bluuebunny/crossref_metadata_2025 huggingface dataset:
Interstellar Molecules - The Optical Region
Authors: McNally D.
Published: March 2016

Considerable attention has recently been given to the observation of interstellar molecules by radio methods. Interstellar molecules have also been given a boost because of excitation by the 3K black body radiation field (to use a convenient description). Nevertheless optical studies of interstellar lines have reached a very low ebb and, with brighter moments, have remained so since the work of Adams (1949).

The years 1937-1942 were the exciting period for optical studies of interstellar molecular lines. It is interesting to note that it was not molecular lines as such that led to the suspicion that molecules might exist in interstellar space but it was the discovery of the diffuse features at 5780, 5797, 6284 and 6614 by Merrill (1934) that led Russell (1935) to speculate on the possibility of their existence. It was Swings and Rosenfeld (1937) who stressed that likely interstellar molecules would be CH, OH, NH, CN and C2. Dunham, Adams and McKellar did much of the work of identifying interstellar lines in the period 1937-1940 and indeed McKellar (1941) had derived an excitation temperature of 2-3 K for CN - a value subsequently rediscovered.
Interstellar Formaldehyde
Authors: Palmer Patrick
Published: March 2016

Formaldehyde (H2CO) was found to be present in the interstellar medium less than 1½ yr ago. This discovery raised a number of new astrophysical problems specific to H2CO such as how is the molecule formed, how is it destroyed, and how do the anomalous energy level populations leading to absorption of the isotropic microwave background arise. In addition, H2CO has provided a new means of studying several problems of long standing interest in astronomy. These include large scale galactic structure, distribution and motions of local gas and dust, and isotopic abundance ratios. A surprisingly large amount of work has been done on these problems in the rather short time since the initial discovery. I will confine myself to a brief summary of the observational aspects, omitting many of the topics that will be discussed in more detail by others later today, and then describe in detail some of our more recent work.
NH3 and H2O Emission in our Galaxy
Authors: Rank D. M.
Published: March 2016

In 1968 NH3 molecules were discovered in gas clouds near the center of our Galaxy. The NH3 molecules showed emission lines in transitions arising from metastable J = K rotational states. NH3 has many transitions at about 1.25 cm; hence, a great deal can be learned about the gas clouds. In particular, 1-1, 2-2, 3-3, 4-4 have excitation temperatures of 24K, 65K, 125K, 203K respectively. Thus, one can determine temperatures very accurately by comparing line strengths to statistical theory. NH3 is particularly useful as an interstellar thermometer since all of these lines can be detected by a single radio telescope with essentially the same beam size. Generally, a telescope measures the antenna temperature TA of an object which is related to the brightness temperature TB of an object by TA=Ωs/ΩA TBj; Ωs/ΩA≤1. TA = TB when Ωs≥ΩA where ΩA is the solid angle of the antenna pattern and Ωs, is the solid angle of the source as seen from the antenna. If measurements can be made with the same telescope, TB for different spectral lines will be simply related to the TA for the lines and one does not have the complication of source size and geometry.
The Interpretation of Xuv Solar Radiation
Authors: Goldberg Leo
Published: March 2016

Solar ultraviolet and X-radiation arriving at the Earth is emitted mainly by highly-charged ions in the outer layers of the Sun, where departures from thermodynamic equilibrium are extreme. Hence the diagnosis of physical conditions from spectral intensities entails the use of accurate cross sections for a variety of physical processes governing the excitation and ionization of emitting ions. Now that the full potential of satellites for solar data acquisition has begun to be realized, the need for atomic data of all kinds is more acute than ever before. In this review, I shall illustrate the importance of laboratory and theoretical investigations for the analysis of solar ultraviolet and X-ray data by referring to five problems to which space experimenters are currently devoting a great deal of attention:

(1)

the temperature minimum at the interface between the photosphere and the chromosphere,

(2)

the temperature and density profiles of the low chromosphere,

(3)

the transition zone at the chromosphere-corona interface,

(4)

the corona,

(5)

solar flares.
The Electron Excitation Rate for the Green Coronal Line at 5303 Å
Authors: Petrini D.
Published: March 2016

The collision strengths for transitions between levels of Fexiv have been calculated using the close coupling and the Coulomb-Born I methods. It is shown that the Coulomb-Born I approximation gives reliable results for highly ionized ions.

The electron excitation rate coefficient for the transition in the 3s2 3p configuration, giving rise to the green coronal line, has been investigated in detail. The quantum defect method, which takes into account the excitation via autoionization levels of FeXIII, has been used. This process greatly increases the excitation rate for low energies of the incident electron.

