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U. S. Naval Observatory Washington, D. C. 20392-5420 ued to advance for The Astronomical Almanac and Astro- nomical Phenomena. The Astronomical Almanac for 2001 was published at the earliest date in over 15 years. Proceed- I. PERSONNEL ings of the U.S. NAO Sesquicentennial Symposium, held last A. Civilian Personnel year, were published during this reporting period. USNO Circular 178, ‘‘List of Active Professional Observatories,’’ Retirements included Alan Bird. by M. Lukac and R. Miller, went to press in June 2000. Tom Corbin retired on Oct. 2, 1999 after a 35-year career Exchange of material also continued with both the Institut de at USNO. F.S. Gauss retired on 2 June, after a 37-year career Mechanique Celeste ͑France͒ and HMNAO. at USNO. A major effort to streamline almanac production is ongo- ing within the NAO. S. Stewart continued to review, docu- B. DoD Science and Engineering Apprenticeship ment, upgrade, and standardize production of Sections E and Program HofThe Astronomical Almanac, as well as documenting the rest of the sections prepared by the U.S. NAO. This infor- The USNO summer intern program for high school and mation and the status of all publications are now on-line college students continued in the summer of 1999. This pro- within the department for easier access and timeliness. Al- gram, called the Science and Engineering Apprentice Pro- manac production software is being moved into an auto- gram ͑SEAP͒, is sponsored by the Department of Defense mated version control system for the purposes of standard- ͑DoD͒ and managed by George Washington University. For ization and archiving. Fiala, M. Stollberg, and Stewart the summer of 2000, the interns, and the departments they continued to convert preparation of page copy from several worked in were: Shawnette Adams ͑Public Affairs͒, Laura software packages to one standard. This has greatly reduced Briskin ͑Time Service͒, Brian Grefenstette ͑Astrometry͒, preparation time. Miller successfully modernized several an- Arthur Hyder ͑Time Service͒, Dean Kang ͑Library͒, Tracy tiquated production procedures, including production of the Klayton ͑Astrometry͒, Steven Movit ͑Astrometry͒, Howard Air Almanac sky diagrams. He also greatly improved ex- Schindel ͑Time Service͒, Diana Seymour ͑Astrometry͒, change of documents and page copy with the British office Henry Smith ͑Astrometry͒, Sabrina Snell ͑Astronomical Ap- by electronic means. Quality control and consistency were plications͒, Lim Vu ͑Earth Orientation͒, Lillian Whitesell emphasized—especially by Lukac, Stewart, and Miller— ͑Astrometry͒, and Sarah Zelechoski ͑Earth Orientation͒. with the entire department staff assisting in the effort. Under the NSF Research Experience for Undergraduates Implementation of plans for major revision of The Astro- ͑REU͒ programs. S. Levine hosted A. Reiffel ͑Yale Univer- nomical Almanac continued. In meetings between staffs of sity͒. the U.S. NAO and HMNAO, it was agreed that the Interna- tional Celestial Reference System ͑ICRS͒ and new funda- II. ASTRONOMICAL APPLICATIONS mental ephemerides of the solar system will be introduced no DEPARTMENT earlier than the edition for 2003. There was much discussion The department continued to perform its core mission of of the contents of Sections F ͑Satellites of the Planets͒ and G providing practical astronomical information and data via ͑Minor Planets and Comets͒, and the possibility of exchang- printed publications, software products, and the World Wide ing responsibilities for their preparation. Web, while maintaining a modest research program in dy- A survey of users of Astronomical Phenomena was dis- namical astronomy to meet future needs. The department’s tributed with the edition for 2002, and will close next year. products were used by the U.S. Navy, other components of An audit of the distribution list of publications on exchange the U.S. government, the international scientific community, was begun, also to close next year. The information will go and the general public. J. Bangert continued to serve as de- into a database to make future distributions more accurate partment head. and timely. The survey of users of The Air Almanac was completed. The percentage of return was rather low, but the A. Almanacs and Other Publications comments were very informative and indicate that the pub- The Nautical Almanac Office ͑NAO͒ continued to be re- lication in its present form will be needed for at least another sponsible for the printed publications produced by the de- 5-10 years by some portion of the users. The feasibility of partment. The NAO continued its collaboration with Her providing this publication in electronic format, such as Por- ͑ ͒ Majesty’s Nautical Almanac Office ͑HMNAO͒ of the United table Document Format PDF files, is being investigated. Kingdom, to jointly publish The Astronomical Almanac, The Nautical Almanac , The Air Almanac, and Astronomical Phe- B. Software Products nomena. A. Fiala, as Chief of the NAO, supervised the USNO portion of this work. G. Kaplan assumed the role of The Product Development Division, headed by N. Oliv- Acting Chief following Fiala’s retirement in June 2000. ersen, continued to be responsible for the department’s soft- During the reporting period, the almanacs for 2001 and ware products. Astronomical Phenomena for 2002 were published. The next STELLA ͑System to Estimate Latitude and Longitude As- annual editions are in preparation. Publication dates contin- tronomically͒, a celestial navigation software tool developed 634 ANNUAL REPORT specifically for the U. S. Armed Forces, continued to be Murison completed a survey of the dynamics of inner widely used throughout the U.S. Navy and Coast Guard. The solar system asteroids. He also investigated the effects of version of STELLA currently in use by the fleet ͑version 1.1͒ asteroid ‘‘noise’’ on the motions of the inner planets. As part is a DOS-based system that is valid through 2004. By the of this investigation, he determined the asteroid mass distri- end of the reporting period, W. Tangren, W. Hultquist, and bution of the main and outer asteroid belts as functions of Oliversen nearly completed development of a new version of position and asteroid diameter, as well as the azimuthally STELLA, specifically designed for Microsoft Windows op- averaged radial distribution. From numerical integrations of erating systems ͑i.e. Windows 95/98, and NT 4.0ϩ͒. The the 310 asteroids with diameter greater than 85 km, Murison new version, STELLA 2.0, retains all of the basic function- found in power spectra of the motions of the inner planets ality that was present in STELLA 1.1, but now features that asteroid noise effects consist of three components: domi- many improvements to the user interface and better integra- nant perturbations from a small number of large asteroids, tion of the component services. P. Janiczek ͑USNO, retired͒ intermediate effects of a few dozen of the next largest aster- is developing the user manual for STELLA 2.0 and con- oids, and a smooth noise background due to many small- ducted extensive tests of pre-release versions of the software. diameter asteroids. Time delay mappings vividly illustrate Kaplan and Bangert also made contributions to the design the destruction of hypersurfaces in phase space due to aster- and evaluation of the product. It is expected that STELLA oid perturbations. 2.0 will be released to the fleet in fall 2000. In related work, Hilton is working on a model to improve Version 1.5 of MICA ͑Multi-year Interactive Computer the ephemerides of the inner solar system planets by replac- Almanac͒, covering the years 1990-2005, continued to be ing all but the largest members of a family of asteroids with distributed for USNO by Willmann-Bell, Inc. ͑http:// a ring of matter whose properties are determined by the size www.willbell.com͒. Significant progress was made in design distribution and proper elements of the family. and development of the next major revision of MICA. MICA Kaplan continued a collaboration with B. Mason and W. 2.0 will feature full Windows compatibility, a revamped user Hartkopf ͑Astrometry Department͒ and K. Aksnes ͑Univer- interface, and many new capabilities. W. Harris added code sity of Oslo, Norway͒ in a project to obtain high-precision to the Cϩϩ computational engine to support a number of relative astrometry of the Galilean satellites using speckle new features, including dates and times of moon phases, lo- interferometry. The USNO speckle camera was improved cal circumstances of eclipses and transits, and other phenom- this year and now has a 10-arcsecond field of view. Speckle ena of solar system bodies. He also made substantial observations can be obtained whenever any two satellites are progress designing the prototype user interface. within this field, although the sharpness of the speckle auto- Minor revisions were made to the C version of the Naval correlation function depends on the separation and the see- Observatory Vector Astrometry Subroutines ͑NOVAS͒ as- ing. The data reduction for several events is proceeding and trometric software package. The current version numbers at some calibration issues are under investigation. the end of the reporting period were 2.0.1 ͑C͒ and 2.0 ͑For- Murison worked on a detailed analysis of the spin dynam- tran͒. These versions of NOVAS support data that conform ics of the FAME astrometric satellite, which was approved to the ICRS as well as to the FK5 system. NOVAS is avail- for NASA funding in September with a projected launch date able for download from the AA department Web site ͑ http:// of June 2004. Following up on an idea by R. Reasenberg aa.usno.navy.mil/AA/software/novas/novas_info.html͒. ͑Harvard/Smithsonian͒, Murison showed how solar radiation pressure, acting on a conical sun shield, could be used to C. Dynamical Astronomy drive the precession of FAME’s spin axis. This use of solar radiation pressure eliminates the need for thruster firings as The Dynamical Astronomy Division, headed by Kaplan, the driving mechanism for the spacecraft’s precession. Muri- maintained a research program in dynamical astronomy son extended his analysis to include solar wind and solar aimed at meeting the department’s future needs and the re- irradiance fluctuation effects on FAME’s spin dynamics. He lated needs of other activities at USNO. incorporated solar irradiance data from the Solar and Helio- M. Murison and J. Hilton continued development of New- spheric Observatory’s VIRGO instrument into the numerical comb, a new high-precision solar system ephemeris program FAME spin dynamics program, and computed the effects of that incorporates object-oriented programming. Progress on the irradiance variations on FAME stellar observations. A Newcomb slowed considerably this year because of Muri- quantitative analysis of these effects was important in the son’s increasing involvement with the FAME astrometric development of a realistic FAME error budget. satellite project ͑see below͒. Hilton completed the part of the Hilton continued work on modeling the effect of indirect Newcomb code that carries out conversions among the six solar radiation on the orbital motion of GPS satellites, spe- different time scales that are used in ephemeris work, and is cifically, radiation reflected off the Earth or refracted through now near completion of the code that computes apparent the Earth’s atmosphere. He is in the process of creating a spherical coordinates of solar system bodies for comparison reflection model of the Earth. with optically determined positions. Murison continued his collaboration with J. Chambers D. World Wide Web Site ͑Armagh Observatory, UK͒ on deriving optimized symplec- tic integration methods. Their work on symmetric integrator The department’s Web site ͑http://aa.usno.navy.mil/AA/͒ algorithms was published in The Astronomical Journal. evolved into an essential mechanism for disseminating astro- Murison continues to work on the nonsymmetric cases. nomical information and data to the user community. Every- U.S. NAVAL OBSERVATORY 635 one on the scientific staff contributed content and support to III. TIME SERVICE DEPARTMENT the site. Murison continued to serve as Webmaster. Demand A. Master Clock Operations for the information and data provided on the site grew sig- nificantly during the reporting period. During peak months, L. Schmidt investigated long-memory statistical processes the site averaged nearly 10,000 user sessions per day. During to determine their applicability to clock data collected at ‘‘normal’’ months, this figure dropped to about 7,000 user USNO. Historical clock models have utilized fractionally in- sessions per day. Furthermore, the department’s site was se- tegrated processes to characterize additive clock noise; thus, lected for addition to the recommended resources on Science she investigated the feasibility of extending these models to a NetLinks, a comprehensive homepage for science educators more general class of fractionally integrated processes. Esti- created by the American Association for the Advancement of mation techniques which make use of the underlying corre- Science ͑AAAS͒. The review of the department’s site states, lation structure of the clock data were analyzed and several ‘‘The...Astronomical Applications Department has done simulations were conducted. Initial results are promising, an excellent job making the dry pages of numerical informa- and work continues. tion of the Nautical Almanac come alive in interactive L. Schmidt determined that the difference between Two- form.’’ Way Satellite Time Transfer ͑TWSTT͒ and fiberoptic cable New features added to the site during this reporting period measurements of Master Clock #2 - Master Clock #3 ͑MC2 included an interactive database of asteroid orbital elements, - MC3͒ is strongly correlated with outdoor temperature fluc- an interactive Julian date converter, algorithms for comput- tuations, and initiated GPS Common-View ͑CV͒ time trans- ing approximate solar coordinates, an improved FAQ and an fer between MC2 and MC3 to enable the temperature depen- expanded date range for calculating moon phases, and infor- dence to be attributed to either TWSTT or fiberoptic cable. mation on the November 1999 transit of Mercury. Since the CV data have become available, however, outdoor The department staff continued to answer questions re- temperature has stabilized and a conclusion is not yet avail- lated to the department’s mission, submitted by e-mail from able. the Web site users. These average several per day, and re- H. Chadsey developed quality control standards for the sponse time is usually about one workday. USNO time operations. He developed an automated alarm system for detecting clock component abnormalities which E. Other Research and Activities was able to detect problems in hydrogen masers and cesium clocks before they impacted the USNO timescale. Murison, Bangert, and Kaplan served on various working L. Breakiron adapted his timescale programs to handle the groups of NASAs Full-Sky Astrometric Mapping Explorer clock data from the new Data Acquisition System ͑DAS͒ ͑FAME͒ satellite project. Bangert chaired a working group time measurement system, including calibration corrections that developed a management plan for the FAME data analy- and reference clock offsets. sis software. J. Skinner developed a software tool that allows the user Stewart performed a detailed analysis of the characteris- to plot a clock’s first differences after the modeled rate has tics of the HI shells in dwarf galaxy Holmberg II, and a study been removed. The purpose of this tool is to allow the user to of the HI supershell in dwarf galaxy IC2574. The latter see any departures from the clock’s model. study, in collaboration with F. Walter ͑California Institute of Skinner made modifications to the steering programs for Technology͒, provided convincing observational evidence Master Clocks #1 and #3 that removed the possibility for that the classical model overestimated the requisite energy multiple corrections for steps in the maser timescale caused for the creation of an HI shell. by the addition, removal, or recharacterization of clocks. Oliversen is a co-investigator with M. Van Steenberg ͑PI͒, M. Miranian constructed a ‘‘Countdown to the year D. Massa, and P. Lawton ͑NASA/GSFC͒ on a recently ac- 2000’’ clock, which was erected at the front gate of the Na- cepted NASA Astrophysics Data Program to develop an im- val Observatory. The clock receives USNO time from the proved extraction algorithm for high-dispersion International GPS satellites and can be set to either countdown the days, Ultraviolet Explorer ͑IUE͒ NEWSIPS Data. hours, minutes, and seconds to the end of the year or display Fiala continued to provide computational support to mem- the current day number and time. bers of the International Occultation Timing Association who take observations of solar eclipses for the investigation B. Global Positioning System GPS Operations of the solar radius. „ … Murison continued to serve as Secretary of the AAS Di- Currently in operation under the control of the Time vision on Dynamical Astronomy ͑DDA͒, and Hilton contin- Scales Division are four STel 5401C Precise Positioning Ser- ued to serve as chair of the DDA Archives Committee. Hil- vice ͑PPS͒ receivers, one TrueTime PPS receiver, one AOA ton has acquired archive donations from several members of TTR-4P Standard Positioning Service ͑SPS͒ receiver, two the DDA, including papers detailing much of the early his- AOA TTR-6 SPS receivers, and one GPS/GLONASS re- tory of the organization. ceiver. Two STel 5401C PPS receivers and one AOA Kaplan continued to serve as the Chair of the Executive TTR-4P SPS receiver are in operation at the Alternate Mas- Committee for the now-annual Washington Area Astrono- ter Clock ͑AMC͒ site. mers Meetings. Kaplan also chaired the Local Organizing The daily downloads of the USNO PPS GPS data to the Committee for IAU Colloquium 180, held at USNO in GPS Master Control Station ͑MCS͒ were successful. The March 2000. GPS timescale was maintained to within ϩ/-20 nanoseconds 636 ANNUAL REPORT

͑ns͒ of UTC͑USNO͒͑its specification is ϩ/-1 microsecond͒ W. King prepared the GPS programs to accommodate the and the yearly average error of UTC transmitted from GPS GPS rollover, which was done with no operational problems. was a record low of 6.23 ns ͑its specification is 28 ns͒. She successfully completed the SIPRNET connection be- F. Vannicola conducted a series of GPS end-of-week roll- tween the USNO PPS systems and the AMC PPS system, over tests using the STI 7200 simulator and the STel 5401C and provided the hardware and software to collect and pro- PPS timing receivers. The tests provided critical information cess data from the new TTR-12 AOA PPS receivers. in order to develop hardware and software workarounds to enable the noncompliant receivers to continue working after C. NTP Operations the GPS rollover that occurred at midnight 21-22 August R. Schmidt expanded the USNO ensemble of Network 1999. All operational USNO GPS PPS and SPS receivers Time Protocol ͑NTP͒ servers, adding machines at Argonne continued to provide reliable time transfer data through the National Laboratories, Chicago, at the University of Florida, rollover and Y2k events. Gainesville, and at the Maui High-Performance Computing Vannicola coordinated the hardware setup of the USNO Facility, Maui, Hawaii. USNO now operates 17 Internet and GPS SPS TTS-2 ͑Motorola͒ receiver built by the Bureau two SIPRnet stratum 1 NTP servers. The total traffic rate on International des Poids et Mesures ͑BIPM͒. Data collection, the servers is now in excess of 450 NTP packets/second. process programs, and scripts for data reduction were cre- ated. D. Time Service Computer Operations Vannicola coordinated the hardware setup of the GPS PPS AOA TTR-12 receivers. Data collection and reduction E. Lukacs installed and administered a network multiple programs and scripts were created and set up to accommo- firewall system that protects the Time Service and the USNO date the wealth of data. Many tests were conducted to iden- AMC site. The firewall provides secure, encrypted virtual tify problems in the areas of Selective Availability ͑SA͒ cor- private networking between the two sites and protection rections, satellite eccentricities, faulty hardware, and from malicious attacks. software bugs. L. Schmidt conducted extensive analyses regarding the E. Alternate Master Clock Operations performance of the ionospheric model. She determined that significant improvements can be made when replacing the S. Hutsell detected, analyzed, and provided resolution for broadcast ionospheric model with measured ionosphere de- nine separate individual GPS frequency standard anomalies lays for common-view time transfer. She also compared and ten other significant operational challenges in 2nd Satel- lite Operations Squadron ͑2SOPS͒. This prevented signifi- ionosphere measurements made by the dual-frequency PPS cant degradation to UTC͑USNO͒ via GPS and the GPS ti- STel receivers at USNO and USNO AMC to IGS estimates mescale. of ionospheric delay. She found that the L1/L2 calibration Hutsell and B. Bollwerk performed extensive trouble- values in use in USNO receivers produced ionospheric delay shooting on unacceptable phase noise that was affecting measurements that were in very close agreement with iono- three AMC cesium clocks. Hutsell, Bollwerk, and P. sphere delays produced by the IGS ionospheric maps. Wheeler isolated the source as a problematic circulation fan L. Schmidt provided, to the GPS Control Segment, USNO motor in chamber A, which Hutsell and Bollwerk replaced, observations validating the operational changes to the GPS permitting the use of three otherwise unusable cesiums in the timing group delay ͑TGD͒ values broadcast by the satellites. AMC timescale. These TGD changes also served to confirm the accuracy of the historical calibrations of USNO SPS GPS timing receiv- ers, centering the difference between UTC͑USNO͒-GPS via F. Two-Way Satellite Time Transfer „TWSTT… PPS and UTC͑USNO͒-GPS via SPS around zero. The GPS The Two-Way Satellite Time Transfer ͑TWSTT͒ program Control Segment also removed SA on 2 May 2000. USNO ͑Wheeler, P. Mai, A. McKinley, J. DeYoung, and G. Luther͒ receivers responded perfectly with SPS receivers now report- has maintained a customer base of eight stations and has ing UTC͑USNO͒-GPS to 6 ns ͑1 sigma at 13 minutes͒. collected revenues in fiscal year 2000 of $360,000. Calibra- L. Schmidt served as GPS Analysis Chairperson on the tion trips were conducted to all sites. Non-profit TWSTT USNO Time Transfer Working Group. As such, she devel- links to Europe and to the National Institute of Standards and oped a plan for completely characterizing GPS common- Technology ͑NIST͒ have been maintained to support UTC, view time transfer and prepared the first two drafts of said and a special calibration trip was completed to Physikalisch- characterization. She also developed and presented a statisti- Technische Bundesantalt ͑PTB͒ Germany to support BIPM cal comparison of the three primary modes of time transfer coordination of UTC. The TWSTT link to the USNO AMC ͑GPS Carrier Phase, CV,TWSTT͒ between USNO and the was also maintained operational and calibrated. X-band USNO AMC. She automated daily common-view compari- equipment was tested and lent to the PTB to establish a sons between USNO and five primary standards laboratories. full-time link to the USNO. This new link will provide im- The difference between CV and TWSTT estimates of clock proved time transfer accuracy between the USNO and Eu- differences of the form USNO-lab is also calculated daily, rope. An X-band Earth station was designed and procured to and analysis tools were created for use by TS staff to monitor replace the Ku-band station operating in Ramstein, Germany. these differences using exponentially weighted moving aver- This station will be installed in September 2000 and will age control procedures. eliminate a $30,000 bill for satellite usage. Three new Satre U.S. NAVAL OBSERVATORY 637 modems have been procured and are under test to replace the neered R&D device. This device will be a rubidium fountain, aging and troublesome NRL-designed modems. The first site and should have trapped, cooled, and launched atoms by the to receive a new modem will be the USNO AMC. end of the fiscal year.

