The tcpcom guide




ALFOSC Fast Photometry Control Program Startup


Important points to get started:


Data files

The tcpcom program produces two types of output files.

Output data directory

All data files is stored in subdirectories below a top level data directory decided for the current date when tcpcom is started.

Filters and such

The tcpcom program can control all wheels in the ALFOSC instrument, as well as the FASU filter wheels.

Normal CCD imaging

The tcpcom program is capable of doing basic CCD imaging, although this option is intended only to get quick images of the current field to set up the fast photometry target list. You will not be able to see the image during readout, but will have to load it into saoimage once it is completely written. The readout program reports the median of the pixel counts as it reads out, which is very useful when doing flat fields. Basic tcpcom keystroke commands for imaging is shown on the menu for screen 0.

Setting up for fast photometry

To start fast photometry on a target it is necessary to follow a very precise procedure that goes in three steps.
  1. Obtain an image of your target field
    • Move the telescope to the target field and start autoguiding.
    • Create a new directory for this specific photometry run by using the `D'-key in the tcpcom window. The directory may exist, but note that old files in this directory will be overwritten.
    • Update the FITS comment and object fields, if you care.
    • In normal full-frame imaging mode, get a picture of the field. (The `E'-key sets exposure time and starts the integration.) Wait about 80 seconds for the readout to complete.
    • Use saoimage to check that the field is good. You may want to move the field to get enough good reference stars within the field. Notice the defects on the CCD, and check that your target and reference stars are not on any obvious defects. Keep moving the telescope and taking images of the field until you are certain that you have a good position. You never move the telescope once you are in place.

  2. Mark your target objects for windowing
    • In the directory where the image of the field was stored, give the command phot < filename >, where < filename > is the name of the image of the field that the telescope currently points to.
    • You should get a saoimage display that (after a while) will show the image of your field, scaled close to the background value to reveal all details.
    • Mark your target, reference stars and sky fields. The order is important, so mark the target first, then all reference stars you want, and finally one or more sky background fields. The key to use is `s' when the image cursor is at the desired position. When done hit `W' to write the window coordinate lists. The file photwins.dat will contain the list of windows in the order they were selected. Channel #1 will be the first entry, and so on. The other file, photwccd.dat, contains the list sorted in the CCD readout direction. This list must be sent to the camera controller to initialise the windowed readout. These two lists are vital to reconstruct the photometry windows when processing the data, so take care that they are not accidentally deleted.
    • The marked windows may not always appear as such, unless the image is scaled 1:1. You can check that the box markers are really there by moving the pointer to the field and watching the magnifier window in the upper right corner of the saoimage display.
    • The interactive saoimage display is slow. Be patient when the marker shows a bell. The cursor will jog back and forth between the terminal where you started saoimage and the saoimage display when the screen is updated. This is just saoimage doing its things. Try not to get confused.
    • See the phot guide for more info on the photometry window setup program.

  3. Start photometric imaging
    • First transmit the window list to the controller by hitting the `w'-key in the tcpcom window. Note that the "TRANSFER MODE" field in the top right corner switches from "FULL FRAME" to "PARTIAL FRAME". (Use the `t'-key to toggle it back to "FULL FRAME" when the fast photometry run is complete.)
    • Set a sequence time interval (`S'-key).
    • Hit the `i'-key. This will do a readout test to measure exactly how long time the current window setup will take to read out. After a few seconds the result is reported and the exposure time is set to the highest value possible with the given sequence time interval.
    • Start the sequence with the `s' key. Give the desired number of frames, or 9999 to run for ever (or until the sequence is aborted with the `a' key).

Now you should leave the tcpcom window alone until you want to abort the sequence. Frames will be retrieved and stored automatically. While tcpcom stores the window frames, you may process the results with the Real Time Photometry program, to get light curves of your targets.


How to exit the tcpcom program.

Before you exit tcpcom, make sure to put the transfer mode back to 'full frame transfer mode', using keystroke 't'. If you forget this, the standard ALFOSC CCD control program BIAS will hang once you make an exposure.

An alternative solution is to reset the CCD controller (staff only).