bluuebunny/crossref_metadata_2025_split huggingface dataset:
Proton Flare Project: Introduction and Summary
Authors: Švestka Z. 
Published: July 2016

All contributions presented at the Friday morning session concerned results of the Proton Flare Project (PFP), which was organized by the IAU Commission 10 under the sponsorship of the IQSY Committee, from May 1 to September 30, 1966. As explained by Z. Švestka in his introductory talk, this project had four main aims:
(1)To observe proton flares shortly after the minimum of the solar activity, when, on the rising part of the solar cycle, some proton flares already appear, but not too many of them, so that the individual proton flare phenomena are fairly isolated. This makes it easy to study all the effects of such a proton flare in the interplanetary space and in the Earth's surroundings, and particularly, it allows a detailed study of the isolated active region, in which the proton flare appears.(2)To get some practical experience in the forecasts of proton flares and verify the reliability and the practical use of them.(3)With the aid of these forecasts, to give to the solar and geophysical observatories and to the launching sites the possibility to get prepared for the coming event. It was hoped that in this way one might get very detailed observations of the proton-flare active region, of the proton flare itself, and of its effects in the interplanetary space and in the Earth's magnetosphere and ionosphere.
Supergranulation at the Center of the Disk
Authors: Frazier Edward N. 
Published: July 2016

The Kitt Peak multi-channel magnetograph was used to make raster scans of the supergranulation at the center of the disk. The scan pattern was arranged to largely cancel out the effects of the 5 min oscillations and the granulation and to enhance visible effects of the supergranulation.The results show vertical supergranular motions. These motions consist of relatively isolated ‘patches’ of downward flowing material, or ‘downdrafts’, with an average speed of 0.1 km/s. These downdrafts coincide with patches of magnetic field, and the speed of the downdraft is linearly proportional to the magnetic field strength (50 to 100 G). These downdrafts are also regions of increased brightness in the chromosphere and photosphere.
The Magnetic and Velocity Fields and Brightness in the Solar Atmosphere
Authors: Gopasyuk S. I. , Tsap T. T. 
Published: July 2016

Simultaneous observations of the magnetic fields, the line-of-sight velocities and brightness were made in active and quiet regions with the Crimean double-magnetograph in the following lines: Hα, K3 Ca II, Hβ, Hγ, Hδ, MgI λ 5184 Å, CaI λ 4227 Å, D1 NaI, BaII λ 4554 Å, CaI λ 6103 Å, FeI λ 5250 Å.It is shown, that in the active regions the horizontal velocity is larger than the vertical one.The mean velocities in the quiet solar photosphere have an isotropic distribution (Gopasyuk and Kalman, 1971).The mean vertical velocities increase exponentially with height in active and quiet regions.The correlation between velocities at different levels in active and quiet regions decreases with the distance between the levels of the formation of spectral lines, and it disappears for the velocities recorded in λ 6103 Å and Hβ, for λ 5184 and Hα lines in active regions and for the velocities recorded in λ 5250 Å and Hα lines in quiet regions.The position of the maximal field strength within a magnetic hill coincides statistically with the zero line of the line-of-sight velocities for active as well as for quiet regions.
Magnetic Fields Measured with the 10830 Å HeI Line
Authors: Harvey J. , Hall D. 
Published: July 2016

Several advantages of near infrared spectral lines for magnetic field measurements are listed. In particular, the 10830 Å multiplet of HeI is well suited for observations of chromospheric magnetic fields.New photoelectric spectroheliograms made with the 10830 Å line reveal a large amount of filamentary fine structure in active regions. This fine structure has important consequences on the interpretation of 10830 Å magnetograms. Except for an association of 10830 Å disk filaments with polarity reversals there is little correlation between absorption features and the 10830 Å longitudinal field. Comparisons of chromospheric and photospheric observations show that the chromospheric field is spatially more diffuse and weaker than the photospheric field.
Interaction of Coronal Material with Magnetic Fields
Authors: Pneuman G. W. , Kopp Roger A. 
Published: July 2016