G. Master Clock Maintenance IV. EARTH ORIENTATION DEPARTMENT A. Kubik replaced 24 cesium beam tubes. Six new cesi- A. Scientific Data Analysis and Prediction ums and one new maser were added to the clock ensemble. Kubik completed the installation of a new MC coax switch The Earth Orientation Department continues to prepare system using FSJ-1 phase-stabilized Heliax and SMA con- Bulletin A, which is the International Earth Rotation Service nectors to eliminate the existing coax and BNC system. King ͑IERS͒ publication of rapid service and predicted values for completed the programs to control the new DAS in Buildings Earth orientation parameters ͑EOPs͒. In addition to twice- 78 and 52, created new programs for steering the Master weekly e-mail distributions of the Bulletin, the EOP product Clock Auxilary Output Generators ͑AOGs͒ which verify that files are automatically updated daily. Because EOP predic- the requested frequency change was correctly received and tion errors increase steadily with time following the most applied, and provided new programs to manually query for recent observations and since the primary Bulletin A con- health and status of any AOG, cesium, or maser. Wheeler tributors provide their results with very rapid turnaround, our and Kubik completed equipment upgrades and testing in daily EOP updates minimize the prediction error for real- preparation for Y2K rollover, King prepared all instrument time users. All EOP product files are freely available by control computers and J. Beish prepared all PCs. Y2K prepa- anonymous ftp via the Web site (http://maia.usno.navy.mil/). ration was completely successful. Wheeler completed the Among the most demanding use for real-time EOP values concept design for a new Master Clock building. Wheeler, is for predictions of GPS orbits, which in turn are used for a D. Judge, Kubik, and J. Eler completed a new antenna sup- variety of applications. A close collaboration is maintained port structure for GPS antennas. Wheeler designed a new DC with the International GPS Service ͑IGS͒ to support this to backup system and Kubik is installing the new systems as activity. An EOP error of 1 milliarcsecond ͑mas͒ corre- funding permits. sponds to a net rotation of the GPS constellation by up to ϳ13 cm at altitude. We estimate that during 1999 the actual Bulletin A prediction errors for 41 hours after the most re- H. USNO Cesium Fountain Development cent data, the maximum latency appropriate for the IGS orbit The USNO cesium fountain saw several successes over predictions, were about 0.8 mas for each component of polar the last year. The first milestone was the observation of mi- motion and about 2.4 mas for UT1 ͑equal to 0.16 millisec- crowave resonance signals ͑the basis of the clock͒ in late onds of time͒. The rotational scatter in the IGS orbit predic- December 1999. These signals were observed after only 8 tions was comparable, indicating the significance of EOP months of work in the new lab spaces. prediction errors. The balance of the fiscal year was spent on improving and During the past year, one new EOP series was added to studying the device. The signal-to-noise ratio was greatly the Bulletin A combination. The VLBI analysis from the improved, and a higher quality local oscillator system was Institute of Applied Astronomy in St. Petersburg, Russia, incorporated into the experiment. The first R&D device has was introduced on 10 August 1999. It is kindly provided by now met the operational goals for short-term stability, and is Z. Malkin and his colleagues, and is based on solutions of operating at slightly better than 2 parts in 10 to the 13th the NEOS 24-hour VLBI observing sessions using the OC- divided by the square root of the time. This result was CAM software system. achieved through the cooperative work of T. Swanson, E. The IGS made a change in its realization of the Interna- Burt, and C. Ekstrom. The efforts of the group were highly tional Terrestrial Reference Frame ͑ITRF͒ on 1 August 1999, collaborative. shifting from 47 ITRF96 to 51 ITRF97 sites for its fiducial Swanson was central to the efforts in atom trapping, cool- network. The polar motion discontinuities associated with ing, and launching in the fountain device. He also set up the change -0.263 mas for x and ϩ0.159 mas for y͒ were several upgrades to the laser synthesis and control systems. determined by the IGS Analysis Center Coordinator and Burt wrote and upgraded the instrument control and data these were applied to the IGS series during its assimilation acquisition code for the computer control of the fountain. He into Bulletin A. also assembled and performed characterizations of the mag- Starting 29 June 2000, the near-term polar motion predic- netic field control systems and temperature regulation sys- tions were modified slightly to rely more heavily on the lat- tems. est observed polar motion rates from the IGS Rapid combi- Up to now, continuous operation has been limited to nation and to enforce rate continuity with the predictions. about 6 hours. The stage is being set for much longer The latest IGS polar motion rates have been included in Bul- ͑weeks͒ unattended data collection with the fountain. This letin A since 11 February 1999. With the steady improve- will allow us to study the long-term behavior of the device as ment in their quality and reliability, an increased weighting compared to the USNO Master Clock. was found to benefit the Bulletin A predictions significantly. Next year will see the results of the long-term operation Efforts are underway to incorporate model predictions of of the cesium fountain. A more vigorous construction pro- the atmospheric angular momentum ͑AAM͒ excitation into gram will also be begun for a second, more heavily engi- the near-term Bulletin A predictions for UT1-UTC. The 638 ANNUAL REPORT

AAM results come from the National Centers for Environ- posium on ‘‘New Aspects of Modelling and Monitoring mental Prediction ͑NCEP͒ using both their analysis products Earth Rotation’’ during the EGS General Assembly in Nice, ͑tabulated at 6-hour intervals͒ and forecast fields ͑at 12-hour France, 24-29 April 2000. In addition, USNO personnel rou- intervals͒ for excitation of length of day ͑LOD͒. Each set of tinely attended meetings of a wide variety of working daily updates is smoothly merged into a continuous time groups, special study groups, boards, and other scientific series extending 5 days into the future. This series will then bodies. be assimilated into Bulletin A by first integrating the LOD Departmental contributions were submitted to two IAU values, then matching the last 5 days before the predictions Commissions for their triennial reports in preparation for the to the geodetic observations of UT1R-UTC and LODR. This upcoming IAU General Assembly in August 2000. Time- methodology has been run in a test mode and will soon be related activities were reported to IAU Commission 31 made operational. ͑Time͒, while EOP-related work was described for Commis- Research continues into the role of the ocean in Earth sion 19 ͑Earth Rotation͒. rotation and gravity field variations on seasonal to interan- nual time scales. Of particular interest have been the predic- tions of the Parallel Ocean Climate Model ͑POCM͒. Results B. VLBI Operations and Correlator indicate that the oceans appear to explain 25-50% of the Delivery of the new Mark IV correlator by the Interna- variations in polar motion not accounted for by the atmo- tional Advanced Correlator Consortium was completed in sphere on time scales ranging from a few years to sub- December 1999 after numerous delays. A similar system was monthly. Corrections for the non-conservation of mass have installed soon afterwards at the Max-Planck-Institute for Ra- been investigated, finding that the correction suggested by dio Astronomy, near Bonn, Germany. The Mark IV cor- ͑ ͒ Greatbatch 1994 has very little effect on polar motion ex- relator is the result of nearly a decade of effort by a consor- citation predicted by POCM over a 10-year comparison span. tium linking a number of institutes and agencies in Europe The observed variations in the ascending nodes of the GPS and the USA. MIT’s Haystack Observatory is the prime con- constellation are being compared with the expected gravity tractor for the unit installed at USNO. field excitations due to the atmosphere, ocean, and surface Though there remain a number of rough edges and some hydrogology, as well as with similar nodal observations for modes yet unsupported, the installation went relatively the LAGEOS satellites. smoothly. Tests demonstrated that all critical processing The IERS is reorganizing its structure, in part to incorpo- modes were functioning, although a number of issues related rate the new international services that have been formed to to the downstream data flow were raised. The initial capabil- coordinate observational and analysis programs within each ity was for four stations of 16 channels or six stations of 8 measurement technique. A Call for Participation was issued channels. The six station operation required two six passes on 15 November 1999 for most of the other components of ͑X-band and S-band separately͒, and only 14 of the possible the new service. The biggest changes will be the addition of 15 baselines could be processed in a single pass. These limi- an Analysis Coordinator with overall responsiblity for IERS tations were overcome within a few months as the software product consistency and creation of Combination Research matured. With the full six-station, 15-baseline capability the Centers, which will develop new approaches for rigorous new correlator handles one station and five baselines more inter-technique combined products. USNO proposed to host than the old Mark IIIA correlator. the IERS Product Center for Rapid Service/Prediction ͑as Most of the Mark IV development difficulties have related well as those for the Celestial Reference Frame and the Con- to the design and replication of the station units ͑SU͒. This ventions͒, which was accepted. The transition to the new component was originally to be developed under direction of service is expected in early 2001. the European JIVE collaborative. However, various prob- USNO personnel have played major roles in organizing or lems and delays have plagued the SUs from the outset. To participating in a number of recent meetings on Earth orien- address them, personnel from Haystack Observatory were tation. IAU Colloquium 178 on ‘‘Polar Motion: Historical forced to redirect their efforts. In July 1999, Haystack per- and Scientific Problems’’ was held 27-30 September 1999 at sonnel reported that the last outstanding problems affecting Cagliari University in Sardinia, Italy. Among other things the SUs were resolved. The fixes were implemented by the this meeting commemorated the centennial of the first obser- fabricating subcontractor and the full complement of eight vations by the former International Latitude Service. IAU SUs was delivered to USNO on 17 September 1999. At Colloquium 180, ‘‘Towards Models and Constants for Sub- about the same time, the final two upgraded Mark IV tape Microarcsecond Astrometry’’, was held at USNO during playback drives were also delivered. These improved the 27-31 March 2000. In addition, a special session on ‘‘Earth processing efficiency of even the old Mark IIIA correlator by Orientation Observations and Models’’ was organized at the allowing networks with several thin-tape stations to be pro- Fall Meeting of the American Geophysical Union ͑AGU͒ on cessed in a single pass. In addition, less reprocessing is nec- 16 December 1999. essary because of the new drives’ superior playback sensitiv- Contributions have also been presented at several other ity and synching ability. The new drives also feature new meetings of note. The XXIInd General Assembly of the In- triple-cap heads which are purported to have better wear ternational Union of Geodesy and Geophysics was held in characteristics and do not require vacuum changes between Birmingham, UK, during 19-30 July 1999. The European thick and thin tapes. Geophysical Society ͑EGS͒ and the AGU held a joint sym- Full functionality of all Mark IV observing modes will U.S. NAVAL OBSERVATORY 639 not be available until 2001 as further work is done by Hay- made during the first half of 2000 using the Kokee-Wettzell stack personnel on the control software. baseline, we have observed the UT1 performance to be at With the Mark IV correlator we lost the ability to process least comparable with the NRAO20-Wettzell baseline and the Mark IIIA mode A. This mode, which was routinely used the formal errors are indeed lower. only for the daily UT1 Intensives sessions, consists of 28 K. Kingham attended an invited review of the correlator channels for both the upper and lower sidebands of 14 fre- at the Joint Institute for VLBI in Europe ͑JIVE͒, including a quency settings. The new correlator is designed for 16 chan- meeting with correlator experts from JIVE, Bonn, and the nels. For this reason, UT1 Intensive observing schedules for VLBA. The review was held during 29-30 September 1999. year 2000 were changed to use the normal mode C ͑14 chan- The JIVE correlator hardware is identical to the Mark IV nels͒. Revisions can be made later to take advantages of correlator installed at USNO. Mark IV upgrades as they become available ͑e.g., 2-bit sam- pling, double speed, etc͒. C. VLBI Analysis The USNO installation was left in a configuration that can The critical development during the past year was modi- be switched back to the old Mark IIIA corrrelator during a fying the program DBEDIT to allow it to read Mark IV transition period. The early Mark IV results have sufferred correlator output data and create VLBI standard databases from a lower processing efficiency than was normal for the suitable for analysis. This task was made much more difficult Mark IIIA due to limitations of the initial control software. by the late delivery of the correlator itself, by the poor defi- As a result, some curtailing of the overall VLBI observing nition of the output data formats, and by the lack of suitable program has been necessary during 2000. As the correlator test data. software is gradually upgraded by Haystack personnel, the Investigation continues into the EOP differences between processing efficiency is improving and the limits on VLBI simultaneous CORE-A ͑NASA͒ and NEOS sessions. It ap- observing will be eased. pears that the apparent nonlinear motions of some of the The first use of geodetic data processed by the new cor- stations used in each network may partly explain thediscrep- relator took place on 13 January 2000 when UT1 measure- ancies. The VLBI geodetic results have been compared with ments from five VLBI Intensive sessions were included in motions observed by colocated GPS sites in an attempt to the IERS Bulletin A update that day. isolate specific stations which may be responsible. The com- One in the series of RDV observing sessions, which use parisons have been inconclusive which may be an indication ͑ ͒ the Very Long Baseline Array VLBA together with up to that the causes are more general. 10 non-VLBA antennas, was designed especially to compare Based to a substantial degree on new radio sources and the output from the VLBA correlator with the Washington new VLBI observations made by USNO, the IERS released Mark IIIA correlator. Such a thorough comparison of corr- Extension 1 of the International Celestial Reference Frame elators and fringe-fitting software had not previously been ͑ICRF͒ in November 1999. The main objectives of this first made. It is hoped that this test using a subnetwork of the maintenance and extension of the ICRF are to provide posi- RDV11 session ͑1-2 October 1998͒ will help to understand tions for extragalactic radio sources observed since July the source of anomalies in the analysis of the RDV data 1995 and to refine the positions of candidate sources from processed at the VLBA. Reprocessing of the RDV11 test additional observations. Secondary objectives include moni- data was completed at the Washington Correlator in Novem- toring sources to ascertain whether they continue to be suit- ber 1999 and the data were exported to colleagues at able for use in the ICRF and improving the data analysis. NASA’s Goddard Space Flight Center for study. USNO personnel attended the General Meeting of the In- In order to accomodate a budget cut of nearly 25%, it was ternational VLBI Service ͑IVS͒ held in Koetzting, Germany decided that USNO support for VLBI operations at Green during 21-24 February 2000. The main program was domi- Bank, West Virginia would end during fiscal year 2000. The nated by broad review presentations. Papers presented from 20-m antenna at Green Bank is operated by personnel of the USNO described early experiences with the Mark IV cor- National Radio Astronomy Observatory ͑NRAO͒. The par- relator and output data, as well as an overview of IGS time- ticipation of Green Bank in geodetic VLBI extends back to related products. Associated with this meeting was a half-day 1979 with the NRAO 140-foot antenna. The observing pro- analysis workshop where an extensive list of specific items gram expanded greatly with the use of the 85-3 antenna in was considered. the NAVNET and NEOS networks, and since 1995 has con- Two key personnel have left the VLBI analysis group tinued with the new 20-m facility. The last 24-hour session at during the past year, which has seriously impacted the Green Bank was the NEOS-A374 run on 27-28 June 2000. project. Adjustments have been made to continue VLBI To fill the gap left in the NEOS network, the Geodetic Sur- analysis activities for the time being, but this may become vey of Canada kindly agreed for Algonquin Park, Ottawa to infeasible in the future. Support for the VLBI operational participate on a weekly basis rather than the previous activities, such as preparing observing schedules, continues monthly rotation. This change began with the first NEOS with some reduction of effort by shifting duties among re- session in July 2000. Kokee Park replaced Green Bank in the maining staff. Responsibility for some software maintenance quasi-daily UT1 Intensive sessions which run with Wettzell. functions historically carried out at USNO has been trans- Given that the Kokee-Wettzell baseline is about 50% longer ferred than Green Bank-Wettzell, it is reasonable to expect that the to other groups. VLBI data analysis is continuing at UT1 performance could be improved. In a series of test runs USNO currently, but it will evenutally end when it is no 640 ANNUAL REPORT longer feasible or when the resources are required to support update of ITRF was nominally aligned globally with the other functions. 