Search results for "astrometry"

Acoustic astrometry with a VLBI-like interferometer

2007

AbstractWe show how loud-speakers, home digital recorders, and a common personal computer can be used to emulate VLBI observations on a small scale. These audio-VLBI observations allow for single-field astrometry (sources within the same interferometric field), differential group-delay astrometry, etc. These experiments can be set up very easily and in many possible configurations. Students may find these experiments very useful to learn about the innermost details of the interferometric technique.

The jet of the Low Luminosity AGN of M81

2013

In this contribution, we summarize our main results of a big campaign of global VLBI observations of the AGN in M81 (M81*) phase-referenced to the radio supernova SN 1993J. Thanks to the precise multi-epoch and multi-frequency astrometry, we have determined the normalized core-shift of the relativistic jet of M81* and estimated both the magnetic field and the particle density at the jet base. We have also found evidence of jet precession in M81* coming from the systematic time evolution of the jet orientation correlated with changes in the overall flux density.

High-Precision Radio Astrometry: The Search for Extrasolar Planets

2007

On reference star recognition and identification

2014

The paper deals with a research in the area of automation of positional star observations. In order to fully employ recent progress in imaging technologies, star image recognition and reference star identification process should gain comparable level of automation. A software package for this purpose has been developed in the Institute of Geodesy of the University of Latvia. It is capable of near-real-time image processing, star identification and astrometric position determination.

High precision astrometry with closure constraints: The triplet 1803+784/1928+738/2007+777

1997

Abstract Improvements in the technique of high precision differential astrometry in VLBI based on the use of triangles of radio sources are reported. Such geometry provides new constraints by taking advantage of “closure”. Results on the relative separations (ranging from 4.6 to 6.8°) of the sources in the triangle 1803+784/1928+738/2007+777 from ionosphere-free delays are shown and “sky closure” verified. A comparison with previous results on the pair 1928+738/2007+777 is also presented.

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…

Absolute kinematics of radio source components in the complete S5 polar cap sample

2004

We observed the thirteen extragalactic radio sources of the complete S5 polar cap sample at 15.4 GHz with the Very Long Baseline Array, on 27 July 1999 (1999.57) and 15 June 2000 (2000.46). We present the maps from those two epochs, along with maps obtained from observations of the 2 cm VLBA survey for some of the sources of the sample, making a total of 40 maps. We discuss the apparent morphological changes displayed by the radio sources between the observing epochs. Our VLBA observations correspond to the first two epochs at 15.4 GHz of a program to study the absolute kinematics of the radio source components of the members of the sample, by means of phase delay astrometry at 8.4 GHz, 15.…

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