The statistical equilibrium populations of the FeXIV levels have been calculated under coronal conditions, and the effective excitation rate coefficient for the green coronal line is given for a wide range of temperatures and densities.
The Relevance to Astrophysics of the Results of Recent Experiments With Colliding Charged-Particle Beams
Authors: Dolder K. T.
Published: March 2016

A summary is given of some recent measurements of the ionization and excitation of positive ions by electrons, and the detachment of electrons from H− by proton and electron impacts. The results are discussed and compared with theory. Conclusions are drawn which are relevant to atomic collision processes which occur in astrophyscial plasmas.
Results Obtained from Observations of Laboratory Plasmas
Authors: Lochte-Holtgreven W.
Published: March 2016

In the visible part of the spectrum, the methods to solve astrophysical problems by laboratory experiments are well known. Electric arcs or shockwaves allow the production of plasmas of known parameters, from which measurements of oscillator strengths, of line broadening effects, and of line shifts are possible. However, there was a difficulty to introduce elements into laboratory light sources which have no volatile compounds. This was particularly difficult for the metals. This difficulty was overcome only recently by burning the electric arc in argon gas containing a few percent of chlorine. When this gas mixture is led over heated metal, some metal-chloride is formed and fed into the arc. In this way, even a very small amount of metal can be investigated, so that the resonance lines of the metals are optically thin. As an example I would like to recall that during the past year Professor Richter at Kiel has succeeded in a redetermination of the absolute oscillator strengths of iron lines, which has allowed to correct the abundance of iron in the Sun’s atmosphere. The abundance turned out to be ten times larger than assumed hitherto, leading to a new conception of the conditions in the photosphere (Kock and Richter, 1968; Garz and Kock, 1969; Garz et al., 1969a, b; Baschek et al., 1970). With this abundance, there is no difference in composition between the solar photosphere, the corona and meteorites. The method used for iron was applied to a number of other elements. The abundance of nickel is of special interest. The ratio of iron to nickel is again the same in the photosphere, in the corona, and in meteorites, being 1:1.25±0.15 (see Figure 1).
Pressure Broadening of UV Lines
Authors: van Regemorter H.
Published: March 2016

Most of the lines in the UV spectra are lines of ions which are formed in high temperature regions where the pressure broadening is caused by electrons and protons. This is the case in O and B type stars for which the theoretical calculation of the width of all the strong UV lines is important in determining both the blanketing effect and the abundances of the elements.

The cores of these strong lines are formed in non-LTE layers near the surface where the electron density is very low. The wings of some of the lines are more easy to interpret, being formed in deeper layers of the star, where one can assume LTE and where the electron density - or in the Sun, the neutral hydrogen density - is such that the pressure broadening is much more important than the natural width.

Two opposite approximations have been applied to the line broadening problem; the impact approximation is generally valid for electrons when the perturbations are so rapid that the collision timeτcis very small compared to the typical time, Δω-1, of importance in computing the profile at the frequencyΔω = ω – ω0measured from the line centre. On the contrary, whenτc≫Δω−1the quasi static approximation may be assumed. Both of these approximations have been considerably improved and efforts have been made recently to develop a unified theory valid from the impact regime to the static regime.
On the Polarization and Anisotropy of Solar X-Radiation During Flares
Authors: Elwert G. , Haug E.
Published: March 2016

From the spectral intensity distribution of solar X-radiation one can conclude that there is a non-thermal contribution, which is effective during the initial phase of a flare. It is reasonable to suppose that the electrons producing the non-thermal radiation have a non-isotropic velocity distribution. Indeed, one should assume that the electrons, during their acceleration, obtain a preferred direction and that only afterwards does their velocity distribution become Maxwellian by means of collisions. Hence the short-wavelength continuous X-radiation in the initial phase of a flare, consisting mainly of bremsstrahlung, should be polarized and should have a non-isotropic angular distribution.

In papers presented to the IAU-Symposia in Budapest 1967 (Elwert, 1968) and in Leningrad last May, the polarization of X-radiation from electrons of a few keV accelerated in solar flares has been calculated using energy distributions based on the observations of Pounds et al. obtained with the satellites Ariel I and OSO-4.
Geodetic Applications of Grazing Occultations
Authors: Dunham D. W.
Published: March 2016

Up to about a century ago, occultations were often used to measure differences in geographical longitude. Extensive geodetic surveys, accurate chronometers, telegraphic communications, and later short-wave radio time services obviated the geodetic need for occultation observations, which are affected by geodetically severe uncertainties of stellar and lunar positions, lunar limb irregularities, and observers’ personal equations. More sophisticated methods of observation would be needed before the Moon could again be useful to geodesy.

During this century, cinematography of Bailey’s beads and the flash spectrum during total solar eclipses have been used to obtain the relative apparent position of the Sun and Moon to an accuracy which could be useful to geodesy. But observational opportunities were rare and few results of geodetic significance have been obtained.
Seeing Effects on Occultation Curves
Authors: Young A. T.
Published: March 2016

‘Seeing’ affects the light-curve of a stellar occultation by the Moon in two ways: the diffraction pattern on the ground is smeared out by atmospheric turbulence, and the pattern also suffers random displacements. These effects are analogous to the familiar image blur and image motion, respectively. However, there is a major difference between ordinary astronomical seeing and the effect on the lunar diffraction pattern: the former is the seeing looking up at the sky from the bottom of the atmosphere, but the latter corresponds to the seeing looking down through the atmosphere at the surface of the Earth.

