Lick Infrared Camera User's Guide

Setting Up and Preparing to Observe

Upon Arriving

Initial setup is performed by the observatory staff. Starting computer programs, initializing the camera, and testing the detector are left to the observer. Upon arriving, confirm that the setup has been completed. Check that the dewar has adequate coolant and, in humid conditions, that the captive air cover has been installed. Consult the Cassegrain Logbook at the 3-meter, or the User's Logbook at the 1-meter for notes by recent users. Check Lirctop's electronic log for the latest updates.

Filling the Dewar

At the 3-meter the dewar is filled by observatory staff, but at the 1-meter it is the observer's responsibility. The LIRC-II dewar is of the twin vessel type. Both vessels use liquid nitrogen. The outer vessel requires refilling every twelve hours; the inner vessel may be filled once a day. Bear in mind, however, that there may be spillage when working at large zenith distances, requiring more frequent refilling. Note that the array may exhibit some instability in the first hour after filling.

Both vessels are filled from the top of the dewar using a funnel with two 90- degree bends. Remove the tubes from the fill holes by unscrewing the knurled couplings, or, if they're frozen solid, carefully pull the hoses themselves out of the couplings. Gently insert the funnel into the inner vessel's fill hole, the one nearest the center of the dewar. The inner vessel generally requires very little nitrogen--minimize spillage by only pouring a small amount at a time into the funnel. The vessel is full when the coolant overflows the fill hole. Move the funnel to the outer vessel's fill hole and proceed in the same manner. The outer vessel will typically require 2 to 3 litres every 12 hours. Avoid spilling nitrogen onto the dewar--loss of vacuum due to a frozen o-ring could end your observing session and damage the camera.

Always replace the rubber hoses, they provide paths for the coolant to flow harmlessly to the floor when the telescope is moved to large hour angles. If they were removed at the couplings, simply screw them back into place. Turn the couplings several threads, but do not tighten. If the hoses were removed from the couplings, reinsert them after they have warmed up and become pliable.

Captive Air Cover

Above about 70% relative humidity, the dewar's input window can fog over. A transparent captive air cover prevents fogging, with negligible light loss and image degradation. The cover is placed over the square, protruding collar of the input window, and its power supply plugged into an AC outlet on the telescope. Use of the captive air cover should be standard operating procedure during the damp winter months, and in all but the driest conditions throughout the year. Condensation on the window not only ruins images, but can permanently damage the window's coating. Use the captive air cover if humidity can be expected to reach 70% or higher anytime during the night

. Should condensation form, call a member of the staff, do not attempt to remove it yourself.


The Data-Taking System

The LIRC-II data-taking program has much in common with the CCD data- taking program on which it is based, and will appear familiar to most Lick users. Here we only discuss those aspects of the data-taker which are unique to the LIRC-II version. A complete review of all data-taking commands is given in
Data-Taking System Guide.

Turn on the NCD terminal and log in as `user' (the password is posted on the keyboard). Start the data-taking program from an `xterm' window by typing `lirc2', or use the pull-down menu. The data-taking program will automatically create three windows: an xterm window displaying the data-taking menu, an image window, and an image control window. Figure 4 shows the x-terminal screen with the image windows, and their parent data-taking window. (You may wish to conserve screen space by reducing the size of the font in the data-taking window. Put the cursor in the window, hold the control key and the right-hand mouse button simultaneously and select `tiny' from the pull-down menu.)

The data-taking window presents a menu for setting observing parameters and controlling observations. The image window displays an image of the last completed observation, or can be used to redisplay a previous frame, stored on disk. The image control window provides options for a variety of measurements and manipulations of the image. Additional windows, including quick row and column plots and a variety of image statistics, may be spawned by the data-taker.

Like the CCD data-taker, the LIRC-II version beeps when an exposure begins, when it ends, and when the readout is complete. This can become tiresome when making the many short integrations typical of near-infrared observing. The `bell' may be turned off by typing `XSET B 0' from an xterm window. Typing `XSET B 1' turns it on again.

Figure 4. The x-window terminalAn x-windows screen, showing the three basic windows of the data-taking program, a plot window, and a Vista window, running Lirctop.