The optical resolution in recent eclipse photographs is now sufficient to illustrate clearly many qualitative features of gas-magnetic field interactions in the solar corona. Close to the Sun where the field is strong, the coronal gas over certain regions of the solar surface can be contained within closed loop structures. However, since the field strength in these regions declines outward rapidly, the pressure and inertial forces of the solar wind eventually dominate and distend the field outward into interplanetary space. The overall configuration is determined by a complex interplay of inertial, pressure, gravitational, and magnetic forces. The present work is oriented toward the understanding of this interaction.Of central importance to this general problem is the typical ‘helmet’ streamer generally overlying a large diffuse bipolar region on the solar surface. A helmet streamer consists of closed magnetic loops near the Sun and open field lines adjacent to and above the loops. The configuration possesses a ‘cusp-type’ neutral point (to be differentiated from a y-type neutral point) at the top of the closed loops. In addition to volume currents, a single sheet current separates the regions of opposite polarity above the neutral point. Below the neutral point, sheet currents also are present between the open and closed regions. These sheet currents are necessary to support the discontinuity in gas pressure which arises since the open region is expanding and the closed region is not. The neutral point problem is discussed in some detail and sample numerical examples are presented.
Observations of the Polar Magnetic Fields
Authors: Stenflo Jan Olof 
Published: July 2016

Results from observations of the polar magnetic fields made in 1968 with the Mount Wilson magnetograph are reported. The field was of south polarity near the heliographic north pole and of north polarity near the south pole. The inversion line of the field was at latitude +70° in the north hemisphere and −55° in the south, which coincides with the position of the polar prominence zones at that time. Observations made simultaneously at the Crimean Astrophysical Observatory are in good agreement with the Mt. Wilson data and confirm the latitude variation of the field.A few hundred of Hale's plates from 1914, which he had used to determine the Sun's general magnetic field, have been remeasured. The plates were automatically scanned with a digitized microphotometer, and the treatment of the data was made with a computer. While the visual measurements by Van Maanen had given a strong general field similar to that of a dipole, the computer reductions did not reveal any significant field (stronger than 5 G) at any latitude.
Nature of the Venus Clouds as Derived from Their Polarization
Authors: Hansen James E. , Hovenier J. W. 
Published: July 2016

The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of particles which have a narrow size distribution with a mean radius ~ 1 μ. The refractive index of the particles is 1.44 ± 0.015 at γ = 0.55 μ with a small normal dispersion, the refractive index decreasing from the ultraviolet toward the infrared. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb.The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venus. A concentrated solution of sulfuric acid (H2SO4–H2O) provides good agreement with the polarization data.
A Modern Look at ‘Interstellar Clouds’
Authors: Heiles Carl 
Published: July 2016

We compare past and present modes of investigation of the structure of the interstellar gas. Many aspects of the interstellar cloud model are invalid.Interstellar optical absorption lines and Hi21-cm emission lines show a number of very large aggregates with properties similar to those of ‘cloud complexes’. At nonzero velocities especially for b<0°, exist optical lines which have no Hicounterparts. These are almost certainly produced in low-density gas clouds; perhaps the intercloud medium is itself cloudy.Maps of Hicolumn density taken over large velocity ranges do not reveal much small-scale structure. This fact cannot easily be reconciled with the statistical analyses of interstellar reddening. The maps do reveal large, coherent gas structures which are often filamentary in shape and at least sometimes aligned parallel to the interstellar magnetic field.Maps of Hicolumn density over small velocity ranges show much small-scale structure, often filamentary in shape. The filaments are almost universally oriented parallel to the interstellar magnetic field and have Doppler velocity gradients along their lengths. In one area the geometry of the field and gas almost exclusively suggests Alfvén-type motions.
Westerbork Observations of the Galactic Supernova Remnants IC 443 and Tycho
Authors: Duin R. M. , Strom R. G. , van der Laan H. 
Published: July 2016

