scholarly journals Distribution and motions of HI in M31

1985 ◽  
Vol 106 ◽  
pp. 437-442
Author(s):  
E. Brinks ◽  
W. B. Burton
Keyword(s):  
High Resolution ◽  
Atomic Hydrogen ◽  
Line Of Sight ◽  
Complete Model ◽  
Previous Survey ◽  
The Past ◽  
The Galaxy ◽  
The One

It has become clear in the past few years that the distribution and kinematics of HI in M31 is far from simple. The new high-resolution survey made with the Westerbork SRT in the 21-cm line of atomic hydrogen by Brinks and Shane (1983) shows this dramatically. Along almost any line of sight through M31 two separate velocity systems are sampled. Based on a previous survey Shane (1978) and later Bajaja and Shane (1982) proposed that the extra component is due to warping of the plane of the galaxy into the direction of and crossing the line-of-sight. Roberts et al. (1978) and Whitehurst et al. (1978) emphasized that the observed profile structure ruled out confinement of the gas to a thin plane. Unwin (1983) reached a similar conclusion on the basis of his survey. The most complete model produced up until now which accounts for the two velocity systems is the one by Henderson (1979), based on the 100-m Effelsberg survey of M31 by Cram et al. (1980)

Boron Abundance in the PopII HD 76932

1988 ◽  
Vol 132 ◽  
pp. 511-514
Author(s):  
P. Molaro
Keyword(s):  
High Resolution ◽  
Preliminary Analysis ◽  
The Other ◽  
Light Elements ◽  
Simultaneous Presence ◽  
The Past ◽  
Upper Limits ◽  
Cool Stars ◽  
The Galaxy ◽  
The Continuum

Aware of the importance of B observations in cool stars we have attempted to search for BI 2496 lines in high resolution IUE spectra of HD 76932, with [Fe/H]=−1.1, and HD 216385, with [Fe/H]=−0.6. Line blending and the impossibility of establishing the continuum level are the major obstacles in such an investigation. Molaro (1987) showed that, in the case of extremely metal-deficient stars, the consequent line-blocking reduction allows us to derive significant upper limits for the B abundance. In HD 140283, [Fe/H]=−3.0, Molaro (1987) derived [B/H]< 2 ×10−11. In HD 76932 a preliminary analysis gives a B abundance of [B/H]< 2 ×10−10, i.e. less than the present “cosmic” value. On the other hand no useful limits can be placed for HD 216385. The presence of an unidentified line, not resolved with IUE, prevents B analysis in cool stars with similar or greater metallicity. Better data with higher spectral resolution and greater photometric accuracy are required to confirm these results. The simultaneous presence of Li in the atmospheres of these stars rules out stellar depletion for B, providing evidence that the B abundance in the Galaxy was lower in the past than it is today. These observations also imply that spallation proccesses were not able to produce significant quantities of B, or other light elements at the beginning of the Galaxy. In particular, spallation processes cannot be adduced as a possible source for the Li observed in the Pop II stars.

scholarly journals SENTINEL-1 INSAR PROCESSING OF CORNER REFLECTOR INFORMATION IN THE NORTHERN-BOHEMIAN COAL BASIN

2016 ◽  
Vol XLI-B7 ◽  
pp. 763-767
Author(s):  
I. Hlaváčová ◽  
L. Halounová ◽  
P. Stanislav
Keyword(s):  
Mining Area ◽  
Line Of Sight ◽  
Corner Reflector ◽  
Coal Basin ◽  
Satellite Line ◽  
The Past ◽  
Additional Processing ◽  
The One ◽  
Processing Steps ◽  
Slope Direction

The mining area previously monitored by TerraSAR-X InSAR is now monitored by Sentinel-1 InSAR. Although the processing of the IWS (TOPS) mode requires additional processing steps and the coregistration has to be performed with the precision of 0.001 pixel (in the azimuth direction), if an area within one burst is processed, such a precise coregistration is not necessary. Information from 11 corner reflectors is evaluated, and significant movements at one of them were detected. Although it seems to be uplift, it is more probable that the movement is in down-the-slope direction, which has a negative sensitivity with regard to the satellite line of sight. The movement is similar to the one detected by TerraSAR-X satellite in the past. At the end of the monitoring period, the movement seems to settle down; future monitoring will show more about the dynamicity of the movement.

scholarly journals The distribution of atomic hydrogen in the galaxy

1958 ◽  
Vol 5 ◽  
pp. 16-22
Author(s):  
H. C. Van De Hulst
Keyword(s):  
The Netherlands ◽  
Radio Astronomy ◽  
Atomic Hydrogen ◽  
Neutral Hydrogen ◽  
The Past ◽  
The Galaxy ◽  
Inner Parts