Special LIRC-II Data-Taking Options

The three options `Number of erases', `Number of prereads', and `Number of coadds' are unique to the LIRC-II version of the data-taker. Note, also, that there is no `fast readout' option, and that in the absence of a shutter, the `dark' option under `observation type' has no effect. Dark exposures are accomplished by moving the filter wheels to their `
dark' positions.

Number of Erases

`Number of erases' sets the number of times the array will be erased before the actual exposure is begun. We recommend two to three erases, depending on the brightness of the target, to insure that there is no residual charge from a previous exposure.

Number of Prereads

`Number of prereads' sets the number of optional zero-second darks (bias frames), used to reduce the effective readnoise in a single exposure. The bias frames are automatically added together, averaged, and held in a buffer until readout, at which time they are automatically subtracted from the target frame. Using prereads lengthens the duty cycle by adding about 3 seconds per preread, before the observation is begun. `Number of prereads' is set to zero in most observing situations.

Number of Coadds

`Number of coadds' sets the number of frames to be coadded before being displayed and saved. Coaddition of several consecutive images is a common infrared observing practice. The data-taker's `coadd' option automates the job by adding the requested number of frames in memory, before the final image is dispalyed and written to disk or tape. When using coadds, bear in mind that only the summed image is saved. Sources of error which might otherwise be recoverable, such as poor guiding or rapid changes in sky background level, will be blurred. To take individual, non-coadded images, set the number of coadds to one.

Use of the coadd option affects the numbering of stored images. Though the observation number increments each time a frame is taken, only the coadded frame is stored, taking as its number the number of the first frame in the coadded series. If, for example, an observation is begun with the observation number at 15, and the number of coadds set to 3, the data-taker will take three exposures--15,16, and 17--add them together, and write them to disk as `d15.ccd'. If another image is made, frames 18, 19, and 20 will be summed and written as `d18.ccd', and so on. Thus, gaps will appear in the numbering of disk images, reflecting the number of coadds making up a given image.

A/D Baseline (bias) Subtraction

In the CCD version of the data-taking system, automatic subtraction of an array's baseline from raw images, is the default. The baseline is computed, subtracted, and stored as the highest number column in an image. The LIRC-II version disables baseline subtraction by default. Baseline subtraction may be enabled from the data-taker by typing `Z' and selecting option four.

Keep in mind that when operating with the default condition of baseline subtraction disabled, the baseline counts will appear in raw images as approximately 2,000 additional DN that must be discounted when estimating flux levels. The plots reproduced in this manual include the baseline.


The Motor Control Program

The motor control program allows the user to position LIRC-II's two internal filter wheels and to select from three possible fields of view by positioning the lens wheel.

Turn on the PC compatible computer and type `lircmc' at the DOS prompt. On startup, the program checks its RS-232 connections with the motor controller; if a problem is detected an error message will appear. (If an error condition occurs, you can check the cable connections at the computer and at the motor controller, try cycling controller power, or call a staff member for help.) After successfully establishing communication with the controller, the program will ask if you wish the wheels to be sent to their `home' positions. Typing `yes' calibrates the positions of the three wheels. Doing so is recommended, especially following an error condition. The controller program's top level screen is illustrated in Figure 5a.

Figure 5a. Motor control program, top level menu.

               L I R C 2    M O T O R    C O N T R O L L E R
               ---------------------------------------------

     BACK WHEEL		        FRONT WHEEL		    LENS WHEEL

 K-band   (1.98-2.42)		Open			Small Field
 J-band   (1.10-1.44) 		ND2  2% trasm.		Medium Field
 Open     .37inc.		SP Filter    		Wide Field
 OII          (1.237)		Open		        Adaptive Opt. Lens
 FeII         (1.644)
 H2 S(1) 1-0  (2.122)
 BrG	      (2.166)
 H2 S(1) 2-1  (2.248)		Front Wheel Posit.: Open
 CO	      (2.295)		Back Wheel Posit. : K-prime
 K-prime  (1.85-2.35)		Lens Wheel Posit. : Medium Field
 H-band   (1.50-1.82)

 D - Go to Dark position		      F - Change filter on front wheel
 K - Go to K-prime & Medium Field Lens        B - Change filter on back wheel
					      L - Change Lens wheel
 Q - Quit the program

The three columns list the contents of the wheels under their respective headings. Filters are not routinely changed, and users can be confident that the lists accurately reflect the contents. The currently selected position of each wheel is displayed at center right; commands are listed at the bottom of the screen.

