Lunar Occultations of the SiO Masers in RLeo

VLBI observations show that the SiO maser emitting regions in oxygen-rich stars are very clumpy and that these clumps extend over a few stellar radii (Mclntosh et al. 1987; Colomer et al. 1992). These observations indicate that the ideal instrument for the study of the SiO masers is an interferometer with baselines covering between a few and several hundreds/thousands km. Such an instrument is so far unavailable.A classical way to get high angular resolution and a full beam synthesis with a single telescope of moderate size is through lunar occultations. This observing technique provides the angular resolution of a single linear antenna several kilometers long. However, at millimeter wavelengths the Fresnel fringes produced by the Moon limb as the source under study is occulted have never been observed. We present here the observation with the 30-m IRAM radio telescope of the v=1 J=2-1 line of SiO during an occultation (and reappearance) of R Leo by the Moon.

Download Full-text

High Quality Imaging for Space VLBI Observations with Ultra High Angular Resolution

Symposium - International Astronomical Union ◽

10.1017/s0074180900221694 ◽

2001 ◽

Vol 205 ◽

pp. 430-431

Author(s):

Sergey Likhachev

Keyword(s):

Angular Resolution ◽

High Angular Resolution ◽

High Quality ◽

Vlbi Observations ◽

Quality Imaging

This presentation focuses on the problems associated with obtaining high quality images from a high orbiting space VLBI (SVLBI) mission. SVLBI intensifies and magnifies all imaging problems, making these problems clearer to understand, though much harder to solve.

Download Full-text

Space-VLBI observations of OH masers

Symposium - International Astronomical Union ◽

10.1017/s0074180900222171 ◽

2002 ◽

Vol 206 ◽

pp. 105-111 ◽

Cited By ~ 2

Author(s):

Vyacheslav I. Slysh ◽

Maxim A. Voronkov ◽

Irina E. Val'tts ◽

Victor Migenes ◽

K.M. Shibata ◽

...

Keyword(s):

Brightness Temperature ◽

Lower Limit ◽

Radio Telescope ◽

Angular Resolution ◽

Main Line ◽

Radio Telescopes ◽

Space Radio Telescope ◽

Vlbi Observations ◽

Interstellar Scattering

We report on the first space-VLBI observations of the OH masers in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The maps of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature 6 × 1012 K was obtained. The masers seem to be located in the direction of low interstellar scattering.

Download Full-text

ALMA and the Future of Millimeter Imaging Observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006080 ◽

2015 ◽

Vol 10 (S314) ◽

pp. 270-275

Author(s):

David J. Wilner

Keyword(s):

Angular Resolution ◽

Planetary Systems ◽

Circumstellar Disks ◽

Direct Access ◽

High Angular Resolution ◽

Dynamical Structure ◽

Millimeter Wavelengths ◽

The Future ◽

Critical Age ◽

Moving Groups

AbstractThe Nearby Young Moving Groups sample the critical age when primordial disks around stars complete their transformation into planetary systems with associated debris. Millimeter wavelengths provide direct access to cool material in these circumstellar disks. The high angular resolution of interferometry at these long wavelengths enables resolved observations of solids in an optically thin regime, as well as the thermal, chemical, and dynamical structure of gas, if present. In this contribution, I briefly review the evolving landscape of millimeter telescopes, with emphasis on the revolutionary capabilities of the new international Atacama Large Millimeter/submillimeter Array (ALMA) and describe pertinent early science results.

Download Full-text

VLBI from the Moon

Highlights of Astronomy ◽

10.1017/s1539299600019377 ◽

1998 ◽

Vol 11 (2) ◽

pp. 985-987

Author(s):

L. I. Gurvits

Keyword(s):

Radio Astronomy ◽

Very Long Baseline Interferometry ◽

Angular Resolution ◽

High Angular Resolution ◽

The Moon ◽

Next Generation ◽

Space Observatory ◽

Long Baseline ◽

The Earth ◽

The Universe

Very Long Baseline Interferometry (VLBI) technique occupies a special place among tools for studying the Universe due to its record high angular resolution. The latter is in the inverse proportion to the length of interferometer baseline at any given wavelength. Until recently, the available angular resolution in radio domain of about 1 milliarcsecond at centimeter wavelengths was limited by the diameter of the Earth. However, many astrophysical problems require a higher angular resolution. The only way to achieve this at a given wavelength is to create an interferometer with the baseline larger than the Earth’s diameter by placing at least one telescope in space. In February 1997, the first dedicated Space VLBI mission, VLBI Space Observatory Program (VSOP), led by the Institute of Space and Astronautical Sciences (Japan) has been launched (Hirabayashi 1997). The VSOP mission opens a new dimension in the development of radio astronomy of extremely high angular resolution and will be followed by other Space VLBI missions. A review of scientific drives and technological challenges of the next generation Space VLBI mission have been discussed, for example, by Gurvits et al. (1996) and Ulvestad et al. (1997).