1996 version, non-zero offsets were discernable for the IGS fiducial subnetwork. These caused polar motion discontinui- D. GPS Analysis ties of -0.263 mas for x and ϩ0.159 mas for y. On 4 June 2000, the IGS adopted its own internal realization of USNO continues to contribute to the IGS for their Rapid ITRF97, referred to as IGS97. This reference frame was de- combination products, consisting of Earth orientation param- termined from a rigorous combination of terrestrial coordi- eters, GPS satellite orbits, and satellite and receiver clocks. nate information from all the IGS Analysis Centers spanning The IGS submission deadline is 16:00 UTC daily for analy- 4 years of GPS data. IGS97 is nominally aligned to ITRF97 sis of observational data from the previous UTC day. During with zero offsets. However, since IGS97 uses only GPS in- the past year, USNO has successfully submitted solutions for formation it is more consistent with other IGS products. Re- all but 16 of the 366 days. The missed days were caused by corrupt data files from the tracking stations or other data lated to this latter change, the IGS implemented a new pro- problems, bugs in the processing scripts. Internet interrup- cedure in March 2000 to ensure consistency between the tions, or operator errors. The average rms, weighted rms, and weekly combination of reference frame results and the final median of the USNO Rapid orbit residuals for the year were orbits. At the same time, a new IGS EOP series was begun 8.5 cm, 7.0 cm, and 6.1 cm, respectively. Typical clock re- which emerges from the same process and is also strictly siduals are about 0.2 ns. consistent with the other products. Tests have shown that the In addition, the USNO operation to determine UT1-like new EOP series agrees within the formal errors with the variations based on analyses of the motions of the GPS orbit established series formed by the direct combination of planes continues. The IERS Bulletin A UT1 combination Analysis Center submissions. These changes complete the depends heavily on this contribution, especially for the rapid process of making all IGS products internally self-consistent service and near-term predictions, but also for filling gaps in to ensure the highest level of precision. the VLBI time series. Although the results continue to be USNO began contributing to the IGS combined predicted excellent, concern has grown that the number of usable GPS orbit products at the end of June 1999 on a comparison-only satellites may be too small. Nine of the satellites that have basis. Our submissions were included in the IGS combina- been used are excellent; two others ͑SVN24 and SVN29͒ tion starting on 8 July 1999. These products are the extrapo- have jumps in their orbit planes when thrusters are used to lated orbits 24 to 48 hours beyond the most recent IGS Rapid unload momentum wheels. Therefore, satellites SVN24 and orbits and are released shortly before the start of the predic- SVN29 were replaced with satellites SVN26 and SVN27. tion day. The prediction strategy is based on an orbital fit to The replacement was done, starting on 15 July 1999, in a several days of the most recent IGS Rapid orbits. If the soft- way to minimize any discontinuity, which should be less ware detects a velocity impulse ͑due to an attitude-control than 10 microseconds. To improve the robustness further, thruster firing͒ within the data span, only data after the im- models were constructed of the motion of the orbit normals pulse are used for the orbit fit. The shortened data span re- for five additional satellites ͑SVN21, SVN30, SVN33, sults in larger errors in the predicted positions. The main SVN36, and SVN40͒. These were added to the operational difficulties have mostly involved the detection of true veloc- process gradually during February - April 2000, raising the ity impulse events and the handling of cases where the ob- number of satellites used to 16. Ignoring problem satellites, served orbital spans are very short. When an orbit can be fit only the last-launched GPS IIA satellite, SVN38 ͑which be- to more than 2 days of recent IGS Rapid orbit data, the came operational in December 1997͒, and the new GPS IIR resulting prediction accuracy is good. When the orbit can satellites remain unused. All other GPS II and IIA satellites only be fit to 1 day of data ͑attitude control events͒, the are dead or have serious problems with their momentum prediction error grows to several meters. Predictions based wheels or solar panels. Further experience must be collected on such short-arc fits are being assigned a larger error esti- with the newer satellites before reliable models can be de- mate. Likewise, those satellites which regularly experience veloped for the UT1-like estimation. velocity impulses are assigned higher errors. Another issue is Changes in the analysis strategy have consisted mostly of improving the modelling of variations in the estimated ad- relatively minor refinements, such as increasing the number justment of the along-track accelerations. Most of the time, and distribution of tracking sites used in each solution. One this parameter changes slowly as a function of Sun angle significant change was the introduction of carrier phase am- from the orbit plane, and the change can be determined by biguity resolution in April 2000, which yielded noticeable tracking successive orbital fits. However, during eclipse sea- improvements in the orbits and Earth orientation parameters. son the variations can be much larger and more rapid. Higher This was only feasible within the strict IGS delivery dead- prediction errors are consequently assigned to eclipsing sat- lines after two faster workstations were received in late 1999. ellites. While considerable refinement of the prediction algo- Version 5.5 of the GIPSY/OASIS-II analysis software was rithm and procedures is ongoing, the process itself runs daily installed operationally on 20 December 1999; the software in a fully automated mode. was developed and is maintained by NASA’s Jet Propulsion Operationally, GPS orbital analyses and predictions have Laboratory ͑JPL͒. grown increasingly challenging due to the advancing age of The fiducial reference frame has been changed twice. On the constellation. The attitude control systems on many of 1 August 1999, the IGS moved from 47 ITRF96 to 51 the older spacecraft, the oldest active having been launched ITRF97 sites for its realization of the ITRF. While the 1997 in 1989, have seriously degraded. The operational manage- U.S. NAVAL OBSERVATORY 641 ment of the system by the U.S. Air Force has evolved pro- eliminated. Also, extrapolated clock values for real-time us- cedures to compensate by using periodic thruster-controlled ers will become much more useful. momentum dumps. Partly to relieve the workload on the op- It is very clear that biases between GPS observable types erations staff, the thruster-controlled system has transitioned exist which depend on the individual satellite as well as on to an automonous mode consisting of more frequent, but receiver type. In particular, codeless receivers operate with smaller momentum dumps. The effect of these thrustings is different distinct pseudorange tracking technologies, some to make the modelling of the GPS orbital dynamics much relying on the narrowband C1 ͑or C/A͒ modulation while more difficult. For the most part, the IGS has developed others use the wideband P1 code. Satellite-dependent biases methods to detect such events and minimize their impact on are observed between C1 and P1 of up to ϩ/- 2 ns. This is of users for the observed products. Orbit predictions for real- no significance for data analysts who process only carrier time users are much more problematic, however. Partly to phase observables. For analysts who use the pseudorange address this circumstance while trying to satisfy the accuracy observations, their estimates for satellite clocks can be af- requirements of the most demanding real-time applications fected. For external timing comparisons, these and other bi- ͑such as monitoring of tropospheric parameters for weather ases must be measured and accounted for as part of the in- forecasting͒, the IGS started to develop a new set of ЉUltra- strumental calibration. For comparisons and combinations of rapidЉ products. These are intended to minimize problems analysis results, consistent sets of biases and procedures with the satellite velocity impulses by moving to an update must be applied. For the P1-C1 biases, the IGS has adopted cycle of every 12 hours from the current 24 hours, and by a new correction procedure and a recommended set of bias reducing the latency between the observed and predicted or- values starting on 2 April 2000. USNO personnel have co- bits from 36 hours ͑on average͒ to 9 hours. While still in a ordinated and documented these procedures for the IGS. preliminary, non-official mode, the IGS Ultra-rapid combi- During the past year the GPS receivers deployed at nation started on 7 March 2000. The first submission of a USNO and at the Alternate Master Clock ͑AMC͒ in Colo- USNO contribution for the Ultra-rapid combination was rado Springs, Colorado, were replaced with newer models. made on 26 March 2000. Up to seven different IGS Analysis The previous AOA TurboRogue SNR-12 RM receivers were Centers now contribute to the Ultra-rapid combination. upgraded to AOA’s new generation SNR-12 ACT models. Two major epoch rollovers occurred during the past year, The pseudorange tracking technology is improved and no and both were largely uneventful for the IGS. The GPS week longer relies on cross-correlation methods. The result is bet- number rolled over from 1023 to 0 at 24:00 UTC on 21 ter signal-to-noise performance, especially at the L2 fre- August 1999. While it was certainly felt within the IGS, quency. Unfortunately, the upgraded receivers suffer regular there was no serious disruption of product delivery. Many failures which require manual restarts. These events corre- sites failed to produce usable navigation files ͑containing the spond to times when the offload of data from the receiver’s broadcast ephemerides͒ or they contained the incorrect week. flashcard memory occur. Extensive communications have Fortunately, these files, while useful, are not essential. A been exchanged with the manufacturer and with other opera- number of receivers experienced difficulties of a wide vari- tors of the same receiver model. Various workarounds have ety, often related to outdated firmware. Data from some re- been attempted, but with limited success. Despite the im- mote sites was interrupted because it was not immediately proved pseudorange data, this problem has severely limited possible to install the latest firmware. As a result, the number the usefulness of these installations for time transfer applica- of IGS fiducial sites was considerably reduced from the 51 tions, which is a prime interest. In late June 2000, a new possible. Despite all these difficulties, the IGS Rapid and receiver firmware version was received from Allen Osborne Predicted products were not interrupted and the performance Associates, which is supposed to address communications was not noticeably degraded. Similarly, the year 2000 tran- management issues between the receiver and computer con- sition was also relatively painless. The only serious analysis troller. Meanwhile a workaround solution is in progress. A software bug found was in a utility used to output orbit files, real-time data offload process is being installed at USNO in which corrupted the date information in the file header. The cooperation with colleagues at the Natural Resources of problem was promptly diagnosed and fixed. Within the Canada. This system appears to circumvent the problem in- larger IGS, data and results continued to flow without inter- duced by using the flashcard memory. ruption although with some difficulties. The major disrup- In August 1999, the antenna cable at the AMC GPS in- tions were all self-inflicted, such as the preemptive shutdown stallation was replaced by Time Service personnel with one of the main data center as a precautionary measure. having much less sensitivity to temperature variations. With The most significant GPS event of the past year was the this change, now both the USNO and AMC sites are decision by the U.S. President to discontinue the intentional equipped with cable and receiver systems that are very well degradation of the GPS clock signals by Selective Availabil- isolated from environmental variations. Using data from ity ͑SA͒ at 04:00 UTC on 2 May 2000. This change now these sites, it is possible to infer the temperature sensitivity allows civilian GPS users to obtain positioning and timing of the Dorne Margolin choke ring antennas for the first time. determinations that are more accurate than before by about a By direct comparison of the observed clock variations be- factor of up to ten. It will likely have many beneficial effects tween these sites with local temperature measurements, em- for users of IGS clock products. For example, the expected pirical temperature coefficients for each system were esti- need for high-rate satellite clock estimates ͑ϳ30-second in- mated. These thermal coefficients most likely apply to the tervals͒ to permit interpolation in the presence of SA is now only uncontrolled components of the systems, the choke ring 642 ANNUAL REPORT antennas. Based on these results, the short-term ͑diurnal͒ sta- and Instrumentation Division during the reporting period. bility of the antennas appears to be better than 2 picoseconds This project also involved the efforts of 19 other NRL, Low- per degree C. The possibility that longer-term effects exist ell Observatory, and contractor personnel, and a major frac- due to sensitivity in the daily average of the pseudorange tion of the efforts of the USNO instrument shop. observations has not been tested and cannot be excluded. Analysis of NPOI observations has led, to date, to 20 The IGS/BIPM Pilot Project to Study Accurate Time and publications in refereed journals and conference proceedings. Frequency Comparisons using GPS Phase and Code Mea- A revised bibliography of all NPOI publications ͑Hutter͒ can surements continues to be quite active. This effort was be found on the new NPOI Web page (Dyck; http:// started in early 1998 jointly by the IGS and the Bureau In- ad.usno.navy.mil/npoi/index.htm). ternational des Poids et Mesures ͑BIPM͒ with the goal of Other data analysis efforts involved the development of developing operational techniques to exploit GPS measure- new software to import NPOI data into the AIPSϩϩ pack- ments for improved availability of accurate time and fre- age, as a first step toward developing synthetic imaging tech- quency transfer globally. USNO represents the IGS in man- niques in the optical, and improving the techniques to com- aging this project, together with the Time Section of BIPM. pensate the measured stellar delays for effects of the During the past year, the IGS began producing preliminary atmosphere. combinations of station and satellite clock estimates submit- The reporting period saw the completion of an almost ted by the IGS Analysis Centers. The new, experimental total reconstruction and reconditioning of the vacuum feed clock combination uses the clock RINEX file format devel- system, the completion of all the remaining ‘‘fast’’ delay oped by the Pilot Project, rather than the conventional lines, and the reconstruction of the optical beam combiner, method of using only the satellite clock information in the all in preparation for the start of full, six-element imaging orbit files. Results are available starting 2 January 2000. The observations with the NPOI. first major progress in calibrating geodetic receivers for tim- After over a year of major reconstruction and expansion ing applications was reported by colleagues at BIPM. They of the array vacuum feed system, delay lines, beam com- carried out the differential calibration of two Ashtech Z12-T biner, and detector housings, regular stellar observations re- receivers by comparing their raw pseudorange measurements sumed at the NPOI on 18 June. Additional work is now with those of classical NBS-type time transfer receivers op- underway to complete two more siderostat stations ͑north erated side by side. They then performed a time comparison astrometric and W07͒ in preparation for the start of full six- between a nearby laboratory and BIPM using both classical station observations in late 2000. time receivers and the calibrated Ashtech Z12-T receivers, Work also continued ͑at a reduced level of activity͒ on the and compared the results. development of an infrared fringe detection capability for the NPOI ͑Dyck and Sudol͒. The original two-way beam com- E. Miscellaneous biner, used for the first demonstration of IR fringe tracking at the NPOI, was reconfigured for three-way beam combina- B. Archinal was profiled in the November issue of Sky & tion. The detector dewars were modified to accept a NIC- Telescope, on pp. 89-90. The piece, by Levy, relates Archi- MOS array ͑on loan from National Optical Astronomy Ob- nal’s background in amateur astronomy. servatories͒. Analysis of the first NPOI IR observations ͑of SEAP student S. Zelechoski finished her project ‘‘Super- ␦ 2Lyr͒ continued, along with the development of limb- luminal Motion in 3C418,’’ with mentoring by K. Kingham darkened disk models for use in interpreting these and future and J. Martin. Her results indicate that jet components in NPOI observations of cool stars. 3C418 were moving at .2 ϩ/- .08 mas/yr ͑7.5c for Hoϭ100 The reporting period also saw the completion of the and qoϭ0.5͒. nearly 2 kilometers of roads surrounding the array, the erec- M. Carter completed her Masters degree work at the Uni- tion of a large equipment storage tent, the installation of versity of Maryland and was awarded her degree in July electrical power and signal-cable conduits on the outer array, 1999. and various computer network and security upgrades at the NPOI site. V. ASTROMETRY DEPARTMENT

