NRAO NEWSLETTER

GREEN BANK

THE GREEN BANK TELESCOPE

Almost all of the effort on the construction site currently is directed toward preparing the R1 module for lifting out of the center portion of the BUS and onto the antenna box structure. This makes it possible to install a large guy derrick in the hole in the BUS left the R1 module. This derrick will be used to pick the BUS modules from the left half of the structure and lift them into the air where they will be transferred overhead to the main derrick which will then place the modules on the box structure. The modules on the right half of the structure will be lifted directly by the main derrick. Altogether, there are 22 modules in the BUS.

In addition, the horizontal feed arm is now complete, and the walkway to the vertical feed arm elevator platform is in place. Wiring to the elevation drives is almost complete. Servo testing of the upper feed arm is currently on hold awaiting the return of the subreflector actuator motors sent out for repair.

S.C. Smith

140 FOOT AVAILABILITY IN 1998

The 140 Foot is thus once again open for new telescope proposals. However, the "final" call for proposals earlier this year resulted in a demand which outstripped the available telescope time by a factor of about 2.5. The Telescope is fully subscribed for the remainder of 1997. A deadline of 3 November 1997 has been established for receipt of proposals for observations in the first half of 1998. There will be another deadline in the spring of 1998 for receipt of proposals for observations in the second half of 1998. Further information will be given in the next Newsletter and on the WWW. As always, proposals to make time-critical observations can be submitted at any time.

F.J. Lockman

VLBA/VLBI

SPACE VLBI: FIRST "HALCA" FRINGES AND IMAGES

The HALCA data in which we detected fringes were recorded at the NRAO OVLBI Earth Station in Green Bank, and received at the AOC on 5/27. A tape recorded for this observation at the Usuda tracking station, and tapes recorded at the Green Bank and Goldstone tracking stations in other test runs, were received subsequently.

For sixteen days, no fringes were detected in any of these tracking passes. Although extensive tests, reported in several previous NRAO Newsletters, had verified nearly all aspects of the correlator's Space VLBI capabilities, we disabled all of the functions except the spacecraft orbit, to ensure they were not somehow preventing detection of fringes. We could operate in this simplified mode in a few carefully selected cases, but still detected no fringes.

The most likely remaining cause appeared to be overall time-setting errors, at all of the tracking stations. Timing in Space VLBI is more difficult than in even the earliest ground-based VLBI observations, where one could ­ and the pioneers of this technique did, sometimes at great effort ­ bring an atomic clock along to establish the local time to sufficient accuracy. In Space VLBI, it is only possible to compute the time on the spacecraft, combining the propagation time to the tracking station with an additional instrumental component, potentially quite large, which depends on the details of all the equipment along the signal path. Some of the conceivable errors in determining this additional offset are much larger than any practical wide delay search in the correlator. Thus, it is essential that the tracking stations determine the offset extremely accurately.

The Green Bank tracking station became the first to do so, suggesting a new timing offset to be searched. This led immediately to detection of fringes, first in the observation described above, and within days in three other test runs for which Green Bank tracking passes were available.

Once having detected fringes, we proceeded immediately to correlate the entire tracking pass in which fringes to HALCA were first discovered. This pass includes only the phased VLA on the ground for the first two hours, which is then joined by the VLBA for a final hour. Despite this relatively sparse coverage, the combined data set was adequate to image the source, which had been selected for this fringe search from a set expected to be extremely compact and relatively strong. The observations indeed yielded an unresolved image of about 2.3 by 0.7 milliarcsec, with peak-to-sidelobe dynamic range of about 100 ­ the first image achieved by the VSOP mission. Such a point image is a strong verification that the entire Space VLBI system is functioning correctly.

With the new timing offset, we have also been able to correlate the entire Green Bank tracking pass in each of seven VSOP in-orbit tests observed through the end of June. One of these, with about 2.5 hours of Halca-VLBA baselines, has already yielded an image of 1156+295, showing a typical VLBI core-jet structure. A VLBA-only image from the same data reveals only a slightly extended single component. Another Halca observation of the same source four days later, involving six telescopes of the European VLBI Network in addition to the VLBA, nicely complements the (u,v) coverage from the original session, so that we anticipate being able to produce a high-quality image despite the limited Halca tracking available with only one tracking station.

Notes added in proof: On 97/7/8, the VLBA correlator detected its first fringes to Halca via the Goldstone tracking station. On 7/9, we detected the VSOP mission's first fringes at 5 GHz, also via Goldstone, and on 7/10 our first fringes via the Usuda tracking station, again at 5 GHz.

