Please accept the following for the aips quarterly report. It's actually a mix of the last two quarter's worth. AIPS quarterly report, 06 April 1998 ------------------------------------ Personnel An agreement outlining the steps in a transition between AIPS and aips++ was reached in early 1998. Distribution 15OCT97 The 15OCT97 version of AIPS has been distributed to 76 sites, running 184 installations (including Solaris, Linux, DEC Alpha, HP and SGI versions). The majority of AIPS distributions are now by ftp. At present it is planned to release 15APR98 in mid April. 15APR98 In August 1997 the decision was made to incorporate Eric Greisen's Charlottesville Experimental Version of AIPS (CVX) as the next version of AIPS after 15OCT97, becoming the 15APR98 version. Extensive testing of the 15APR98 version in Socorro and Charlottesville identified a a modest number of bugs in the new version, some of which were also in previous versions. Some of the improvements found in the 15APR98 version are several new interactive and non-interactive data editing tools (some of which had been ported to 15OCT97 previously), improved bandpass calibration methods, improved tools for examining the quality of calibration, and enhancements to the interactive imaging/self-calibration tasks. New algorithms to allow single-dish beam-switched continuum imaging were included, as well as enhancements to the 12m spectral-line on-the-fly imaging. Solutions to the Y2K problem, remote display capability, and data files in excess of the classical 2-Gbyte limit (also available in 15OCT97) have all been implemented into the 15APR98 version. Non-coplanar imaging has been added to the basic imaging task IMAGR. Previous imaging tasks, when making images well away from the original phase-tracking direction, corrected phases to the center of the image, but did not re-project the interferometer coordinates. The 15APR98 version of IMAGR allows a "3D" option in which the interferometer coordinates are re-projected so that all fields imaged are tangential to the celestial sphere. Hardware performance Recent hardware performance tests yielded some promising results. The latest version of g77 does a significantly improved job of optimization during the f2c conversion and the C compilation (our theory), resulting in significant performance improvements. On the standard "DDT" test, a Pentium Pro 200 (dual-processor) went from 3.6 AIPSMarks under f2c to 6.7 AIPSMarks with g77. On a well-equipped Pentium II 300MHz PC, the results went from 4.6 to 9.6 AIPSMarks. Sun's Ultra 5 (low-end) computer was found to give 4.3 AIPSMarks while an Ultra 30 gave 10.0. Full results of all recent AIPS benchmarking can be found via the AIPS homepage. Documentation The VLBI chapter in the `AIPS Cookbook' user manual was completely revised, to include extensive documentation on the use of AIPS for Space VLBI data analysis. New understanding, developed as work with VSOP observations proceeds, is being incorporated continuously into an electronically-accessible version. General developments A Van Vleck correction has been added to FILLM. Initial tests show a substantial decrease in artifacts for very bright, extended sources. Parallelization We are currently introducing support for shared-memory multiprocessor machines into the AIPS computational libraries. FRING has been adapted to take advantage of more than one processor and shows significant savings in execution time when multiple processors are used. Our initial parallelization efforts are targeted at the SGI Origin series of computers, taking advantage of NRAO's Origin 200. Code written for SGI's machines can easily be adapted to run on machines that support the OpenMP standard. Many of the changes required to support parallel execution have also proved to be beneficial on single-processor systems so that all AIPS users can be expected to benefit from the parallelization initiative. Real-time VLA data filling The possibility to fill VLA data in real time remains a popular method for AOC-based users to inspect and reduce their data rapidly. In 1997, some new bugs were fixed, increasing the general robustness of the system. Cause for concern is the limited bandwidth between the VLA and the AOC, which remains an obstacle preventing large spectral line data sets or high time resolution continuum data sets to be filled in real time without loss of data. The August 1997 upgrade of the operating system software on the real time FILLM server at the VLA site uncovered a severe problem with filling VLA data in real-time. Small packets from the VLA real time computers would intermittently hang the visibility server on miranda and any on-going or subsequent FILLM's would not get visibility data. This problem was resolved at the beginning of November 1997. Space VLBI Developments in AIPS Most of the Space VLBI enhancements to AIPS had been completed and tested, as extensively as possible using simulated Space VLBI data, prior to the launch of Halca. AIPS was used effectively throughout the initial fringe-search phase. Later stages of data analysis -- calibration and imaging -- appear to function normally for Space VLBI observations, at least superficially, and were used with some success to produce a number of images from early VSOP observations. Careful study of the imaging stage, including development of optimal techniques for using the AIPS imaging tasks, however, is just beginning. Over the past year we have added facilities for storing the position of orbiting antennae with AIPS data. The position and velocity vectors of the satellite may be tabulated as a function of time in an orbit (OB) table, together with several derived quantities such as the orientation of the antenna, and mean orbital elements may be stored in the antenna (AN) table. Several AIPS tasks, including OBEDT, UVFIX, and VPLOT, can make use of the data stored in these tables HALCA has a relatively small dish collecting area and a high system temperature compared with ground-based antennae. Combined with the fact that sources are more highly resolved on longer baselines, this means that the signal is usually weak on ground-space baselines. In some cases it may be necessary to add the signal from several baselines (using closure relations) to find fringes to the space antenna. This technique has always been available in FRING but has also been incorporated into the baseline-oriented fringe fitting program BLING during the past year. BLING has also been made more efficient (its run-time performance has improved by more than an order of magnitude) and has been adapted to cope with the large ranges of delay and rate that must searched in some space VLBI experiments.