A. Navy Prototype Optical Interferometer „NPOI… B. Double Star Programs The period of this report saw the completion of major During the year, transition was made from a 386-based upgrades to many of the systems of the Navy Prototype Op- control system to a more powerful Pentium- and Windows- tical Interferometer ͑NPOI͒ on Anderson Mesa, Arizona, that based system written by E. Holdenried. This software, a con- enhance its sensitivity and complete its full imaging capabil- trol program for the speckle camera, is for use on both laptop ity. Development and operation of the NPOI continued under and desktop computers. The desktop version operates a the overall direction of D. Hutter and D. Mozurkewich Naval frame grabber that acquires pixel data directly from the CCD Research Laboratory ͑NRL͒. Other Interferometry Division camera and produces directed vector auto-correlations staff directly involved in the NPOI project included J. Ben- ͑DVA͒ in real time. This version can also apply ‘‘darks’’ to son, D. Dodd, H. Dyck, N. Elias, M. Germain, A. Hajian, J. the CCD frames and allows the selection of three different Horne, C. Hummel, W. Ketzeback, T. Nordgren, and J. Su- sizes of scan areas. Both the quality of the DVAs, the speed dol. David Dodd and John Horne are new USNO employees. at which they can be acquired, and the ease of use have Hajian and B. Pohl were transferred to the Data Reduction improved due to these efforts. The time tagging of the DVAs U.S. NAVAL OBSERVATORY 643 has recently been improved to allow the observation of Ju- were organized. Mission and tasking statements were written piter events ͑i.e., when two moons of Jupiter appear close and milestones set by the WG chairs. enough together that they can be observed as a ‘‘double F. Harris continued involvement in the FAME project, star’’ by the speckle camera͒. W. Hartkopf and B. Mason constructing a test-bed CCD slow-scan readout system built prepared programs for creating new observing lists based on around an EEV 2Kx4K thinned CCD. Harris took data with currently available data. G. Wycoff, Hartkopf, and Holden- the CCD installed on a precision translating stage within a ried checked new observing lists with the Tycho-2 catalog to thermal-vacuum chamber at Lockheed Martin, and delivered improve position and magnitude information. Reduction of the data for analysis to USNOFS and Lockheed. Harris made the October, 1999 McDonald Observatory observing run a presentation of this experiment to the NASA board review- continues. Reduction of USNO speckle data was completed ing the FAME project, presented an overview of the experi- the next day and all data obtained in 1999 are currently in ment at the ESO CCD Detector Conference in Garching, press. Germany, and coauthored a paper on the experiment given at At the end of the report period the WDS catalog contained the SPIE Conference in Munich, Germany. He designed and 83,283 systems based on data from 510,560 observations. constructed prototype electronics for repeating the experi- During the year 1,542 new systems and 29,948 new obser- ment at full FAME speed. D. Monet supported the thermal- vations were entered into the database by Wycoff and Mason vacuum chamber testing for FAME CCDs and provided near primarily from the Tycho-2 catalog and data from speckle real-time reductions and measures of data quality. interferometry. However, data continue to be added from F. Harris served on the FAME CCD vendor selection other sources as well due to constant perusal of available committee. Harris wrote the CCD testing specifications, and journals by Wycoff. New data request software has been visited four of the six original candidate vendors to assess written which extracts data from the WDS, orbit, and delta-m their technical merits. Harris was asked by Lockheed Martin catalogs. engineers to contribute to the design of the FAME flight Wycoff prepared a list of systems suitable for first orbits CCD electronics. ͑ either systems with at least 99 observations or systems with J. Bangert chaired the FAME MO&DA Software Man- a 30 degree change in position angle or 30% change in sepa- agement working group, which produced a document outlin- ͒ ration . Investigation of the systems selected continues by D. ing a FAME Software Management Plan to address develop- ͑ ͒ Seymour SEAP student , Mason, and Hartkopf. Analysis of ment methodology, standards, and configuration control for systems with existing orbits continues as well. The long- th the operational data analysis pipeline software. awaited 5 Orbit Catalog is nearing completion, due to ef- S. Urban chaired the FAME MO&DA Input Catalog forts by Hartkopf with assistance by Mason. The most im- Working Group. Urban produced the first simulator catalog. ͑ ͒ portant tasks were to 1 determine relative weights to be It consists of 83,090 Hipparcos stars. It is envisioned that it ͑ ͒ assigned to all binary star observers, and 2 determine ob- will be used to test algorithms for the pipeline and simulator. jective criteria for grading published orbital elements. To Hence, it has not only positional data, but parallax, proper ϳ that end 80,000 observations were collected from the WDS motion, photometry and errors. As a member of the Input ϳ for 730 good orbits. The resulting residuals were used for Catalog Working Group. N. Zacharias, as a member of the determining relative weights of various observers/telescopes/ FAME Input Catalog working group, investigated the prob- equipment as a function of binary separation. Also, lem of scanning through the Milky Way. ϳ100,000 observations for ϳ900 orbits in the Worley and th A. Fey chaired the FAME MO&DA ICRF/FAME Frame Heintz 4 orbit catalog. Objective means were then devel- Tie Working Group. Fey searched the Veron-Cetty and oped for recreating orbit grades similar to the Worley & Veron list of ‘‘Quasars and Active Galactic Nuclei’’ ͑8th Ed.; Heintz scale. Factors included mean separation residuals, 1998͒ for extragalactic objects brighter that 15th magnitude, angle and phase coverage, number of observations, and num- in support of the FAME project. A total of 66 quasars and 16 ber of orbital revolutions included in the data. New grades BL Lac objects fit the selection criteria. Fey also searched were determined for most of the ϳ2400 orbits in the catalog the NRAO/VLA Sky Survey ͑NVSS͒ for radio sources at the by the end of June 2000. Hartkopf was elected Vice Presi- location of the brightest quasars from the Veron-Cetty and dent of IAU Commission 26. Veron list. A total of 36 of the 66 quasars are located within 15arcsec of a NVSS radio source detection. C. Full-sky Astrometric Mapping Explorer FAME Fey, D. Boboltz, Gaume, K. Johnston, and M. Claussen „ … ͑NRAO͒ prepared and submitted a VLA observing proposal In October 1999 the National Aeronautics and Space Ad- entitled ‘‘Radio Star Observations for a FAME/ICRF Frame ministration ͑NASA͒ selected the FAME satellite to be Tie.’’ funded for launch in 2004. Phase B ͑Preliminary Design͒ is Activities in the FAME Mission Simulators and the Pipe- scheduled to begin in September 2000. FAME is a collabo- line working groups centered in several areas. Monet’s ac- ration between USNO, the Smithsonian Astrophysical Ob- tivities included development of point spread function simu- servatory, NRL, and Lockheed Martin. lation and fitting algorithms in addition to the baseline suite S. Horner, serving as Mission Operation & Data Analysis of functional fitting algorithms. N. Zacharias also studied ͑MO&DA͒ lead for the FAME project, accepted a position simulated 1-dim and 2-dim CCD data with the FAME profile with Lockheed Martin. R. Gaume was appointed MO&DA width and noise characteristics. M. Murison developed a lead. Numerous FAME MO&DA working groups ͑WGs͒ FAME spin dynamics simulator program. This program was 644 ANNUAL REPORT used to study motion of the spacecraft, particularly the effect This removes the need for vacuum systems and exotic mate- of changes in the planned FAME solar angle on astrometric rials in the construction of the FTS, since the laser metrology accuracy. Urban investigated the FAME solar angle trade can now sense all thermal, vibrational, and other motions study from the perspective of previous work performed by experienced by the starlight beam. members of the Hipparcos project. Using his spin dynamics Light was successfully recorded on the CCD detector. simulator program, Murison studied the effects on in-scan This involves the construction of a fiber switchyard to allow motion, cross-scan motion, and field rotation of several dy- alignment ͑using a diode laser͒ and injection of starlight. namical processes ͑including gravity gradients, magnetic T. Rafferty has been working on an 18-inch telescope, torques, and radiation fluctuations͒. Various members of the which Hutter arranged to send from Flagstaff. The telescope Pipeline and Simulator Working Groups worked on refining optics are in good shape, but the electronics package is not and developing the simulator and pipeline data flow dia- available. Replacement parts are on order. If the pointing of grams. The Pipeline Working Group also discussed post- this telescope can be stabilized, then it will serve as an ex- centroiding data reduction algorithms. Two methods appear cellent way of gathering starlight to test the velocity stability most viable. One utilizes a method similar to the Hipparcos of the FTS. ‘‘great-circle’’ reductions; the other method involves de- The state of the instrumental subsystems as of the end of tailed physical modeling of spacecraft dynamical motions. fiscal year 2000 is: Gaume and Fey designed and began development of a 1͒ Opto-mechanical layout of interferometer: The layout Web site to support the FAME Project and Science teams. is complete except for a single mirror ͑for the final delay Fey, Gaume, and L. Treadway prepared and submitted mul- line͒ which is due to arrive at the end of September. Align- tiple procurements for FAME computing facilities hardware ment procedures for the entire instrument have been com- and software. P. Seidelmann, as chair of the FAME Science pleted. The fiber switchyard is completely functional, and Team, organized a meeting of the FAME Science Team in has been demonstrated to allow injected light to pass through February 2000. the entire FTS ͑except for the missing delay line͒, and be focused onto CCD. 2͒ Metrology system: Data recording is complete. Staff D. Fourier Transform Spectrometer „FTS… are still awaiting the controllers for the AOMs and a digital A simple FTS was designed for a modest budget, and was lock-in amplified. These units have been ordered, and once deployed in Flagstaff, Arizona at the NPOI site. Participants these units arrive, 1 week will be required to align them and in this endeavor were Hajian, R. Hindsley, Nordgren, and to fine-tune their operation. Pohl. The 42-inch telescope at Lowell Observatory was used 3͒ Fringe system: Data recording is complete. Pohl’s soft- and a fiber was stretched between this aperture and the NPOI ware has been tested. Progress continues on small additional inner room. Despite no stellar data being recorded, the trip functions which will serve to optimize observing efficiency was critical to performing a final shakedown of the instru- ͑e.g. database of observed stars, plots showing the delay line ment. The lessons learned during this run have been invalu- waveform, etc.͒. able in constructing the next generation of the FTS. During the end of 1999 and the beginning of 2000, Hajian developed a new algorithm for performing sparse data acqui- E. Space Interferometry Museum SIM sition using the FTS. This means that instead of acquiring „ … hundreds of thousands of scans each with an integration time After the retirement of T. Corbin, Mason took over as PI of 1 ms, the same spectrum can be reconstructed with only a of the SIM Grid Star Project. Observing of targets accessible few thousand scans each of several 100 ms duration. This with NPOI has been completed with the McDonald 2.1-m obviated the need for an expensive CCD and real-time data telescope. Late in the year, time was obtained on the 4-m acquisition system, and greatly simplified the FTS design. telescopes for an observing program which will observe po- The algorithm was implemented in a C-based environment tential grid candidates for another scientifically justified pro- by Pohl and extensively tested. Pohl confirmed that the algo- gram, thus allowing us to complete our SIM obligation in the rithm works efficiently, and discovered that the algorithm area of speckle interferometry. was robust enough to solve for the edge wavelengths of the Urban performed regular updates of the SIM grid star list bandpasses, which greatly simplified the calibration process and provided observing target lists to E. Horch ͑Rochester during data acquisition. Institute of Technology͒ as requested. Tremendous progress has been made by Pohl in the soft- L. Winter and Rafferty made double star observations ware. Pohl has written and tested the basic data acquisition with a CMOS and a CCD camera in Washington, DC at the and post-processing systems for the FTS. This is a major 26-inch refractor and on Mt. Hamilton using the Lick 20- accomplishment, and has enabled us to more completely and inch astrograph. A preliminary reduction of the data showed efficiently debug the FTS while we completed the construc- that the USNO grid star selection for SIM should be done tion of the hardware. with a CCD camera and a long focal length refractor. Using Based on previous experience, construction of a new FTS the USNO 26-inch refractor and a Photometrics CH250 CCD began in December 1999, and is still continuing to the camera with a KAF4200 Kodak CCD the stacked short ex- present. During the construction phase, Hajian changed the posure images could be combined to enhance the dynamic design so that the metrology beam completely tracks the star- range of the CCD in order to obtain a dynamic range of 7.5 light beam throughout the entirety of the instrumentation. mag. U.S. NAVAL OBSERVATORY 645

Fey, Boboltz, N. Zacharias, Johnston, and Gaume pre- emission, although unusual for a compact extragalactic pared and submitted a Space Interferometry Mission Key source, is not the result of a GL. Science proposal for NASA AO-00-OSS-01. The proposal Using the USNO-A2.0 catalog Gaume performed frame was entitled ‘‘Astrophysics of Reference Frame Tie Ob- reduction and orientation of several infrared images of the jects.’’ G34.3ϩ0.2 star forming region. The infrared images in- cluded J, H, and K band images taken with the USNO IR- CAM using the Flagstaff 61-inch, and L band images taken F. Fundamental Reference Frames—Radio with a prototype Aladdin chip using the KPNO 4-m, and K band HST NICMOS images. When the proper tie is made The VLBA astrometric/geodetic experiments RDV17, between the optical, infrared and radio frames and the infra- RDV18, RDV19, RDV20, and RDV21 were observed ͑in red, and radio images are overlaid, an astrophysically inter- support of the International Celestial Reference Frame͒. esting offset between the radio and IR emission is noted, and Boboltz scheduled a Celestial Reference Frame ͑CRF͒ astro- a first detection of the massive early-type star exciting the metric VLBI experiment which was observed on August 17, radio HII region is seen in the Aladdin L-band ͑3.5 micron͒ 2000. image. In support of FAME and SIM, eight optically bright radio Fey calibrated and imaged VLBA data on the extragalac- stars ͑Algol, Gamma Ori, Sigma Gem, HR 5110, Sigma-2 tic source 2023ϩ336. Images at 13, 6, 3.6, and 2 cm lead to CrB, P Cyg, IM Peg, and OU And͒ were observed using the the conclusion that the complex radio emission of the source VLBA ͑experiments BB120a-h͒. Observations took place is the result of anisotropic radio wave scattering due to from February 2000 through May 2000 with 6 hours of propagation through the turbulent interstellar medium. The VLBA time per source. Boboltz, in collaboration with Phil- data do not fit the simple picture of angular broadening in lips of MIT Haystack Observatory observed the 43-GHz SiO which an intrinsically point-like source is diffractively maser emission towards the long period variable Mira using broadened into an almost Gaussian brightness distribution the VLBA. Six epochs of data were recorded from Novem- and call into question the very existence of a ‘‘scattering ber 1999 through April 2000. disk.’’ USNO and Paris Observatory ͑PO͒ have jointly submitted Boboltz reduced the two epochs of VLBA observations a proposal to the International Earth Rotation Service ͑IERS͒ ͑BG087a and BG087b͒ of the radio star HR5110, and com- to become the International Celestial Reference System pared the resulting positions to those of Lestrade et al. and Product Center ͑ICRF PC͒. Hipparcos. These observations were part of a joint NPOI/ USNO and PO have now come to agreement on the divi- VLBA test project to connect the radio and optical reference sion ͑between the two organizations͒ of tasks that will make frames. up the ICRS PC, and the final draft of the proposal has been Fey facilitated transfer of ownership of a H-maser fre- signed and submitted to the IERS Directing Board for accep- quency standard and MkIIIA DAS from NRL to USNO. tance. Original acquisition cost of this equipment is estimated at The International VLBI Service ͑IVS͒ directing Board ac- approximately $700K. The equipment is currently on loan to cepted the FRF Division as an IVS Special Analysis Center. the Australia Telescope National Facility ͑ATNF͒ at Parkes, Fey will serve as the primary scientific/technical contact. The Australia, where it will be used as part of the joint USNO/ Center will provide the IVS with intrinsic structure informa- ATNF Southern Hemisphere reference frame observing pro- tion on ICRF sources at radio wavelengths. gram. An S2 VLBI data recorder was installed at the USNO Boboltz finished reduction and imaging of VLBA experi- Kokee Park Geophysical Observatory for use in the joint ments RDV08 and RDV09 for maintenance of the ICRF and USNO/Commonwealth Science and Industrial Research Or- added approximately 360 new images to the RRFID. Fey ganization ͑CSIRO͒ astrometric observations in support of finished calibration and started imaging of the VLBA experi- the ICRF. ment RDV07. Gaume processed several VLBAϩ ͑RDV͒ ex- A CSIRO postdoc was hired to coordinate the joint periments through GLOBL-SOLVE to determine UT1. The USNO/CSIRO astrometric observations in support of the goal was to ascertain the quality of the UT1 measurement, as ICRF. The postdoc is currently scheduled to assume duty in determined from RDV experiments, as compared to other October 2000, at which time Southern Hemisphere astromet- VLBI UT1 series. Boboltz re-reduced VLBA radio star ob- ric and imaging observations will commence. servations of HR5110 ͑BG087a and BG087b͒. Fey self- Ginger Leonard ͑Thomas Jefferson High School, Vir- calibrated and imaged VLA data on the gravitational lens ginia͒ started an internship with Fey, Gaume, and Boboltz. candidate source 1445-161. A 13000:1 dynamic range image Her first task was to examine the Radio Reference Frame at 3.6 cm shows two sources: the quasar 1445-161 with a Image Database ͑RRFID͒ looking for evolutionary changes flux density of 0.481 Jy and a ‘‘new’’ source with flux den- in the images of individual ICRF sources as a function of sity of 0.664 mJy. This previously undiscovered weak source time. is located about 2.6 arcsec to the northeast of 1445-161, but is outside the ring of optical emission, further complicating G. Fundamental Reference Frames—Optical interpretation of this unusual source. Fey calibrated and imaged VLBA data on the gravita- The observational program for the extragalactic link to the tional lens candidate source 1445-161. Images at 18, 13, 6, UCAC project continued ͑N. Zacharias as PI͒. In three ob- and 3.6 cm lead to the conclusion that the complex radio serving runs ͑October, December, March͒ Rafferty and N. 646 ANNUAL REPORT