J.D. Romney

A VLBI PUBLICATION SPEED RECORD

J.M. Wrobel

VLBI NETWORK CALL FOR PROPOSALS

It is expected that European VLBI observing during the next year will be dominated by observations with the VSOP satellite.

It is recommended that proposers use a standard cover sheet for their VLBI proposals. Fill-in-the-blanks TeX files are available by anonymous ftp from ftp.cv.nrao.edu, directory proposal or via the VLBA home page on the WWW. Printed forms, for filling in by typewriter, are available on request from Betty Trujillo, AOC, Socorro.

Any proposal requesting NRAO antennas and antennas from two or more institutions in the European VLBI network constitutes a Global proposal. Global proposals must reach both Network's Schedulers on or before the proposal deadline date; allow sufficient of time for mailing. In general, fax submissions of global proposals will not be accepted. Proposals requesting use of the Socorro correlator must be sent to NRAO even if they do not request the use of NRAO antennas; proposals for the use of the Bonn correlator must be sent to the MPIfR if they do not request the use of any EVN antennas. For Global proposals, or those to the EVN alone, send proposals to:

R. Schwartz
Max Planck Institut fur Radioastronomie
Auf dem Hugel 69
D 53121 Bonn
Germany

For proposals to the VLBA, or Global proposals, send proposals to:

Director
National Radio Astronomy Observatory
520 Edgemont Road
Charlottesville, VA 22903-2475
USA.

Proposals may also be submitted electronically, in Adobe Postscript format, to proposevn@hp.mpifr-bonn.mpg.de or propsoc@nrao.edu, respectively. Care should be taken to ensure that the Postscript files request the proper paper size.

B.G. Clark

REQUEST FOR VLBA IMAGES

Images are sought on the basis of visual appeal and scientific significance. While striking visual impact helps for public-education and media purposes, we also want images that illustrate important scientific advances as well as those that show a variety of astronomical phenomena as seen with VLBI resolution. We prefer images in the form of FITS or PostScript files. For caption information, please give either a brief description or a reference to a published description.

For information, and to arrange a file transfer, contact Dave Finley at the AOC ((505) 835-7302 or dfinley@nrao.edu).

D.G. Finley

VLA

VLA CONFIGURATION SCHEDULE

The maximum antenna separations for the four VLA configurations are: A-36 km, B-11 km, C-3 km, D-1 km. The BnA, CnB, and DnC configurations are the hybrid configurations with the long north arm, which produce a round beam for southern sources (south of about -15 degrees declination).

Approximate Long-Term Schedule

Observers should note that some types of observations are significantly more difficult in daytime than at nighttime. These include observations at 327 MHz (solar and other interference; disturbed ionosphere, especially at dawn), line observations at 18 and 21 cm (solar interference), polarization measurements at L band (uncertainty in ionospheric rotation measure), and observations at 2 cm and shorter wavelengths in B and A configurations (tropospheric phase variations, especially in summer). They should defer such observations for a configuration cycle to avoid such problems. In 1997, the D configuration daytime will be about 16^h RA and in 1998 the A configuration daytime will be about 0^h RA.

Time will be allocated for the VLBA on intervals approximately corresponding to the VLA configurations, from those proposals in hand at the corresponding VLA proposal deadline. The first observations with the VLBA and the HALCA long-baseline interferometry satellite were done in May, and increasing amounts of observing time will be devoted to this through the summer, approaching a long term average of about 30 percent of VLBA observations devoted to space VLBI.

Any proposal requesting NRAO antennas and antennas from two or more institutions affiliated with the European VLBI network is a Global proposal, and must be sent to the EVN scheduler as well as to the NRAO. VLBA proposals requesting only one EVN antenna, or requesting unaffiliated antennas, are handled on a bilateral basis; the proposal should be sent both to NRAO and to the operating institution of the other antenna requested. Coordination of observations with non-NRAO antennas, other than members of the EVN and the DSN, is the responsibility of the proposer.

B.G. Clark

AOC COMPUTING STATUS

Installation of a dedicated SPARCstation IPC as our WWW and anonymous ftp server is imminent. We urge users to access these sites using the generic "www.nrao.edu" and "ftp.aoc.nrao.edu" addresses, which will make the actual switch transparent.

Local computer support at the AOC received a boost when we hired two new people: Tom Wilson will be responsible for further developing our Web site, for supporting visitors and staff in areas related to non-NRAO software systems (IRAF, IDL, TeX, etc.), and in lending programming support to projects such as the VLA archive project. Victor Kiff joins the systems support staff. His arrival enables us to streamline contact between users and system staff. We have devoted one office to user support and have introduced a generic "nmhelpdesk" account for visitors and staff to receive prompt help.

