منابع مشابه
The Reconciliation of Optical and Radio Positions
Reconciliation of optical and radio postions is basically a matter of reconciling positional reference systems. For example, the question of whether, for a given source, there is a real physical off-set between the optical and radio centroid at a given frequency cannot be properly inves tigated until the reference systems have been securely established. In the more sophisticated case of the co...
متن کاملCelestial positions in radio and optical
We discuss the importance of the direct link between the most accurate radio and optical reference frames that will become possible with the next-generation space as-trometry missions in about a decade. The positions of more than 500 active galactic nuclei that are common in the precise Very Long Baseline Interferometry (VLBI) catalogues and the Sloan Digital Sky Survey (SDSS) Data Release 4 (D...
متن کاملHigh-precision VLBI astrometry of radio-emitting stars
Multiple-epoch phase-referenced VLBI observations of 11 radio-emitting stars have been conducted as part of an astrometric program to link the Hipparcos optical reference frame to the radio extragalactic reference frame. We present the VLBI positions, proper motions and trigonometric parallaxes from this program in the ICRF (International Celestial Reference Frame). These astrometric parameters...
متن کاملDetermination of optical positions for 23 extragalactic radio sources
AB S TRACT The optical counterparts of 23 extragalactic radio sources, of which 13 are in the southern hemisphere, have been observed by three telescopes equipped with CCDs. By reference to the Astrographic/Tycho (ACT) Reference, Carlsberg Meridian (CMC), Positions and Proper Motions (PPM), Hipparcos (HIP) and Lick Northern Proper Motion (NPM) catalogues, the positions of the 23 objects have be...
متن کاملMapping radio emitting-region on low-mass stars and brown dwarfs
Strong magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7) have emerged from a number of radio observations, including the periodic beams. The highly (up to 100%) circularly polarized nature of the emission point to an effective amplification mechanism of the high-frequency electromagnetic waves – the electron cyclotron maser (ECM) instability. Several anisotropic veloc...
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ژورنال
عنوان ژورنال: Astronomy and Astrophysics Supplement Series
سال: 1996
ISSN: 0365-0138,1286-4846
DOI: 10.1051/aas:1996160