Zacharias alternately acquired data at the Cerro Tololo Inter- matched with the USNO-A2.0 catalog. Plots produced by American Observatory ͑CTIO͒ 0.9-m telescope for a total of Hall showed that they are from multiple systems not in the about 120 sources. Parallel observing at the astrograph pro- USNO-A2.0. vided reference stars at the same epoch, using the same spec- The final result is the first USNO CCD Astrograph Cata- tral bandpass ͑579-642 nm͒. During each visit at CTIO main- log ͑UCAC1͒, which contains only stars with at least two tenance of the astrograph was performed. M. Zacharias images on astrograph CCDs and with a unique match to an migrated software for Radio Optical Reference Frame early epoch for proper motions. The mean positional preci- ͑RORF͒ reductions from an HP workstation to a Linux PC. sion of all 27.4 million stars, covering about 85% of the The collaboration with M. Assafin ͑Brazil͒ continued with Southern Hemisphere, is 31 mas. Stars in the 10-14 mag additional observing of a sample of the RORF sources at the range are precise to about 20 mas and the limiting magnitude Laboratorio Nacional de Astrofisica 1.6-m telescope. is Rϭ16. The errors of the proper motions are about 1 to 3 N. Zacharias was assigned the lead for the section mas/yr for stars in Tycho-2, and about 9-15 mas/yr for faint ‘‘Maintain the link to the Hipparcos catalog’’ in the IERS stars utilizing the A2.0 catalog. N. Zacharias and Urban sub- proposal for a joint Paris Observatory and USNO ICRS mitted a paper on UCAC1 for publication. The UCAC1 is product center. publicly available on a CD-ROM and about 300 copies were distributed. Hall found 1,142 galaxies in the UCAC1 out of 34,716 H. USNO CCD Astrograph Catalog „UCAC… galaxies listed in the SPM 2.0 area. The magnitude distribu- On 15 December 1999 the first field on the equator was tions confirm that only a small fraction of galaxies ‘‘con- observed. Over 18,000 survey fields could be completed this taminate’’ the UCAC1. Hall studied double stars by com- year, reaching a total of 44,529 by the end of June 2000, paring positions from the UCAC data with the WDS. exceeding 50% sky coverage. So far over 132,000 frames M. Zacharias matched the UCAC with the SPM 2.0 and were taken with the 4k camera, resulting in 2.1 TB of com- Tycho-2 catalogs. Systematic differences as a function of pressed raw data. This year 4,268 and 2,253 frames were magnitude reach 15 mas, while as a function of RA or Dec taken for RORF and calibration fields respectively. amplitudes up to 40 mas are present. N. Zacharias wrote a Most of the nightly observing and daily preparations were paper about the UCAC1 - Tycho-2 comparison with contri- run by the two night assistants D. Castillo and M. Martinez, butions from Urban, M. Zacharias, and E. Hoeg ͑Copen- with M. Zacharias running most of the daily evaluation of hagen University, Denmark͒. the astrograph data. At the end of July 1999, N. and M. A comparison with SPM 2.0 done by M. Zacharias in a Zacharias moved back from Chile to Washington. Proce- small area ͑12.5h RA, -35 Decl.͒ revealed an average exter- dures were set up to allow remote quality control of the nal error of 250 mas for USNO A2.0 positions with system- observing. atic errors up to 300 mas. Holdenried continued to provide patches to the PC1 soft- A comparison done by Wycoff between the USNO-A2.0 ware and Hennessy and Gauss managed the computers. Raf- and ACT catalogs showed offsets of about 200 mas in right ferty and N. Zacharias worked on specs for a new CCD ascension and declination south of -18 degrees. This explains camera for the astrograph. D. Hall wrote extensive software the offset of about 5 mas/yr found in the UCAC1 proper to compile, maintain, and access the database. Hall also read motions of faint stars when compared to the SPM proper each tape arriving from CTIO, and ran reductions for verifi- motions. cation. Hall modified existing software to run in a batch A comparison of UCAC with FASTT ͑R. Stone, NOFS͒ mode, allowing him to process several tapes per day. and CMT ͑D. Evans, Cambridge Universtiy, UK͒ data in a N. Zacharias continued with improvements to the quality sparse equatorial field is consistent with an external error of control software and handled the darks and flat reductions. about 35 mas for UCAC positions. He developed software to detect streaks on frames affected M. and N. Zacharias constructed a position-only catalog by the shutter problem. Software streak removal works suf- ͑r06͒ for 38.4 million stars including all survey fields ob- ficiently well only for relatively faint streaks, requiring the served until 31 May 2000. These data were given to the identification of ‘‘bad’’ cases for re-observing. Hall modified 2MASS and SDSS projects as well as to Yale University in this software for batch operation and ran it on all applicable the SPM collaboration. data, completing the streak checking by late 1999. N. Zacharias improved the systematic error corrections I. PlanetsÕSatellites ͑mainly the Charge Transfer Efficiency ͑CTE͒ model͒ in as- trometric solutions of the UCAC data in preparation for the Observations of the major planets Mars through Neptune, UCAC1 reductions. M. and N. Zacharias reduced all accept- plus 13 minor planets, were sent to the USNO’s AA Dept, able 79,931 CCD frames taken until November 1999 to ob- the Jet Propulsion Lab, and the Bureau des Longitudes in tain mean positions of 32 million stars. The positions are on Paris, France for ephemeris development. These observa- the ICRS using Hipparcos, Tycho-1, and ACT as references. tions were made from 1985 through 1996 under the USNO’s Wycoff provided Urban with a cross-reference of those po- Pole-to-Pole Program, and reduced to the Hipparcos refer- sitions and the USNO-A2.0, Tycho-2, and AC2000 star po- ence frame by Rafferty and Holdenried. sitions. This was used by Urban in computing proper mo- D. Pascu and J. Rohde, in collaboration with summer in- tions for the majority of UCAC1 stars. Wycoff also provided terns Martinka and Grefenstette, continued their astrometric, Hall with lists of several hundred UCAC1 stars that were not photometric and dynamical analysis of CCD observations of U.S. NAVAL OBSERVATORY 647 the Lagrangian librating satellites of Saturn, Helene͑SXII͒, reported on last year; this year’s work dealt primarily with Telesto͑SXIII͒ and Calypso͑SXIV͒, the Uranian satellites stars with photocenter ͑i.e. blended͒ positions in the Astro- I-V, and Jupiter satellites, Amalthea͑JV͒, and Thebe͑JXIV͒. graphic Catalogue ͑AC͒, but resolved by the Tycho data pro- Pascu, Rohde, and Seidelmann ͑in collaboration with as- cessing. In order to provide proper motions for these, the tronomers from several institutions͒ continued analysis of Tycho team decided to combine the AC data with a com- 1997 images of Triton and four inner satellites of Neptune: puted, Tycho photocenter position. These represent the last Proteus, Larissa, Galatea, and Despina. While mean motion major set of stars to be computed. They were forwarded to E. corrections were derived for each of the moons, a small dis- Hoeg ͑Copenhagen University, Denmark͒, who is heading crepancy between the separation and position angle solutions the Tycho-2 project. was detected, which suggested an error in the reference Preliminary release of the Tycho-2 catalog was made Au- planes of the observations or theories of the satellites. For gust 8, 1999. It contains 2,539,913 of the brightest stars. Proteus, the rms of the solution was 5 mas. Astrometric accuracies are magnitude dependent: positional A new photometric analysis, using the VEGAMAG sys- errors range from about 5 to 100 mas; proper motion errors tem, confirmed the leading/trailing brightness asymmetry for are typically from 1 to 3 mas/year. Triton; however, it did not support the episodic reddening in Urban and Wycoff help prepare the guide to the data that ͑B-V͒ reported earlier. New photometry for Proteus indicated is included on the Tycho-2 CD-ROM. During the 6-month a leading/trailing brightness asymmetry larger than that of period between the preliminary and public release, substan- Triton, but also consistent with charged-particle collisions. tial data verification took place utilizing observations from Photometry of the three fainter moons is continuing. Our the 2MASS project as well as the UCAC. The validation results were reported at the Triton/Pluto Workshop in Sep- processes showed the data to be of high quality. The Tycho-2 tember and at the DPS meeting in October. catalog was released to the public 8 February 2000. B. Hicks and Urban mailed 250 of the CDs to colleagues worldwide. J. Southern Proper Motion Program SPM Utilizing the photometry from the Tycho-2 data to better „ … determine color and magnitude equations, Urban performed In January, 2000, I. Platais began work at the USNO as a another reduction on the AC data. Wycoff performed numer- USRA contractor to work on the Yale Southern Proper Mo- ous tests to verify the data; some of these results necessitated tion program ͑SPM͒. The glass photographic plates from this further modifications to reduction software. program are being measured on the USNO’s Precise Mea- suring Machine ͑PMM͒ in Flagstaff. L. DoD Requirements Three major tasks have been accomplished during this period: USNO was contacted by Naval Surface Weapons Center ͑ ͒ 1. Platais in collaboration with T. Girard, V. Kozhurina- NSWC concerning a list of stars. Urban, aided by Corbin, Platais, and W. van Altena ͑Yale University͒ developed a Gauss, and Rafferty, evaluated the list. The results were for- software package to make complete astrometric reductions of warded to NSWC, with some suggested changes. In some the ͑PMM͒ measures of SPM plates. This includes prepara- instances, new astrometry was computed specifically for this tion of input data, selection of UCAC stars in each SPM catalog. In addition, several DoD contractors requested for ͑ field, construction of input catalog for further reductions, and clarification on astrometric issues e.g. what is the best cata- photometric and astrometric reductions of PMM measure- log to use under specific circumstances, photometric re- ͒ ments. sponses of various detectors, etc. 2. Platais and T. Girard tested several fields for the pres- ence of residual systematic errors in the PMM measurements M. Other Catalogs ͑ comparing direct and reverse measurements and with re- To analyze Hipparcos problem stars, individual epoch ͒ spect to the PDS measures and developed a new approach to TAC 2.0 data from an intermediate reduction step were re- perform a digital ‘‘re-focussing’’ of the original PMM data. quested ͑M. Odenkirchen, Bonn University, Germany͒.M. A substantial improvement in the final positional accuracies Zacharias constructed a file with 3,351,492 individual posi- has been achieved. tions. 3. Platais has reduced all non Milky Way SPM fields in N. Zacharias compared the final secondary reference star the following declination zones: -30,-35,-40,-45, and -50 de- catalog ͑C. de Vegt, Hamburg University, Germany͒ of grees. These comprise about 1/3 of all SPM fields. In May 80,000 stars in ICRS source fields ͑epochs 1975 to 1991͒ Platais, Girard, and V. Kozhurina-Platais released a proto- with UCAC data. Systematic errors up to 40 mas were found type catalog of the UCAC stars measured on the SPM first due to a lack of high quality proper motions for RϾ12 mag epoch plates. The total number of objects in this catalog is stars. For stars brighter than 12th magnitude, the systematic 2,815,858. It has been shown that the SPM data in combina- differences are on the 10 mas level. tion with the UCAC catalog produce proper motions with the standard error of 4.3 mas/yr. N. Sloan Digital Sky Survey The Sloan Digital Sky Survey is approaching an opera- K. Washington Proper MotionsÕTycho-2 tional state. The Astrometric pipeline routinely produces as- Proper motions for the Tycho-2 catalog were completed trometric fits to 90 mas, well below the 260 mas require- by Urban and Wycoff. Most of the 2.5 million stars were ment. During the year a ‘‘running means’’ version of the 648 ANNUAL REPORT pipeline has replaced a polynomial-based methodology. The structed 76 Long Delay Line pop-up mirror and completed running means algorithm more accurately tracks errors in the the Avalanche Photo Diode assemblies for NPOI. The shop instrument position angle more accurately than the completed several Wide Angle Star Acquisition mounts and polynomial-based solution. The UCAC is used as the refer- shipped them to the NPOI site. ence catalog for the extreme southern portions of the Sloan The shop constructed many parts for the cesium fountain survey area, and the ACT catalog is used for the northern clock for Time Service. This project consisted of machining Sloan area. As UCAC reaches full-sky coverage, the Sloan many precision parts from exotic materials to exacting toler- astrometric reductions are expected to be redone. ances. Hennessy worked with Princeton astronomer Izevic about The shop had numerous phone cons with the University an observing project to confirm candidate RR Lyrae stars of Washington, Seattle about the procedures and techniques found with the Sloan Digital Sky Survey telescope. An ob- of machining the parts for the spectrometer for the Sloan serving proposal to use the University of Virginia 1-m tele- Telescope. scope at Fan Mountain was submitted and granted time. Six The shop manufactured several components for the FTS stars proposed by Izevic were observed, and all six found to project including the fiber connector assembly for the 40- be variable, although a period luminosity relationship could inch telescope in Flagstaff for the FTS experiment. not be determined. The shop manufactured a photographic plate holder for deVegt to use thick plates on the Lick Observatory instru- O. Measuring Machines ment. The shop spent considerable time designing and con- L.Winter assembled and upgraded the Hamburg Observa- structing the time ball for the Millennium ceremony New tory’s HAM1 measuring machine after its arrival from Ham- Year’s eve. burg, Germany. The CCD camera of that machine was The shop designed and built many parts for the Starscan changed to a higher resolution type ͑Electrim EDC1000U͒ to Measuring Engine this period, including a light source, plate use the HAM1 machine for digitizing photographic plates. A holder, and camera adapter. first calibration was carried out that showed the machine to be in good condition and gave a measuring error of 0.3 mi- crons. The software for the HAM1 machine was rewritten for R. Miscellaneous the Windows 95 operating system and changed to process Urban continued as chairman of the IAU group ‘‘Densi- the larger images of the new CCD camera. fication of the Optical Reference Frame.’’ N. Zacharias con- With the help of Rafferty and the USNO shop, Winter tributed as member of the IAU Task Group on Designations, started the modification of the StarScan measuring engine. A the SOC of the IAU Working Group on Sky Surveys, and the large-format CCD camera equipped with a telecentric lens IAU Working Group on Reference Frames ͑densification͒. was mounted on the focusing unit cannibalized from Ham- burg Observatory’s HAM2 measuring machine, and the plate holder of HAM2 was mounted on a new rotating disk. The VI. NAVAL OBSERVATORY FLAGSTAFF STATION machine was calibrated and demonstrated that it is capable of „NOFS… measuring star positions to an accuracy of 0.2 micrometer A. Astrometry for high-contrast emulsions. The same software as written for the HAM1 machine is used to digitize the photographic 1. Parallaxes and Proper Motions plate and to analyze the resulting footprint images. C. Dahn continued to oversee the CCD trigonometric stel- lar parallax efforts. The 61-inch Strand Astrometric Reflector P. Computers was employed for this project on a total of 156 nights during the report year. Two different cameras continue to be used in The USNO AD computer systems were configured to this program. One ͑referred to as Tek2k͒ employs a ‘‘bare’’ work behind a firewall. This greatly increases the security, at Tektronix 2048x2048 CCD and is used for targeting stars the expense of a small loss of convenience. Hennessy con- fainter than Rϳ12. The second ͑designated ND9͒, also em- tinued replacing aging and obsolescent HPUX computers ploys a Tektronix 2048x2048 CCD, but witha3mmdiam- with pentium based Linux systems. Both the main Web eter neutral density attenuation spot mounted directly in front server and the major compute nodes were replaced. The new of the chip, providing 9.0 magnitudes of compensation, and machines run from 10 to 300 times faster than the machines permitting stars as bright as Rϭ4 to be targeted. they replace. The AD computers made it through the Y2K The Tek2k program has been operating since February changeover without any Y2K bugs. 1992 and parallax determinations now have been completed for 128 stars. During the present report year, concentration Q. Instrument Shop has been placed on obtaining distances to a selection of The shop concentrated mainly on the construction of the brown-dwarfs with L and T spectral types, primarily discov- Optical Interferometer this period. The shop constructed all ered by the 2MASS and SDSS collaborations. To date, reli- of the parts for 21 elevator vacuum cans and sent several able preliminary parallaxes have been determined for 17 cans assembled to the site. This brings the total to 34. The L-dwarfs, ranging in spectral types from L0 to L8. Since the shop constructed the Narrow Angle Trackers and all of the T-dwarfs identified to date are all very faint at wavelengths related parts for the Klinger mirror mounts. It also con- accessible with CCDs, only three are being attempted at U.S. NAVAL OBSERVATORY 649 present and reliable preliminary results have yet to be National Observatory 4-m and 2.1-m telescopes show that achieved for any of these. Now that Astrocam is operating results at least as good can be obtained with an Aladdin InSb with a science-grade Aladdin near-IR array ͑see below͒,we 1024x1024 detector. A full report of these test results will be anticipate rapid success in determining parallaxes for ex- given in a paper being prepared for The Astronomical Jour- tremely red targets ͑like T-dwarfs͒ using this instrument. The nal. remaining targets on the Tek2k program include degenerates, In fall 2000 NOFS will begin a near-infrared parallax and late-type dwarfs, late-type subdwarfs, and a variety of special proper motion program to complement the CCD-based astro- interest objects, such as central stars in planetary nebulae. metric program. The infrared program will concentrate on T- The formal precisions of relative parallaxes determined and late L-dwarfs which have little flux at optical wave- from the Tek2k CCD observations continue to fall typically lengths. Approximately 20-30 objects will be on the initial in the ϩ/-0.3 to ϩ/-0.6 mas range after 3-5 years of observ- program using either J, H, or K’ filters. This program will ing. The most precise relative parallax achieved to date has a use an Aladdin InSb 1024x1024 detector in the Astrocam formal standard error of ϩ/-0.16 mas and 9 determinations imager ͑see Section D͒ at the NOFS 61-inch telescope. now have formal errors better than ϩ/-0.30 mas. The proce- Based on the above test results, it is expected that distance dure for using photometric parallaxes of the individual ref- determinations to 2% or better for a majority of the currently erence stars in each field for determining corrections from known L- and T-dwarfs will be obtained within a two to relative parallax to absolute parallax has proved to be three year observation series. successful—with several notable exceptions involving fields located within 10 degrees of the Galactic Equator. In such 2. 8-inch Flagstaff Astrometric Scanning Transit fields, where the total reddening at a distance of a typical Telescope (FASTT) reference star ͑ϳ1 kpc͒ can vary from E͑B-V͒ϭ0.3 to E͑B- FASTT continued to make CCD observations this past V͒ϭ1.1 and the distribution of the absorbing material along year under the direction of R. Stone. All positions are now the various lines of sight is unknown, the total uncertainty in determined differentially using reference stars taken from the the correction from relative parallax to absolute parallax can Tycho-2 catalog. Positional accuracies of ϩ/- 60 mas are easily be as large as ϩ/-0.5 mas and occasionally more. Con- routinely achieved in each coordinate for well-exposed sequently, for distant targets, such as the central stars in plan- single observations, while the errors for the faintest objects etary nebulae, this uncertainty is the primary contributor to observed ͑V ϳ 17.5͒ are about 3-times larger. Magnitudes the uncertainty in our derived absolute parallaxes. Detailed are also determined, with accuracies ranging from ϩ/-0.02 to spectrophotometric observations of every reference star in ϩ/-0.10 mag, depending on the SNRs obtained. such fields will be required to improve the situation. During this report period, clocked-antiblooming operation The ND9 program began routine observations in Decem- of the CCD while in scan mode was developed. This allows ber 1995, targeting a selection of 72 objects, mostly sdF-G accurate positions of faint satellites to be obtained without stars, solar analogs, periodic variables, Field Horizontal contamination from the much brighter planet in close prox- Branch stars, and Mira variables with apparent brightnesses imity. All aspects of the telescope’s operation ͑target selec- in the range 5.2ϽVϽ9.5. After 4ϩ years of observations, the tion, observation, and reduction to final position and magni- preliminary solutions continue to show very good agreement tude͒ have been automated. Hence, human involvement with Hipparcos parallax determinations. The ND9 results ap- consists only of routine maintenance of the instrument and pear to be somewhat inferior to what is being achieved with preparing data for publication. Tek2k. However, this is most probably due to the less satis- This past year, FASTT positions were determined for a factory reference star frames available for many of the ND9 total of 387,000 stars. In addition, 32,300 observations of fields, even with 9.0 magnitudes of compensation. asteroids, and 1,200 observations of planets and planetary The current intention is to complete the ND9 observations satellites were obtained. Because of the great success of the in about a year, de-commissioning the ND9 camera, and Hipparcos spacecraft mission, there is no longer a need for commissioning a new camera ͑ND5͒ which will provide 5.0 ground-based absolute positions of stars brighter than Vϭ12 magnitudes of compensation. This camera will be used on at FASTT-level precisions/accuracies. Hence, the FASTT stars with apparent magnitudes in the 9.0 to 13.0 range. observing program now consists of projects that Hipparcos The infrared group led by F. Vrba and including H. was unable to achieve, such as long-term observations of Guetter, A. Henden, and C. Luginbuhl, completed a program solar system objects, extension of the Hipparcos catalog to of obtaining astrometric test observations of NGC 7790 and fainter magnitudes ͑V Ͼ 12͒, and monitoring the accuracy of M67 using a NICMOS III detector in the IRCam imager at the Hipparcos link to the ICRF reference system. the NOFS 61-inch telescope. These observations were de- signed to test the astrometric capabilities of modern infrared 3. Solar System Astrometry detector arrays in preparation for the initiation of an infrared The majority of the FASTT observations of planets and parallax and proper motion program of low mass stars envi- planetary satellites were made in support of a continuing sioned to start in late 2000 at NOFS ͑see below͒. These tests contract with JPL. Various spacecraft missions being sup- show that astrometric accuracies of about 10 mas for a single ported by these observations include NEAR, Deep Space 1 measurement for well-exposed stars are routinely obtainable ͑DS1͒, Cassini, and the proposed Pluto-Kuiper Express. The at wavelengths between 1.2 and 2.2 microns. Preliminary DS1 mission is now on its way to Comet Borrely, for an results obtained with NOAO instrumentation at the Kitt Peak encounter in September 2001. FASTT is obtaining astrom- 650 ANNUAL REPORT etry of several ‘‘beacon’’ asteroids which could be used for that were solved by making changes to the real-time data navigation of the DS1 spacecraft. Many FASTT observations analysis performed by the data acquisition system. This code were also obtained of: the Galilean satellites; the Jovian detects and centroids bright astrometric reference stars. Ad- outer satellites ͑Himalia, Elara, and Pasiphae͒; several Satur- ditionally, in light of these data taken under actual survey nian satellites ͑Tethys, Dione, Rhea, Titan, Hyperion, Iape- observing conditions ͑great circle drift scanning͒, the astro- tus, and Phoebe͒; Uranus and its satellites Titania and and metric pipeline has been extensively modified to improve Oberon; Neptune and Triton; and Pluto. The observations of robustness and to reduce residuals. The astrometry appears to the satellites of the outer planets are primarily being em- deliver systematics no worse than a few tens of milliarcsec- ployed to improve the planetary ephemerides. As with the onds ͑mas͒ and rms residuals of typically 100-120 mas. 1998 - 1999 data taken with the FASTT, there is generally Observations of SDSS photometric standards using the excellent agreement between the observed positions and Flagstaff Station’s 40-inch telescope were concluded this JPL’s DE405 predicted positions. With few exceptions, the year. These observations, conducted by A. Smith ͑University mean ͑FASTT - DE405͒ differences are under 50 mas in of Wyoming͒, spanned approximately 20 months and define each coordinate. The positions for these objects are being the SDSS photometric standard system. published in an on-going series in The Astronomical Journal Though still in the early stages of the survey, SDSS con- by Stone and F. Harris. tinues to deliver exciting science. SDSS has now found the Most of the over 32,000 FASST asteroid observations large majority of all known high-redshift ͑z Ͼ 3.5͒ quasars, made this year were on objects having identification numbers including the current record holder at zϭ5.8. A number of L- under 2000. All positions were determined differentially in and T-dwarfs have been discovered, including so-called the ICRF using ACT/Tycho-2 reference stars. These data are ‘‘transition’’ or intermediate objects between L and T clas- being used to study the kinematics of asteroid classes, to sification. A dozen faint high latitude carbon stars have been predict occultation events, to determine dynamical masses found. for selected asteroids, and to support JPL spacecraft mis- Pier has been involved in Galactic structure studies with sions. Due to the high accuracy of the FASTT positions, SDSS data. Evidence for remnant tidal streams has been predictions for occultation events can now be made with a found in the spatial distribution of Horizontal Branch stars. very high level of reliability and a record number of occul- A number of Galactic structure studies are underway, and as tations was observed last year. FASTT has also determined more of the sky is observed, the SDSS database will provide the positions for many thousands of stars along the path of a rich resource for Galactic astronomy studies. Munn contin- the Centaur asteroids 5145 Pholus and 10199 Chariklo in ued supporting the SDSS Operational Database. order to identify future occultation events. The Centaurs are Harris, Pier, Hajian, and Hindsley investigated how the most likely Kuiper Belt Objects ͑KBOs͒ that have been per- emission-line flux from planetary nebulae would affect the turbed into the inner solar system and because of their broad-band colors observed by SDSS. They concluded that greater brightnesses can be studied in detail. In March 2000, the colors should be very distinctive, and can be used to minor planet 2000 ED14 was expected to pass close enough identify halo planetary nebulae candidates in the SDSS sur- to Earth to allow radar ranging from Arecibo Observatory. B. vey area. Canzian and Guetter obtained images of it on two nights, The discovery of carbon stars in SDSS data is being lead using the 61-inch telescope. These observations were re- by B. Margon ͑University of Washington͒. USNO is analyz- duced by A. Monet and reported to the Minor Planet Center. ing their proper motions using PMM measurements of the These data allowed a significant improvement in the com- stars on early-epoch Schmidt plates. The proper motions are puted orbit for this object, which was successfully ranged necessary to determine whether the stars are nearby dwarf later that month. carbon stars or very distant halo giants. Fourteen carbon stars A. Monet continued her collaboration with E. Bowell have now been discovered with SDSS. ͑Lowell Observatory͒ to obtain astrometry of near-Earth as- A study of white dwarf stars observed by SDSS is being teroids. Until this year, all of the observations made at NOFS lead by H. Harris. Both photometric and spectroscopic SDSS for this project have utilized FASTT. Plans are now being data are already yielding many new white dwarfs. As an made to use the 1.3-meter instead, since many of the NEAs example, 113 were found in 78 square degrees of sky, where now being discovered are too faint for the smaller telescope. only 18 were known previously. Many stars with unusual In addition, A. Monet, H. Harris, and Stone have been in- spectra have already been discovered. Accurate photometry, cluded as scientific collaborators in a research proposal sub- positions, and proper motions add enormously to the data for mitted by Bowell to NASA for a new project to search for these stars. KBOs with the 1.3-m telescope. 5. Precision Measuring Machine (PMM) 4. Sloan Digital Sky Survey (SDSS) The PMM program, directed by D. Monet, has completed J. Munn, J. Pier, G. Hennessy ͑Astrometry Department͒, the scanning of the available portions of POSS-I OϩE, and R. Hindsley ͑NRL͒ continued working on the SDSS as- POSS-II UJϩJϩFϩN, ESO-R, SRC-J, SERC-ERϩEJ, trometric pipeline. During this year, data covering many AAO-RϩN, NPM, and SPM. At last count, it has scanned hundreds of square degrees of sky have been obtained and more than 16,000 plates, processed more than 16 trillion pix- reduced through the astrometric pipeline. Close examination els, and logged more than 10 billion detections. With the of the data and astrometric results revealed a few problems baseline scanning complete, PMM can now be tasked with U.S. NAVAL OBSERVATORY 651 scanning historically and/or scientifically significant plate ar- 6853 processed through IRAF. The known variable was chives. The first of these is the collection of plates rejected found to be a Mira with 214-day period. Approximately 30 from the POSS-I survey. In most cases, the plates are of high other variable stars were identified out of the 7,000 stars enough quality to merit scanning, and they contain irreplace- measured in the field. able historical data. Observations continue of new gamma-ray burst ͑GRB͒ Canzian finished a research paper with D. Monet, H. Har- localizations by Henden, Vrba, Luginbuhl, Guetter, and Can- ris, and J. Liebert and M. Fisher ͑University of Arizona͒, and zian. While no counterparts were discovered directly by the I. Reid ͑University of Pennsylvania͒ detailing a search for NOFS GRB team, many photometric observations were stars with large proper motion using PMM scans of POSS-I made and included in papers for those fields with optical and POSS-II survey and rejected plates in about 40 fields afterglow candidates. Photometric sequences were made by around the sky. The main result is that the Luyten Half Sec- Henden of many GRB localizations. Several GRB localiza- ond catalog of proper motion stars is mostly complete, con- tions were also observed with either IRCam or Astrocam, straining the possible population of halo white dwarf stars. resulting in infrared photometry of two optical transients: Some new proper motion stars were also discovered. grb991216 and grb00015. S. Levine continued to transcribe the PMM pixel archive In collaboration with B. Sumner ͑Bureau of Meteorology, from 8mm tape to DLT, as part of the effort to make the Australia͒, Henden is preparing a third paper on sequences in pixel data available. The PMM pixel and catalog data are cataclysmic variable fields. This paper will give accurate co- now available to the general astronomical community ordinates and identifications for newly discovered variables, through the NOFS web server (http://www.nofs.navy.mil/ as well as quiescent magnitudes for a majority of the stars. data/FchPix). The data include the scans of multiple epochs Henden worked with a group of dedicated AAVSO ama- and colors of the northern and southern Schmidt photo- teurs with CCD cameras on obtaining high precision light ͑ ͒ graphic sky surveys approximately 8,000 plates , and find- curves of several eclipsing binary systems. ing charts generated from the USNO-A2.0 and ACT cata- Henden monitored the X-ray nova J1859ϩ226 as part of a logs. The pixel server began operation in January 2000. collaborative space/ground-based effort with A. Castro- ͑ Levine, D. Monet, and M. Edwards Dickinson College/ Tirado ͑LAEFF, Spain͒ to understand this object. ͒ NSF REU Program worked on a project to search for high A program was continued in collaboration with J. Greiner proper motion stars in the southern sky, using PMM scans of ͑AIP͒ to search for orbital periodicity in the K-band light the AAO-R survey plates, and plates rejected by the survey. curve of the X-ray source GRS 1915ϩ105. Observations are continuing by Vrba, Guetter, Henden, and Luginbuhl. ͑ B. Photometry Levine worked with A. Bosh and M. Buie Lowell Obser- vatory͒ and G. Tovmassian ͑IA-UNAM, Mexico͒ to success- 1. Individual Objects fully observe the occultation of the star GSC0645-01130 by Guetter completed the BVI photometry for stars on the Saturn and its rings on the night of 2/3 December 1999. The ND9 parallax program. Guetter derived better values of JHK data will be used to probe the structure of the rings and colors and magnitudes in the CIT system for standards stars atmosphere. observed with IRCAM during the period 1994 to 2000. The infrared group completed a program using IRCam to Henden and U. Munari ͑University of Padova, Italy͒ com- obtain JHK photometry of