Search results for "interferometry"
showing 10 items of 343 documents
Changes in the trajectory of the radio jet in 0735+178?
2001
We present multi-epoch 8.4 and 43 GHz Very Long Baseline Array images of the BL Lac object 0735+178. The images confirm the presence of a twisted jet with two sharp apparent bends of 90$^{\circ}$ within two milliarcseconds of the core, resembling a helix in projection. The observed twisted geometry could be the result of precession of the jet inlet, but is more likely produced by pressure gradients in the external medium through which the jet propagates. Quasi-stationary components are observed at the locations of the 90$^{\circ}$ bends, possibly produced by differential Doppler boosting. Identification of components across epochs, since the earliest VLBI observations of this source in 1979…
VSOP monitoring of the Quasar 1928+738
1999
One limitation of the VSOP (VLBI Space Observatory Program) mission is that several famous superluminal sources such as 3C273 cannot be monitored with good uv-coverage throughout the lifetime of the VSOP Mission at regular intervals that are spaced closely enough to follow the evolution in the fine-scale source-structure. The reason for this is that the HALCA spacecraft cannot#observe sources outside certain restricted ranges of sun angle, defined to be the time variable angle between the source and the sun. However sources that lie within 10 degrees of the ecliptic poles can be observed throughout the year and observations are not restricted to narrow temporal windows. Furthermore, the bes…
Discovery of shell-like radio-structure in SN1993J
1995
The radio-luminous supernova SN 1993J in M81 offers an unprecedented opportunity to study with high linear resolution the details of the growth of a supernova radio structure by means of the VLBI technique.
High-Resolution Radio Imaging of Young Supernovae: SN 1979C, SN 1986J, and SN 2001gd
2005
The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.
Opto-digital tomographic reconstruction of the Wigner distribution function of complex fields.
2008
An optical-digital method has been developed to obtain the Wigner distribution function of one-dimensional complex fields. In this technique an optical setup is employed to experimentally achieve the Radon-Wigner spectrum of the original signal through intensity measurements. Digital tomographic reconstruction is applied to the experimental spectrum to reconstruct the two-dimensional Wigner distribution function of the input. The validity of our proposal is demonstrated with experimental data, and the results are compared with computer simulations.
Atmospheric turbulence in phase-referenced and wide-field interferometric images
2010
Phase referencing is a standard calibration procedure in radio interferometry. It allows us to detect weak sources by using quasisimultaneous observations of closeby sources acting as calibrators. However, atmospheric turbulence may introduce strong differences in the optical paths of the signals of the target and calibrator and affect, or even waste, phase referencing in cases of relatively large calibrator-to-target separations and/or bad weather. The situation is similar in wide-field interferometric observations. We present the results of a Monte Carlo study of the astrometric precision and sensitivity of an interferometric array (a realization of the Square Kilometre Array, SKA) in pha…
Common-path phase-shifting lensless holographic microscopy
2010
We present an approach capable of high-NA imaging in a lensless digital in-line holographic microscopy layout even outside the Gabor's regime. The method is based on spatial multiplexing at the sample plane, allowing a common-path interferometric architecture, where two interferometric beams are generated by a spatial light modulator (SLM) prior to illuminating the sample. The SLM allows phase-shifting interferometry by phase modulation of the SLM diffracted beam. After proper digital processing, the complex amplitude distribution of the diffracted object wavefront is recovered and numerically propagated to image the sample. Experimental results are reported that validate the proposed metho…
Bidirectional Nonorthogonal Schardin-Lau Interferometer
1990
We discuss the formation of self-images of a 2-D grating composed by two rulings of equal period, but in-plane rotated. We describe the in-register condition for setting the lensless Lau effect, with this type of gratings; and we propose to use the above configuration for interferometrically visualizing, in noncoherent light, phase structures, in two nonorthogonal directions.
VLBI Observations of a Complete Sample of Radio Galaxies. VII. Study of the FR I Sources 3C 31, 4C 35.03, and 3C 264
1997
We present results from global VLBI and VLA observations of three FanaroU-Riley type I radio gal- axies, 3C 31, 4C 35.03, and 3C 264, at a frequency of 5 GHz. In all three cases, we observe asymmetric parsec-scale structures consisting of a compact core and a single jet pointing in the direction of the more prominent kiloparsec jet. We interpret such alignment as evidence for the relativistic nature of FR I radio jets at parsec scales. Comparing the VLBI and VLA images of these sources, we —nd a progressive deceleration of the plasma —ow from parsec to kiloparsec scales. We consider another —ve FR I radio galaxies studied previously by us and —nd that, in a set of eight FR I objects, the es…
The AB Doradus system revisited: The dynamical mass of AB Dor A/C
2017
We report new radio interferometric observations of the quadruple pre-main-sequence (PMS) system ABD oradus. From these observations, combined with existing VLT near-infrared relative astrometry, we have refined the estimates of the dynamical masses of the system. In particular, we find component masses of 0.86 ± 0.09M⊙ and 0.090 ± 0.003M⊙ for ABD or A and ABD or C, respectively. These dynamical masses, coupled with temperatures and luminosities, allow for comparison with theoretical stellar models. The case of ABDorC, in terms of calibration of evolutionary models of low-mass young stars has been widely reported in previous studies. In this contribution, we compare the measured properties …