Results 21 to 30 of about 256 (175)

Science with radio pulsar astrometry [PDF]

Proceedings of the International Astronomical Union, 2012
AbstractHigh precision astrometry on radio pulsars can provide model-independent estimates of their distances and velocities. Such estimates serve to calibrate models of the Galactic electron density distribution, thereby improving distance estimates for the entire pulsar population.
openaire   +1 more source

Radio source structures in VLBI astrometry [PDF]

Symposium - International Astronomical Union, 1988
In astrometry, celestial radio sources with extended structures are useful. An algorithm to correct for structure in VLBI delays and delay rates is developed. The radio source NRAO140 is mapped from data with limited u-v coverage by the hybrid method and the Maximum Entropy procedure.
Patrick Charlot, Jean-François Lestrade, Claude Boucher   +2 more
openaire   +1 more source

Probing the Heart of Active Narrow-line Seyfert 1 Galaxies with VERA Wideband Polarimetry

The Astrophysical Journal, 2023
We explored the parsec-scale nuclear regions of a sample of radio-loud narrow-line Seyfert 1 galaxies (NLSy1s) using the VLBI Exploration of Radio Astrometry wideband (at a recording rate of 16 Gbps) polarimetry at 22 and 43 GHz.
Mieko Takamura, Kazuhiro Hada, Mareki Honma, Tomoaki Oyama, Aya Yamauchi, Syunsaku Suzuki, Yoshiaki Hagiwara, Monica Orienti, Filippo D’Ammando, Jongho Park, Minchul Kam, Akihiro Doi   +11 more
doaj   +1 more source

Improving the Reference Frame by Radio–and Optical Astrometry of Radio Stars [PDF]

International Astronomical Union Colloquium, 1991
AbstractA longterm program of precise radio – and optical astrometry of selected radio stars has been conducted in the last decade by our observatories using the VLA and astrographs on both hemispheres. Positions of 54 stars north of −26 deg. declination including 6 MASER stars have been obtained.
Chr. de Vegt, N. Zacharias, K.J. Johnston, R. Hindsley   +3 more
openaire   +1 more source

Ray tracing-based delay model for compensating gravitational deformations of VLBI radio telescopes

Journal of Geodetic Science, 2022
The precision and the reliability of very long baseline interferometry (VLBI) depend on several factors. Apart from fabrication discrepancies or meteorological effects, gravity-induced deformations of the receiving unit of VLBI radio telescopes are ...
Lösler Michael, Eschelbach Cornelia, Greiwe Ansgar, Brechtken Rainer, Plötz Christian, Kronschnabl Gerhard, Neidhardt Alexander   +6 more
doaj   +1 more source

Improving the Accuracy of Radio Astrometry [PDF]

International Astronomical Union Colloquium, 2000
AbstractThe International Celestial Reference Frame (ICRF) is currently realized by the radio positions of compact extragalactic objects obtained by the technique of Very Long Baseline Interferometry (VLBI). The positions of the defining sources with the highest quality are estimated to be accurate at the 0.25 milliarcsecond (mas) level.
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CCD astrometry of faint compact extragalactic radio sources. III. [PDF]

Astronomy & Astrophysics, 2001
Optical positions relative to the Hipparcos Catalogue (ESA 1997) have been obtained for the optical counterparts of 28 faint (B 20 23) southern compact extragalactic radio sources (CERS). Most of these sources are not adequately observable (or simply not visible) by means of direct photography with a conventional wide- eld telescope, so the positions ...
E. Costa, P. Loyola
openaire   +6 more sources

VERA’s 20 yr Evolution in Science and Technology

Galaxies
We review the past 20 yr evolution of VERA (VLBI Exploration of Radio Astrometry) in both science and techinology. VERA is a VLBI array in Japan which consists of four 20 m-diameter telescopes, originally dedicated to phase-referencing VLBI astrometry ...
Mareki Honma, Tomoya Hirota, Tomoaki Oyama, Akiharu Nakagawa   +3 more
doaj   +1 more source

The VERA project (VLBI Exploration of Radio Astrometry) [PDF]

Proceedings of the International Astronomical Union, 2004
VLBI – Very Long Baseline Interferometry – is a radio interferometry technique which provides the highest spatial resolution observations to human kind. But at the present, the accuracy of the astrometry observations is limited by the atmospheric light path variations and instrumental phase errors, and only group delay measurements are used.
Hideyuki Kobayashi, Noriyuki Kawaguchi, Seiji Manabe, Toshihiro Omodaka, Katsunori Shibata, Mareki Honma, Yoshiaki Tamura, Osamu Kameno, Tomoya Hirota, Hiroshi Imai   +9 more
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Inferring Io's Internal Properties by Combining Gravity Measurements and Volcanic Activity

Journal of Geophysical Research: Planets, Volume 131, Issue 9, September 2026.
Abstract With its extreme geological activity, Io represents an archetype for tidally heated exoplanets/moons and provides insight into early stages of terrestrial planet evolution. Decades of ground‐based observations and multiple space missions have refined our understanding of Io, yet it remains debated where inside Io the tidal heating takes place.
A. Veenstra, M. Rovira‐Navarro, W. van der Wal   +2 more
wiley   +1 more source