We have measured the H I absorption toward pulsar B0329+54 using the Green Bank Telescope during 18 epochs between 2002 June 30 and 2003 October 10. Three observing epochs consisted of a continuous period of 20 hr each, while 15 epochs were 1-2 hr each. We calculate the structure function of H I absorption variations toward the pulsar on timescales of 10 minutes to 16 months, which using the proper motion of 95 km s-1 and the parallactic distance of 1.03 kpc measured toward B0329+54 (Brisken et al.), corresponds to angular scales of 0.37 μas to 23.8 mas and samples structures between 0.0025 and 12.5 AU, assuming H I gas halfway to the pulsar and ignoring scintillation effects. We find no evidence for any turbulent H I absorption fluctuations toward B0329+54, with the following upper limits on Δτ for various absorption features: 0.026 at -31, -21, -18, and +4 km s-1; 0.12 at -11 km s-1; and 0.055 at -1 km s-1.

We observe significant dust-correlated emission outside of H II regions in the Green Bank Galactic Plane Survey (-4° < b < 4°) at 8.35 and 14.35 GHz. The rising spectral slope rules out synchrotron and free-free emission as majority constituents at 14 GHz, and the amplitude is at least 500 times higher than expected thermal dust emission. When combined with the Rhodes (2.326 GHz) and Wilkinson Microwave Anisotropy Probe (23-94 GHz) data, it is possible to fit dust-correlated emission at 2.3-94 GHz with only soft synchrotron, free-free, thermal dust, and an additional dust-correlated component similar to Draine & Lazarian spinning dust. The rising component generally dominates free-free and synchrotron for ν ≳ 14 GHz and is overwhelmed by thermal dust at ν ≳ 60 GHz. The current data fulfill most of the criteria laid out by Finkbeiner and coworkers for detection of spinning dust.

New 21 cm H I observations have revealed a giant H I cloud in the Galactic plane that has unusual properties. It is quite well defined, about 150 pc in diameter at a distance of 5 kpc, and contains as much as 105 M☉ of atomic hydrogen. The outer parts of the cloud appear in H I emission above the H I background, while the central regions show H I self-absorption. Models that reproduce the observations have a core with a temperature ≲40 K and an outer envelope as much as an order of magnitude hotter. The cold core is elongated along the Galactic plane, whereas the overall outline of the cloud is approximately spherical. The warm and cold parts of the H I cloud have similar and relatively large line widths, ~7 km s-1. The cloud core is a source of weak, anomalously excited 1720 MHz OH emission, also with a relatively large line width, which delineates the region of H I self-absorption but is slightly blueshifted in velocity. The intensity of the 1720 MHz OH emission is correlated with NH derived from models of the cold core. There is 12CO emission associated with the cloud core. Most of the cloud mass is in molecules, and the total mass is greater than 2 × 105 M☉. In the cold core the H I mass fraction may be ~10%. The cloud has only a few sites of current star formation. There may be ~100 more objects like this in the inner Galaxy; every line of sight through the Galactic plane within 50° of the Galactic center probably intersects at least one. We suggest that G28.17+0.05 is a cloud being observed as it enters a spiral arm and that it is in the transition from the atomic to the molecular state.

The radio source 1413+135 is remarkable for a number of reasons; 1) it is 18 times more variable at 8 GHz cm wavelengths than at 2.3 GHz, 2) it is one of the few (∼4) sources where radio absorption lines of H1, CO, HCN and other molecules (Wiklind and Combes 1994 A&A 286:L9) have been detected, and 3) it appears to be a young radio source (< 104 years, Perlman et al. 1996, A. J. 111:1839.), which has not yet produced kilo parsec scale radio lobes. Our HALCA+VLBA image have resolved compact jet components near the core, and future observations will measure the angular velocity of these components.

The radio astronomy satellite HALCA was launched by the Institute of Space and Astronautical Science in 1997 February to participate in Very Long Baseline Interferometry (VLBI) observations with arrays of ground radio telescopes. HALCA is the main element of the VLBI Space Observatory Programme (VSOP), a complex international endeavor involving over 25 ground radio telescopes, five tracking stations and three correlators. Simultaneous observations with HALCA's 8 meter diameter radio telescope and ground radio telescopes synthesize a radio telescope over twice the size of the Earth, enabling the highest resolution 1.6 GHz and 5 GHz images to be made.

We present several applications of the AIPS++ environment as applied to the development of the Green Bank Telescope as well as current astrophysical problems. In particular, we demonstrate the use of AIPS++ in building tools for analyzing data at various points along the data stream, from diagnosing receivers and calibration, to data reduction and scientific modeling.

High angular resolution images of extragalactic radio sources are being made with the Highly Advanced Laboratory for Communications and Astronomy (HALCA) satellite and ground-based radio telescopes as part of the Very Long Baseline Interferometry (VLBI) Space Observatory Programme (VSOP). VSOP observations at 1.6 and 5 gigahertz of the milli-arc-second-scale structure of radio quasars enable the quasar core size and the corresponding brightness temperature to be determined, and they enable the motions of jet components that are close to the core to be studied. Here, VSOP images of the gamma-ray source 1156+295, the quasar 1548+056, the ultraluminous quasar 0014+813, and the superluminal quasar 0212+735 are presented and discussed.

