National Rcufio ** Astronomy Observing iumman) Observatory 2002 NATIONAL RADIO ASTRONOMY OBSERVATORY Observing Jummanj 2002 5tatiitio April 2003 (Revised 05/01/03) Scientific Highlights m Observing 5ummarij 2002 i • THE DEFLECTION OF RADIO WAVES CAUSED BY A MOVING OBJECT-On September 8,2002, when Jupiter passed within 3.7' of a strong quasar, astronomers used the VLBA and Effelsberg to measure the deflection of the quasar produced by the gravitational field of Jupiter. By alternating observations of the quasar with two other nearby calibrators, the position of the quasar on September 8, compared with that on four other days, was measured to an accuracy less than 10 microarcsec. This accuracy is a factor of three better than previous VLBI observations, and much more accurate than any other astrometric method. By using a similar technique, the determination of the parallax of objects more than 10 kpc distant, the tracking of spacecraft to an accuracy of 30 meters near Jupiter, and the measurement of the proper motion of objects in M31 to 5 km/sec over 10 years, can be obtained. The measurement confirmed that the deflection of the quasar is associated with the retarded position of Jupiter, and the result is in agreement with the prediction of General Relativity (GR). There is lively discussion among physicists about which parameters(s) of GR are measured by this experiment: the speed of gravity, the speed of light, or the post-parameterized Newtonian parameter Ot,. The interpretation depends on how GR is generalized in order to incorporate a speed of gravity which is not equal to the speed of light. However this experiment, as well as those associated with the binary pulsar and lunar laser ranging, are consistent with the speed of gravity equal to the speed of light. • DISCRETE HI CLOUDS IN THE GALACTIC HALO-GBT observations of the Galactic HI halo in the inner Galaxy show that in many directions the halo consists of previously unresolved clouds, some of which are more than 2 kpc from the Galactic plane, corotating with the disk below. These clouds provide evidence that supernova- powered "galactic fountains" continually blast superheated gas into the halo. In previous, lower-resolution 21 cm observations the cloud ensemble appeared nearly continuous, suggesting incorrectly that the HI halo was diffuse. It now appears that much if not all of the HI halo is concentrated into clouds with sizes of a few tens of parsecs, and masses of 50 to 100 solar masses. The clouds were discovered about 5 kpc from the Earth toward the galactic center. • THE NATURE OF THE FAINTEST GALAXIES - Surveys of the faintest radio objects using the VLA and optical images from HST, Keck and Subaru show that most of these objects are galaxies with redshifts greater than one. The nature of their emission is important in determining the evolution and interaction of galaxies at early cosmological epochs. Two processes are believed important to their radiative properties: massive star formation, and active galactic nuclei. One of the best discriminators between these processes is the angular size of the emission regions: if less than -0.1 arcsec (-50 pc at z=l), then their radiative temperature exceeds 106 degrees and the emission cannot be produced by star formation. In March 2002, the VLBA+GBT+Effelsberg imaged at 1.4 GHz a 6'x6' region in the field SA13 with 0.02" resolution. Within this region, -100 objects above 50 ujy had already been detected with the VLA, and optical images down to 26-mag identified > 90% of the objects. The combination of radio telescopes achieved an rms image noise of 7 ujy. Analysis of the images suggests that less than 10% of the radio sources contain emission within 0.04 arcsec components—the size expected for AGN activity. Thus, the early evolution of galaxies appears to be driven mostly by starburst phenomena rather than the AGN phenomenon. Scientific Highlights Nub Observin? Jummanj 2002 NVSS SHOWS EFFECT OF GALAXY'S MOTION THROUGH THE UNIVERSE - The standard cosmological model has passed another test, performed using data from the NRAO VLA Sky Survey (NVSS). The dipole temperature anisotropy in the cosmic microwave background (CMB) has indicated the Milky Way is moving at about 370 km/s relative to the "rest frame" of the universe. If the standard model is correct, a similar dipole should be seen as an enhancement in the surface density of distant galaxies in the direction of motion. Using the NVSS data, investigators found just such an enhancement, in the same