Selecting `H' will cause the positions of all three wheels to be reinitialized to their home positions. This is a useful recalibration procedure if there is any doubt as to their correct positions. To change the position of any wheel, type `F', `B', or `L' (Front, Back, or Lens wheel) followed by a carriage return. This will invoke a screen like the one illustrated in Figure 5b, displaying the wheel's contents and a number corresponding to each position. From this screen's menu the observer selects the desired filter by entering the code number followed by a carriage return, initiating the movement and returning the program to the main menu. The program automatically removes backlash while repositioning the wheel.

Figure 5b. Motor control program, second level menu, back filter wheel.

x

                 L I R C 2    M O T O R    C O N T R O L L E R
                 ---------------------------------------------

                    Filter		       Enter Code
                    H2 S(1) 1-0  (2.122) ________	1
                    BrG		 (2.166) ________	2
                    H2 S(1) 2-1  (2.248)    _____	3
                    CO	         (2.295)    _____	4
                    K-prime      (1.85-2.35) ____	5
                    H-band       (1.50-1.82) ____	6
                    K-band       (1.98-2.42)_____	7
                    J-band       (1.10-1.44) ____	8
                    Open  .37inc. _______________	9
                    OII          (1.237) ________	10
                    FeII         (1.644) ________	11


        Current Back wheel position is: K-prime
	Enter the new position _


Recording Data

The data-taking system allows images to be recorded on disk, 8-mm tape, both, or neither. Most observers choose to record only to disk during the course of the night, thus improving the observing duty cycle slightly by saving the time needed to write each incoming image to tape. The data are then typically written to tape in the morning, and sometimes FTPed to a remote site, as well. Data quality casette tapes may be purchased on the mountain.

The data-taking system includes some tape commands. Tapes may also be initialized, positioned for appending, and written using Vista's `exabyte' and `totape' commands.

The observatory archives all data taken with facility instruments on the 3- and 1-meter telescopes, including LIRC-II. Archival tapes are intended as a backup in the event of the accidental loss of data. They are not meant to substitute for the observer's backup. Archiving is customarily done at the end of each observing run. However, if the number of stored frames begins to task the available disk space, so that the disk must be cleared before the end of your run, you should notify a technician that an interim archival backup should be made. (The first indication that you're growing short of disk space is the message, from the data-taker, that the data disk is full and that it has begun writing to the vista disk.)

Observatory archiving has proven to be a worthwhile, but time consuming, process. This is particularly true for the very large number of images associated with infrared runs. Please make our job easier by deleting unnecessary frames before we archive, or informing the telescope technician if your data need not be saved, as, for example, calibration frames for a night during which no data were taken.

Some of LIRC-II's setup, such as focusing, is done with the data-taker operating in a continuous loop. This can generate a great many frames which, if inadvertantly recorded, rapidly swallow disk space. Be sure to turn recording off at such times.


Lirctop

Lirctop is a top-level, menu-driven program which calls a variety of Vista procedures for performing routine tasks such as making calibrations, taking repetitive exposures, dithering, mosaicing, and performing tests. Lirctop is largely self-explanatory and includes online help.

To run Lirctop, open a Vista window by selecting `Vista' from the pull down menu which appears when pushing the left-hand mouse button with the cursor in the gray area between windows. A blue Vista window is created. (You may wish to conserve screen space by reducing the size of the font in the Vista window. Put the cursor in the window, hold the control key and the right-hand mouse button simultaneously and select `tiny' from the pull- down menu.) Type `rp lirctop' to load the program, type `go' to run it. See the Lirctop Manual for a complete description of its functions.


Choosing a TV Camera

For acquisition and guiding, the observer may opt for either the standard cassegrain TUB TV camera or LIRC-II's boresite TV camera. Both share the same controller and are nominally the same type of camera. The boresite system is two to three magnitudes less sensitive, and has a somewhat narrower field of view than the TUB system. Nevertheless, we recommend using the boresite system whenever possible. The TV cameras are compared below.

