Accurate determination of the successive moments of the sun: a new window open on the sun's interior

2002 ◽  
Vol 29 (12) ◽  
pp. 2089-2092 ◽  
Author(s):  
J.P. Rozelot ◽  
S. Godier
Keyword(s):  
Accurate Determination ◽  
The Sun

scholarly journals The Open Cluster M67 as a Fundamental Standard of Reference for Stellar Properties

1985 ◽  
Vol 111 ◽  
pp. 361-364
Author(s):  
Kenneth Janes
Keyword(s):  
Open Cluster ◽  
Accurate Determination ◽  
Distance Modulus ◽  
The Sun ◽  
Distance Measurements ◽  
Photoelectric Photometry ◽  
Sources Of Error ◽  
Motion Studies ◽  
Stellar Properties

With the possible exception of the Hyades, M67 is the best-studied star cluster. Accurate photoelectric photometry exists well down onto the main sequence and proper motion studies have isolated cluster stars from the field. From photometry and spectroscopy, its composition is determined to be almost exactly the same as the Sun, with an age about one-half billion years less. This similarity to the Sun permits an accurate determination of distance to M67 independently of other distance measurements. Using the Sun as a reference, the distance modulus of M67 is found to be 9.48 mag. An extensive analysis of possible sources of error leads to an uncertainty (standard error) of ± 0.15 mag., with the chief sources of error being the color index of the Sun, the composition of the cluster, and its age. The M67 distance uncertainty compares favorably with Hanson's (1975) Hyades modulus of 3.29 ± 0.08.

Introductory remarks

1978 ◽  
Vol 284 (999) ◽  
pp. 1-2
Keyword(s):  
Great Barrier Reef ◽  
Royal Society ◽  
Accurate Determination ◽  
The Sun ◽  
Barrier Reef ◽  
The South ◽  
The Face ◽  
The Universe ◽  
Do So

What we are here to discuss concerns the Great Barrier Reef of Australia. It is very fitting that we should do so in this place, because the Royal Society was intimately concerned with events that led to its discovery in 1770. We go back to 1716, to a communication printed in Latin in the Philosophical Transactions by Edmond Halley, then Savilean Professor of Geometry at Oxford and Secretary of this Society. There, and for no less an objective than the more accurate determination of the dimensions of the Universe, he drew attention to the unique opportunities to that end to be presented by observing the transits of Venus across the face of the Sun due on 6 June 1761 and 3 June 1769. In the event international observations in the former year were largely fruitless, giving added reason for adequate observations in 1769. One of the conclusions of the specially appointed Transit Committee of the Society was that one site for observation should be in the South Seas.

scholarly journals VLBI Observations of Turbulence in the Inner Solar Wind

1996 ◽  
Vol 154 ◽  
pp. 65-75
Author(s):  
Steven R. Spangler
Keyword(s):  
Solar Wind ◽  
Accurate Determination ◽  
The Sun ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Outer Corona ◽  
Very Long Baseline Array ◽  
Made In

AbstractI discuss the use of Very Long Baseline Interferometer (VLBI) phase scintillations to probe the conditions of plasma turbulence in the solar wind. Specific results from 5.0 and 8.4 GHz observations with the Very Long Baseline Array (VLBA) are shown. There are several advantages of phase scintillation measurements. They are sensitive to fluctuations on scales of hundreds to thousands of kilometers, much larger than those probed by IPS intensity scintillations. In addition, with the frequency versatility of the VLBA one can measure turbulence from the outer corona ~ 5 –10 R⊙ to well past the perihelion approach of the Helios spacecraft. This permits tests of the consistency of radio propagation and direct in-situ measurements of turbulence. Such a comparison is made in the present paper. Special attention is dedicated to measuring the dependence of the normalization coefficient of the density power spectrum, on distance from the sun. Our results are consistent with the contention published several years ago by Aaron Roberts, that there is insufficient turbulence close to the sun to account for the heating and acceleration of the solar wind. In addition, an accurate determination of the relationship could aid the detection of transients in the solar wind.