The observed properties of the diffuse ionized gas (DIG) in our Galaxy are not easily reconcilable with simple photoionization models. Photoionization models, however, can reproduce the observed properties of H II regions. This suggests that there are different or additional physical processes at work in the DIG. We have developed a model of the DIG whereby it is ionized by a relatively soft ionizing spectrum (T-eff less than or equal to 32,000 K) and is also heated by an additional thermal mechanism: the dissipation of turbulence. This model predicts the same electron temperature, [N II] lambda 6583/H alpha ratio, [S II] lambda 6716/H alpha ratio, and He I lambda 5876/H alpha ratio as observed in the DIG. The model suggests that the observed [O III] emission from the diffuse interstellar medium (ISM) does not originate from the oxygen in the DIG. Without the turbulent thermal heating term, this model will not reproduce the observed properties of the DIG. The dissipation of turbulence may also be important in other phases of the ISM.

We have recently published observations that specify most of the turbulent and mean plasma characteristics for a region of the sky containing the interstellar diffuse ionized gas (DIG). These observations have provided virtually all of the information necessary to calculate the heating rate from dissipation of turbulence. We have calculated the turbulent dissipation heating rate employing two models for the interstellar turbulence. The first is a customary modeling as a superposition of magnetohydrodynamic waves. The second is a fluid-turbulence-like model based on the ideas of Higdon. This represents the first time that such calculations have been carried out with full and specific interstellar turbulence parameters. The wave model of interstellar turbulence encounters the severe difficulty that plausible estimates of heating by Landau damping exceed the radiative cooling capacity of the interstellar DIG by 3-4 orders of magnitude. Clearly interstellar turbulence does not behave like an ensemble of obliquely propagating fast magnetosonic waves. The heating rate due to two other wave dissipation mechanisms, ion-neutral collisional damping and the parametric decay instability, are comparable to the cooling capacity of the diffuse ionized medium. We find that the fluid-like turbulence model is an acceptable and realistic model of the turbulence in the interstellar medium once the effects of ion-neutral collisions are included in the model. This statement is contingent on an assumption that the dissipation of such turbulence because of Landau damping is several orders of magnitude less than that from an ensemble of obliquely propagating magnetosonic waves with the same energy density. Arguments as to why this may be the case are made in the paper. Rough parity between the turbulent heating rate and the radiative cooling rate in the DIG also depends on the hydrogen ionization fraction being in excess of 90% or on a model-dependent lower limit to the heating rate being approximately valid. We conclude that the dissipation of turbulence is capable of providing a substantial and perhaps major contribution to the energy budget of the diffuse ionized medium.

The Faraday rotation measures of 38 extragalactic sources have been measured with the Very Large Array in order to provide new information on the properties of plasma turbulence in the interstellar medium. Of particular interest is the possibility that such Faraday rotation measurements can provide information on the magnetic field component of interstellar turbulence. The observations were made in an area of the sky from 1(h)50(m) to 3(h)10(m) right ascension and from 32 degrees to 44 degrees declination. This area is unique in that it is the only region away from the Galactic plane where the Ha intensity has been mapped completely, both spatially and in velocity. The rotation measures were found to vary in a relatively smooth fashion across the entire region. The magnitudes of the mean rotation measure and emission measure were found to be consistent with a simple Galactic model consisting of an exponential disk of scale height 1 kpc and midplane density 0.03 cm(-3), together with an azimuthal or bisymmetric spiral Galactic magnetic field of 3-4 mu G. The structure functions of rotation measure and emission measure were analyzed in order to extract information on the nature of the plasma turbulence in the interstellar medium in this direction. A comparison was made between the observed rotation and emission measure structure functions and theoretical structure function expressions, which are presented here for the first time. We find that the observed structure functions are consistent with a turbulence model in which both density and magnetic field fluctuations have Kolmogorov spectra. The outer scale of this turbulence is about 4 pc. For larger scales (corresponding to angular spacings delta theta greater than or equal to 0 degrees.1) the turbulence appears to be two-dimensional. For all angular scales, the level of the rotation measure structure function is larger than would be expected from only plasma density fluctuations of known characteristics in an otherwise uniform Galactic magnetic field. The data require, in addition to the plasma density fluctuations, a turbulent magnetic field with a rms amplitude of similar to 1 mu G. To the authors' knowledge, this represents the first measurement of magnetic field fluctuations in the interstellar plasma on spatial scales that appropriately may be described as turbulence.

We present radio continuum observations of comet Hyakutake C/1996 B2 at 8.35 and 14.35 GHz with the NRAO OVLBI Earth Station at Green Bank. Three sets of observations were made from 22:50 UTC 1996 March 27 to 19:09 UTC 1996 March 28, from 18:30 to 20:30 UTC on 1996 April 17, and from 15:40 to 20:30 UTC on 1996 April 18. No radio continuum emission from comet Hyakutake C/1996 B2 was detected during any of these observations. The lack of radio continuum emission from comet Hyakutake C/1996 B2 at 8.35 and 14.35 GHz allows us to constrain the radio flux in the X-ray-emitting region of comet Hyakutake C/1996 B2 to be S8.35GHz ≤ 5.3 × 10-27 W m-2 Hz-1 and S14.35GHz ≤ 2.8 × 10-27 W m-2 Hz-1. The angular size of the NRAO OVLBI Earth Station's primary beam is well matched to the size of the region of the diffuse X-ray emission from comet Hyakutake C/1996 B2.