatory position and time (the Use computer s clock box on the Date and Time tab should be checked, the North America daylight-savings option selected, and 5.0 entered in the TimeZone field) are set correctly. They should already be. 19. Then in the Telescope menu item of TheSky, choose Link Establish Link. The telescope-position bullseye will appear on the screen at the current telescope position. If a link cannot be established, check the cable-switch box. 20. Turn the TCS electronics TRACK/OFF switch to TRACK. This should change the RA rate from zero to on the TCS monitor screen. 21. Choose a bright star ( V 2 mag) close to the zenith in TheSky s display. Click on it to bring up an information window, center the star in the display if you want (button in lower left corner of information window), and command the telescope to slew to the star (fourth button from the right at the bottom of the information window. If anyone is near the telescope, announce, Slewing! Then click OK on the dialog box that asks you to confirm the slew. Be sure to have someone watching the telescope s movement; HALT MOTORS immediately if the scope is not moving appropriately. If you want to go to an object for which you know the name, use the Edit Find menu item. 22. With the dome paddle, turn the dome slit in front of the telescope. Check visually to see that the telescope is pointing in the right direction: for example, one can stand behind it and look for the target through the dome slit, in line with the telescope. With the telescope paddle, center the star in the field, and focus the telescope. The SET mode (hold down the paddle button with that name) provides a good speed for moving the star within the guider field, and for focusing. If the telescope is way out of focus, the image will not look starlike: it will look like an illuminated image of the primary mirror, with the shadow of the secondary mirror and its supports superimposed. When you have focused so that stars look point-like, record the FOCUS position on the TCS monitor display, in the Observing log book. Note that the telescope pointing changes fastest in SLEW mode, next fastest in SET, and very slowly if neither SLEW nor SET is used. (Ask an old astronomer what good that slow mode would be.) Note also that the telescope focus changes fastest if SET is used, and changes very slowly if it is not. (This step is rarely required) If you don t see the star, zoom the display in on TheSky until the display is just a few fields-of-view across. If there are any stars visible in the field you may identify them by comparison to the display (eyepiece or CCD), and move the telescope to the target accordingly. If not, move the telescope around systematically in a grid pattern of, say, ¾-field-of-view steps, using TheSky s display to guide you, and find your target. If you still can t, then start over at step In the Initialization menu of TCS, set the telescope position to the current RA and Dec of the star. For this you need the current-epoch coordinates those you ll find closest to the top of the star s information window in TheSky, and not to be confused with the J2000 coordinates you ll find further down that window. Now you should be able to point the telescope confidently to other objects, either with TheSky or 5

6 with TCS. It will be helpful if the TCS telescope position is updated occasionally, in the manner described above, with the coordinates of subsequent objects that are centered in the eyepiece. This is especially important if some of your targets are far apart on the sky, and/or far from zenith. 24. For viewing the bright Moon, there is a variable Moon filter (crossed polarizers) in the drawer of the desk up on the dome floor. For viewing nebulae, there is a nebular filter ([O III] nm line) in the same spot. To install either, carefully remove the eyepiece, screw the appropriate filter on the bottom of the eyepiece, and replace the eyepiece. Don t forget to remove it before you observe a fainter or continuously-emitting object. Telescope shutdown 1. Turn TRACK/OFF switch OFF. 2. Slew telescope south to the service position, and put covers and tarp back on. Do this before shutting the dome. 3. On TCS Movement menu, set telescope to zenith (5 <Enter>) and enable slew (7 <Enter>). 4. Once the telescope has arrived at zenith, push in the HALT MOTORS button on the TCS front panel. 5. Move the dome until the slit is directly over the doorway that leads to the deck. Close the dome, lock the gears of the dome-slit mechanism, and secure the doors with the hooked rubber strap. Again, make sure that whatever may fall into the dome when the doors move gets cleaned up, and doesn t get on the equipment. 6. Make sure everything electronic or optical in the dome is protected by a tarp, that the CCD camera is unplugged, and that no electronics (e.g. the CCD camera power supply) remains on the dome floor. 7. Close and lock the door to the deck. 8. Shut down TheSky, and the UIC on which it runs. 9. Turn the TCS SYSTEM POWER switch OFF. 10. Unplug the console in the control room. 11. Make a brief entry in the observing log book. Be sure to report any problems to Dan, Kurt or Carol. 12. Make sure that ALL of the doors to the rooms inside the dome are closed. 13. Turn off the circuit breakers not marked with yellow tape, that you turned on, on the way in. 14. Lock the door behind you. 15. If you went into the Gannett House, make sure that its doors are locked. Pay special attention to the double patio doors as these have a somewhat unusual lock: one has to pull up on the handle, rather like cocking a rifle, in order to enable the lock latches. Test these doors to make sure they re locked. Even if you didn t enter the house, please make sure that the floodlights outside the house are 6