Download Full-text

Low Frequency Radio Astronomy from the Moon

Highlights of Astronomy ◽

10.1017/s1539299600019389 ◽

1998 ◽

Vol 11 (2) ◽

pp. 988-989

Author(s):

D.L. Jones ◽

K.W. Weiler

Keyword(s):

High Frequency ◽

Angular Resolution ◽

Low Frequency ◽

High Angular Resolution ◽

Radio Sources ◽

The Moon ◽

Interstellar Scintillation ◽

Wide Range ◽

Lunar Farside

AbstractThe radio sky at frequencies of several MHz and below is essentially unexplored with high angular resolution due to refraction and opacity in the Earth’s ionosphere. An interferometer array in space providing arcminute resolution images would allow a wide range of problems in solar, planetary, galactic, and extragalactic astronomy to be attacked. These include the evolution of solar and planetary radio bursts, interplanetary and interstellar scintillation, the distribution of low energy cosmic rays and diffuse ionized hydrogen in our galaxy, the determination of spectral turnover frequencies and magnetic field strengths in galactic and extragalactic radio sources, searches for “fossil” radio galaxies which are no longer detectable by high frequency surveys, and searches for new sources of coherent radio emission. In addition, it is likely that unexpected objects and emission processes will be discovered by such an instrument, as has often happened when high resolution observations first become possible in a new spectral region. The Moon can provide shielding from terrestrial interference (and from the Sun half of the time) and consequently the lunar farside surface offers an ideal site of a low frequency radio array.

Download Full-text

Linear polarization in the nucleus of M87 at 7 mm and 1.3 cm

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937315 ◽

2020 ◽

Vol 637 ◽

pp. L6

Author(s):

E. Kravchenko ◽

M. Giroletti ◽

K. Hada ◽

D. L. Meier ◽

M. Nakamura ◽

...

Keyword(s):

Faraday Rotation ◽

Linear Polarization ◽

Radio Galaxy ◽

Angular Resolution ◽

Polarization Plane ◽

High Angular Resolution ◽

Time Interval ◽

Long Baseline ◽

Millimeter Wavelengths ◽

Very Long Baseline Array

We report on high angular resolution polarimetric observations of the nearby radio galaxy M87 using the Very Long Baseline Array at 24 GHz (λ = 1.3 cm) and 43 GHz (λ = 7 mm) in 2017–2018. New images of the linear polarization substructure in the nuclear region are presented, characterized by a two-component pattern of polarized intensity and smooth rotation of the polarization plane around the 43 GHz core. From a comparison with an analogous dataset from 2007, we find that this global polarization pattern remains stable on a time interval of 11 yr, while showing smaller month-scale variability. We discuss the possible Faraday rotation toward the M87 nucleus at centimeter to millimeter wavelengths. These results can be interpreted in a scenario where the observed polarimetric pattern is associated with the magnetic structure in the confining magnetohydrodynamic wind, which also serves as the source of the observed Faraday rotation.

Download Full-text

Small-Angle Electron Scattering (SAES) of Polymers

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100117467 ◽

1985 ◽

Vol 43 ◽

pp. 78-79

Author(s):

Ralph Oralor ◽

Pamela Lloyd ◽

Satish Kumar ◽

W. W. Adams

Keyword(s):

Electron Scattering ◽

Small Angle ◽

Angular Resolution ◽

Structural Features ◽

Objective Lens ◽

High Angular Resolution ◽

Push Button ◽

First Case ◽

Diffraction Mode ◽

Very High

Small angle electron scattering (SAES) has been used to study structural features of up to several thousand angstroms in polymers, as well as in metals. SAES may be done either in (a) long camera mode by switching off the objective lens current or in (b) selected area diffraction mode. In the first case very high camera lengths (up to 7Ø meters on JEOL 1Ø ØCX) and high angular resolution can be obtained, while in the second case smaller camera lengths (approximately up to 3.6 meters on JEOL 1Ø ØCX) and lower angular resolution is obtainable. We conducted our SAES studies on JEOL 1ØØCX which can be switched to either mode with a push button as a standard feature.

Download Full-text

Large-angle convergent-beam electron-diffraction study of coherent precipitates and decorated dislocations

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100167470 ◽

1996 ◽

Vol 54 ◽

pp. 1002-1004

Author(s):

J.M.K. Wiezorek ◽

H.L. Fraser

Keyword(s):

Electron Diffraction ◽

Angular Resolution ◽

Large Angle ◽

Electron Diffraction Study ◽

Convergent Beam Electron Diffraction ◽

Crystal Defects ◽

High Angular Resolution ◽

Beam Electron ◽

Diffraction Plane ◽

Convergent Beam

Conventional methods of convergent beam electron diffraction (CBED) use a fully converged probe focused on the specimen in the object plane resulting in the formation of a CBED pattern in the diffraction plane. Large angle CBED (LACBED) uses a converged but defocused probe resulting in the formation of ‘shadow images’ of the illuminated sample area in the diffraction plane. Hence, low-spatial resolution image information and high-angular resolution diffraction information are superimposed in LACBED patterns which enables the simultaneous observation of crystal defects and their effect on the diffraction pattern. In recent years LACBED has been used successfully for the investigation of a variety of crystal defects, such as stacking faults, interfaces and dislocations. In this paper the contrast from coherent precipitates and decorated dislocations in LACBED patterns has been investigated. Computer simulated LACBED contrast from decorated dislocations and coherent precipitates is compared with experimental observations.

Download Full-text