The Boresite Camera

The boresite camera can reach stars of approximately 17th to 18th visual magnitude at the 3-meter, and 15th to 16th at the 1-meter, under the best conditions. Diffuse objects are more difficult. Moonlight can dramatically reduce the camera's ability to reach faint objects. Beyond these limits, it may be necessary to resort to the TUB camera, which, on a clear, dark night, can see objects at the limit of the old Palomar Sky Survey (about 19th magnitude) at the 1-meter. However, if the boresite is adequte to acquire a target, it is the preferred camera.

The boresite system does not require the introduction of a plane diagonal mirror, thus eliminating a significant source of thermal emission which is present when guiding with the TUB camera.

Observing is easier with the boresite camera. It receives its light from the visible portion of the telescope beam reflected from the dichroic beamsplitter (refer to frontispiece or back cover), and is therefore centered on the same patch of sky as the infrared array. This simplifies observing by eliminating the need to offset the TV camera or telescope to allow the target to reach the infrared array. If you choose to use the boresite camera, especially if you are the first to use it following a run with TUB camera, or if you switch from one to the other, changing TV cameras.

The TUB Camera

Despite its disadvantages, the TUB camera may be necessary for acquiring faint sources. The 3- and 1-meter TUB cameras guide on patches of sky adjacent to the target. At both telescopes, a perforated diagonal mirror must be inserted to allow light from the target to pass through to the infrared camera. This mirror represents a significant source of thermal emission.

After acquiring a target with the TUB camera at the 1-meter, the telescope must be offset to allow light from the target to reach the detector. Offsets specific to LIRC-II are recorded in the Users' Log book. Use the most recent offsets recorded therein. Offsetting the telescope is described in the Nickel Telescope User's Manual, and is part of the regular training for 1-meter observers.

The TUB Diagonal Mirror

As noted above, an additional mirror is required to use the TUB camera at either telescope. The backside of this mirror faces LIRC-II and is seen by the infrared array as a source of thermal emission. At the 3-meter, the diagonal is in place when mirror position #3 is selected. At the 1-meter, the mirror is inserted by moving the switch behind the sliding door in the rack below the TV camera controller to the `in' position.

Thermal emission from the diagonal mirror increases background ten to twenty percent at K-band, and affects flat-fielding in all bands. Thus, flats for images made when using the TUB camera must also be made with the diagonal mirror in place (mirror position 3 at the 3-meter; `diagonal in' at the 1-meter).

If you do not plan to guide your exposures, you can acquire targets with the TUB camera and remove the diagonal after offsetting the telescope and before beginning the exposure. You must, however, remember to reinsert the diagonal for acquiring the next object, and remove it again for observing.

If observing with the boresite camera, be sure that the mirror is removed. Mirror position #4 withdraws the mirror at the 3-meter. At the 1-meter, move the TUB diagonal switch to the `out' position.

TV Camera Fields

Figure 6 shows the fields of view and orientations for both TV cameras, at both telescopes, with the camera controller in binning mode 2. Note that while the TUB and boresite plate scales are comparable, vignetting narrows the boresite's field of view. Also note that with the TUB camera at the 1-meter, the cardinal directions are rotated 30, due to TUB rotation. The directions on the array itself remain vertical and horizontal for all setups (see
Figure 2).

Figure 6. TV cameras' directions and fields of view (note slight vignetting in boresite fields)

The TUB camera will have been set in advance to its nominal focus position (7.6 at the 1-meter) by a technician, but may require slight adjustment (see `folding flat mirrors' in the Nickel Telescope User's Manual).

The bore-site camera may need to be focused by the observer at the 1-meter, or, at the 3-meter, by the telescope operator at the observer's request. If, after the telescope has been focused on the infrared array, the bore-site image is not well- focused, correct it by rotating the focusing ring on the lens attached to the bore-site camera.