7 turned off. There s a switch for these lights, between the garage doors, that may be partially hidden by ivy. 16. Make sure the gate is locked securely behind you. If you used the set of keys in the lockbox, replace them. Now you are ready to drive home. Be careful of the deer. CCD camera startup Figure 5: SBIG ST-9E camera and CFW-8 filter wheel mounted on the back of the Mees 24 telescope. In this orientation, the rows and columns of the imaging chip lie E-W and N-S. 1. The camera-filter wheel assemblies (henceforth cameras ) are mounted by their snouts, in the split cylinder on the bottom of the eyepiece box. A good fit usually requires wrapping a metal shim around the snout, below the ridge at its mouth. In turn a shim inches thick is usually about right. If such a shim is not present, make one from the box of brass shim stock you ll find in the gray metal cabinet in the control room. 2. Place a hose clamp around the camera end of the split cylinder, wrap the shim around the camera snout, and carefully insert the snout into the cylinder. Tighten the hose clamp with a flat screwdriver, and ensure that the cylinder grips the snout tightly. Attach the camera s grounding strap with the 1/4-20 screw on the eyepiece box adjacent to the cylinder. Run a piece of duct tape diagonally between the metal posts surrounding the camera, to prevent the camera from dropping to the floor if the snout loosens. Make sure the tape does not block the camera s fan. 3. The rows and columns of the CCDs are parallel to the flat, connector-bearing side of the camera body; thus it will be most convenient if this side lies along a cardinal direction. Usually we orient it to lie east-west, 45 from the sides of the eyepiece box, with the connectors facing north, as shown in Figure 5. 7

8 4. Plug all the cables into the camera s lower body: the filter wheel cable to the CFW connector, the USB cable that s threaded through the telescope base, and the camera power supply. Make sure that nothing else interferes mechanically with any of these cables. Turn the camera power supply on. 5. Point the telescope to a bright star. Center the star in the eyepiece field of view; then swing the diagonal mirror into the CCD-camera-viewing position, and return to the control room. 6. Start the CCD camera s laptop computer (Figure 6) and let it boot into Windows. Identify the lone USB cable among those that emerge from the right-hand conduit terminal, and plug this into one of the computer s USB ports. Conduit terminals CCD camera computer USB cable Figure 6: CCD camera computer in action in the control room. 7. Run CCDSoft, the program that we use to control SBIG CCDs, by doubleclicking on the icon on the computer s desktop. 8. Use the Camera item on the menu to bring up the camera-control window (Figure 7). Most of your work in taking images with the CCD camera involves commands found under the tabs on this window. Start by choosing the Setup tab. Verify that the camera and filter wheel listed in the first two dropdown boxes are those you have on the telescope (almost certainly an SBIG ST-9E/9XE and an SBIG CFW-8, and that no focusor is selected. Choose the Imager radio button and at least the Save images with UTC and Auto contrast checkboxes, and then push the Connect button. The Imager Status line will change to Ready when the connection is made. Next click the Temperature button and set the CCD temperature to -5 C, checking the Fan on and Shut down temperature regulator boxes as well. 8

9 9. Next, put the Clear filter (i.e. no filter at all) in the beam, by choosing the Take Image tab and the Filter dropdown box. 10. Then choose Focus Tools tab. Check the Continuous box, set the exposure and delay to 0.05 sec and 0 sec in the leftmost dropdown boxes, and click the Take Image button. In a new window a continuous sequence of images should then appear. If you centered the bright star precisely in the eyepiece, this star should appear in the images, perhaps quite overexposed. Figure 7: CCDSoft camera control window. Paddle button pressed... N Star moves on image W E S Figure 8: paddle-button response for the camera orientation shown in Figure 5. The telescope moves in the directions indicated by the buttons, of course, so in this orientation the image has north down and east right; that is, it s upside down compared to the way we usually display celestial images (north up, east left). 11. Note which way the star moves in response to the paddle buttons. If the camera is oriented as in Figure 5, this will be within a few degrees of the pattern shown in Figure 8. If it is not oriented in this way, we strongly suggest you make it so, or at least make a similar diagram of the motions. 12. If the bright star does not appear in your images, try one or more of the following: (a) Take the diagonal mirror out of the beam. (b) Increase the exposure time to a few seconds, which should enable you to see the scattered-light halo of the star, and to move the star onto the CCD. (c) Move back to eyepiece mode and center the star in the eyepiece field more precisely. (Note that the eyepiece field of view is about 17 arcmin in diameter, and the ST-9 camera field of view is square and 5.1 arcmin on a side.) 9

