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Observing Overview: Taking the Data

The Only Command You Really Need: observe

With the ARCON software, one takes data with a single command: observe. The astronomer will be prompted for the information necessary for controlling the exposure. This includes the following:

An example of taking a 300 second object exposure is shown in Figure 1. Note that in each query the user is also presented with a default value that s/he could invoke simply by hitting [CR]; these default values are just the previous entries. Once the title is entered, the user is informed what the name of the image will be; this name can either consist of the exposure type as a root name (such as ``obj") with a consecutive number attached, or of a single root name (such as ``n1") with a consecutive number appended, depending upon how the obspars parameters are set.

If all goes well, the user will be given a one-line reminder of what the image name will be, followed by a one line ``status" report, which gives the CCD name (MM2 in the case of the WIYN Mini-Mosaic), the format, the binning, and the gain setting.

NOTE: All observing commands must be issued from the ``DATA ACQUISITION window" and NOT from the ``DATA REDUCTION" window. We will describe these windows later.

Useful Windows: Exposure in Progress!

As the exposure progresses, the alert observer will notice several other windows of potential interest. In the upper left corner the exposure time will begin counting down, displayed in easy-to-read large green lettering.

Another window of interest is the ``ARCON Status" window, also in the upper left, which shows which picture is in progress, the dewar temperatures, how many pictures remain in the sequence, and a status of what is happening. (``INTEGRATING", ``READING", or ``CONTINUOUSLY_ERASING".)

There is also a long skinny window listing the 8 filters loaded into the filter wheel, with the current filter high-lighted. Although it looks tempting to try to change filters by clicking on this window, that will not work.

Coming to the End

At the end of the exposure, several things will occur:

On the other monitor, you will find the ``DCA Console Monitor" and a standard IRAF ximtool window.

The ``Data Capture Agent" (DCA) is the means by which the data is ``captured" from the ARCON CCD controller and moved to the user-friendly IRAF environment. Of interest in the DCA Console is the image file name, the filter name in use, and the fraction of the image that has been captured, and the amount of disk space you've used. Depending upon the exposure type, the DCA will see to it that appropriate ``on-the-fly" reductions are done to make the display in the ximtool more meaningful. For instance, an ``object" exposure will have a bias level subtracted and then divided by one of the standard flat-field exposures of the appropriate filter. This is all done purely for display purposes; your data are not actually altered in any way. The image will be displayed in the ximtool as the data is captured, so that shortly after the read-down completes you can have a very good impression of what your data actually looks like.

Doing More with more

Did you like that last exposure and want to do some more just like it? There is a command to help you out: more. To do two more exposures with the same parameters (exposure type, filter setting, telescope setting, exposure length, title) of the previous observe command, do a

more 2

and you will be told what images are being written to disk.

DOOBS: Your Way to Easier Data Collection

Often you may wish to execute a series of exposures through various filters and of various times. Perhaps you know that you want a series of 5 exposures of the dome flat through each of 3 filters, each with a different time.

You could also use doobs on a series of object exposures; however, it would require you to enter the relative focus offset you desire, corresponding to each filter in the parameters for wheel1. This is one of the unresolved issues described later; we will revise this when it is working correctly.

A sample run is shown in Fig. 2.

Interrupting, Changing, or Terminating an Exposure

The ARCON software allows you to pause and resume an exposure, change the exposure time, or terminate an exposure right then, with the following commands:

In the event that you have asked for a series of integrations (either by using more or by specifying multiple exposures via the observe command, stop and abort will end the entire series. The tchange command will operate only on the current image, and not affect subsequent exposures in the sequence; i.e., if you change the exposure time of the second exposure of a series of five dome flats from 60 sec to 30 seconds, the third, fourth, and fifth ones will exposed for 60 sec. Thus if you are really unhappy with the exposure times, you will need to use stop or abort and reissue the observe command.

How to Get Help

IRAF comes with on-line documentation that gives the nitty-gritty of each command. Simply type help more to see the help page for the more command. You can get a hard-copy of this help page by directing the output to the laser writer:

help more | lprint


Next: The Parameters Files
Previous: Introduction
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Thu Aug 24 09:59:47 MST 2000