The Global Oscillation Network Group (GONG) Project is a community-based activity to operate a six-site helioseismic observing network, to do the basic data reduction, provide the data and software tools to the community, and to coordinate analysis of the rich data set that is resulting. GONG data is available to any qualified investigator whose proposal has been accepted; however, active membership in a GONG Scientific Team encourages early access to the data and the collaborative scientific analysis that the Teams are undertaking. Information on the status of the Project, the scientific investigations, as well as access to the data is available at www.gong.noao.edu.
The 1999 GONG annual meeting (GONG '99) will be held in Tucson, 22-24 March. We expect this meeting to provide a forum for discussion of work in progress to understand the physics of modes of moderate and high spherical harmonic degree, the data analysis methods needed to extract the appropriate description of their properties, and the physics of the solar interior that can be derived from them. We address scientific issues posed by both the ground-based and space-borne experiments. In view of GONG's 11-year observing, and strong support from the National Academy of Sciences' Study of Ground-Based Solar Research (Parker Committee) for the 10242 camera upgrade, the GONG Science Teams will work on the refinement of the high-resolution data processing that GONG+ should start providing in mid-2000.
The network of GONG telescopes has again demonstrated a great degree of reliability during the last quarter of 1998, with the vast majority of down time due to the scheduled preventive maintenance (PM) shutdowns: Udaipur (8 days in October), Learmonth (10 days in October), and Big Bear (8 days in November). For the first time, a single, two-person PM team made back-to-back visits to Udaipur and Learmonth (26 consecutive days), and although certain advantages were realized (e.g. minimized jet-lag), this will not likely be a common practice.
The Mauna Loa instrument was inoperative for approximately seven hours, due to a power outage which affected the entire observatory. The UPS kept the equipment running for an hour or so, but was unable to handle the prolonged blackout. Once the power was restored, the system resumed operational status. Various other system glitches and reboots were responsible for about three hours worth of lost images network-wide.
The mirror-fogging problem, which occurs primarily at Big Bear after a cold, damp night, has not been particularly bothersome so far this winter. This season has been much drier than previous winters; however, we would like to believe that the more frequent replacement of desiccant cartridges is helping solve the problem. The Big Bear staff are now replacing the desiccant when conditions warrant, superseding the less-frequent PM visits.
The lens-slide assembly (the mechanism that moves an additional lens into the light path for the purpose of obtaining calibration images), is showing some signs of age. We have had to call on the Big Bear staff on several occasions to apply a quick fix, and now, other sites are beginning to show signs of a potential problem as well. In response, we have incorporated a complete overhaul of the assembly (disassemble, clean, re-lubricate, and reinstall) into the PM task list. It is hoped that the added maintenance will solve this problem.
We rely greatly on our on-site staff to handle the failed equipment and to keep the network down-time to a minimum. The total number of images lost due to general hardware problems is equivalent to approximately nine hours of data (the exabyte drives are responsible for most of the hardware-related downtime). These hours reflect the total time that any site was inoperative regardless of weather conditions or whether another site was acquiring good images at the time.
We would like to welcome two ETS employees, Rich Lund, and Sang Nguyen, a former GONGster, into the operations group, each is working part-time for the project. They are working with the current instrumentation, both in-house and in the field, and have already begun to participate in the camera upgrade effort.
The p-mode reprocessing campaign (data that have been reprocessed or initially processed with the improved p-mode pipeline) added GONG months 1, 2, and 3, which were not previously processed, boosting the available data set to months 1-34 (950507-980911). Low-l time series and power spectra were produced from the first six GONG months and compared with the six-month power spectra that began with GONG month 4. Despite some concerns about angular registration during the startup of network operations, we are confident about the reliability of the spectra from the first six months, and believe that the month-long spectra are adequate for identification of mode frequency information. This effort completes the reprocessing campaign which began in mid-1997.
During the past quarter, month-long (36-day) velocity, time series, and power spectra were produced for GONG months 31, 32, 33, and 34 (ending 980911), with respective fill factors of 0.77, 0.85, 0.75, and 0.82. The project also produced tables of mode frequencies for GONG month 6, 9, 12, 27, 28, 29, 30, and 31. These mode frequencies were extracted from power spectra that was produced from 108-day time series.
Sean McManus joined the GONG Project on 18 November and will be producing global p-mode data products in addition to continuing the development of the Project's web-page.
The frequencies of the solar oscillations have now been determined for all nine independent 108-day blocks covering the period 28 September 1995 to 1 July 1998. During this time, solar activity has rapidly increased with the onset of cycle 23. The GONG measurements clearly show the expected increase in the basic frequencies of the oscillations, and in addition, it is now possible to detect very small shifts (a few nanoHz) at the very start of the new cycle. The GONG frequencies also show more subtle variations (of the so-called "even" splittings) that are well-correlated with the activity level, and which appear to be linked to the spatial distribution of the magnetic field.
The multi-taper spectral analysis is in the final testing stage. A random-restart test, which will verify that the determination of frequencies from multi-tapered spectra is insensitive to the initial guess, is underway. Once completed, multi-tapering will be included in the routine pipeline processing of the GONG spectra.
As discussed in the last Newsletter, we no longer temporally deconvolve the spectra. Instead, a scheme has been developed to correct the estimated line widths and amplitudes for the effects of an incompletely filled time series. The new algorithm was derived by comparing deconvolved and non-deconvolved spectra with varying temporal fill factors, and it works quite well. In fact, the results with this method indicate that it may be possible to measure solar-cycle related variations in the widths and amplitudes.
The leakage-matrix calculation has been greatly improved; however, it does not yet incorporate all known processing and observational effects: the modulation transfer function (MTF) and the vector nature of the oscillatory velocity field must still be implemented.
The Analysis Team has initiated the study phase for planning the development and rewrite of a new peakfind program, and because it is well-known that the step of determining the oscillation parameters is the most difficult stage in the data reduction process, this effort will not be taken lightly. In order to break new ground and avoid duplicating previous efforts, our current concept of the new algorithm will likely include the simultaneous fitting of multi-tapered spectra observed in velocity and intensity, an asymmetric line-profile model, explicit treatment of the leakage matrix, and a multi-dimensional fit.
Silicon Mountain Designs has delivered eight production cameras, and once tested and evaluated, the two cameras, which were originally purchased for the GONG Lab and Tucson shelter feasibility study, will be returned for modification. At this point, optical and electronic tests indicate that the performance is well within our specifications, except for a minor discrepancy regarding temperature regulation, which SMD is working hard to correct. In addition, DNA Enterprises has delivered the initial camera electronics prototype, which will boost our software development efforts, and they are proceeding with a beta version of the data acquisition software, with expected delivery in late-January.
In a parallel effort, we are proceeding with fabrication of two prototype data-caching chassis which will house the data storage peripherals. Upon completion of testing, these units will be installed at the Tucson facility, which will mark the beginning of the upgrade process.
The camera development team has been strengthened by the arrival of Tad Morgan, a real-time programmer, who will be helping to develop the software interfaces required by the new and upgraded hardware.
John Leibacher