This downward-looking seeing is of concern to people engaged in aerial photography and satellite reconnaissance, and has been studied theoretically from this point of view. It also enters into the theory of stellar scintillation, because the seeing blurs out the scintillation shadow pattern just as it blurs out the occultation diffraction pattern.
Photoelectric Observations of Occultations in Japan
Authors: Sinzi A. M.
Published: March 2016

In Japan, photoelectric observations of occultations were made for the first time in 1951.

For about ten years after that, observations were made partly for geodetic purposes in order to determine the position of Japan with reference to islands in the Pacific, Phillippine and Taiwan.

The geodetic datum of Japan, which is currently adopted, suffers seriously from the vertical deflection. The amount of this deflection is supposed to be about 10″ in latitude and 20″ in longitude.

This project of occultation geodesy was, however, not so successful, because of the following two reasons: (1) Poor efficiency of data acquisition due to weather. We need good weather at two stations; the distance between them is usually over 1000 km. (2) Difficulty of correction for the Moon’s limb. For geodetic purposes, the atlas of the Moon’s limb by Dr Watts is still insufficient.

Therefore, the project of occultation geodesy was replaced by satellite geodesy.
A Preliminary Analysis of Photoelectric Occultation Measurements
Authors: Pansch E. , de Vegt Chr.
Published: March 2016

Photoelectric occultation traces of 5 stars are discussed which have been obtained with the 60 cm refractor of the Hamburg-Observatory during 1969/70. All traces show remarkable deviations from the usual Fresnel point-source pattern. Most details of these traces can be interpreted assuming the stars to be unresolved doubles. A short description of the equipment and the observational procedure is given.
Some Recent Observations of Occultations by the Moon
Authors: White Nathaniel M.
Published: March 2016

A program for the measurement of diffraction patterns resulting from the lunar occultations of stars was begun at the Lowell Observatory by Rakos (1964), resumed by him in 1967 and continued by Pettauer through the summer of 1969. The expected results were accurate timing of occultations and hence accurate position measurements, the discovery of close double stars, and the determination of stellar diameters. The author is continuing the program using new equipment designed by R. E. Nather of the University of Texas.

The equipment was built at the Lowell Observatory and put into operation on its new 42-in. reflector in March, 1970.
Photoelectric Occultation Observations of Regulus and the Pleiades
Authors: Berg Richard A.
Published: March 2016

The dual channel photometer is mounted on the tailpiece of the 32-in.ƒ/16 reflector at McCormick Observatory’s Fan Mountain Station. A 50-50 beam splitting mirror distributes the light to two EMI 6256 S/A photomultipliers. A focal plane diaphragm admits an area of sky of 100 sec2 of arc, and UBV or narrow-band filters are used to isolate spectral regions. The photoelectrons are fed through preamplifiers and amplifiers to a specially designed integrated-circuit photon counting instrument. The preamplifiers are attached as closely as possible to the photomultiplier anodes, while the remaining circuits are housed separately. A Sony TC-200 stereo tape recorder is used to record the output signal from the counter, and an oscilloscope is used for real-time monitoring of the counter operation during occultations.
Occultation Studies at the Dominion Astrophysical Observatory
Authors: Morbey C. L. , Hutchings J. B.
Published: March 2016

During the last year studies of lunar occupations have begun at the Dominion Astrophysical Observatory. Since the acquisition of a Fabri-Tek (model FT 1074) signal averager and analyser, twelve occultations have been observed but only one has been reduced and a comparison made with a theoretical model. The observed diffraction pattern for this occultation was found to correspond with an almost point source model.

The exposure meter photomultiplier (EMI type 6094) on the 48 in. telescope has been used for all observations to date. A preamplifier mounted close to the photomultiplier housing directs the amplified signal to a circuit which controls the D.C. level of the signal before being applied to the signal averager.
Closing Remarks
Authors: Evans David S.
Published: March 2016

Several things are clear from this Joint Discussion. Interest in this type of work is wide and could be wider. The subject touches on an immense range of topics from geodesy and celestial mechanics to astrophysics. Observations at different observatories do not conflict with each other, but rather reinforce one another. This is true of timings, but still more true of observations of binary stars and of stars with perceptible angular diameters. There is no real difficulty in identifying as double a wide pair with a separation of the order of 0˝.01. Duplicate observations from different places are necessary if we are to infer the conventional parameters of position angle and separation for a given pair. Duplicate observations are still more essential in cases explainable as close pairs with separations less than 0˝.01.
Remarks on the Role of Pulsars in Cosmic Ray Production
Authors: Ginzburg V. L.
Published: March 2016

This discussion is concerned with the production of cosmic rays in supernova explosions. In particular, we are discussing the role of pulsars (which we all believe to be neutron stars) in this process. I should like first to recall that (so far as I am aware) the idea that neutron stars form in supernova explosions, and that this phenomenon is relevant to cosmic rays, was first proposed by Baade and Zwicky in 1934. The argument was originally based on energy considerations, and further estimates indicated that supernovae could indeed be the main source of cosmic rays (ter Haar, 1950). When radioastronomical data later showed that supernova remnants definitely contained large numbers of relativistic electrons, there could be no doubt that they were sources of cosmic rays as well (and it became quite probable that they were indeed the major source of such particles). The growth of these ideas can be studied in historical perspective in Rosen’s (1969) compilation of papers on cosmic ray origin theories. As is so often the case, this subject has developed in a cyclic and repetitious fashion. I wish to make this point because I feel that my own contribution to these theories has sometimes been overestimated - though I hope I cannot myself be blamed for this.

