The predecessors of the BIMA Xfiles were Unix C-shell (csh) scripts with command line interfaces. Tcl/Tk scripting allowed for rapid development of graphical user interfaces (GUIs). By leveraging existing programs rather than rebuilding everything from scratch, Tcl/Tk also allowed for rapid deployment. Observers familiar with the predecessor scripts quickly grasped the new functionality and appreciated the ease of use. By bundling together many previously separate tasks under a common graphical interface, these applications have made for a much more efficient and pleasant experience for the BIMA observer.
Before Xscribe, the BIMA schedule was composed simply by using a text editor. Time was allocated in an ASCII graph format and Scribe then parsed this into an observing program that drove the array. Scribe was Xscribe's predecessor, a Unix csh script which relied heavily on the awk and sed pattern matching utilities. This scheme was deployed for three years until it could not cope with new scheduling pressure.
The availability of 1mm receivers meant there was a need for dynamic scheduling. Successful 1mm observing requires lower atmospheric opacity and higher atmospheric stability than for 3mm observing. Because such conditions are unpredictable in the long term, 1mm observing cannot be scheduled a priori. Thus, when the atmospheric window opens and closes, there must be a scheme to efficiently substitute appropriate projects.
Xscribe addresses this need by rendering the schedule in a graphical editor. The Xscribe GUI is modeled as a tabbed notebook, with two primary pages for maintaining the schedule and summary of observations. Figure 1 shows the schedule page, which includes the graphical editor.
The schedule page also features a secondary tabbed notebook. There are pages here for exporting the Xscribe native graphic format into ASCII list, ASCII graph, and master script formats. The ASCII formats are automatically made available on the WWW. There is also a page for editing the project database, which lists priority and coordinate information.
The master script drives the array and launches an automated quality analysis after each project is done. Each archived quality report includes diagnostic plots in GIF format. The entire quality archive is accessible from Xscribe's summary page, shown in Figure 2.
The site observer by definition uses Xscribe on-line. At the start of an observing season, the BIMA scheduler sends two initial lists to the observatory: the schedule and project database. These templates are generated as part of the automated proposal pipeline at the University of Illinois. They are imported into Xscribe, after which the schedule and database evolve as the observing season proceeds.
Xscribe is flexible enough to set up for off-line users. For example, the program is installed for the BIMA scheduler at the University of Illinois. It has HTTP transfer capability so that off-line users may download the updated ASCII lists from the observatory and import them into the local Xscribe session.
Interferometric observations usually require a point source calibrator to be observed together with the science source. The goal is to remove time dependent atmospheric phase fluctuations. To reduce any direction dependent errors, the angular separation between the two targets should be minimal. At the same time, the calibrator should be sufficiently strong to satisfy signal to noise requirements.
To help make a decision, the BIMA calibrator database is plotted in the Xplore GUI, with both symbol color and size indicating flux strength. The scrollable viewport has an adjustable field of view. Clicking on a calibrator shows information such as specific flux and angular separation from the viewport center (science target position). A graph above the star chart shows how much the two targets overlap each other in terms of LST range.
If the Tcl/Tk extension BLT is available, then clicking on a calibrator will also show its flux history on a line graph. If the BIMA data analysis package (MIRIAD) is available, then planetary positions are calculated as well. These optional features again take advantage of external components and applications. Like Xscribe, Xplore is flexible enough to set up for off-line users. It has HTTP transfer capability so that the off-line user may download an updated calibrator database from the observatory.
Sensors continually monitor the array and the archived data are a valuable resource for diagnosing problems. Xplotwatch is a data mining tool. The Xplotwatch GUI allows the user to easily choose arbitrary combinations of antennas, sensors, and dates. The data are rendered as either antenna based or sensor based plots. The time (abscissa) axis may be a fraction of a day or several concatenated days, for studying short or long scale trends respectively.
Several critical sensors have an associated alarm. An alarm will trigger if the monitored data falls out of tolerance range. Often the problem cannot be repaired immediately. The Xfixwatch GUI may be used to selectively disable the alarm. The GUI allows any combination of sensors and antennas to be easily selected. It is also trivial to disable a given sensor for all antennas, or disable all sensors for a given antenna.
The most critical time of an observation is during the beginning. The Xaudio GUI offers a choice of entertaining sound effects which will be played when a project starts.
I am grateful to Rick Forster, Marc Pound, and Peter Teuben for enlightening discussions and encouragement. Thanks to the users of the BIMA Xfiles for their useful feedback.