G.A. van Moorsel

NRAO 1998 SYNTHESIS IMAGING SUMMER SCHOOL

The school will entail a week of lectures on aperture synthesis theory and techniques at a level appropriate for graduate students in astrophysics. Practical tutorials demonstrating data collection, calibration, and imaging of both VLA and VLBA data will be given.

There will be a nominal registration fee, sufficient to cover only the cost of the meeting. Our budget is unable to provide financial support for attendees. Lodging for participants will be at local motels.

G.B. Taylor, C. Carilli, & T. Hankins

12 METER

12 METER TELESCOPE PARTICIPATION IN THE MARS PATHFINDER AND GLOBAL SURVEYOR MISSIONS

J.G. Mangum

MAJOR SUMMER SHUTDOWN PROJECTS AT THE 12 METER TELESCOPE

(1) Dome inspection and repair.

(2) Automation enhancements to receiver tuning software.

(3) Installation of the central cold load calibration system.

(4) Installation of a new digital phase lock system.

(5) Improvements to the receiver and IF system to increase continuum sensitivity.

J.G. Mangum & D.T. Emerson

ON-THE-FLY ANALYSIS AT NRAO TUCSON

J.G. Mangum

IN GENERAL

MILLIMETER ARRAY

The second significant development of the last quarter was a meeting held in Charlottesville to discuss the feasibility of merging the MMA and the European Large Southern Array (LSA) into a common, joint project. Both projects have been studying potential sites in Chile. Although the projects have somewhat different scientific emphases, it is clear that both projects have requirements for outstanding sites and could realize cost saving were they to share a common site. Could we envision a single array on this common site that would satisfy the scientific goals of both communities? For two days delegations representing the LSA and the MMA discussed the possibilities.

The two groups agreed that if a common array were to encompass the scientific scope defined by both the LSA and the MMA, it would of necessity be larger than either project alone. Further, it was agreed that there is much to be gained scientifically with such an array. The delegations resolved to form a partnership to explore the union of the two projects. Specifically, the partnership will study the technical, logistical, and operational aspects of a joint project. Of particular importance, the two antenna concepts currently under consideration in the U.S. and Europe will be studied to identify the antenna size and design, or combination of sizes, best able to address the scientific needs of the two communities. Working groups have been organized that utilize the expertise in each community's research institutions and universities to explore the issues associated with a merger of the LSA and MMA. The working groups are to report and a decision taken on proceeding to the next steps toward a joint project by the end of the year. Finally, both delegations recognized the importance of the Japanese plans to build the Large Millimeter/Submillimeter Array (LMSA) and agreed that cooperative activities with the LMSA should and would continue.

R.L. Brown

USERS COMMITTEE MEETS

The Committee expressed its concern that the loss of the Brookhaven National Laboratory operating contract not affect AUI's Cooperative Agreement with the NSF for operation of the NRAO. The Committee strongly endorsed the continued management of the NRAO by AUI.

The Committee asked that the policy regarding user-built instrumentation be re-stated to make it clear to all users under which conditions observing equipment custom built by individual users would be maintained by the Observatory and made available to all users.

The Committee strongly endorsed the report of the Bridle Committee on policies regarding large scale observing proposals.

The Observatory was encouraged to continue the tradition of open communications with its user community and to press on with the current effort to improve the availability of documentation, reports, technical memos, manuals, etc., on the WWW.

The Users Committee also wanted to express its strong interest in seeing that NRAO improve its educational outreach activities, i.e., to explain why the science done with radio telescopes is important to society.

Support for the operation of the 12 Meter Telescope is strong. NRAO was encouraged to keep the 12 Meter running until the Millimeter Array (MMA) begins operation or there is general access for U.S. observers to an alternative large aperture single dish millimeter telescope. The Committee asked for a plan to be published that would make clear the future course of operations of the 12 Meter. The Committee was pleased to see progress on receiver systems, even though progress is slow on many projects due to lack of personnel. On-The-Fly mapping was noted as a particularly significant advance in capability, one that should also be implemented on the Green Bank Telescope (GBT). The construction of a new spectrometer was endorsed and the synergy with that for the GBT was noted. Expansion of the time allocated to millimeter wavelength VLBI was strongly encouraged.

The Committee expressed its disappointment in the delays in completing the GBT. At the same time, the Observatory was encouraged to expand the number of scientists in Green Bank, plan for first science by sponsoring a workshop, and continue to test GBT systems and train personnel on the GBT instrumentation mockup to minimize the time required for telescope commissioning. Concerns over the stability of the fiber optic IF transmission system are fading now that initial tests of a gain control system show it to be successful. NRAO was urged to continue operation of the 140 Foot, with more general observing in addition to the orbiting VLBI support that was planned, until the completion of the GBT.