Introductory remarks

1978 ◽  
Vol 291 (1378) ◽  
pp. 3-4
Keyword(s):  
Royal Society ◽  
Accurate Determination ◽  
The Sun ◽  
Barrier Reef ◽  
James Cook ◽  
The Face ◽  
George Iii ◽  
The Universe ◽  
Do So

What we are here to discuss concerns the Great Barrier Reef of Australia. It is very fitting that we should do so in this place, because the Royal Society was intimately concerned with events that led to its discovery in 1770. We go back to 1716, to a communication printed in Latin in the Philosophical Transactions by Edmond Halley, then Savilean Professor of Geometry at Oxford and Secretary of this Society. There, and for no less an objective than the more accurate determination of the dimensions of the Universe, he drew attention to the unique opportunities to that end to be presented by observing the transits of Venus across the face of the Sun due on 6 June 1761 and 3 June 1769. In the event international observations in the former year were largely fruitless, giving added reason for adequate observations in 1769. One of the conclusions of the specially appointed Transit Committee of the Society was that one site for observation should be in the South Seas. A direct appeal to George III produced one of the earliest grants of money for purely scientific purposes, and even more to the point the Admiralty was in almost enthusiastic agreement. Sweeping aside the Committee’s proposal that Dalrymple should head the expedition, the Admiralty selected Mr James Cook, previously surveyor of the lower reaches of the St Lawrence and of the coasts of Newfoundland. He was now commissioned Lieutenant of H. M. S. Endeavour , and the transit was to be observed from the island of Tahiti recently discovered by Wallis on H. M. S. Dolphin .

scholarly journals White Dwarf Probes of Interstellar Deuterium

2000 ◽  
Vol 198 ◽  
pp. 485-486
Author(s):  
Wayne Landsman
Keyword(s):  
High Resolution ◽  
Interstellar Medium ◽  
White Dwarf ◽  
White Dwarfs ◽  
Accurate Determination ◽  
The Sun ◽  
Local Interstellar Medium ◽  
Space Telescope ◽  
Imaging Spectrograph

We review the advantages of using hot white dwarfs (WDs) as probes of the deuterium abundance in the local interstellar medium. We then discuss advantages of the Space Telescope Imaging Spectrograph (STIS) for such observations, as compared with earlier observations with the Goddard High Resolution Spectrograph (GHRS). The GHRS Ly α profile of the white dwarf HZ 43 is probably modified by the hot ‘hydrogen wall’ surrounding the Sun; but despite this complication, the sightline remains a promising one for an accurate determination of the deuterium abundance in the local interstellar medium.

Captain Cook and the transit of Venus of 1769

1969 ◽  
Vol 24 (1) ◽  
pp. 19-32 ◽  
Keyword(s):  
Seventeenth Century ◽  
Accurate Determination ◽  
Favourable Condition ◽  
Base Line ◽  
The Sun ◽  
Favourable Case ◽  
The Earth ◽  
Planetary Orbits

The motions of the planets among the stars even if observed with instruments capable of no greater accuracy than one minute of arc can be analysed to produce orbits whose relative sizes are known quite accurately. Kepler, for example, gave the correct shape of the planetary orbits as ellipses with the Sun in one focus. He was also able to assert that the squares of the periodic times were proportional to the cubes of the semi axes major, without being able to determine the length of any one of these axes in terms of the mile. As a matter of fact he thought that the scale was less than onesixth of what we now know it to be. To calibrate the scale of the planetary orbits against a terrestrial scale it is enough to measure any one interplanetary distance by triangulation from a terrestrial base line, of which the angle at the apex is necessarily small. So long as only the classical planets were known, the most favourable case is presented by the planet Mars, which approaches to within a distance of 4278 times the diameter of the Earth. Under the most favourable condition (of observing Mars at its closest approach from opposite ends of a diameter of the Earth) the angle at the apex of the triangle would be 1/4278 radian or 48 seconds of arc (so that the parallax, which is the semiangle, is 24 seconds of arc). There are many reasons why an accurate determination of the parallax of Mars was not easy to be accomplished by seventeenth-century astronomers. However, if early astronomers had settled the parallax of Mars at its closest approach to the Earth, they would have known the ratios of the distance between the planet and the Earth to the distances of either body from the Sun, from the orbits whose relative sizes were perfectly well known.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

A quantitative approach to inner shell losses

1978 ◽  
Vol 36 (1) ◽  
pp. 526-527 ◽  
Author(s):  
R.D. Leapman ◽  
P. Rez ◽  
D.F. Mayers
Keyword(s):  
Energy Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Accurate Determination ◽  
Background Intensity ◽  
Core Excitation ◽  
Quantitative Basis ◽  
Cross Section Differential ◽  
Bound Electrons