It would not be appropriate to consider cosmic ray origins in detail during this discussion. I have in my case given my present views elsewhere (Ginzburg, 1969, 1970). The following remarks will deal specifically with the role of pulsars.
The Absolute Magnitudes of the RR Lyrae Stars
Authors: Woolley Richard
Published: March 2016

The absolute magnitudes of pulsating variable stars, both RR Lyrae stars and Cepheid variables, may be assessed from observation in three ways: by the classical method of statistical parallaxes, by their occurrence in star clusters whose distance is otherwise known, particularly by ascertaining the position of the main sequence in the HR diagram, and by the Baade-Wesselink method of determining stellar diameters.

As regards the first of these, the method of statistical parallaxes, the RR Lyrae stars lend themselves to this better than do the Cepheid variables, because the velocities relative to the Sun are so much larger. RR Lyrae radial velocities are frequently as high as 200 km/sec or even 300 km/sec, and as many of the stars lie at distances between 1000 and 1500 pc the proper motions of the transverse velocities may be expected to be as high as 0”.050 per annum. And, indeed, many investigations have been made recently, among which one may mention those by Plaut, by van Herk, and by the Royal Greenwich Observatory.
Ultraviolet Astronomy
Authors: Wilson R.
Published: March 2016

Ultraviolet astronomy is in a phase of very rapid development and any review of the new techniques involved is necessarily conditioned by the fact that most of the work is in a preparatory stage. This paper, therefore, will not be restricted to a discussion of those techniques which have undergone the ultimate test of their effectiveness, i.e., an actual space mission, but will include a consideration of those techniques which are still under development. Some omissions are therefore inevitable.

The presentation is divided into three categories: (a) the vehicle and its stabilisation (if any), (b) the optics, and (c) detectors. Category (a) presents the major new technological problems and contributes the greater part of the total cost. Experience in the other categories of optics and detectors had, of course, reached an advanced and sophisticated level at the time of the advent of the rocket, but new and difficult problems have been posed mainly by their operation in a space environment, but also by their use in the ultraviolet region of the spectrum.
Recent Results on Extragalactic Cosmic X-Ray Sources from Rocket and Balloon Flights
Authors: Clark G. W.
Published: March 2016

Two experiments carried out recently at M.I.T. gave results which bear on the problems of extragalactic X-ray sources. One of these is the work of a group under the direction of Hale Bradt (Bradt et al., 1967), who used an attitude-controlled Aerobee rocket to scan a portion of the sky which included the radio galaxy M 87 (Virgo A). Among their detectors were two banks of argon-filled, 2 mil beryllium window proportional counters, each with an effective area of 350 cm2 and a mechanical collimator giving a 2° × 20° FWHM field of view. The fields of view were crossed so that their long directions made an angle of 60° with one another. Aspect was determined to within 5 min of arc by star photography.
X-Rays Radiation of a Neutron Star as a Result of Gas Accretion
Authors: Zel’dovič Ja. B.
Published: March 2016

The accretion of gas on the surface of a neutron star is a source of energy, which can be converted into X-rays radiation. Accretion can ascertain a far greater lifetime of an X-ray star than the radiation of internal energy.

The source of gas could be a cloud of intergalactic gas. If the neutron star is a component of a binary system, the gas could come from the other (non-neutronic) star.

The idea of accretion and evaluation of energetic balance were given by Zel’dovič (1964) and Zel’dovič and Novikov (1964, 1965) and Salpeter (1964). Shortly the idea of accretion was mentioned by Šklovskij (1967).

The motion of gas and radiation spectra idealised case of spheric symmetry are studied now by N. Shakuro and Zel’dovič.
On the Lithium Abundance in Sunspots and the Undisturbed Solar Atmosphere
Authors: Dubov E. , Prokof’ev V. , Severny A.
Published: March 2016

The difference between abundances of such elements as Li, Be, B in active regions on the Sun and in the undisturbed atmosphere, if it exists at all, could be considered a very important indication on the possible nuclear reaction in active regions and on the rate of diffusion of elements inside magnetic fields of sunspots. One of the authors from the considerations of λ6707 Å has an estimated (Dubov, 1955) Li abundance in the undisturbed solar atmosphere as log N(Li) = 0·93 (taking log N(H) = 12·0), which is close to the later results (Goldberg et al., 1960). In sunspots we can expect that the first doublet λ6103 of Li diffuse series appears. The preliminary consideration (Dubov, 1964) showed that Li abundance in sunspots could be several times larger than the above estimate for the undisturbed atmosphere. This result forced us to consider as carefully as possible the region of λ6103 in eight spectra of four sunspots taken with the aid of the echelle-grating spectrograph of the Crimean observatory with a dispersion of 1 Å/mm and measured resolving power 0·03 Å. The consideration of the Zeeman pattern of this line shows that at the field strengths we had in sunspots (2000–3000 gs) the line should be diffuse band with width ~0·23 Å, and taking into account the broadening of the line the halfwidth of the line has not to be smaller than 0·25 Å.
The AGK3, SRS and Related Projects
Authors: Scott Francis P.
Published: March 2016

