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1997 STATISTICS Cover: Radio Image of the Supernova Remnant W50

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1997 STATISTICS Cover: Radio Image of the Supernova Remnant W50 NATIONAL RADIO O B S S u E M R M V A I R N Y G ASTRONOMY OBSERVATORY 1997 STATISTICS Cover: Radio image of the supernova remnant W50. The image was made with the Very Large Array at 1.4 GHz from a mosaic of 58 individual images. The regions of most intense radio emission are shown in red while regions of lower brightness are colored blue. The W50 remnant is powered by the dying star SS433 seen near the center; helical filaments of radio emission can be seen emanating from SS433. Observers: G. Dubner, F. Mirabel, M. Holdaway, M. Goss NATIONAL RADIO ASTRONOMY OBSERVATORY Observing Summary 1997 Statistics March 1998 SCIENTIFIC HIGHLIGHTS The first VLSI Satellite project, the VLBI Space Observatory Program (VSOP), has been successful. The Japanese HALCA satellite, launched in February, observed the radio source PKS 1519-273 at 1.6 GHz on 22 May, together with the VLBA and VLA. The data were correlated successfully in Socorro on 12 June and an image was produced a few days later. The image, a point source, confirmed the proper operation of the entire system, including the Green Bank ground station and the VLBA correlator. Since mid-1997, VSOP has made a transition from in-orbit checkout to general scientific observing. Nearly 50 scientific observations have been processed by the VLBA correlator and released to the investigators. Several images of compact extragalactic radio sources have been produced at 1.6 and 5 GHz, with considerably higher resolution than is available with ground-only VLBI at the same frequencies. Numerous scientific results from these images are expected to be published over the next year. The 12 Meter Telescope has conducted extensive measures of the Martian CO absorption in support of the Mars Global Surveyor (MGS), which entered Mars orbit on 12 September. The MGS is an orbiter mission to conduct the first global mapping of the surface mineralogy, topology, and magnetic fields, at high-to-medium resolution. The 12 Meter CO data, taken regularly over the past year, and at three-day intervals since September, are used to provide atmospheric sounding measurements of the martian atmosphere in support of the aerobraking maneuvers of the MGC orbiter, which dips into the upper atmosphere in order to circularize its orbit. The CO data provide measures of the dust heating of the lower atmosphere (0-50 km), which in turn provide early warning of associated changes in the atmospheric densities encountered by the MGS orbiter. The CO 2-1 absorption has also produced highly accurate measures of the pressure changes at 70 km altitude, which show a very good correlation with the density changes seen by MGS. For example, the CO data showed cold, dust-free conditions as MGS entered orbit, and also indicated a significant trend of increasing temperatures up to 21 September, as a result of increasing dust loading of the lower atmosphere. It will soon be possible to determine whether the current dust behavior is a short-term phenomenon such as observed during the March-July period, or is the beginning of truly global dust storm activity on Mars. A large HI supershell has been discovered near the Galactic plane in Aquila. Observations with the 140 Foot Telescope show an irregular spherical shell sitting atop a well-defined massive cone which connects to a molecular cloud in the Galactic Plane. The shell extends at least 550 pc up into the Galactic halo. The system requires the energy of 10-100 superaovae over 10 million years for its creation. It is associated with a complex of supemovae, star-forming regions and HE regions, some of which may have been induced by a shock wave related to formation of the supershell. The VLA and VLBA have made the first detection of radio emission from a Gamma-Ray Burster. The gamma-ray burst was detected by the BeppoSAX satellite on 8 May and the VLA observed the region within four hours. Radio emission was first seen on 13 May, and VLBI detection was made on 16 May, yielding a position accurate to less than a milliarcsecond. Continued monitoring shows the object to be variable in both intensity and spectral index, and to have a proper motion no greater than 50 milliarcseconds per year. If the fluctuations are the result of scintillation due to inhomogeneities in the interstellar medium, the angular size of the source in the first few weeks was ~ 3 microarcseconds, a linear size of 1017 cm at a distance of 1028 cm. The subsequent damping of the scintillations is presumed due to relativistic expansion of the fireball to an angular