Microanalysis by EELS has been developing rapidly and though the general form of the spectrum is now understood there is a need to put the technique on a more quantitative basis (1,2). Certain aspects important for microanalysis include: (i) accurate determination of the partial cross sections, σx(α,ΔE) for core excitation when scattering lies inside collection angle a and energy range ΔE above the edge, (ii) behavior of the background intensity due to excitation of less strongly bound electrons, necessary for extrapolation beneath the signal of interest, (iii) departures from the simple hydrogenic K-edge seen in L and M losses, effecting σx and complicating microanalysis. Such problems might be approached empirically but here we describe how computation can elucidate the spectrum shape.The inelastic cross section differential with respect to energy transfer E and momentum transfer q for electrons of energy E0 and velocity v can be written as

Fast calibration of CBED patterns for quantitative analysis

1993 ◽  
Vol 51 ◽  
pp. 674-675
Author(s):  
M.A. Gribelyuk ◽  
M. Rühle
Keyword(s):  
Reciprocal Lattice ◽  
Accurate Determination ◽  
Incident Beam ◽  
Crystal Thickness ◽  
Structure Model ◽  
Beam Direction ◽  
Transmitted Beam ◽  
Reciprocal Vector ◽  
On Line

A new method is suggested for the accurate determination of the incident beam direction K, crystal thickness t and the coordinates of the basic reciprocal lattice vectors V1 and V2 (Fig. 1) of the ZOLZ plans in pixels of the digitized 2-D CBED pattern. For a given structure model and some estimated values Vest and Kest of some point O in the CBED pattern a set of line scans AkBk is chosen so that all the scans are located within CBED disks.The points on line scans AkBk are conjugate to those on A0B0 since they are shifted by the reciprocal vector gk with respect to each other. As many conjugate scans are considered as CBED disks fall into the energy filtered region of the experimental pattern. Electron intensities of the transmitted beam I0 and diffracted beams Igk for all points on conjugate scans are found as a function of crystal thickness t on the basis of the full dynamical calculation.

Computer-Assisted High-Re Solution TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 162-163
Author(s):  
F.A. Ponce ◽  
H. Hikashi
Keyword(s):  
Signal To Noise Ratio ◽  
Accurate Determination ◽  
Computer Software ◽  
Video Camera ◽  
Image Contrast ◽  
Objective Lens ◽  
Computer Assisted ◽  
Optical Parameters ◽  
Astigmatism Correction

The determination of the atomic positions from HRTEM micrographs is only possible if the optical parameters are known to a certain accuracy, and reliable through-focus series are available to match the experimental images with calculated images of possible atomic models. The main limitation in interpreting images at the atomic level is the knowledge of the optical parameters such as beam alignment, astigmatism correction and defocus value. Under ordinary conditions, the uncertainty in these values is sufficiently large to prevent the accurate determination of the atomic positions. Therefore, in order to achieve the resolution power of the microscope (under 0.2nm) it is necessary to take extraordinary measures. The use of on line computers has been proposed [e.g.: 2-5] and used with certain amount of success.We have built a system that can perform operations in the range of one frame stored and analyzed per second. A schematic diagram of the system is shown in figure 1. A JEOL 4000EX microscope equipped with an external computer interface is directly linked to a SUN-3 computer. All electrical parameters in the microscope can be changed via this interface by the use of a set of commands. The image is received from a video camera. A commercial image processor improves the signal-to-noise ratio by recursively averaging with a time constant, usually set at 0.25 sec. The computer software is based on a multi-window system and is entirely mouse-driven. All operations can be performed by clicking the mouse on the appropiate windows and buttons. This capability leads to extreme friendliness, ease of operation, and high operator speeds. Image analysis can be done in various ways. Here, we have measured the image contrast and used it to optimize certain parameters. The system is designed to have instant access to: (a) x- and y- alignment coils, (b) x- and y- astigmatism correction coils, and (c) objective lens current. The algorithm is shown in figure 2. Figure 3 shows an example taken from a thin CdTe crystal. The image contrast is displayed for changing objective lens current (defocus value). The display is calibrated in angstroms. Images are stored on the disk and are accessible by clicking the data points in the graph. Some of the frame-store images are displayed in Fig. 4.

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