Continuum observations of IC 443 were made at 21 cm with a resolution of 23″×59″. The appearance in the radio continuum is very similar to the optical appearance. Since the radio emission is nonthermal, this requires a mechanism that can enhance the synchrotron volume emissivity within thermal filaments, which emit strong optical radiation. We suggest compression of gas and magnetic fields in a shock.Tycho's remnant has been observed both at 21 cm (resolution 24″ × 27″) and at 6 cm (resolution 7″ × 8″). Most of the fine scale structure is resolved. The similarity at the two wavelengths indicates a remarkable constancy in the spectral index of features down to a scale of 20″.
Morphology and Power of Radio Sources
Authors: Scheuer P.A.G. 
Published: July 2016

I want to make two points:
1.Observations suggest that the hot-spots move about either because the beam precesses (e.g. Ekers et al. 1978; Lonsdale & Morrison 1980) or more discontinuously, as in sources like 3C351 that have multiple hot-spots (Laing 1981). The natural interpretation is that the hot-spot at the end of the beam slides over the inner surface of a ‘cavity’ filled with very hot dilute ex-hot-spot material (Scheuer 1974), extending the cavity at various places at different times. Such a ‘dentist's drill’ model has various consequences:
(i)The mean speed (length/age) at which the cavity elongates may be considerably smaller than the instantaneous speed V of the hot-spot, estimated in the customary way from pressure balance:
(ii)Remark (i) raises the possibility that giant radio sources have become so long because their jets are unusually constant in direction. NGC6251, which is over 2 Mpc long, has a jet whose direction has not wavered by more than a few degrees in ∼ 107 years (Saunders et al. 1981).(iii)We should not be surprised by sources whose hot-spots lie some way behind the extreme ends of the source; this may merely mean that the beam at present impinges on one side of the ‘cavity’. 3C285 is a typical example; a more persuasive case is the Np component of 3C219 (Perley et al. 1980).2.Most of the radio emission of most really powerful radio sources comes from their hot spots. Contrariwise, straightforward equipartition calculations on models lead to at least as much emission from the ‘cavity’ as from the hot-spots (Scheuer 1974). While there are several possible explanations, one in particular is suggested by Laing's (1981) extensive data on 40 sources. He lists the synchrotron lifetimes in the hot-spots for electrons radiating at 15 GHz, and while these exceed the light crossing times, they do so by only one or two orders of magnitude. One expects flow through the hot spots at some fairly small fraction of the speed of light; the synchrotron loss cutoff in the hot-spot is then expected to appear in the mm or infra-red region. Expansion of the hot-spot material into the cavity shifts the loss cutoff to a much lower frequency. If the expansion is adiabatic (certainly an oversimplification) the ratio of loss cutoff frequencies is equal to the ratio of energy densities. We cannot use this relationship directly in the more interesting cases, as we cannot estimate the energy density (or even the size) of a ‘cavity’ that we cannot observe. However, we can estimate the cutoff frequency within the hot-spots (for some assumed streaming speed), and Figure 1 shows that the most powerful hot-spots have loss cutoff frequencies in the 10–100 GHz range, implying cutoff frequencies in the ‘cavity’ that could well be below 1 GHz.
Wolf-Rayet Phenomena
Authors: Conti P. S. 
Published: July 2016

I have been asked to review in broad terms the concept of Wolf-Rayet (W-R) phenomena, that is, to outline what we currently know about the properties of stars showing such phenomena and to indicate the directions in which future work is leading. I thought I would begin by listing the characteristics of W-R spectra to which probably all the participants at this Symposium will be able to agree. These can readily be adapted from Thomas (1968) who discussed them at the Boulder W-R Symposium. The characteristics of W-R spectra are as follows:
(1)They are primarily an emission line spectrum superimposed on a “hot” continuous spectrum.(2)P Cygni absorption components are observed for some lines in some stars; a fact not realized in 1968 was that a very few W-R stars have intrinsic absorption lines (e.g. The Balmer series in HD 92740 — Niemela (1973).(3)The emission lines represent a wide range of excitation and ionization. This level is often higher than indicated by simple modeling of the continuous spectrum.(4)The emission lines are broad, corresponding to widths of hundreds to thousands of kilometers per second; widths often differ among various ions in the same star.(5)The W-R stars can be divided into two subtypes: These are the WN types, in which the ions of nitrogen dominate, and the WC types, in which the ions of carbon (and oxygen) dominate. Both sub-types have strong lines of helium; in a few cases, hydrogen lines, in emission, are also observed (Underbill 1968).
The NAVOBSY/NRL Program for the Determination of Earth Rotation and Polar Motion
Authors: Johnston K. J. , Spencer J. H. , Mayer C. H. , Klepczynski W. J. , Kaplan G. , McCarthy D. D. , Westerhout G. 
Published: July 2016