This report consists of a brief summary of the status of a number of programs of an international nature which are now in progress at various observatories of the world. These programs have received strong endorsements from Commission 8 of this Union, as well as from a number of international organizations interested in accurate positions and motions of the stars to the 9th magnitude of brightness. Among the organizations and conferences which have explicitly endorsed the programs are:

(1) The Symposium on Coordination of Galactic Research, Groningen, 1953.

(2) Conference on the Problems of Astrometry, Evanston, 1953.

(3) Astrometric Conference, Pulkovo, 1954.

(4) Conference on Astrometry, Brussels, 1955.

(5) International Union of Geodesy and Geophysics, 1954 and 1963.

(6) International Astronomical Union, 1955.

(7) Second Astrometric Conference, Cincinnati, 1959.

(8) First Inter-American Conference on Astronomy, La Plata and Cordoba, 1959.

(9) Meeting on Problems of Astrometry and Celestial Mechanics, La Plata, 1960.

(10) Committee on Space Research, COSPAR, 1966.
Études sur l’emploi de Recouvrements de Plaques pour l’établissement de Catalogues Photographiques
Authors: Lacroute P.
Published: March 2016

Le but de cette étude est la recherche des possibilités et des limites de l’emploi des recouvrements de clichés.

Le travail n’est pas terminé. Un travail plus complet sera publié dans quelques mois.
The Magnetodynamic Model of Quasars
Authors: Ozernoj L.M.
Published: March 2016

Although the energy problem is one of the main difficulties of the cosmological interpretation of quasar red-shifts, there is no need to go beyond conventional physical laws in seeking an explanation. Various proposals have been made which differ in important details. I believe a suitable basis for a theory of quasars to be a supermassive plasma configuration, the matter of which is in mostly regular motion in a magnetic field. Such a magnetodynamic configuration I shall call a ‘magnetoid’. On this model a quasar is a galaxy with a dense non-stellar nucleus, the magnetoid, which gives rise to the characteristic non-thermal luminosity. The mass of the quasar is determined by its stars while the parameters of the magnetoid depend on the stage of evolution or conditions of formation in a similar way to those of radiogalaxies or active nuclei of galaxies.
On the Origin of the Algol Systems
Authors: Plavec M.
Published: March 2016

The 4th edition of the Finding List for Observers of Eclipsing Variables (Koch et al, 1963) contains 145 sufficiently well-observed eclipsing binaries brighter than 8·5m at maximum light. Among them, 59 binaries, or 41%, are systems with both components on the main sequence. The second largest group, 52 binaries or 36% of all systems, are systems similar to Algol. These can be characterized as follows:

(1)

The primary (more massive) components are main-sequence stars, fitting well into the mass-luminosity relation defined by visual binaries and by eclipsing binaries with both components on the main sequence (detached systems).

(2)

The secondary components are of later spectral type than the primaries, and can be best characterized as subgiants. They are overluminous for their mass as well as for their spectral class.

(3)

As a rule, the secondary components fill their respective critical Roche lobes (innermost Lagrangian surfaces).
Arguments Indicating that Ap and Am Stars are Evolved Spectroscopic Binaries
Authors: van den Heuvel E.P.J.
Published: March 2016

Roughly three types of evolution of spectroscopic binaries may occur:

Case (a): the primary fills its Roche limit already before the end of core hydrogen burning;

Case (b): the primary fills its Roche limit after core hydrogen exhaustion but before the onset of helium burning, and

Case (c): the primary does not fill its Roche limit before the end of core helium burning.

Since long-period variables of Population I as well as Population II may reach radii of 10 AU, case (c) will occur in systems with periods up to 100 years. Since about 50% of the A and B stars are spectroscopic binaries, many evolved spectroscopic binaries are expected to occur in the galactic system. Computations show that, using the mass-ratio distribution of unevolved systems derived by Kuiper, the number of systems with one evolved component is expected to be at least as large as the number of unevolved systems, in the spectral regions A and B.
A Description of the Lunar Orbiter Spacecraft
Authors: Taback Israel
Published: March 2016

The U.S. Lunar Orbiter Spacecraft Program was conceived to search out potential Apollo landing sites, and to return detailed photographic coverage of the lunar surface for scientific study. The first flight was launched in August 1966, and the successful launch of the fifth orbiter was in August 1967. All five were successful and returned to Earth a large amount of photographic data.

