8,738 research outputs found
Very long baseline interferometry
S-band stations with dual tracking capability have been used to gather double differential very long baseline interferometry data on Apollo 16 and Apollo 17. This was accomplished by simultaneously receiving both monochromatic radio signal emissions at each of two separated receiving stations, transmitting these data to a central processing facility, and calculating the differences between Doppler angular rates to determine the motion of the lunar roving vehicle
Principles of very-long-baseline interferometry
The basic principles of very-long-baseline interferometry as related to its use in the determination of vector baselines, polar motion, and earth rotation are presented. Aspects relevant to geodetic applications that involve observations of extragalactic radio sources are covered. The instrumentation used in these observations and the basic observables and their simplest interpretation are described. Complications of the interpretation due to the various geophysical 'signals' and nongeophysical 'noise' that affect the observables are considered
Photon Mass and Very Long Baseline Interferometry
A relation between the photon mass, its frequency, , and the deflection
parameter, , determined by experimentalists (which characterizes the
contribution of space curvature to gravitational deflection) is found. This
amazing result allows us to conclude that the knowledge of the parameters
and is all we need to set up gravitational bounds on the photon mass.
By considering as inputs the most recent measurements of the solar
gravitational deflection of radio waves obtained via the Very Long Baseline
Interferometry, upper bounds on the photon mass are estimated.Comment: Accepted for publication in International Journal of Modern Physics
A very long baseline interferometry sky survey
A systematic very long baseline interferometry (VLBI) sky survey, undertaken to find a suitable set of compact celestial radio sources from which a more complete VLBI reference frame can be constructed, discussed. The survey was conducted by searching known celestial radio sources for compact components by means of VLBI observations. Baseline lengths were about 7 x 10 to the 7th power RF wavelengths (lambda = 13.1 cm), so the spatial wavelengths being sampled by the interferometer were generally on the order of a few milliarcseconds. Hence, the radio sources detected have a measurable portion of their total flux density contained in components that are no more than a few milliarcseconds in angular extent. Existing information of radio sources were used as clues to source size
Precision surveying using very long baseline interferometry
Radio interferometry measurements were used to measure the vector baselines between large microwave radio antennas. A 1.24 km baseline in Massachusetts between the 36 meter Haystack Observatory antenna and the 18 meter Westford antenna of Lincoln Laboratory was measured with 5 mm repeatability in 12 separate experiments. Preliminary results from measurements of the 3,928 km baseline between the Haystack antenna and the 40 meter antenna at the Owens Valley Radio Observatory in California are presented
Radiowave scattering and ultra-long-baseline interferometry
Interstellar scattering can irretrievably blur the images of compact radio sources when examined with extremely high resolution. Because of this effect, diffraction limited observations of extragalactic sources with an Earth-Moon baseline will only be possible at frequencies above about 7 GHz, in which case the resolution will be approx. = to or less than 20 microarcsec. Preliminary observations to determine the potential usefulness of such resolving power are discussed. The simplest of these would consist of a search for interstellar scintillations in compact sources at 10 GHz, which would provide an effective resolution about equal to that of an Earth-Moon baseline at this frequency. Also important in this context is the development of very long baseline interferometry in near-Earth orbit, as any ultra high resolution observations, if appropriate, would require intermediate baselines for mapping
Imaging "Pinwheel"nebulae with optical long-baseline interferometry
Dusty Wolf-Rayet stars are few but remarkable in terms of dust production
rates (up to one millionth of solar mass per year). Infrared excesses
associated to mass-loss are found in the sub-types WC8 and WC9. Few WC9d stars
are hosting a "pinwheel" nebula, indirect evidence of a companion star around
the primary. While few other WC9d stars have a dust shell which has been barely
resolved so far, the available angular resolution offered by single telescopes
is insufficient to confirm if they also host "pinwheel" nebulae or not. In this
article, we present the possible detection of such nebula around the star
WR118. We discuss about the potential of interferometry to image more
"pinwheel" nebulae around other WC9d stars.Comment: To be published soon in the conference proceedin
A publication database for optical long baseline interferometry
Optical long baseline interferometry is a technique that has generated almost
850 refereed papers to date. The targets span a large variety of objects from
planetary systems to extragalactic studies and all branches of stellar physics.
We have created a database hosted by the JMMC and connected to the Optical Long
Baseline Interferometry Newsletter (OLBIN) web site using MySQL and a
collection of XML or PHP scripts in order to store and classify these
publications. Each entry is defined by its ADS bibcode, includes basic ADS
informations and metadata. The metadata are specified by tags sorted in
categories: interferometric facilities, instrumentation, wavelength of
operation, spectral resolution, type of measurement, target type, and paper
category, for example. The whole OLBIN publication list has been processed and
we present how the database is organized and can be accessed. We use this tool
to generate statistical plots of interest for the community in optical long
baseline interferometry.Comment: To be published in the SPIE'2010 conference on "Optical and Infrared
Interferometry II
Observation of double star by long-baseline interferometry
This paper serves as a reference on how to estimate the parameters of binary
stars and how to combine multiple techniques, namely astrometry, interferometry
and radial velocities.Comment: F. Millour, A. Chiavassa, L. Bigot, O. Chesneau, A. Meilland \& P.
Stee. What can the highest angular resolution bring to stellar astrophysics?,
69-70, EDP sciences, 2015, EAS publication series, 978-2-7598-1833-4.
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