Changing TV Cameras

The 1-meter observer changes between the TUB and boresite cameras by changing the switch labeled `TV Select' on the panel below the TV camera controller (the `IR' position selects the boresite camera). However, the observer must be aware of two adjustments that must be made when cameras are switched: resetting the telescope coordinates and changing the guide matrix (at the 3-meter, the telescope operator will handle camera changes).

Resetting the Telescope

For instruments other than LIRC-II, the telescope coordinates at the 1-meter are set to bring objects into the field of the TUB camera. When changing to the boresite camera--or back to the TUB camera--the coordinates must be reset. This is most commonly required on the first night of a LIRC-II run, following an instrument change, but will also need to be done whenever cameras are switched. At the 1-meter, resetting the coordinates is the observer's job.

Choose a bright star near zenith. Run its coordinates through Setel, the position correction program (using Setel is part of the routine training for first time Nickel telescope users). Acquire the star with the camera for which the coordinates are currently set. This may not be obvious, so try both cameras, remembering to move the diagonal mirror to the `in' position for the TUB camera. Center the star on the TV monitor.

Offset the telescope according to the most recently recorded LIRC-II offsets in the Users' Logbook. If you found the star with the TUB camera, offset the telescope in the direction that moves the star from TUB camera to detector. If you found it on the boresite camera, offset the telescope in the opposite direction. After the offset is complete, switch cameras and confirm that the star is now visible on the TV monitor. Recenter the star on the monitor using the camera you will use for observing. Rerun the coordinates through Setel. Reset the telescope coordinates to match Setel's corrected position by using the black buttons and the rate and direction switches, next to the right ascension and declination readouts. It will also be necessary to update the hour angle readout. Always use a star near zenith. Do not reset the coordinates to compensate for pointing errors at large hour angles. Check the newly calibrated coordinates by going to another bright star nearby.

Alternatively, you can try setting directly to the TV camera of your choice by using the finder telescope. Again, select a bright star near zenith and set the telescope according to Setel's corrected position. Find the most recent entry in the users' logbook illustrating the positions of stars for LIRC-II, with respect to the finder's reticle. Looking through the finder, move the star to the appropriate spot on the reticle. Confirm that the star is on the TV, then reset the coordinates as described above. Make a drawing in the logbook, even if it's the same as the one to which you referred, showing the position of the star on the reticle. Indicate which TV camera the star refers to, and that it was made for LIRC-II.

See the Nickel Telescope User's Manual for more instructions on offsetting the telescope, and resetting telescope coordinates.

Resetting the Guide Matrix

To account for the differences in orientation and scale of the TV fields for various instruments, the autoguider requires a rotation matrix--a set of numbers entered into Telco via the PET computer--appropriate to the current instrumental setup. The guide matrix for LIRC-II differs according to which TV camera is selected, and which telescope is being used. Telco automatically adopts a guide matrix appropriate to the TUB camera. The boresite camera, however, requires a unique matrix that must be entered manually.

At the 3-meter, the telescope operator is responsible for the guide matrix. At the 1-meter, the observer enters the boresite matrix by turning on the PET computer and inserting the floppy disk labeled `LIRC-II Boresite Version' and pressing the shift and `run' keys. To restore the TUB camera matrix, insert the customary floppy, and press the shift and `run' keys.

Should the 1-meter's boresite matrix floppy disk be lost or unreadable, the matrix may be entered from the keyboard. At the PET's basic prompt, type the following:
MS% = 20
FF% = 0 (this sets the guider to cassegrain)
MS% = 18
TU% = 900(this enters a TUB angle of 90 degrees)
MS% = 23
S1% = 1 (these set the guide matrix coefficients)
S2% = -1
S3% = -1
S4% = -1
SYS(40972)(this sends the information to Telco)


Focusing the IR Camera

LIRC-II has no internal focus adjustment; focusing is instead accomplished by moving the telescope's secondary mirror with respect to the instrument. Nominal telescope focus is 060.00 at the 3-m, and 295 at the 1-m. These numbers are approximate and will depend on the field of view selected, as well as on temperature. Judging best focus may be done by eye or by using Vista's stellar statisitics capability as described below.

Choose a star of about tenth (3-meter) or eighth (1-meter) visual magnitude. Bear in mind that the peak DN of a star image will increase as it comes into focus--choose a star that will not saturate the detector when well-focused.