Presented in this paper is a short description of the spacecraft system with particular emphasis on the photographic system. The intent is to supply information which will permit a better understanding of the photographic data to be presented by Dr. William Brunk in the following paper.
The Next Decade of Theoretical Solar Physics
Authors: Kuperus M.
Published: March 2016

Exactly a decade ago an international conference on solar physics took place in Utrecht on the occasion of the late Prof. Minnaert’s 70th birthday. Since then, much has happened. Many new instrumental devices were developed or refined. Completely new observational techniques were applied in the XUV and radio wavelengths and in particle detection.

This all resulted in an explosion of new data. Moreover new problems appeared of course. It also resulted in an explosion of papers on solar physics. Actually many more contributions appear than reasonably can be absorbed by the periodical Solar Physics, of which the first volume appeared in 1967. At that time the editors were not at all sure that they would receive enough papers to maintain such a journal. But were there major problems solved recently?

At first I would be inclined to think that, notwithstanding the enormous efforts spent in solar physics, little has been achieved and no spectacular breakthroughs have been found. This impression, probably shared by many more colleagues, becomes stronger if one tries to find a line of progress in ‘classical’ problems of solar physics. We still do not have a satisfactory theory of the Sun’s differential rotation and the Sun’s outer convection zone. One may argue that this is due to our bad knowledge of the interior structure which is not accessible to direct observation. Solar activity and the formation of sunspots is now believed to be a direct consequence of differential rotation and cyclonic convective motions and therefore suffers from the same uncertainties.
The Next Decade in Observational Solar Research
Authors: Beckers J. M.
Published: March 2016

The last two decades have been exceptionally fruitful for astrophysics. Because of very rapid developments, especially in the area of observational astrophysics, our view of the Universe has been substantially completed, challenged and altered. Solar Physics has very much been part of this progress. Developments in space and ground-based technology have virtually completely opened up the entire spectrum of solar electromagnetic and corpuscular radiations. Electromagnetic radiation of the sun can now be studied from gamma ray wavelengths shorter than 10-4 Å to radio wavelengths as long as 1014 Å, a range of approximately 60 octaves. Continuing improvements of spatial resolution of the Sun at all these wavelengths and concommitant development of our theoretical understanding of both the radiative and magneto-hydrodynamic processes on the Sun have made solar physics an exciting field to those interested in the Sun per se, as well as to those who view the Sun as a star whose study aids us in the understanding of astrophysics in a broader sense.

A committee of The National Academy of Sciences in the United States under the chairmanship of J. L. Greenstein conducted between 1969 and 1971 a study of the needs of astronomy in the next decade. I took part in this study and it is probably because of this that I was asked to give this review on the next decade in observational solar physics. This review is therefore partly based on the results of the discussions in that committee and in its solar panel. Most of this review will reflect, however, my own opinions.
Astronomical Units, Constants and Time-Scales
Authors: Wilkins G. A.
Published: March 2016

As I have already reported (Trans. IAU XVA, 9, 1973), the Working Group on Units and Time-scales was not able to reach any firm conclusions on whether the concepts of the astronomical unit and ephemeris time should be retained or replaced by the SI unit of length (metre) and atomic time. This disagreement was not unexpected as the membership was deliberately chosen to cover a wide spectrum of opinion. The following comments and suggestions represent a middle-of-the-road approach that is intended to meet the requirements of most astronomers and others who use the astronomical data. It has been suggested to me that this approach is not appropriate for use in those precise applications where relativistic concepts are necessary, and that therefore we should abandon completely the use of astronomical units of mass, length and time. There are, however, many applications where Newtonian concepts are perfectly adequate, and astronomical units are widely in use because of their general suitability and convenience. We should therefore continue to define a system of astronomical units, but should state quite clearly their relationships to SI units. An individual may use either system according to the circumstances, and standard conversion factors will be available for use by those who prefer the other system.
Interpretation of Carbon Stars Spectra from Model Atmospheres Computations
Authors: Querci F. , Querci M.
Published: March 2016

The first part of this paper presents a grid of model atmospheres for carbon stars in which the most striking feature is the inclusion of the molecular line blanketing effect of CO, CN and C2 through opacity probability distribution functions. The techniques and the main results have been fully discussed in previous papers (Querci, 1972; Querci et al., 1972 and 1973), and consequently we will give just a rapid description asking the reader to refer to these papers for details. However, the grid has been extended here to lower temperatures.

The second part presents original results from the M. Querci’s ‘Thèse d’Etat’ (1974), and concerns the computation of synthetic spectra. A kind of grid of synthetic spectra has been computed from each model atmosphere, that is to say for each particular effective temperature and gravity, over a selected spectral range. The influence of the gravity and of the effective temperature on the computed spectra and the problem of the line cutting procedure are considered. Finally, comparisons with a high resolution infrared spectrum of a carbon star are made.