The joint program of NAVOBSY/NRL is discussed.The United States Naval Observatory (NAVOBSY) and the Naval Research Laboratory (NRL) are collaborating in a program to apply radio interferometric techniques to the determination of variations in Earth rotation, polar motion, and improved astronomical position reference systems. Investigations of VLBI and connected interferometer techniques and radio sources for astrometic application have been in progress for several years as part of the NRL radio astronomy program, and currently NRL and NAVOBSY are carrying out experimental programs to investigate VLBI time transfer techniques and UT determination using the connected element interferometer of the NRAO in Green Bank. Some previous results of observations using the Green Bank interferometer and proposed plans for operation as a dedicated system over a period of time to evaluate effectiveness for precise determination of Earth rotation parameters are discussed.
On the Effective Use of Lunar Ranging for the Determination of the Earth's Orientation
Authors: Silverberg Eric C. 
Published: July 2016

Lunar ranging data have been routinely available since September of 1970, but many problems of a varying nature have delayed the establishment of a world-wide lunar ranging network. As a result, we must re-examine the role which this program can play in the determination of the Earth's rotation and polar motion. Although there are many technical difficulties now inhibiting the widespread use of this technique there seems little doubt but that we can overcome these problems and achieve routine, accurate orientation determinations. The more difficult questions concern how an Earth rotation campaign should now be configured to use the equipment and resources in the best way.Despite considerable progress by other techniques, the failure to develop a lunar capability for Earth orientation determinations would result in a serious loss of information. Lunar monitoring of long-term effects in the Earth's rotation rate and the relationship of the lunar orbital parameters to a stellar reference frame are two tasks for which there is little redundancy. However, the most cost-effective usage of station resources may not require daily measures, but only periodic, accurate snapshots of the Earth's rotational position relative to the Moon. If some satellite laser ranging facilities could treat the Moon as an object of opportunity, but were able to elevate the program to priority status when global conditions were favorable, the incremental cost of gathering the required lunar data might be drastically reduced. Even though these cost savings could not be achieved without daily communication between cooperating stations, such a detailed interaction is not unreasonable to consider.
Quiet Sun at Metric and Decametric Wavelengths
Authors: Lantos P. 
Published: July 2016

In 1950, a few years after the detection of the Sun at radiowavelengths by Southworth (1945), two important points were already established:
1— The theory (Martyn 1946, Ginzburg, 1946) indicates that the thermal bremmstrahlung is dominant.2— The transfer calculations by Smerd (1950) and the total flux measurements (Pawsey 1946, Pawsey and Yabsley, 1949) lead to a coronal temperature of one million degrees.
Some Characteristics of Ultra-Fast Time Structures Superimposed on Impulsive mm-Wave Bursts
Authors: Kaufmann P. , Strauss F. M. , Opher R. 
Published: July 2016