10 13. With the control-room paddle, focus the image of the bright star roughly, and move it to the center of the image. Initialize the TCS telescope position with this star s current coordinates, as in step 23 of the Telescope Setup instructions. 14. On the UIC, choose a fainter star near the bright one ( V = 5 10 mag) and command the telescope to slew to this star. Center it in the image, and focus this stellar image precisely. In doing so you should keep the exposure time down (0.05 sec will still be OK), and observe the FWHM width and maximum signal in the star s image as a function of focus setting. Read the signals by placing the cursor on the star s pixels and noting the readout in the lower left corner of the CCDSoft window. Scan the focus setting in one direction only (in or out), by 5-10 focus-position units per step. Find the position that gives the smallest FWHM and largest peak signal, reset the focus to that position in the same direction as your scan: move the focus substantially past optimum in the reverse direction, and then move in your original scan direction to the optimum value. Record this value, and that of the FWHM (the visual seeing), in the observing logbook. Pixels are spaced by 0.6 arcsec; what is the seeing in arcsec? 15. Back on the Setup tab, click the File Defaults button to record the name(s) of the observer(s) in the data file headers; then on the AutoSave tab to choose a folder in which to save images (Choose Folder button) and a File name prefix (e.g. MyName_TodaysDate). Select the FITS radio button and check the AutoSave on box. Now you are ready to take images in earnest. Taking data Figure 9: Take Image tab of the camera-control window, used to select filters, exposure times, dark current subtraction and flat fielding, and to command exposures. 1. You ll be using the Take Image tab of the camera-control window (Figure 9) to acquire most of your data. For short exposures it is convenient to specify Light and AutoDark in the Image dropdown boxes, which automatically takes dark frames and subtracts them from the signal images. If you ll be taking lots of images with the same longer exposure time, though, it s better to save a dark image at that exposure (choose Dark in the Frame dropdown) and subtract that same dark frame from the 10

11 whole stack of images using Image Reduce Dark Subtract from the CCDSoft menu. Similarly for flat fields: choose Flat-Field in the Frame dropdown, then Image Reduce Flat Field from the menu. 2. If the sky is dark, make the exposure time as long as possible without telescope tracking errors streaking the images. If the moonlight is bright it will not help to integrate so long; just integrate long enough that the sky background is substantial ( units), and take multiple exposures with the intention of averaging them. 3. Use of FITS as the default file format helps one keep track of the parameters of the observations: look at a file header by using View File Information on the CCDSoft menu, and you ll see that such things as UTC, exposure times and delays, identity of the filter in use, type of image (target data, dark frame, flat field, ) and CCD temperature are recorded for you. FITS format, of course, also matches essentially all professional astronomical software. Note that if you accidentally take a bunch of data in SBIG s native format, you can convert it to FITS in bulk, using programs downloadable from the SBIG website. 4. Our SBIG CCD cameras all have two CCDs: one for taking images, and a smaller one beside it called the Autoguider. As its name implies, this chip is intended to detect stars in the field adjacent to that under study, and enable the telescope to track one of them and thus stay pointed in the same place during long exposures on the main CCD. We don t presently have the TCS computer set up to use the second CCD for automatic guiding, although we could. On the other hand one can always view the autoguider image using the Autoguide tab on the camera-control window, and use the control-room paddle (not the buttons on the Autoguide display!) to keep the stars in their original places; this is how guiding used to be done years ago for long photographic exposures. (See item 22 in the Telescope Setup list, and again ask an old astronomer for details.) 5. If you want to take color images (e.g. Figure 10), and know what the exposure times should be, then use of the commands on the Color tab will streamline your work. Experiment with them. CCD camera shutdown 1. Close CCDSoft on the camera-control computer. 2. Disconnect the USB cable from the computer. Back up in the dome, unplug the USB and power cables from the camera. Hang the camera end of the USB cable on the string from which the paddles hang, and stow the camera s power supply in the CCD camera s case, in the control room. 3. Usually it is OK to leave the camera mounted on the telescope. If you are taking it back to campus, though: carefully remove the duct tape, loosen the 1/4-20 screw and detach the ground strap, and then carefully loosen the hose clamp with a flat screwdriver, enabling the camera to slide down into your waiting hands. Unplug the filter-wheel cable. Unscrew the snout from the camera body, and replace it with the threaded cover/pinhole camera found in the camera s case, taking care not to let any particles accumulate on the filters. (If stuff gets on the filters, blow it off with clean compressed air; usually there s a can in the gray cabinet in the control room.) Stow camera, snout and shim in the CCD camera case. 11

12 Figure 10: example color image of the planetary nebula NGC 7662 in Cygnus (a.k.a. the Blue Snowball Nebula), taken in bright moonlight on 6 September 2009 with the Mees 24 telescope and the SBIG ST-9E camera. The exposure time was 1 minute in each of the B, V and R filters. The colors were balanced so as to make A0 V stars look white, and are shown on a linear scale. 12