The conclusion summarizes the experimental progress that must be made in order to be able to make meaningful comparisons between predictions and observations.
The Third and Fourth Moments of the Local Stellar Velocity Distribution
Authors: Miller R. H.
Published: March 2016

The velocity moments through the fourth order were calculated for a subset of 870 astrophysically selected stars from Gliese’s catalog. An essential part of this program was the determination of the covariances of estimates of the moments; both sampling and observational error contributions were taken into account in evaluating the total covariance matrix. In applications to the study of galactic structure, the Gliese stars are regarded as tracers of the galactic potential. The moments found are consistent with conventional assumptions about symmetries of the galaxy. Certain galactic parameters, such as the curvature in the law of rotation and the asymmetric drift, were studied with the help of the values obtained for the moments.
Influence of a Spiral Gravitational Field on the Observational Determination of Galactic Structure
Authors: Lin C. C. , Yuan C. , Roberts W. W.
Published: March 2016

To investigate the nature and the extent of the influence of a spiral gravitational field on the observational determination of galactic structure, we examine several models of the solar vicinity, including a spiral gravitational field and the accompanying shocks. (These models are described in the Appendix.) We calculate the radial motions and the proper motions that would be observed from the solar vicinity. We then treat these theoretically calculated data by the conventional methods used for analyzing observational data. In this way, we hope to recover the galactic parameters originally adopted in our models. The accuracy of this process is then a measure of the uncertainty in the existing determinations of galactic constants, because of the influence of the spiral gravitational field.
How Can It All Be Stable?
Authors: Toomre Alar
Published: March 2016

My contribution to this Joint Discussion can hardly be termed very novel or original. Rather, I just want to call your attention here to two headaches - one perhaps only a hangover, but the other a real migraine. Sooner or later these two headaches beset anyone who persists in asking how the random motions of stars in the only vicinity where we tolerably observe them can possibly jibe with the sensible presumption that not only our neighborhood but this entire Galaxy should by now be reasonably stable.

There is of course nothing strictly ‘local’ about any problem involving the far-reaching gravity. Yet if some conceivable instability of our collection of nearby stars comes even close to deserving such a label, it is surely the Jeans instability or tendency toward gravitational collapse. After all it is not difficult to estimate (e.g., Toomre, 1964) that the most troublesome of such incipient clumpings ought to have significant dimensions (such as half-wavelengths) of the order of 3 or 4 kpc. Even the latter scale is probably not too large a fraction of our distance from the galactic center for ‘local’ analyses in the WKBJ spirit to remain coarsely trustworthy.
Gravitational Collapse and the Formation of the Solar Nebula
Authors: Larson R. B.
Published: March 2016

Most theories of the origin of the solar system begin by assuming that, at the time of its formation or shortly afterwards, the Sun somehow acquired a disc-like ‘solar nebula’ in which the planets later formed by accretion. The presently available gravitational collapse calculations, while not yet sufficiently sophisticated to delineate in detail the processes involved, at least support the plausibility of this idea and suggest that the solar nebula may have formed by the accretion or capture of leftover proto-stellar material into orbit around the early Sun. Infall of matter into the disc probably continued for roughly 105 to 106 yr, and may have produced transient strong heating effects through the thermalization of the infall energy in shock fronts. It seems likely that the satellite systems formed in a basically similar way through the capture of residual solid matter into orbit around the planets.

A more complete discussion of gravitational collapse and the formation of the solar system has been given in The Origin of the Solar System, ed. H. Reeves, p. 142. (Paris: CNRS).
Supernova Remnants
Authors: Van den Bergh S.
Published: March 2016

The present structure and recent changes in Cas A are discussed. On the deepest available exposures the optical remnant of this supernova is seen to consist of an almost complete shell. The southern part of this shell is outlined by knots that have developed during the last decade. It is pointed out that moving nebulosity in which [O III] radiation is particularly strong is distributed differently from nebulosity in which the [O III]/[S II] ratio is more nearly normal. Observation of the motions of individual knots suggests a model in which dense blobs of matter, which have a highly anomalies composition, become luminous as they plough through a stationary interstellar (or circumstellar) medium.
Astronomy and the Laws of Physics
Authors: Morrison P.
Published: March 2016

The metaphor of physical law - a range of orderly behavior within certain authoritative constraints - has not escaped the historians of ideas. That scheme, in all its forms, east and west, gained its earliest strength from astronomy itself. The search for measured order in heaven is old and widespread; two instances from ancient China and pre-Columbian Mexico will make the point.

For our modern science, two universals rule: that of particulate matter - from neutrons to C2 H5 OH - and the only unsaturable force, long-range gravitation. The phenomena of astronomical scale are mainly examples of kinetic motion resisting for a time that untiring attraction, under the virial theorem. Matter is everywhere familiar, apart from the deep and puzzling question of what seems to be the large-scale failure of matter-antimatter symmetry.
Recent Transient X-Ray Sources
Authors: Willmore A.P.
Published: March 2016

Prior to the launch of the Ariel V satellite in 1974, four transient X-ray sources had been observed. We placed the study of sources of this type amongst the major objectives of the satellite, and so ensured that the spacecraft ground centre was capable of quick reaction, and that experimenters had rapid access to their data, so that new transients could be rapidly recognised, and an observing programme for them produced and carried out. This has been very successful - in its first 18 months of operation the satellite made observations of at least 14 transients.