To focus by eye, take repeated, unrecorded exposures, incrementing the telescope focus slightly each time--about 1-2 units at the 3-meter or about 5 units at the 1-meter. Always moving the telescope focus in one direction to avoid backlash in the focus mechanism. The `expose' command, in Lirctop's `observing' submenu, may be used to automatically take multiple exposures. Remember to turn `recording' off in the data-taker, when taking frames which need not be saved.

A more quantitative, though not necessarily more accurate, approach uses the data-taking system's stellar statisitcs routines. Take a single exposure by typing `r' from the the data-taking window, with the parameters set for an unrecorded exposure of an appropriate length. Choose `Itv' from the image control window to create the Itv window. Choose `pick stellar stat loc' from the Itv window, click on the star image, and choose `do stats'. Yet another window will appear, with various statistics for the star (this is also a good way to measure the precise pixel location and the peak and approximate integrated DN of an object). From the Itv window, select `add to focus file' and enter the telescope's focus position at the prompt. Change the focus as recommended above-- remembering to move in the same direction to avoid backlash--and repeat the procedure on another image . After three iterations, a plot of image size vs. focus position will begin to be drawn in the statisitics window, along with a suggested focus. Expect more or less scatter of the data points as a function of seeing.

The size of the seeing disk may be directly measured by using the plotting capability in the data-taker's image display window.

The various filters are very close to parfocal, but the three fields of view are not. Refocus after changing fields of view.

The focus should be routinely checked at least once during the night, and more often if the outside temperature has been changing.


Mapping the Array

Mapping the position of the array onto the TV image saves time and guesswork later on, and aids the accurate placement of targets on the best regions of the detector. The process differs slightly depending on whether the TUB or boresite camera is used. The former requires offsetting the telescope for each mapped point, the latter only requires moving the star with respect to the detector since the boresite camera sees the same field as the array.

After finding a bright star, set selection one in the data-taker for unrecorded exposures, of a length appropriate to the star, and use Lirctop's `expose' option to take repeated exposures. Move the telescope so that the star is in one corner of the array.

If using the TUB camera, change to mirror position two (3-meter) or offset the telescope (1-meter) to bring the star back to the TV field. Mark its position on the TV screen with a grease pencil. Offset back to the IR camera, reposition the star to the opposite corner of the array, and repeat the process. If using the boresite camera, simply mark the star's position on the TV screen when it is positioned at one corner of the array, move the star to the opposite corner, and repeat.


Checking Collimation

Well-formed, unvignetted images depend on proper alignment of the IR camera. Collimation is generally very stable. The dewar's internal optics are fixed, and not subject to loss of alignment. Occasionally, however, small changes in the tip or tilt of the dichroic beamsplitter result in loss of collimation.

Collimation is easily checked by observing the out-of-focus image of a star. From the motor control program, select the intermediate field of view for the test. This is the only lens position suitable for testing collimation, as it alone has the central obscuration to which the incoming beam is aligned.

Select a relatively bright star--say 7th visual magnitude on the 3-meter, 5th on the 1-meter. Drive the telescope well out of focus, so that the star forms an image of the primary about one-third the size of the array. Center the image on the array. Integrate long enough to obtain a well exposed image, without saturating. You may wish to use the `expose' command under Lirctop's `observing' option to make continuous exposures while adjusting the size, position, and brightness of the image, but remember to turn `recording' off in the data-taker.

If the camera is properly collimated, the shadow of the secondary mirror, at the center of the image of the primary, will coincide with the central obscuration on the dewar's intermediate lens assembly. The resulting image will show only one central shadow, similar to the one on the right in Figure 7. If the camera is out of collimation, the two central spots will not coincide and the image will show two central shadows, something like the image on the left.

Figure 7. A well-collimated vs. a poorly-collimated image

If the camera is found to need collimating, call a member of the staff. Collimation is performed by manually tilting the dichroic beamsplitter while monitoring the defocused star image and is strictly a two-person operation, requiring one person at the computer, the other at the instrument. The person adjusting the dichroic must be a telescope technician or support scientist.