The Committee noted the usefulness of the Very Large Array (VLA) sky surveys, the new capability the Q-band receiver system has enabled, the project to widen the IF bandpass from 50 to 80 MHz, the prospect of 74 MHz receivers with Naval Research Lab support, and the near-completion of the new archive of all VLA data. They suggested the Socorro on-line reservation system for visitors be implemented at the other sites. The Committee strongly urged that the VLA OBSERVE program be upgraded, as a high priority. The plans to hold an Imaging Synthesis Summer School (17-19 June 1998) were noted with hopes that use of the AIPS++ imaging processing system would be included.

NRAO was encouraged to continue the effort to improve the Very Long Baseline Array (VLBA) operating efficiency. Strong encouragement was given to implementing dynamic scheduling. The switch to using only thin tape for recording data to be correlated with the VLBA correlator was endorsed. The Committee is pleased to see initial progress on the pulsar gating mode, called for implementation of a burst mode, urged that an improved amplitude calibration process be finished soon, and expressed hopes that fringes would be detected in orbiting VLBI (HALCA) data.

The Committee gave a high priority to developing plans for a VLA upgrade, bringing the 1970s era electronics to the level expected in the 21st century, improving the antennas, and adding antennas to fill in the uv-spacings intermediate to those of the VLA and VLBA. Current proposals pending at the NSF to complete the Q-band system and to link the Pie Town VLBA antenna in real time to the VLA were noted with the hope that matching funds and Foundation approval would be forthcoming.

Improvements in computing hardware capability available to users during the past year were noted as well as improvements in networking. NRAO was encouraged to continue to replace aging computers with modern machines. The Committee expressed a willingness to endure the inconvenience that implementation of better computer security measures would impose.

The Committee noted the importance of AIPS and the improvements that have been made in AIPS. Much of the improvements have gone into CPU-heavy tasks such as IMAGR; the Committee would like to see more effort in interactive tasks as well, for example, TVFLAG and LISTR. The Committee was pleased to hear that an effort is being made to address parallelization of AIPS routines to take advantage of RISC multiprocessor architectures. Strong encouragement was given to developing a plan for merging AIPS and AIPS++.

The Committee applauded the progress in AIPS++: a limited beta release, implementation of several synthesis imaging tasks, use of AIPS++ as a base for the Parkes multi-beam and telescope control and analysis software. It was suggested that beta tester workshops be held in Socorro to bring together the programmers and expert users. A number of specific items were noted for improvement in the next release. The Committee was excited over the possibility of including in AIPS++ an AIPS wrapper that would allow an AIPS++ user access to the full functionality of classic AIPS. The Committee was disappointed to see that no published scientific paper has yet to appear based on data analysis using AIPS++. It recommended that there be more easily accessed management information, that development of documentation continue, and that documentation be maintained in an easily accessed, web-browsable fully-indexed data base. It was the Committee's stated opinion that user efforts to test AIPS++ should be matched by efforts of the NRAO staff scientists.

The Committee was pleased to see a request for funding of a design and development phase of the MMA in the NSF proposed budget for 1998. The Observatory was urged to follow through with its plans to pursue this development phase with the involvement of the university millimeter astronomy groups. The recommendation that the MMA be sited in northern Chile was strongly endorsed. The Committee was concerned that the prospects for finding international partners might not be all that good, given economic conditions abroad, and urged the NRAO to approach the NASA Origins program. There is an obvious strong overlap in scientific goals between those of the MMA and Origins. It was hoped that the next Decade Report would highlight the MMA and NRAO was encouraged to hold a science workshop in preparation for the upcoming decade review.

The Committee noted the value of the technology development done in the Central Development Laboratory, a continuing flow of mixers, amplifiers, and other devices that advance the state- of-the-art. Involvement in the MAP project has strained the lab and delayed delivery of devices for other projects, but it was felt the involvement was worthwhile in the return of a better infrastructure for the lab and the development of amplifiers useful to all of radio astronomy.

NRAO was encouraged to continue its efforts in spectrum management. Of particular importance are the tests to be conducted with the Motorola Iridium project. In these matters, the Committee urged the NRAO to interact regularly with other observatories in establishing policy.

Don Backer will chair the Committee for its 1998 meeting.

R.S. Foster, Chair Users Committee

(Naval Research Laboratory)

AIPS++ STATUS

T.J. Cornwell

NRAO JANSKY LECTURE AND SYMPOSIA

E.R. Schulman, J.J. Wiseman, & R.A. Perley

VLA PROJECT HONORED BY NEW MEXICO ENGINEERS

D. G. Finley