SummaryThe use of increased sensitivity and temporal resolution at mm-wavelengths has revealed a number of novel features associated with solar activity (Kaufmann et al., 1979a). Of particular interest are the ultra-fast time structures superimposed on impulsive bursts. They are distinguished by time scales and repetition rates much shorter than the impulsive times scales. For weak bursts at λ = 13mm (i.e., few s.f.u.) the superimposed spikes are separated in time by several seconds. For moderate fluxes (i.e., 100 s.f.u.) the repetition rate of superimposed spikes is ~ 10–15 per second (i.e., time interval between two repeated spikes ~ 80 msec). For bursts larger than 500 s.f.u. the predicted times between repeated ultra-fast structures are shorter than 10 msec. Various examples have been studied with a time resolution better than 10 msec. (Kaufmann et al., 1979b). The impulsive flux level increases with the repetition rate of the ultra-fast component, following a nearly linear relationship. The simplest interpretation suggests that the injected spikes are associated with the bursting source function and are quasi-quantized in energy (Kaufmann et al., 1979b).
Shapley's Era
Authors: Hogg Helen Sawyer 
Published: July 2016

I am greatly pleased to have a chance to speak at this Symposium about Harlow Shapley, the man who was probably responsible, more than any other, for the shape my life has taken.In my talk this morning I am repeating a few of the remarks I made at the Centennial Celebration for the birthday of Harlow Shapley last October 17 at the Harvard College Observatory. Some of the people here today were present then, and I trust they will excuse the repetition. But my talk today has a different slant.
Computer Aided Near Earth Object Detection
Authors: Scotti James V. 
Published: July 2016

The Spacewatch program at the University of Arizona has pioneered automatic methods of detecting Near Earth Objects. Our software presently includes three modes of object detection: automatic motion identification; automatic streak identification; and visual streak identification. For automatic motion detection at sidereal drift rates, the 4σ detection threshold is near magnitude V = 20.9 for nearly stellar asteroid images. The automatic streak detection is able to locate streaks whose peak signal is above ~4σ and whose length is longer than about 10 pixels. Some visually detected streaks have had peak signals near ~1σ.Between 1990 September 25 and 1993 June 30, 45 new Near Earth asteroids, two comets and two Centaur's have been discovered with the system. An additional six comets, five Near Earth asteroids, and one Centaur were also “re-discovered”. The system has directly detected for the first time Near Earth Objects in the complete size range from about 5 kilometers to about 5 meters. Each month ~2,000 main belt asteroids are also detected.Future upgrades in both hardware, software, and telescope aperture may allow an order of magnitude increase in the rate of discovery of Near Earth Objects in the next several years. Several of the techniques proposed for the Spaceguard Survey have already been tested by Spacewatch, and others will need to be tested in the near future before such a survey can be implemented.
Dynamics of Comets: Recent Developments and New Challenges
Authors: Fernández Julio A. 
Published: July 2016

There is a broad consensus that long-period comets come from a huge reservoir surrounding the solar system, as proposed originally by Oort. Yet, the classical picture of the Oort cloud has substantially changed during the last decade. In addition to passing stars, the tidal force of the galactic disk and giant molecular clouds have also been identified as major perturbers of the Oort cloud. In particular, the latter may be responsible for limiting the size of the stable Oort cloud to no more than ≈ 104AU, i.e. about one tenth of the classical Oort's radius.Most comets are injected into the planetary region by the quasi-steady action of the tidal force of the galactic disk. The concentration of aphelion points of dynamically young comets toward mid-galactic latitudes is a consequence of its dominant influence. The frequency of comet passages into the inner planetary region could experience significant fluctuations with time as the Oort cloud meets random strong perturbers. The observed ordered pattern of most comet aphelia, associated with the galactic structure, argues against a recent strong perturbation of the Oort cloud.The origin of the Jupiter family has become another point of intense debate. Jupiter family comets may come from a transneptunian comet belt -the Kuiper belt- from where they can reach the planetary region through chaotic motion. The Kuiper belt has become accessible to large telescopes, as shown by the recent discoveries of 1992QB1 and 1993FW, possibly belt members. The major challenge will be to explore the region usually inaccessible to external perturbers that goes from ~30 AU to a few thousand AU. A significant mass may have been locked there from the beginnings of the solar system, giving rise to an inner core that feeds the outer or classical Oort cloud. Our aim will be to briefly discuss some of the topics summarized here.