Search results for "interferometry"
showing 10 items of 343 documents
Differential astrometry over 15°
1999
Abstract We observed the pair of radio sources 1150+812 and 1803+784 in November 1993 with a VLBI array, simultaneously recording at 8.4 and 2.3 GHz. We determined the angular separation between the two sources with submilliarcsecond accuracy by using differential techniques. This result demonstrates the feasibility of high precision differential astrometry for radio sources separated in the sky by almost 15°, and opens the avenue to its application to larger samples of radio sources.
Multi-wavelength VLBI phase-delay astrometry of a complete sample of radio sources
2007
AbstractWe report on the first global high-precision (differential phase-delay) astrometric analyses performed on a complete set of radio sources. We have observed the S5 polar cap sample, consisting of 13 quasars and BL Lac objects, with the VLBA at 8.4, 15, and 43 GHz. We have developed new algorithms to enable the use of the differential phase-delay observable in global astrometric observations. From our global analyses, we determine the relative positions between all pairs of sources with typical precisions ranging from 10 to 200 μas, depending on observing frequency and source separation. In this paper, we discuss the impact of this observable in the enhancement of the astrometric prec…
Three-Dimensional Mapping and Ranging of Objects Using Speckle Pattern Analysis
2010
In this chapter, we present two novel approaches for 3-D object shape measurement and range estimation based on digital image processing of speckle patterns. In the first one, 3-D mapping and range measurement are retrieved by projecting, through a ground glass diffuser, random speckle patterns on the object or on the camera for a transmissive and reflective configuration, respectively. Thus, the camera sensor records in time sequence different speckle patterns at different distances, and by using correlation operation between them, it is possible to achieve 3-D mapping and range finding. In the second one, the 3-D mapping and ranging are performed by sensing the visibility associated with …
VLBI-selected sample of Compact Symmetric Object candidates and frequency-dependent position of hotspots
2011
The Compact Symmetric Objects (CSOs) are small (<1 kiloparsec) and powerful extragalactic radio sources showing emission on both sides of an active galactic nucleus and no signs of strong relativistic beaming. They may be young radio sources, progenitors of large FRII radio galaxies. We aim to study the statistical properties of CSOs by constructing and investigating a new large sample of CSO candidates on the basis of dual-frequency, parsec-scale morphology. For the candidate selection we utilized VLBI data for 4170 extragalactic objects obtained simultaneously at 2.3 and 8.6 GHz (S and X band) within the VLBA Calibrator Survey 1-6 and the Research and Development - VLBA projects. Prope…
Imaging of SN 1993J
2005
SN 1993J has been imaged with VLBI, and its angular expansion monitored, for almost ten years. The images show shell-like radio structures with almost circular symmetry. SN 1993J expands according to models of shock excited emission. The angular expansion has a changing deceleration rate and is best modeled with two different slopes. The swept-up mass estimate at an age of 3159 days (∼0.4 M⨀), comparable to the low-mass envelope, favors a binary scenario. The observed spectral index of SN 1993J has slowly flattened since age 1000 days onward (α has changed from −1 to −0.67 at an age of 2820 days).
High-resolution observations of SN 2001gd in NGC 5033
2005
We report on 8.4 GHz VLBI observations of SN2001gd in the spiral galaxy NGC5033 made on 26 June 2002 and 8 April 2003. Our data nominally suggests a relatively strong deceleration for the expansion of SN2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 8 April 2003, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of E_min =(0.3-14) 10^{47} ergs, and a corresponding equipartition average magnetic field of B_min = (50--350) mG. We also present multiwavelength VLA measurements of SN2001gd, which are well fit by an optically thin, synchrotron spectrum, partially absorbed by thermal p…
A distorted radio shell in the young supernova SN1986J
2002
We report here on 5 GHz global very-long-baseline interferometry (VLBI) observations of SN 1986J, 16 yr after its explosion. We obtained a high-resolution image of the supernova, which shows a distorted shell of radio emission, indicative of a deformation of the shock front. The angular size of the shell is $\sim4.7 {\rm mas}$, corresponding to a linear size of $\sim6.8 \times 10^{17} {\rm cm}$ for a distance of 9.6 Mpc to NGC 891. The average speed of the shell has decreased from $\sim$7400 \kms in 1988.74 down to about $6300 {\rm km s^{-1}}$ in 1999.14, indicative of a mild deceleration in the expansion of SN 1986J. Assuming a standard density profile for the progenitor wind ($\rho_{\rm c…
Precise measurement of the dynamical masses in AB Doradus
2007
AbstractThe radio stars ABDor A and ABDor B (=Rst137B) are the main components of the ABDoradus system. Both stars are double (ABDor A/ABDor C and ABDor Ba/ABDor Bb) and usual targets of astrometric instruments at optical (Hipparcos), infrared (VLT), and radio (VLBI) wavelengths. From a combination of all astrometric data available, we have obtained precise limits to the dynamical mass of both binaries in AB Doradus. The determination of the mass of ABDor C (0.090±0.003 M⊙) is important, since this object constitutes one of the few calibration points used to test theoretical evolutionary models of low-mass young stars. Follow-up observations both in radio (VLBI) and optical wavelengths (VLT…
Phase Reference VLBI Astrometry for Mira-Type Stars
2003
We carried out phase reference VLBI observations at 43 GHz between SiO masers in Mira type variables and adjacent extragalactic continuum source with VLBA. Main aim of this observation is determination of spatial distribution between SiO maser spots at v = 1 and v = 2, J=l→0 transition. Although the standard calibration was successful for each source, the phase reference calibration have not been successful. However, we will determine the absolute positional difference of each SiO maser spot within about 1 milli arcsecond due to the structure effect of reference source if the phase reference VLBI is successful
Normal metal - insulator - superconductor interferometer
2003
Hybrid normal metal - insulator - superconductor microstructures suitable for studying an interference of electrons were fabricated. The structures consist of a superconducting loop connected to a normal metal electrode through a tunnel barrier . An optical interferometer with a beam splitter can be considered as a classical analogue for this system. All measurements were performed at temperatures well below 1 K. The interference can be observed as periodic oscillations of the tunnel current (voltage) through the junction at fixed bias voltage (current) as a function of a perpendicular magnetic field. The magnitude of the oscillations depends on the bias point. It reaches a maximum at energ…