Of these transients, five form a rather well defined class whose properties are rapidly becoming clearer. This class I shall call the “classical” transient. The remainder form a much more miscellaneous collection which cannot be clearly distinguished from the normal X-ray sources. There is some indication that the classical transients include two species, so to start with I shall describe one of each which has been particularly well-observed by Ariel V and SAS-3.
X-Ray Bursts
Authors: Clark George W.
Published: March 2016

Most of the variable phenomena of high-luminosity (≳1036erg s−1) stellar X-ray sources can be explained, at least qualitatively, within the general framework of binary accretion models in which thermal X-rays are emitted in the vicinity of a neutron star or blackhole by plasma that has flowed downhill from the surface of a nuclear burning companion and been heated by conversion of its gravitational potential energy. The yield of X-ray energy in this process is so high, exceeding in some cases 0.1c2per unit mass, that X-ray luminosities in excess of 104L⊙can be generated with accretion rates of only ˜10−BM⊙per year. Since the transfer process depends strongly on many parameters that specify the relevant properties of two stars and their interaction, one finds a remarkable variety and range of X-ray phenomena. If the compact object is a magnetized neutron star, rotation will cause its X-ray emission pattern to sweep over a distant observer and thereby produce regular pulsations like those observed with periods in the range from 1 to 103seconds. Orbital motions can cause regular eclipses and absorption dips like those observed with periods in the range from hours to days. Changes in the rate of mass loss by the nuclear burning star or in the transfer efficiency can account for the variations in intrinsic X-ray luminosities that appear as flares, novae and on-off transitions. Irregularities in the flow of plasma near the compact star can also affect the intrinsic luminosity and appear as erratic fluctuations, spikes and shot-noise in the observed intensity.
The Surface of Venus as Revealed by Venera 9 and 10 Probes
Authors: Florensky C.P.
Published: March 2016

The landers Venera 9 and 10 transmitted to Earth television pictures of the immediate vicinities of landing sites. The pictures were taken by optical-mechanical panoramic cameras looking from view-ports at about 0,9 meter above the ground. The nominal field of view is 40°x l80°. The width of one element of the picture (camera resolution) is 21 minutes of arc. The pictures were subsequently treated by computer enhancement. The first results of panorama analysis were published elsewhere (1,4).

Venera 9 landed at the point 32°N, 291°E on the rather steep (˜20°) slope covered by angular sharp-edged rock fragments. The fragments have a horizontal dimension of up to 50 or 70 cm, and a vertical dimension of no more than 15 to 20 cm. Some of the fragments demonstrate the evidence of layering approximately parallel to the flattening of fragments. The surface between fragments is darker than the fragment surfaces of the same orientation and seems to be composed mainly of particles of a size less than the resolution of the camera. The on-board gamma-spectrometer reveals that the radioactivity of the surface at Venera 9 site is similar to radioactivity of basaltic rocks of the Earth ( 2 ).
X-Rays from Clusters of Galaxies
Authors: Culhane J.L.
Published: March 2016

The discovery of the extended sources of X-ray emission associated with clusters of galaxies was undoubtedly one of the most significant observations carried out by the Uhuru satellite (Gursky et al (1971), Giacconi et al (1974)). At the present time, there are more than 30 identifications and suggested associations of X-ray sources with clusters of galaxies although extended emission has been directly observed in less than 10 cases.

The mechanism for X-ray emission from such large objects is of considerable interest. X-rays could be generated by the inverse Compton interactions of microwave background photons with populations of relativistic electrons distributed throughout the clusters. Alternatively the radiation may be due to Bremsstrahlung from hot (T ≃ 108 °K) gas which constitutes an intracluster medium. Progress in understanding the extended X-ray sources and in determining the emission mechanism has come from observations of the X-ray structure and spectra of the cluster sources and it is the purpose of this review to present the current status of these observations.
The Microwave Background Radiation in the Direction of Clusters of Galaxies
Authors: Gull S.F.
Published: March 2016

The discovery of powerful X-ray sources associated with rich clusters of galaxies has led to the prediction that these clusters contain large amounts of hot gas. A necessary consequence of the existence of such gas is the Compton scattering of cosmic microwave background radiation by hot electrons (Sunyaev & Zeldovich 1972). As a result, some of the microwave photons are re-distributed with slightly higher energies and the effect may be observed as a small diminution in the background temperature. The effect is expected to be ≈0.5 mK for the gas clouds associated with cluster X-ray sources.

Previous attempts to detect this effect have not been successful. I present here the results of two further attempts; by Lake & Partridge using the 36’ telescope at Kitt Peak, and by Gull ’ Northover (1976) using the 25-m telescope at the SRC Chilbolton Observatory. Both groups used similar, twin-beam systems, comparing the temperature of the background radiation in the directions of various known X-ray clusters with that at points ≈15 arcmin distant. In order to minimize the effect of non-thermal background sources, it is desirable to observe at the highest frequency compatible with atmospheric stability. Gull & Northover, using a frequency of 10.6 GHz, accumulated 670 hours of observations, whilst Lake & Partridge, who did not have to contend with British weather, selected the more difficult frequency of 33 GHz, but could only manage 80 hours integration.