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Deep space navigation presents significant challenges due to the unavailability of Global Navigation Satellite System (GNSS) signals and severe signal attenuation over interplanetary distances. Traditional terrestrial systems, such as NASA…
We have obtained mas-scale resolution very long baseline interferometry (VLBI) images of a sample of Seyfert 1 and Seyfert 2 galaxies at 5 GHz (wavelength, $\lambda$ = 6 cm). The Seyferts of the two types were chosen to be matched in…
Very Long Baseline Interferometry is capable of measuring the gravitational delay caused by the Sun and planet gravitational fields. The post-Newtonian parameter $\gamma$ is now estimated with accuracy of $\sigma_{\gamma}=2\cdot 10^{-4}$…
For Very Long Baseline Interferometry (VLBI), the fringe spacing is extremely narrow compared to the field of view imposed by the primary beam of each element. This means that an extremely large number of resolution units can potentially be…
We have been developing a novel interferometer formed directly between a Very Long Baseline Interferometry (VLBI) radio telescope and a Global Navigation Satellite Systems (GNSS) antenna/receiver. This interferometer is enabled by the High…
Very Long Baseline Interferometric (VLBI) observations of quasar jets enable one to measure many theoretically expected effects. Estimating the significance of observational findings is complicated by the correlated noise in the image…
We describe a new method which achieves high precision Very Long Baseline Interferometry (VLBI) astrometry in observations at millimeter wavelengths. It combines fast frequency-switching observations, to correct for the dominant…
Space very long baseline interferometry (VLBI) has unique applications in high-resolution imaging of fine structure of astronomical objects and high-precision astrometry due to the key long space-Earth or space-space baselines beyond the…
Very long baseline interferometry (VLBI) astrometry is used to determine the three-dimensional position and proper motion of astronomical objects. A typical VLBI astrometric campaign generally includes around ten observations, making it…
Cosmology with large interferometric telescopes is a rich and largely unexplored subject, involving three types of measurement: astrometric measurement of absolute distances and proper motions, dispersions of relative proper motions, and…
The radio sky at lower frequencies, particularly below 20 MHz, is expected to be a combination of increasingly bright non-thermal emission and significant absorption from intervening thermal plasma. The sky maps at these frequencies cannot…
We propose a new technique to obtain super-resolution images with radio interferometer using sparse modeling. In standard radio interferometry, sampling of ($u$, $v$) is quite often incomplete and thus obtaining an image from observed…
Long baseline radio interferometers can provide some interesting opportunities for future SETI searches. Known advantages (compared to single dishes or beam-formed arrays), include the large reduction in false-positives due to the…
Astronomers usually need the highest angular resolution possible, but the blurring effect of diffraction imposes a fundamental limit on the image quality from any single telescope. Interferometry allows light collected at widely-separated…
Very Long Baseline Interferometry (VLBI) observations can provide the position of compact radio sources with an accuracy of order 50 micro-arcseconds. This is sufficient to measure the trigonometric parallax and proper motions of any object…
The knowledge of receiver beam shapes is essential for accurate radio interferometric imaging. Traditionally, this information is obtained by holographic techniques or by numerical simulation. However, such methods are not feasible for an…
Very long baseline radio interferometry (VLBI) with ground-based observatories is limited by the size of Earth, the geographic distribution of antennas, and the transparency of the atmosphere. In this whitepaper, we present Capella, a…
The extraordinary astrometric accuracy of radio interferometry creates an important and unique opportunity for the discovery and characterization of exo-planets. Currently, the Very Long Baseline Array can routinely achieve better than 100…
The space astrometry mission GAIA will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the GAIA frame and the International Celestial…
VLBI astrometry allows coordinates of celestial radio sources to be determined with submilliarcsecond accuracy. In particular, with differential VLBI astrometry, the standard errors of relative positions and proper motions can be as small…