approximately 60 extreme sub- pleted UBVRI observations of two sets of symbiotic stars. dwarfs, many of which are on the USNO parallax and proper Other projects with Munari included photometry of the pre- motion program. The resultant colors and magnitudes have cursor for Nova Aql 1999, measurement of the discovery uncertainties of typically 0.02 mag and form a tight locus in plates for the cataclysmic variable XY Psc, and studying the the J-H, H-K color-color diagram, clearly separated from nearby open cluster NGC 6738. main sequence stars. Henden finished the BVRI photometry for monitoring of The infrared group began a program using IRCam to ob- nearby, high proper motion RR Lyrae variables with R. tain JHK photometry of late M- and L-dwarfs and JH pho- White ͑University of Arizona͒. tometry of T-dwarfs, as a supplement to the USNO parallax Henden and K. Honeycutt ͑Indiana University͒ have and proper motion program. Approximately 9, 43, and 12 started a monitoring project on the stunted outburst eclipsing M-, L-, and T-dwarfs, respectively, are on this program to dwarf nova UU Aqr. Time-resolved photometry of the better determine the J-H, H-K color-color locus of the eclipses before, during, and after stunted outbursts will be lowest-mass main sequence stars. compared with models. J. Fischer and C. Dudley ͑NRL͒ began a supernova search In collaboration with L. Cook ͑CBA California͒, Henden program at near-infrared wavelengths using the Astrocam completed a monitoring project for the Mira variable discov- imager at the USNO 61-inch telescope. ered as part of the search for SGR 1815-14. An unusual flaring object in the galaxy NGC 3432 was at The first of many data-mining exercises of the 61-inch first thought to be a possible optical transient from an unde- parallax field images was started by Henden and H. Harris. tected gamma-ray burst. However, after extensive UBVRI The field of the planetary nebulae NGC 6853 was picked as photometric monitoring at the USNO 40-inch telescope by a test case since a known ͑but unpublished͒ variable star Vrba, Henden, Luginbuhl, and Canzian it was found to more appears in the field. Pipeline scripts to process such datasets likely be a Luminous Blue Variable ͑LBV͒. Additional col- were developed by Henden and the 200 images of NGC laborative work with researchers at the KAIT telescope ͑Uni- 652 ANNUAL REPORT versity of California, Berkeley͒, Ohio State University, and camera is being completed. Hardware and software are being the Klet Observatory ͑Czech Republic͒ has resulted in good developed and tested to provide fully automated operation. photometric coverage and several spectra being obtained Astrometry of short exposures ͑1 minute or less͒ taken thus during the period until a month after outburst. far gives accuracies of 20-30 mas for a single observation of stars to magnitude 18. Some initial testing has been done 2. Star Clusters with P. Seitzer ͑University of Michigan͒ for the feasibility of Luginbuhl continued his work on photometric variability studying space debris in or near geosynchronous orbit. of solar-type stars in the Galactic cluster Messier 67 with G. Henden, in collaboration with F. Harris, has continued the Lockwood ͑Lowell Observatory͒. development of 1.3-m CCD mosaic camera local intelligence Vrba continued collaborations with V. Straizys, A. Ka- using the PIC 17C44 microcontroller. F. Harris continued zlauskas ͑Vilnius Observatory, Lithuania͒, and R. Boyle electronic and mechanical design of the camera for the 1.3-m ͑Vatican Observatory͒ to obtain Vilnius photometry of red- telescope, and made operational the electronics to operate the dened stars in the Pelican Nebula, Collinder 428, and several filter-guider assembly. other star formation regions using the Tek 2048x2048 CCD Stone developed code for reducing 1.3-m CCD observa- at the USNO 40-inch telescope. tions to positions and magnitudes using reference objects During its 1998 outburst episode Vrba, Henden, Lugin- located in each CCD frame. Preliminary tests involved data buhl, and Guetter, along with collaborators D. Hartmann taken with one of the 1.3-m camera SITE 2048 x 4096 ͑Clemson University͒ and S. Klose ͑Tautenburg Observa- CCDs, and an analysis of standard astrometric fields ob- tory, Germany͒ monitored the SGR 1900ϩ14 gamma-ray lo- served with the 1.3-meter telescope showed accuracies of calization error box at I- and J-bands at the USNO 61-inch ϩ/-40 mas or better. Moreover, systematic errors that vary telescope to search for variable objects. While none were with location on the SITE chip were also found. The latter found, Henden created deep composite images of the local- might result from the surface of the thinned SITE chip being ization from these images. The brightest three stars near the distorted by its mounting. error box center were subtracted and a small cluster and halo A. Monet continued work on the astrometric reduction were discovered. This cluster is similar to that found in the package she developed for use with the 1.3-m telescope. localization for SGR 1806-20 ͑A&A, 1999, 350, 891͒. Working with H. Harris and with input from D. Monet, she Vrba, Henden, Guetter, and Luginbuhl continued work refined the star finder, improved the frame matching algo- with K. Stassun and R. Mathieu ͑University of Wisconsin͒ rithm, wrote a new mean place routine, and expanded the and T. Mazeh ͑Tel Aviv University, Israel͒ to determine disk least-squares fitting program. Test observations were reduced properties of Orion pre-main sequence stars for which they using the USNO-A2.0, FASTT, and UCAC catalogs, and in have previously measured rotation periods. During this year each case the internal errors matched those of the reference 10 micron photometry was obtained of selected stars to catalog. search for inner-truncated disks. It was found that stars lack- F. Harris continued involvement in the FAME project, ing near-infrared excesses in general do not possess disks, constructing a test bed CCD slow-scan readout system built truncated or otherwise. around an EEV 2Kx4K thinned CCD. He took data with the CCD installed on a precision translating stage within a 3. Extragalactic Objects thermal-vacuum chamber at Lockheed Martin Space Sys- Levine continued working with J. Gallagher and C. Con- tems ͑LMSS͒, and delivered the data for analysis to NOFS selice ͑University of Wisconsin͒ observing dwarf galaxies in and LMSS. He made a presentation of this experiment to the the Virgo cluster as part of a project to understand the origins NASA board reviewing the FAME project, presented an and evolution of early-type dwarf galaxies. overview of the experiment at the ESO CCD Detector Con- ference in Garching, Germany, and coauthored a paper on C. Spectroscopy the experiment given at the SPIE Conference in Munich, Germany. He designed and constructed prototype electronics A photometric study of the variable stars in the Draco for repeating the experiment at full FAME speed. dwarf spheroidal galaxy was almost completed by H. Harris, F. Harris served on the FAME CCD vendor selection H. Smith ͑Michigan State University͒, and N. Silbermann committee. He wrote the CCD testing specifications, and vis- ͑California Institute of Technology͒. About 300 variables ited four of the six original candidate vendors to assess their have been studied and classified, most of them RR Lyrae technical merits. He was asked by LMSS engineers to con- stars, and 22 with the characteristics of background QSOs. tribute to the design of the FAME flight CCD electronics. Spectra of QSO candidates taken with the WIYN 3.5-m tele- D. Monet’s activities in USNO’s FAME satellite project scope by Harris and Munn show that at least 80 percent are, included development of point spread function simulation in fact, QSOs. and fitting algorithms in addition to the baseline suite of functional fitting algorithms. He supported the thermal- D. Instrumentation vacuum chamber testing of FAME CCDs and providing near The 1.3-m telescope, built by DFM Engineering, was in- real-time reductions and measures of data quality and inves- stalled, after 3 years waiting for the optics to be figured by tigated the many concept studies associated with developing Kodak. A camera with a SITe 2Kx4K CCD detector, giving FAME from the proposal phase to a spacecraft that can be a 20x40 arcmin field, is in operation while a six-CCD mosaic built. J. Hobart constructed various electronics equipment to U.S. NAVAL OBSERVATORY 653 support FAME CCD evaluation and development. possible halo for the LMC using number counts derived from Astrocam, the 0.8-5.0 micron imager built under contract the USNO-A2.0 catalog. The initial results of this work show by Mauna Kea Infrared ͑MKI͒ was delivered in August that the center of the possible LMC halo is misaligned with 1999. This camera uses an Aladdin 1024x1024 array detector respect to the center of the bar, and almost coincides with the with Offner reimaging optics giving a scale of 0.34 arcsec/ centroid of the planetary nebula population. pix and a field of view of approximately 5.8x5.8 arcmin at Levine, G. Bell ͑SAIC͒, and A. Schweitzer ͑Honeywell the USNO 61-inch telescope. Until April 2000 Astrocam was Loveland͒, are working on a project to model the orbits of operated with an engineering grade array, after which a sci- dwarf spheroidal galaxies orbiting the Milky Way, in an at- ence grade Aladdin array was installed by MKI and USNO tempt to better constrain the mass of our galaxy, and to try personnel. It is currently equipped with a variety of wide and and determine the origin of these satellite galaxies. Levine narrowband filters between 0.9 and 3.5 microns. Since deliv- and L. Aguilar ͑IA-UNAM, Mexico͒ have continued to work ery, Astrocam has been primarily used in an engineering on a project to help quantify the importance of dynamical evaluation mode and to set up fields for the infrared astro- interactions between galaxies on the overall evolution of gal- metric program. IRCam, the previous USNO imager using a axies in and outside galaxy clusters. NICMOS III detector, has been retired from service. USNO and NOAO continued involvement in the Aladdin F. Other Scientific Studies project to develop 1024x1024 InSb sensor chip arrays ͑SCAs͒ at Raytheon Infrared Operations ͑formerly Hughes Luginbuhl was invited by the Hubble Heritage Team Santa Barbara Research Center͒. Additional monies input ͑Noll et al., STScI͒ to participate in the selection process for last year produced two high quality, four-quadrant, science a HST Hubble Heritage Project target, utilizing observing grade SCAs; the first science grade arrays actually produced time allocated to the Team (see http://heritage.stsci.edu/). He for the Aladdin consortium. One of these was installed in the participated in the preparation of a phase 2 observing plan USNO imager Astrocam. It has very few bad pixels, but does for the object selected ͑the Horsehead Nebula͒. have two regions of lower quantum efficiency covering Vrba and Henden continued working with H. Fliegel and about 10% of the device near the edges. These seem to flat- L. Warner ͑The Aerospace Corp.͒ on photometric monitoring ten well with the interpolated flat scheme developed by Lug- of GPS satellites. The resultant B-, V-, R-, and I-band light- inbuhl. Two final arrays are currently near completion, after curves as a function of Sun-GPS-observer phase angle are fit which USNO and NOAO will cease involvement with two to models of reflected light specularity in order to understand Aladdin development program, as these devices are now surface degradation. The results for four block II and IIa commercially available, which was the goal of the Aladdin satellites appear to be more consistent with particle bom- program. bardment of the satellites than with outgassing as a cause for F. Harris monitored the proposed increase in cellular tele- loss of reflectivity with time. New observations this year phone repeater installations near Flagstaff, to guard against included extending the observed wavelength range to the potential microwave signal interference impacting on the op- U-band for GPS SV 15 and SV 17 and to the J-, H-, and eration of low-light-level detectors at present and future tele- K-bands for SV 17. This satellite displays a smooth reflected scopes for NOFS. energy distribution between 0.36 and 2.2 microns, at least at The 24-inch telescope was removed and donated to the mid-phase angles. Booneville, MS Middle School. Hobart, A. Bird, S. Sell, and Hobart maintained the Time Service Data Acquisition A. Rhodes provided considerable information and sugges- System ͑DAS͒ that collects timing data for the LORAN sta- tions to the architect designing the new observatory. Hobart tions in the western part of the U.S. Hobart completely re- also modeled the 24-inch optics to determine the best ar- built the DAS and installed a new computer. rangement for visual observing. Preparations were made by Henden and shop personnel G. Miscellaneous for the arrival of The Amateur Sky Survey ͑TASS͒ Mark IV Guetter, Canzian, Hobart, F. Harris, Levine, Luginbuhl, camera system. This system will be used to make a photo- A. Monet, Stone, and Vrba participated in giving public metric survey of the northern sky, and should be delivered in tours and lectures. Almost 550 visitors toured the USNO August 2000. Flagstaff facilities, including those who visited during NOFS’ participation in the Annual Flagstaff Festival of Sci- E. Theoretical Studies ence. Canzian is analyzing interferometric HI emission line data Luginbuhl spent considerable effort during the past year on the spiral galaxy NGC 4321. The data are being used to on issues related to light pollution, outdoor lighting codes, verify the radius of the corotation resonance of its spiral and development of properties near the Flagstaff Station. pattern through study of velocity perturbations in the HI gas. Two years of effort has led to the publication, through the Levine worked with L. Sparke ͑University of Wisconsin͒ and International Dark-Sky Association ͑IDA͒, of the IDA Out- E. Noordemeer ͑University of Utrecht, Netherlands͒ on nu- door Lighting Code Handbook, edited and principally writ- merical studies of the dynamics and kinematics of galaxy ten by Luginbuhl with assistance from other planners, as- bars and disks that are off-center in large halos. Levine is tronomers and members of the IDA. As work on the working with A. Reiffel ͑Yale University/NSF REU Pro- Handbook neared completion, several presentations on the gram͒ on a project to determine the distribution of mass in a Handbook and lighting codes in general were given at IDA 654 ANNUAL REPORT national and regional meetings. During the year Luginbuhl and Mass of the Pleiades from a 2MASS-USNO Proper also consulted with several communities as they drafted, re- Motion Search,’’ Bull. Amer. Astron. Soc. 32, 868. vised, and enacted outdoor lighting codes, including Cotton- Ansari, S. M. R., and Dick, S. J. ͑eds.͒͑1999͒. ‘‘History of wood, Camp Verde, and Tucson, Arizona. At the beginning Oriental Astronomy,’’ in Highlights of Astronomy, Vol. of the report year Luginbuhl attended and presented two pa- 11: Joint Discussion 17 of the XXIIIrd General Assembly pers at the IAU-UN Special Environmental Symposium 196 of the IAU, held in Kyoto, Japan, 18-30 August 1997, held in Vienna, Austria. These papers are ‘‘Why Astronomy edited by J. Andersen ͑Dordrecht: Kluwer͒, p. 693. Needs Low Pressure Sodium Lighting’’ and ‘‘Using DMSP Armstrong, J. T., Hindsley, R. B., Mozurkewich, D., Hajian, nighttime imagery to evaluate lighting practice in Arizona.’’ A. R., Germain, M. E., and Nordgren, T. E. ͑2000͒. A. Monet has continued to serve as the WebMaster for the ‘‘Estimating Errors in Stellar Angular Diameters: Does the NOFS Website, although the usual webmaster duties are ac- NPOI See the Pulsation of Cephei?,’’ in Interferometry in tually shared among Canzian, Levine, and her. The external Optical Astronomy, 27-29 March 2000, Munich, Ger- NOFS Website now includes a pixel server for the PMM many, SPIE Proceedings vol. 4006, edited by P. J. Lena frames, an asteroid ‘‘tutorial’’ for use by the Flagstaff Festi- and A. Quirrenbach ͑Bellingham, Wash.: SPIE, Interna- val of Science, as well as extensive public-affairs type infor- tional Society for Optical Engineering͒, p. 634. mation on the Flagstaff Station, its instrumentation, and ma- Armstrong, J. T., Nordgren, T. E., Germain, M. E., Hajian, jor research projects. A. R., Hindsley, R. B., Hummel, C. A., Mozurkewich, D., and Thessin, R. N. ͑2000͒. ‘‘Diameters of delta Cep and VII. GENERAL eta Aql from the NPOI,’’ Bull. Amer. Astron. Soc. 32, Over 5,000 people visited the USNO in Washington dur- 878. ing the report period as part of the Monday night tours, co- Assafin, M., Zacharias, N., Andrei, A. H., and Viera Martins, ordinated by Public Affairs Specialist G. Chester. In addi- R. ‘‘Optical Positions of Extragalactic Radio Sources us- tion, on 6 May, approximately 1,500 people attended an ing the UCAC1,’’ in Towards Models and Constants for open house for Astronomy Day. Numerous special tours Sub-Microarcsecond Astrometry: Proceedings of the were given for the Vice President, Congress, Navy, and other 180th Colloquium of the International Astronomical government officials. Union held at the U.S. Naval Observatory, Washington, The USNO Millennium Committee sponsored a variety of D.C., 27-30 March 2000, edited by K. J. Johnston, D. D. activities to inaugurate the Year 2000, and implemented the McCarthy, B. J. Luzum, and G. H. Kaplan ͑Washington, millennium celebrations for the U. S. Navy. A ‘‘Countdown D.C.: U.S. Naval Observatory͒,p.68. to the year 2000’’ clock was erected at the 34th and Massa- Azoubib, J., Lewandowski, W., Nawrocki, J., and Matsakis, chusetts Avenue gate. By order of the Secretary of the Navy, D. ͑1999͒. ‘‘Continental and Intercontinental Tests of on New Year’s Eve USNO dropped a time ball in Washing- GLONASS P-code Time Transfer,’’ in ION GPS-99: Pro- ton ͑from its main building͒ for the first time since 1936. ceedings of the 12th International Technical Meeting of Secretary of the Navy Richard Danzig triggered the ball drop the Satellite Division of the Institute of Navigation, held in commemoration of the first method for time dissemination in the Nashville Convention Center, Nashville, Tennes- in the United States, inaugurated at the Naval Observatory in see, USA, 15-18 September 1999 ͑Alexandria, Va.: Insti- 1845. The ball drop was followed by fireworks on the north tute of Navigation͒, CD-ROM, p. 1053. side of the main building. More than 1,000 general public Azoubib, J., Lewandowski, W., Nawrocki, J., and Matsakis, witnessed the ball drop, as well as numerous VIPs. In con- D. ͑1999͒. ‘‘Some Tests of GLONASS Precise Code junction with Commission 41 of the IAU, S. Dick coordi- Time Transfer,’’ in Proceedings of the 1999 Joint Meet- nated an around-the-world time ball drop at 20 sites in eight ing of the 13th European Frequency and Time Forum and countries on six continents. Many of the sites triggered the the 53rd IEEE International Frequency Control Sympo- ball drop by signal from the GPS satellites, for which the sium, held in Micropolis, Besanc¸on, France, 13-16 April Naval Observatory provides the time. These activities will be 1999 ͑Piscataway, N.J.: Institute of Electrical and Elec- repeated for the inauguration of the millennium on 1 January tronics Engineers͒, vol. 1, p. 263. 2001. Numerous public and media inquiries continued to be Bangert, J. A. ͑1999͒. ‘‘The Astronomical Applications De- answered regarding the date for the beginning of the millen- partment Today,’’ in Proceedings, Nautical Almanac Of- nium. fice Sesquicentennial Symposium, held at the U.S. Naval Dick continued duties as President of IAU Commission Observatory, Washington, D.C., March 3-4, 1999, edited 41 ͑History of Astronomy͒. Dick also continued work on the by A. D. Fiala and S. J. Dick ͑Washington, D.C.: U.S. history of USNO. Naval Observatory͒, p. 227. P. Seidelmann continued as President of IAU Division I Bangert, J. A. ͑1999͒. ‘‘The Future of Almanac Data in the ͑Fundamental Astronomy͒, and as President of the Celestial United States,’’ in Proceedings, Nautical Almanac Office Mechanics Institute. He is Chairman of the FAME Science Sesquicentennial Symposium, held at the U.S. Naval Ob- team. servatory, Washington, D.C., March 3-4, 1999, edited by A. D. Fiala and S. J. Dick ͑Washington, D.C.: U.S. Naval VIII. PUBLICATIONS Observatory͒, p. 405. Adams, J. D., Stauffer, J. R., Monet, D. G., Skrutskie, M. F., Bangert, J. A. ͑1999͒. ‘‘Introductory Remarks,’’ in Proceed- and Beichman, C. A. ͑2000͒. ‘‘Results on the Structure ings, Nautical Almanac Office Sesquicentennial Sympo- U.S. NAVAL OBSERVATORY 655