direction as the CMB's temperature dipole. Detecting this enhancement, at about the 1% level, required first subtracting nearby radio sources from the NVSS data, leaving only sources presumed to be at cosmological distances. VLBA MEASURES NINE NEW PULSAR PARALLAXES-The VLBA has been used to measure nine new pulsar parallaxes, doubling the number of pulsars with accurate (errors of only 2%) distance measurements. Such results allow determination of the absolute luminosities and radiation efficiencies of pulsars, and, for thermally emitting neutron stars, promise the possibility of directly constraining the neutron star radius and thus the nuclear equation of state at high densities. Combined with measurements of proper motion, also completed in this study, this work helps constrain the pulsar velocity distribution and hence the symmetry of supernova explosions. WATER MASERS ABOUT ACTIVE GALACTIC NUCLEI -22 GHz water masers have been observed toward the nuclei of 16 known sources in AGNs. These are the most sensitive data of this kind obtained to date. The high-quality GBT spectra make it possible to distinguish some features for the first time. By tracking the velocities of these features over several epochs, it will be possible to study the dynamics of molecular gas within a parsec of the central engine. New maser features are seen in most of the recent spectra, and in two galaxies (NGC 1386, NGC 5506), a weak, broad base of HjO emission is detected under previously identified narrow components. Some spectra cover more than 10,000 km/s of velocity space, though maser features are generally seen within a few hundred km/s of the systemic velocity of the host galaxy. This project marks the initial scientific application of the active surface of the GBT, and the wide-band (200 and 800 MHz) spectrometer modes. YOUNG STAR PROBABLY EJECTED FROM TRIPLE SYSTEM - Analysis of nearly 20 years of VLA data leads researchers to conclude that a young, low-mass star passed within about 2 AU of a more massive, close binary system in the 1995-1998 time frame, causing a dramatic change in its orbit probably leading to its ultimate gravitational escape from the system. The result supports longstanding indications from computer simulations that such ejections occur in multiple-star systems. Ejections of low-mass protostars from their parent systems, and the resultant halt to accretion, could provide one explanation for the formation of brown dwarfs. Observing Hours Ob)ervin^ummary2002 3 40 - 30 1 1 1 1—ll—1 ■ ■ Hi■i o o HH est. est. est. 3 20 x i ft*vJ ■i - ■ i 1 3 O 1 X 1 10 1990 91 92 93 94 95 96 97 98 99 2000 01 02 03 04 05 Calendar Year 140 Foot □ GBT | | 12 Meter Fl VIA VLBA Figure 1. This figure shows the hours for observing on each telescope during the last 16 years. It includes astronomical observing, testing, calibration, and commissioning. ■31 Distribution of Scheduled Observing Time rR&> 0bservinfiumrnanj2oo2 GBT VLA VLBA n hi 2001 02 1993 94 95 96 97 98 99 00 01 02 1993 94 95 96 97 98 99 00 01 02 Calendar Year Calendar Year Calendar Year * pflS'li'Fl ** mmmm NRAO Staff Visitors Testing and Calibration Includes Research Associates Includes Students 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. Green Bank Telescope Summary NVO Observin;Jummanj2002 100 - - 80 "S - r V. 60 / *s - \ / & 40 ■ A - N/ V- 20 / / - f* +s -/ Calendar Year Observing Testing, Maintenance & Calibration Lost Time FigureS. 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 commissioning, maintenance, and calibration; and the percentage of time lost due to equipment failure, bad weather, and radio interference. ■51 Very Large Array Telescope Summary two Observing iummaru 2002 6 100 80 c 60 u £ 40 20 0 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Calendar Year Observing Testing, Maintenance & Calibration Lost Time 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 system testing, maintenance, and calibration; and the percentage of time lost due to equipment failure, bad weather, and radio interference. Very Long Baseline Array Telescope Summary Observin? Jummarij 2002 7 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Calendar Year Observing Testing, Maintenance & Calibration Lost Time Figure 5. 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. It should be noted that about 15 percent of the time cannot be scheduled as it results from the time difference across the array; this is reflected as a difference in the time between the end of one program and the start of the next.