It is my privilege to report here about the investigations of the distribution of neutral hydrogen in the Galaxy. These observations, conducted by the Netherlands Foundation for Radio Astronomy, were made at Kootwijk and reduced at the Leiden Observatory. More than a dozen persons have participated in this work during the past year. Among them are Prof. Oort and myself, but I should mention three in particular: C. A. Muller has perfected the instruments even further and has supervised the observations that were made during 24 hr a day. G. Westerhout has supervised most of the reductions at Leiden and has prepared the map and model of the outer parts of the Galaxy. M. Schmidt has unravelled the situation in the inner parts of the Galaxy, on the basis of his observations made for this purpose.

scholarly journals Interstellar sodium and Galactic structure. A high-resolution survey

1985 ◽  
Vol 106 ◽  
pp. 325-328
Author(s):  
E. Maurice ◽  
A. Ardeberg ◽  
H. Lindgren
Keyword(s):  
High Resolution ◽  
Spectral Resolution ◽  
Absorption Lines ◽  
High Spectral Resolution ◽  
Line Of Sight ◽  
Substantial Part ◽  
Galactic Rotation ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
The Galaxy

Observation of absorption lines produced by interstellar gas is a straight-forward way to determine column densities and velocities along the line of sight of interstellar clouds. In practice, peculiar motions often mask galactic rotation and/or cause line blending. We have made a study of absorption lines of interstellar sodium covering a substantial part of the Galaxy at extremely high spectral resolution.

scholarly journals SENTINEL-1 INSAR PROCESSING OF CORNER REFLECTOR INFORMATION IN THE NORTHERN-BOHEMIAN COAL BASIN

2016 ◽  
Vol XLI-B7 ◽  
pp. 763-767
Author(s):  
I. Hlaváčová ◽  
L. Halounová ◽  
P. Stanislav
Keyword(s):  
Mining Area ◽  
Line Of Sight ◽  
Corner Reflector ◽  
Coal Basin ◽  
Satellite Line ◽  
The Past ◽  
Additional Processing ◽  
The One ◽  
Processing Steps ◽  
Slope Direction

The mining area previously monitored by TerraSAR-X InSAR is now monitored by Sentinel-1 InSAR. Although the processing of the IWS (TOPS) mode requires additional processing steps and the coregistration has to be performed with the precision of 0.001 pixel (in the azimuth direction), if an area within one burst is processed, such a precise coregistration is not necessary. Information from 11 corner reflectors is evaluated, and significant movements at one of them were detected. Although it seems to be uplift, it is more probable that the movement is in down-the-slope direction, which has a negative sensitivity with regard to the satellite line of sight. The movement is similar to the one detected by TerraSAR-X satellite in the past. At the end of the monitoring period, the movement seems to settle down; future monitoring will show more about the dynamicity of the movement.

scholarly journals The Absorption by the Interstellar Medium of 80 MHz Radio Emission from Galactic Supernova Remnants

1972 ◽  
Vol 25 (4) ◽  
pp. 429 ◽  
Author(s):  
GA Dulk ◽  
OB Slee
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Interstellar Medium ◽  
Flux Density ◽  
Electron Density ◽  
Supernova Remnants ◽  
Line Of Sight ◽  
The Galaxy

High resolution 80 MHz observations of 20 galactic supernova remnants have been made with the Culgoora radioheliograph. More than half of the sources have an unexpectedly low flux density at 80 MHz, probably as a result of free?free absorption taking place in the inner arms of the Galaxy. The observations imply an r.m.s. electron density of about 0�1?0�5 cm?3 along the line of sight. This large value for the electron density seems to require a greater ionizing flux than that which occurs in the solar vicinity.

scholarly journals Analysis of galaxy kinematics based on Cepheids from the Gaia DR2 Catalogue

2021 ◽  
Vol 502 (3) ◽  
pp. 4377-4391
Author(s):  
V V Bobylev ◽  
A T Bajkova ◽  
A S Rastorguev ◽  
M V Zabolotskikh
Keyword(s):  
Density Wave ◽  
Rotation Velocity ◽  
Proper Motions ◽  
The Past ◽  
Spiral Density Wave ◽  
Classical Cepheids ◽  
The Galaxy ◽  
Galaxy Kinematics ◽  
The One ◽  
Gaia Dr2

ABSTRACT To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalogue are used in large part. Our working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at the solar distance is V0 = 240 ± 3 km s−1. In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be R0 = 8.27 ± 0.10 kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at the present time and in the past. Therefore, the value of the wavelength λR, θ is in the range [2.4–3.0] kpc, the pitch angle iR, θ is in the range [−13○, −10○] for a four-arm pattern model, and the amplitudes of the radial and tangential perturbations are fR ∼ 12 km s−1 and fθ ∼ 9 km s−1, respectively. Velocities of Cepheids older than 120 Myr currently give a wavelength λR, θ ∼ 5 kpc. This value differs significantly from the one we obtained from samples of young Cepheids. An analysis of the positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength λR, θ = 2.7 kpc and amplitudes of radial and tangential perturbations fR = 7.9 km s−1 and fθ = 5 km s−1, respectively.