sium, held at the U.S. Naval Observatory, Washington, ciation of Lunar and Planetary Observers Computing Sec- D.C., March 3-4, 1999, edited by A. D. Fiala and S. J. tion, http://www.m2c3.com/alpocs/tdl2000/ Dick ͑Washington, D.C.: U.S. Naval Observatory͒,p.1. celestialdimensions01232000/celestial_dimensions.htm Beish, J.D., ͑1999͒. ‘‘Are Cloud Bands On Mars Rare Or Beish, J. D. ͑2000͒. ‘‘Nuts and Bolts of Computing the Not?,’’ Association of Lunar and Planetary Observers In- Ephemeris - Part Four,’’ The Digital Lens: Newsletter of ternet WebPage: The Mars Section, http:// the Association of Lunar and Planetary Observers Com- www.lpl.arizona.edu/ϳ rhill/alpo/marstuff/ puting Section, http://www.m2c3.com/alpocs/tdl1999/ cloudbands.html. nutsbolts08301999/TDL-4.html Beish, J. D. ͑1999͒. ‘‘Are Observed White Areas On Mars Beish, J.D. ͑2000͒. ‘‘Practical Calculations for the Newton- Real?,’’ Association of Lunar and Planetary Observers ian Secondary Mirror,’’ The Digital Lens: Newsletter of Internet Web Page: The Mars Section, http:// the Association of Lunar and Planetary Observers Com- www.lpl.arizona.edu/ϳ rhill/alpo/marstuff/ puting Section, http://www.m2c3.com/alpocs/tdl2000/ whiteareas.html telescopemath 06202000/field1.htm Beish, J. D. ͑1999͒. ‘‘Astronomical Seeing,’’ The Digital Beish, J. D. ͑2000͒. ‘‘Some of the ’Astronomical Seeing’ Lens: Newsletter of the Association of Lunar and Plan- Scales,’’ The Digital Lens: Newsletter of the Association etary Observers Computing Section, http:// of Lunar and Planetary Observers Computing Section, www.m2c3.com/alpocs/tdl1999/seeing10031999/ http://www.m2c3.com/alpocs/tdl2000/seeing01212000/ Seeing2.html The%20Seeing% 20Scales.htm Beish, J. D. ͑1999͒. ‘‘Meteorological Survey of Mars For Beish, J. D., ͑2000͒. ‘‘Tubes for Reflecting Telescopes,’’ Opposition Years 1965-1995,’’ The Digital Lens: News- Amateur Astronomy 25, 26. letter of the Association of Lunar and Planetary Observers Breakiron, L. A. ͑ed.͒͑2000͒. Proceedings of the 31st An- Computing Section, http://www.m2c3.com/alpocs/ nual Precise Time and Time Interval ͑PTTI͒ Systems and tdl1999/meterological10199/MOM.html Applications Meeting, held at Dana Point, California, 7-9 Beish, J. D. ͑1999͒. ‘‘Nuts and Bolts of Computing the December 1999. Washington, UC.: U.S. Naval Observa- Ephemeris-Part Two,’’ The Digital Lens: Newsletter of tory. the Association of Lunar and Planetary Observers Com- Brumberg, V. A., Bretagnon, P. Capitaine, N., Damour, T., puting Section http://www.m2c3.com/alpocs/tdl1999/ Eubanks, T. M., Fukushima, T., Guinot, B., Klioner, S. nutsbolts08301999/TDL-2.html A., Kopeikin, S. M., Krivov, A. V., Seidelmann, P. K., Beish, J. D. ͑1999͒. ‘‘Nuts and Bolts of Computing the and Soffel, M. H. ͑1999͒. ‘‘General Relativity and the Ephemeris - Part Three,’’ The Digital Lens: Newsletter of IAU Resolutions,’’ in Highlights of Astronomy, Vol. 11: the Association of Lunar and Planetary Observers Com- Joint Discussion 3 of the XXIIIrd General Assembly of puting Section, http://www.m2c3.com/alpocs/tdl1999/ the IAU: Precession-Nutation and Astronomical Con- nutsbolts10031999/Tdl-3.html stants in the Dawn of the 21st Century, held in Kyoto, Beish, J.D. ͑1999͒. ‘‘Sand Ships of Mars,’’ Association of Japan, 18-30 August 1997, edited by J. Andersen ͑Dor- Lunar and Planetary Observers Internet Web Page: The drecht: Kluwer͒, p. 194. Mars Section, http://www.lpl.arizona.edu/ϳrhill/alpo/ Burgasser, A. J., Kirkpatrick, J. D., Brown, M. E., Reid, I. marstuff/sandshps.html N., Gizis, J. E., Dahn, C. C., Monet, D. G., Beichman, C. Beish, J. D. ͑1999͒. ‘‘Windows International Mars Patrol A., Liebert, J., Cutri, R. M., and Skrutskie, M. F. ͑1999͒. Astronomical Calculator WIMP,’’ The Digital Lens: ‘‘Discovery of Four Field Methane ͑T-Type͒ Dwarfs with Newsletter of the Association of Lunar and Planetary Ob- the Two Micron All-Sky Survey,’’ Astrophys. J. 522, servers Computing Section, http://www.m2c3.com/ L65. alpocs/tdl1999/wimpinfo00031999/WIMP.html Burgasser, A. J., Brown, M. E., Kirpatrick, J. D., Cutri, R. Beish, J. D., ͑2000͒. ‘‘Discrete Topographic and Orographic M., McCallon, H., Kopan, G., Gizis, J. E., Skrutskie, M. Clouds of Mars,’’ Association of Lunar and Planetary Ob- F., Liebert, J., Reid, I. N., Monet, D. G., Dahn, C. C., and servers Internet Web Page: The Mars Section, http:// Beichman, C. A. ͑2000͒. ‘‘Discovery of a Brown Dwarf www.lpl.arizona.edu/ϳ rhill/alpo/marstuff/discrete.htm. Companion to Gliese 570ABC: A 2MASS T Dwarf Sig- Beish, J. D. ͑2000͒. ‘‘Drawing Mars,’’ J. Assoc. Lunar nificantly Cooler than Gliese 229B,’’ Bull. Amer. Astron. Plan.Obs. 42, 36. Soc. 32, 876. Beish, J. D. ͑2000͒. ‘‘A German Equatorial Mount for the Burgasser, A. J., Kirkpatrick, J. D., Cutri, R. M., McCallon, Planetary Telescope,’’ The Digital Lens: Newsletter of H., Kopan, G., Gizis, J. E., Liebert, J. Reid, I. N. Brown, the Association of Lunar and Planetary Observers Com- M. E., Monet, D. G., Dahn, C. C., Beichman, C. A., and puting Section, http://www.m2c3.com/alpocs/tdl2000/ Skrutskie, M. F. ͑2000͒. ‘‘Discovery of a Brown Dwarf mountmath05222000/mount.htm Companion to Gliese 570ABC: A 2MASS T Dwarf Sig- Beish, J. D. ͑2000͒. ‘‘Martian Volcanoes on HST Images,’’ nificantly Cooler than Gliese 229B,’’ Astrophys. J. 531, Association of Lunar and Planetary Observers Internet L57. Web Page: The Mars Section, http://www.lpl.arizona.edu/ Burt, E. A., Swanson, T. B., and Ekstrom, C. R. ͑1999͒. ϳrhill /alpo/marstuff/ VOLCANO.htm ‘‘Cesium Fountain Development at USNO,’’ in Proceed- Beish, J. D. ͑2000͒. ‘‘Measuring Celestial Dimensions with ings of the 1999 Joint Meeting of the 13th European Fre- Micrometers,’’ The Digital Lens: Newsletter of the Asso- quency and Time Forum and the 53rd IEEE International 656 ANNUAL REPORT

Frequency Control Symposium, held in Micropolis, Be- itz, 1907-1998,’’ Bull. Amer. Astron. Soc. 31, 1605. sanc¸on, France, 13-16 April 1999 ͑Piscataway, N.J.: Insti- Dick, S. J. ͑2000͒. ‘‘Cosmotheology: Theological Implica- tute of Electrical and Electronics Engineers͒, vol. 1, p. 20. tions of the New Universe,’’ in Many Worlds: the New Carter, M. S., Cook, P., and Luzum, B. ͑1999͒. ‘‘A History Universe, Extraterrestrial Life, and the Theological Impli- of Women in the Nautical Almanac Office,’’ in Proceed- cations, edited by S. J. Dick ͑Philadelphia, Pa.: Templeton ings, Nautical Almanac Office Sesquicentennial Sympo- Foundation Press͒, p. 191. sium, held at the U.S. Naval Observatory, Washington, Dick, S. J. ͑2000͒. ‘‘Extraterrestrials and Objective Knowl- D.C., March 3-4, 1999, edited by A. D. Fiala and S. J. edge,’’ in When SETI Succeeds: The Impact of High- Dick ͑Washington, D.C.: U.S. Naval Observatory͒,p. Information Contact, edited by A. Tough ͑Bellevue, Wa.: 165. Foundation for the Future͒,p.47. Carter, M. S., and Carter, W. ͑2000͒. ‘‘Seth Carlo Chandler, Dick, S. J. ͑2000͒. ‘‘Interstellar Humanity,’’ Futures 32, 555. Jr.: The Discovery of Variation of Latitude,’’ in Polar Dick, S. J. ͑ed.͒͑2000͒. Many Worlds: the New Universe, Motion: Historical and Scientific Problems, Proceedings Extraterrestrial Life, and the Theological Implications. of the 178th Colloquium of the International Astronomi- Philadelphia, Pa.: Templeton Foundation Press. cal Union, held in Cagliari, Sardinia, Italy, 27-30 Septem- Dick, S. J. ͑2000͒. ‘‘Plurality of Worlds,’’ in Encyclopedia ber 1999, ASP Conference Series vol. 208, edited by S. J. of the Scientific Revolution from Copernicus to Newton, Dick, D. McCarthy, and B. Luzum ͑San Francisco, Ca.: edited by Wilbur Applebaum ͑New York: Garland Pub- Astronomical Society of the Pacific͒, p. 109. lishing͒, p. 508. Chadsey, H. ͑2000͒. ‘‘An Automated Alarm Program for Dick, S. J. ͑2000͒. ‘‘Polar Motion: A Historical Overview on HP5071A Frequency Standards,’’ in Proceedings of the the Occasion of the Centennial of the International Lati- 31st Annual Precise Time and Time Interval ͑PTTI͒ Ap- tude Service,’’ in Polar Motion: Historical and Scientific plications and Planning Meeting, held in Dana Point, Ca., Problems, Proceedings of the 178th Colloquium of the In- 7-9 December 1999, edited by L. A. Breakiron ͑Washing- ternational Astronomical Union, held in Cagliari, Sar- ton, D.C.: U.S. Naval Observatory͒, p. 649. dinia, Italy, 27-30 September 1999, ASP Conference Se- Chambers, J. E., and Murison, M. A. ͑2000͒. ‘‘Pseudo-High- ries Vol. 208, edited by S. J. Dick, D. McCarthy, and B. Order Symplectic Integrators,’’ Astron. J. 119, 425. Luzum ͑San Francisco, Ca.: Astronomical Society of the Charlot, P., Viateau, B., Baudry, A., Ma, C., Fey, A., Pacific͒,p.3. Eubanks, T. M., Jacobs, C., and Sovers, O. ͑2000͒. ‘‘A Dick, S. J. ͑2000͒. ‘‘William Markowitz ͑1907-1998͒,’’ in Proposed Astrometric Observing Program for Densifying Polar Motion: Historical and Scientific Problems, Pro- the ICRF in the Northern Hemisphere,’’ in International ceedings of the 178th Colloquium of the International As- VLBI Service for Geodesy and Astrometry 2000 General tronomical Union, held in Cagliari, Sardinia, Italy, 27-30 Meeting Proceedings, held in Ko¨zting, Germany, 21-25 September 1999, ASP Conference Series vol. 208, edited Feb. 2000, NASA Conference Publication CP-2000- by S. J. Dick, D. McCarthy, and B. Luzum ͑San Fran- 209893, edited by N. R. Vandenberg and K. D. Baver cisco, Ca.: Astronomical Society of the Pacific͒, p. 335. ͑Hampton, Va.: National Aeronautics and Space Admin- Dick, S. J., McCarthy, D., and Luzum B. ͑eds.͒͑2000͒. Polar istration, Langley Research Center, Scientific and Techni- Motion: Historical and Scientific Problems, Proceedings cal Information Program͒, p. 168. of the 178th Colloquium of the International Astronomi- Corbin, B. G. ͑1999͒. ‘‘Bibliographic Resources for the His- cal Union, held in Cagliari, Sardinia, Italy, 27-30 Septem- torian of Astronomy,’’ Bull. Amer. Astron. Soc. 31, 1553. ber 1999, ASP Conference Series vol. 208. San Francisco, Corbin, T. E. ͑1999͒. ‘‘Commission 8: Positional As- Ca.: Astronomical Society of the Pacific. tronomy,’’ in Transactions of the International Astro- Dick, S. J., McCarthy, D., and Luzum B. ͑2000͒. ‘‘Preface,’’ nomical Union, vol. XXIIIB, Proceedings of the Twenty- in Polar Motion: Historical and Scientific Problems, pro- Third General Assembly, 18-30 August, 1997, Kyoto, ceedings of the 178th Colloquium of the International As- Japan, edited by J. A. Andersen ͑Dordrecht: Kluwer͒,p. tronomical Union, held in Cagliari, Sardinia, Italy, 27-30 85. September 1999, ASP Conference Series vol. 208, edited Dick, S. J. ͑1999͒. ‘‘History of the American Nautical Alma- by S. J. Dick, D. McCarthy, and B. Luzum ͑San Fran- nac Office,’’ in Proceedings, Nautical Almanac Office cisco, Ca.: Astronomical Society of the Pacific͒, p. xiii. Sesquicentennial Symposium, held at the U.S. Naval Ob- Douglass, G. G., Mason, B. D., Germain, M. E., and Worley, servatory, Washington, D.C., March 3-4, 1999, edited by C. E. ͑1999͒. ‘‘Speckle Interferometry at the US Naval A. D. Fiala and S. J. Dick ͑Washington, D.C.: U.S. Naval Observatory. IV.,’’ Astron. J. 118, 1395. Observatory͒,p.11. Douglass, G. G., Mason, B. D., Rafferty, T. J., Holdenried, Dick, S. J. ͑1999͒. ‘‘Observations of the Leonids over the E. R., and Germain, M. E. ͑2000͒. ‘‘Speckle Interferom- Last Millennium,’’ in Highlights of Astronomy, Vol. 11: etry at the US Naval Observatory. V.,’’ Astron. J., 119, Joint Discussion 23 of the XXIIIrd General Assembly of 3071. the IAU: The Leonid Meteor Storms: Historical Signifi- Dyck, H. M. ͑2000͒. ‘‘Interferometry With Two Tele- cance and Upcoming Opportunities, held in Kyoto, Japan, scopes,’’ in Principles of Long Baseline Stellar Interfer- 18-30 August 1997, edited by J. Andersen ͑Dordrecht: ometry, edited by P. R. Lawson, JPL Publication 00-009 Kluwer͒, p. 1007. ͑Pasadena, Ca.: Jet Propulsion Laboratory͒, p. 185. Dick, S. J., and McCarthy, D. D. ͑1999͒. ‘‘William Markow- Ekstrom, C. R. ͑1999͒. ‘‘Precise Timing,’’ Science 286, 248. U.S. NAVAL OBSERVATORY 657

Ekstrom, C. R., Torcaso, F., Burt, E. A., and Matsakis, D. N. Annis, J., Bahcall, N. A., Bakken, J. A., Bastian, S., Ber- ͑1999͒. ‘‘Estimating the Stability of N Clocks with Cor- man, E., Boroski, W. N., Briegel, C., Briggs, J. W., Brink- relations,’’ in Proceedings of the 1999 Joint Meeting of mann, J., Carr, M. A., Colestock, P. L., Connolly, A. J., the 13th European Frequency and Time Forum and the Crocker, J. H., Csabai, I., Czarapata, P. C., Davis, J. E., 53rd IEEE International Frequency Control Symposium, Doi, M., Elms, B. R., Evans, M. L., Federwitz, G. R., held in Micropolis, Besanc¸on, France, 13-16 April 1999 Frieman, J. A., Fukugita, M., Gurbani, V. K., Harris, F. ͑Piscataway, N.J.: Institute of Electrical and Electronics H., Heckman, T. M., Hennessy, G. S., Hindsley, R. B., Engineers͒, vol. 1, p. 168. Holmgren, D. J., Hull, C., Ichikawa, S.-I., Ichikawa, T., Fan, X., Strauss, M. A., Gunn, J. E., Lupton, R. H., Carilli, Ivezic, Z. E., Kent, S., Knapp, G. R., Kron, R. G., Lamb, C. L., Rupen, M. P., Schmidt, Gary D., Moustakas, L. A., D. Q., Leger, R. F., Limmongkol, S., Lindenmeyer, C., Davis, M., Annis, J., Bahcall, N. A., Brinkmann, J., Brun- Long, D. C., Loveday, J., MacKinnon, B., Mannery, E. J., ner, R. J., Csabai, I., Doi, M., Fukugita, M., Heckman, T. Mantsch, P. M., Margon, B., McKay, T. A., Munn, J. A., M., Hennessy, G. S., Hindsley, R. B., Ivezic, Z., Knapp, Nash, T., Newberg, H. J., Nichol, R. C., Nicinski, T., G. R., Lamb, D. Q., Munn, J. A., Pauls, A. G., Pier, J. R., Okamura, S., Ostriker, J. P., Owen, R., Pauls, A. G., Rockosi, C. M., Schneider, D. P., Szalay, A. S., Tucker, Peoples, J., Petravick, D., Pier, J. R., Pordes, R., Prosapio, D. L., and York, Donald G. ͑1999͒. ‘‘The Discovery of a A., Rechenmacher, R. Richards, G. T., Richmond, M. W., High-Redshift Quasar without Emission Lines from Sloan Rivetta, C. H., Rockosi, C. M., Sandford, D., Sergey, G., Digital Sky Survey Commissioning Data,’’ Astrophys. J. Sekiguchi, M., Shimasaku, K., Siegmund, W. A., Smith, Lett. 526, L57. J. A., Stoughton, C., Szalay, A. S., Szokoly, G. P., Fan, X, Strauss, M. A., Schneider, D. P., Gunn, J. E., Lup- Tucker, D. L., Vogeley, M. S., Waddell, P., Wang, S.-I., ton, R. H., Yanny, B., Anderson, S. F., Anderson, J. E., Weinberg, D. H., Yasuda, N., and York, D. G. ͑2000͒. Jr., Annis, J., Bahcall, N. A., Bakken, J. A., Bastian, S., ‘‘High-Redshift Quasars found in Sloan Digital Sky Sur- Berman, E., Boroski, W. N., Briegel, C., Briggs, J. W., vey Commissioning Data: II. The Spring Equatorial Brinkmann, J., Carr, M. A., Colestock, P. L., Connolly, A. Stripe,’’ Astron. J. 119, 1. J., Crocker, J. H., Csabai, I., Czarapata, P. C., Davis, J. E., Fenton, P., Klepczynski, W., Powers, E., and Douglas, R. Doi, M., Elms, B. R., Evans, M. L., Federwitz, G. R., ͑2000͒. ‘‘Time Transfer using WAAS: An Initial At- Frieman, J. A., Fukugita, M., Gurbani, V. K., Harris, F. tempt,’’ in Proceedings of the 31st Annual Precise Time H., Heckman, T. M., Hennessy, G. S., Hindsley, R. B., and Time Interval ͑PTTI͒ Applications and Planning Holmgren, D. J., Hull, C., Ichikawa, S.-I., Ichikawa, T., Meeting, held in Dana Point, Ca. , 7-9 December 1999, Ivezic, Z. E., Kent, S., Knapp, G. R., Kron, R. G., Lamb, edited by L. A. Breakiron ͑Washington, D.C.: U.S. Naval D. Q., Leger, R. F., Limmongkol, S., Lindenmeyer, C., Observatory͒, p. 191. Long, D. C., Loveday, J., MacKinnon, B., Mannery, E. J., Fey, A. L. ͑1999͒. ‘‘Maintenance of the ICRF: Radio,’’ in Mantsch, P. M., Margon, B., McKay, T. A., Munn, J. A., Highlights of Astronomy, Vol. 11: Joint Discussion 7 of Nash, T., Newberg, H. J., Nichol, R. C., Nicinski, T., the XXIIIrd General Assembly of the IAU: The New In- Okamura, S., Ostriker, J. P., Owen, R., Pauls, A. A., ternational Celestial Reference Frame, held in Kyoto, Ja- Peoples, J., Petravick, D., Pier, J. 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