Lirctop's functions are divided into six main categories: Observations, Calibrations, Tests, Quick Reductions, Lirclog, and Help. These invoke one or more submenus with a variety of choices, described below. The source code resides in a collection of subroutines in the directory /procedure/lirctop, and may be examined, though not altered or added to, by users. However, we welcome suggestions for the addition of new functions and improvements to exisiting ones. Report bugs to tony@ucolick.org.

Vista's--and therefore Lirctop's--interaction with the data-taking system is limited, and it has none with the LIRC-II motor controller. It can set the integration time, choose which preset selection to use, start an exposure, and make small telescope moves. With the exception of the `,a href="#nod">Nod' function, Lirctop always uses the parameters set in selection one of the data-taking system. Functions which prompt for integration times may change the integration time in selection one. Some functions move the telescope between target exposures. These will ask the user in advance if he or she wishes the procedure to pause before and after each exposure, to enable or disable the autoguider. (To resume a paused procedure, type `continue', or simply `c' as it is usually aliased in Vista.)

Error trapping is weak in Lirctop, and incorrect input can crash the program, returning you to the Vista prompt. If this happens, simply type `go' to start again.

Selections which move the telescope include the option of pausing the procedure between moves to enable or disable the autoguider. If using the autoguider, you should reply `yes' to this question, as moving the star off the guide reticle while guiding is enabled will cause errors in the track rate, resulting in poorer guiding.

Expose takes multiple exposures without moving the telescope.

The user is prompted for the number of exposures. The exposures are made using the parameters in selection one of the data-taker. Expose may be used as a continuous loop by entering an arbitrarily large number of exposures. This is particularly useful for focusing, checking collimation, and other operations requiring many short, repeated exposures. (Remember to turn recording off in the data-taker, if images need not be saved.) There is, however, no graceful way to terminate the exposures before the requested number has been made, but it may be done gracelessly by typing `control-c'. This will cause Lirctop to terminate completely. Simply type `go' to restart the program.

Remember that with n coadds selected, each exposure is the sum of n frames. Remember also to turn off recording in the data-taker when appropriate.

Nod moves the telescope between a starting and an offset position, the requested number of times, takes the requested number of exposures at each position, and returns the telescope to the starting position when all the exposures have been completed. Nod is useful for moving between target and sky positions. To help with recordkeeping, exposures at the starting position are all made with selection one in the data-taking system, while all those made at the offset position use selection two. For example, selection one and two could have identical parameters, except that the labels might read `target' for selection one, and `sky' for selection two.

The user is prompted for a single set of right ascension and declination offsets, in arcseconds, which define the distance between the start and offset positions. Offsets are given in terms of telescope movement--remember that targets will appear to move in the opposite direction with respect to the array.

The user is prompted for the number of exposures at each position, the number of iterations of the sequence, and whether the program should pause before and after moves, to allow enabling or disabling of the autoguider. Remember that with n coadds selected, each exposure is the sum of n frames.

Dither moves the telescope according to a predetermined pattern. The offsets can be entered from the keyboard, read from a user-created file, or from a `canned' file.

In the first three cases below, the user is prompted for the number of exposures at each position, the number of iterations of the entire sequence, and whether the program should pause before and after moves, to allow enabling or disabling of the autoguider. The telescope always returns to its starting position on completion of the observations. Exposures are made according to the parameters in selection one of the data-taking system. Remember that with n coadds selected, each exposure is the sum of n frames.

Read offsets from a file This dithering option reads a series of telescope offsets from a user- created file, written and stored to disk using the `Define a new dither pattern' selection, in the dithering submenu (see below). All dither files must reside in the /procedure/lirctop directory. To protect your own dither files from being accidentally overwritten, save a copy in your personal directory. The user is prompted for a file name. If it is a valid file, the program will prompt the user for observing parameters before executing the observation.

Use a canned dither pattern This dithering option offers a choice of two ready-made patterns: a right triangle or rectangle. The user interactively defines a pattern's size and orientation. The program then prompts for observing parameters before executing the observation.

Canned dither patterns always move in a clockwise direction. Right triangles begin at the intersection of the base and leg; rectangles begin at the upper left corner.

Enter offsets from the keyboard This option allows a dither pattern to be entered at the keyboard. The user is prompted for input in terms of the number of points in the pattern, and the size of each move in arcseconds for both declination and right ascension. The program then prompts for observing parameters before executing the observation. This option is similar to `Define a new dither pattern' below, but executes the pattern without necessarily storing it to a file. After execution, the user is asked whether he or she wishes to save the pattern.

Define a new dither pattern This selection permits the user to interactively define a dither pattern to be stored in a file. The user is prompted for an output file name, and then for input defining the pattern in terms of the number of points in the pattern, and the size of each move in arcseconds, for both declination and right ascension. The file is automatically saved in /procedure/lirctop, where it can be read by the dithering procedure. This function does not execute the pattern. To do so, the user must select dithering again, choose the `Read offsets from a file' option, and enter the name of the newly created file.

All mosaics begin at the upper left-hand corner of the pattern. The observer may either point the telescope to the starting position, or answer `yes' when queried whether to begin at the center. In the latter case, the observer points to the middle of the mosaic, and lets the program automatically move the telescope to the upper left-hand corner, before beginning exposures. Remember that with n coadds selected, each exposure is the sum of n frames.

Darks allows the user to make unilluminated dark frames at exposure times equivalent to his or her target frames.

An unlimited number of frames, at a maximum of ten different exposure times, may be automatically made. The program prompts for the number of different exposure times, the times themselves, and the number of frames at each exposure time. Exposures are made according to the parameters in selection one of the data-taking system. Remember to set the filter and lens wheels to their `dark' positons.

Sky Flats takes the requested number of exposures, while moving the telescope a small distance between each exposure.

The user is prompted for the integration time, and the size of the telescope offset, in arcseconds. We recommend a minimum of 10 arcseconds.

Bear in mind that twilight sky brightness changes rapidly, and that integration times must be adjusted accordingly. We suggest monitoring the flux of the incoming twilight sky frames, and keeping the integration time appropriately adjusted. You may change the integration time for the next frame, during the readout of the previous one, or you may choose to take only a few exposures each time you run `sky flats', changing the integration time after each sequence.

Bias takes the requested number of zero-second dark frames for bias subtraction. Remember to set the filter and lens wheels to their `dark' positons.

Dark and Noise Levels This procedure measures the array's dark current and readnoise. Note that in the course of running the test, a Vista image window, its associated control window, and a plot window will be created, if they do not already exist. This may take a half a minute or so. The procedure pauses between the dark and noise tests to allow the user to examine the results of the former. Type `continue' (or simply `c' as it is usually aliased in Vista) to resume. The test is fully described in Testing the Array.

Array Stability This procedure checks the constancy of the system by taking a series of exposures with a uniform source of illumination, or a series of darks, and comparing the mean DN levels of the series, inside one or more user-defined boxes. It is fully described in Testing the Array.

Quick Sky Subtraction This procedure performs a subtraction of two images, usually a source frame (or a sum of several source frames) and a sky frame.