The Contribution of Intermediate-Voltage, High-Resolution Electron Microscopy In Materials Science: An Appraisal

1990 ◽  
Vol 48 (1) ◽  
pp. 478-479
Author(s):  
John L. Hutchison
Keyword(s):  
High Resolution ◽  
Materials Science ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
The Past ◽  
Resolution Electron ◽  
Extreme Sensitivity ◽  
Electron Microscopes ◽  
New Generation ◽  
Small Metal Particles

Over the past five years or so the development of a new generation of high resolution electron microscopes operating routinely in the 300-400 kilovolt range has produced a dramatic increase in resolution, to around 1.6 Å for “structure resolution” and approaching 1.2 Å for information limits. With a large number of such instruments now in operation it is timely to assess their impact in the various areas of materials science where they are now being used. Are they falling short of the early expectations? Generally, the manufacturers’ claims regarding resolution are being met, but one unexpected factor which has emerged is the extreme sensitivity of these instruments to both floor-borne and acoustic vibrations. Successful measures to counteract these disturbances may require the use of special anti-vibration blocks, or even simple oil-filled dampers together with springs, with heavy curtaining around the microscope room to reduce noise levels. In assessing performance levels, optical diffraction analysis is becoming the accepted method, with rotational averaging useful for obtaining a good measure of information limits. It is worth noting here that microscope alignment becomes very critical for the highest resolution.In attempting an appraisal of the contributions of intermediate voltage HREMs to materials science we will outline a few of the areas where they are most widely used. These include semiconductors, oxides, and small metal particles, in addition to metals and minerals.

The Contribution of Phonon-Scattered Electrons to High-Resolution Electron Micrographs of Crystals

1990 ◽  
Vol 48 (1) ◽  
pp. 62-63
Author(s):  
H. Kohl
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
High Resolution Electron Microscopy ◽  
Static Potential ◽  
Qualitative Comparison ◽  
The Past ◽  
Resolution Electron ◽  
High Resolution Images ◽  
High Resolution Electron Micrographs ◽  
Extract Information

High-Resolution Electron Microscopy is able to determine structures of crystals and interfaces with a spatial resolution of somewhat less than 2 Å. As the image is strongly dependent on instrumental parameters, notably the defocus and the spherical aberration, the interpretation of micrographs necessitates a comparison with calculated images. Whereas one has often been content with a qualitative comparison of theory with experiment in the past, one is currently striving for quantitative procedures to extract information from the images [1,2]. For the calculations one starts by assuming a static potential, thus neglecting inelastic scattering processes.We shall confine the discussion to periodic specimens. All electrons, which have only been elastically scattered, are confined to very few directions, the Bragg spots. In-elastically scattered electrons, however, can be found in any direction. Therefore the influence of inelastic processes on the elastically (= Bragg) scattered electrons can be described as an attenuation [3]. For the calculation of high-resolution images this procedure would be correct only if we had an imaging energy filter capable of removing all phonon-scattered electrons. This is not realizable in practice. We are therefore forced to include the contribution of the phonon-scattered electrons.

Al-Rasm al-ʿUthmānī: Towards Correct Pronunciation and the Preclusion of Ambiguity

2011 ◽  
Vol 13 (2) ◽  
pp. 201-171
Author(s):  
Nāṣir Al-Dīn Abū Khaḍīr
Keyword(s):  
Specific Pattern ◽  
Writing Style ◽  
The Third ◽  
The Past ◽  
Different Ages ◽  
Correct Pronunciation ◽  
The One ◽  
The Mind

The ʿUthmānic way of writing (al-rasm al-ʿUthmānī) is a science that specialises in the writing of Qur'anic words in accordance with a specific ‘pattern’. It follows the writing style of the Companions at the time of the third caliph, ʿUthmān b. ʿAffān, and was attributed to ʿUthmān on the basis that he was the one who ordered the collection and copying of the Qur'an into the actual muṣḥaf. This article aims to expound on the two fundamental functions of al-rasm al-ʿUthmānī: that of paying regard to the ‘correct’ pronunciation of the words in the muṣḥaf, and the pursuit of the preclusion of ambiguity which may arise in the mind of the reader and his auditor. There is a further practical aim for this study: to show the connection between modern orthography and the ʿUthmānic rasm in order that we, nowadays, are thereby able to overcome the problems faced by calligraphers and writers of the past in their different ages and cultures.

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