size no longer subject to scintillation. The object is also observed optically, and has a minimum redshift of z = 0.85, thus greatly strengthening the case for cosmological distances to these objects. The long-chain cyanopolyyne species HCnN has been reliably identified in the molecular cloud TMC-1 via observations at the 140 ft telescope of two consecutive transitions (J= 39-38 and J = 38-37). The observations are based on frequencies expected from 2 laboratory work at the Center for Astrophysics. The column density of HCnN is 2.8 x 10" cm" . The abundance of the cyanopolyynes thus decreases smoothly from HC5N to HC,^, the decrement from one to the next being about 6 for the longer carbon chains. This detection of HCnN, a molecule with a molecular weight (147 amu) nearly twice that of the amino acid glycine, demonstrates that detectable quantities of fairly large organic molecules can form in extraterrestrial sources under conditions markedly different from those on Earth. Several programs to study the physical and chemical composition and the evolution of comet Hale-Bopp have been performed at + the 12 Meter Telescope. Studies of CO, CN, CS, H2S, HCO , H2CO, CH3OH and HCN have chronicled the chemical evolution and the temperature of the comet as it approached perihelion. The first detection of HNC has been made in a comet, and yields a ratio [HNC]/[HCN] - 0.5, close to values found in dark clouds. This ratio suggests that Hale-Bopp was formed from pristine interstellar matter and did not undergo much processing in the presolar nebula. The AGN galaxy NGC4258 continued to provide impressive results during 1997. VLBA/VLA observations of the warped disk of H20 molecules surrounding a supermassive object at the galaxy's core have yielded a precise position for the central object, presumably a black hole with 3.5xl07 solar masses. Proper motions have been measured for individual maser spots within the disk. Continuum emission has been detected in the nuclear region, and shows an offset from the calculated position of the central object consistent with the jet model proposed by Blandford and Konigl in 1979. The proper motion detections will allow a trigonometric determination of the distance to NGC4258 to within five percent. OBSERVING HOURS est. est. est. 30 1985 86 87 88 89 90 91 92 93 94 95 96 97 98 99 2000 Calendar Year 140 Foot £2] 12 Meter ^ VLA □ VLBA Figure 1. This figure shows the hours for observing on each telescope during the last decade. Includes astronomical observing, testing, and calibration. DISTRIBUTION OF SCHEDULED OBSERVING TIME 12 Meter 140 Foot VLA VLBA 8-B :• ■ •:•: ■ :* - v< •••■ *.•■ .V V. iV V •*•' SL lU V. M 7 ^ n o o "■^ © :mm m 1 \ 3 ! imm O Wi7 14 1 'm S A 'm'A 'A m, x22 Ji nWi ■§■? ^IIIIH 1988 89 90 91 92 93 94 95 96 97 1988 89 90 91 92 93 94 95 96 97 1988 89 90 91 92 93 94 95 96 97 1993 94 95 96 97 Calendar Year Calendar Year Calendar Year Calendar Year NRAO Staff Y//\ Visitors Kggfl Testing and Calibration Figure 2. These graphs show the number of hours scheduled for testing and calibration, and for observing by the NRAO staff and by visitors on each telescope system. 12 METER RADIO TELESCOPE SUMMARY 100 -- A 80 1 r s n A A i ^ 1 X / i * i / \ ^C 1 JL - ^ r / ^ / \ / \ A / ■\ X * 60 1 A A n A r 1 t J i A f 1 A r l A Z 3 £ - u D: 40 I [ U ULf - Y ^ V Y 20 J V / I 7 \i V l 0 1 ^ L i V i V 1 1 i V * v r <* .- & S v V J i .-• '«** ^ X ?: ^i /' ' j P**' »*»' > !•' V t > J.. A ^ > Calendar Year Observing Installation, Maintenance and Calibration — — Equipment Failure, Weather and Interference Figure 3. This summary for each quarter of the calendar year shows the percentage of the total time in the year (8760 hours) that the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. The telescope is removed from service for a period of four to six weeks each summer during the wet season. This period is used for maintenance and upgrading of the instrument. 140 FOOT RADIO TELESCOPE SUMMARY 100 "^ _ ^ M. ^ ^ mm «■ A ^ 80 L^ ^ ▼ % - C ^ - « 60 - - & 40 - - 20 ^k, •s ^ A "•; V, * 4 A .-, • •* ^■^ ■ •« ..- V. .^^^. '^. IT *►-. ,-*•"• Calendar Year Observing Installation, Maintenance and Calibration — — Equipment Failure, Weather and Interference Figure 4. This summary for each quarter of the calendar year shows the percentage of the total time in the year (8760 hours) that the telescope was scheduled for observing; for routine calibration, maintenance, and installation of new experiments; and the percentage of time lost due to equipment failure, bad weather, and radio interference. VERY LARGE ARRAY TELESCOPE SUMMARY 100 - - 80 *> /V ,^, ,B',i \0 - — "^ ^ V ^ ^" "* ^ ■■ s " *" ^ ^ '" -*- 3 60 V - - ou 40 N K s^ •N ^m _ —.
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