bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Systems for Spectroscopic Telescopes
Authors: Dunham T.
Published: July 2016

Astronomical spectrographs are usually mounted at one of three focal positions on a reflecting telescope: (1) the Newtonian focus, at the top of the telescope tube, with only one reflection from the primary mirror, where the spectrograph must be small and light, and designed for low resolution on faint objects; (2) the Cassegrain focus, behind the cell of the primary mirror, with a total of two reflections, where the spectrograph can be appreciably larger, to give intermediate resolution; and (3) the coude focus, at a fixed location below the end of the polar axis, with three, four or five reflections, where there is no limit to the size of the instrument, and where resolution is limited only by the brightness of the object and the light efficiency of the system. This is the ideal location for image tubes, Fabry-Perot interferometers, and equipment for Fourier spectroscopy.
The Solar U-Burst at Metre Wavelengths
Authors: Labrum N. R. , Stewart R. T.
Published: July 2016

The U-burst, first identified by Maxwell and Swarup and Haddock, is a type of solar radio event lasting ~ 10 s in which the frequency of the emission at first drifts rapidly downwards, then increases again. On the dynamic spectrum record the burst has the appearance of an inverted letter U.
Light Scattering in Reflection Nebulae
Authors: Shortt I. R.
Published: July 2016

Much of the information regarding the nature of solid particles in interstellar space has been gained through the study of the line-of-sight extinction of starlight and the polarization of starlight by these particles. Study of the optical properties of these particles can be extended through consideration of the scattering of stellar radiation in reflection nebulae. This type of approach requires the adoption of models for the star-nebula system, and the grain type to be considered. These models are then used in a theory which describes the scattering of light by an ensemble of small particles, as applied to dust nebulae. Results are thus obtained for the colour of the nebula as a function of distance from the illuminating star. These results can then be compared with the corresponding results of experimental broad-band photometry.
Supernova Remnants, Pulsars and X-Ray Sources
Authors: Milne D. K.
Published: July 2016

From an assessment of recent high-resolution galactic radio surveys, in the continuum and in the H109oc recombination line, the author has detected or confirmed over 90 non-thermal sources, most likely all supernova remnants.1 The distances to each of these objects have also been estimated, from an empirical surface-brightness linear-size relationship derived from 15 remnants whose distances are known from either a comparison of the radial velocities and proper motions of filaments in the nebula, neutral hydrogen absorption measurements, or association of the remnant with an object of known distance. In this note we wish to remark on the galactic distribution of supernova remnants and the possible association of these objects with pulsars and X-ray sources.
OH Emission from Protostars
Authors: Johnston I. D.
Published: July 2016

There is a large body of evidence to suggest that the anomalous OH emission sources—particularly those which are classified as class I sources—are associated with protostars. It is also known, from the theories brought forward over the past four years, that maser action can be caused by quite a variety of non-equilibrium situations. It is argued here that one particular kind of non-equilibrium situation which can plausibly be expected to exist in protostars is very similar to that proposed previously in the electron-pumping model, and that, in this new context, it can mimic most of the observed features of class I sources.
Formation of Line Spectra—A Review
Authors: Jefferies J. T.
Published: July 2016

A typical stellar spectrogram shows a vast number of spectral lines. Each of these has its characteristic shape and strength which must, in some way, reflect the structure of the atmosphere in which the radiation arose. It seems reasonable that from all this profile data we should be able (and with considerable redundancy) to infer a good deal about the physical structure of the radiating gas, and a major effort has correspondingly been devoted to clarifying the physical basis of spectral line formation, i.e., exactly how the atmospheric structure and the atomic properties are reflected in the line profiles. This problem, however, is far from solved : Few, if any, of the profiles of strong lines can be predicted in detail from model atmospheres, nor have analyses of the profiles yielded unambiguous data on the atmospheric structure. Indeed, as recently as 1967, the participants at a conference in Bilderberg (Holland) concluded that no data at all which had been obtained from line profile analyses was worthy of inclusion in specifying the solar atmospheric model. Evidently, then, the problem of line formation is not trivial ; in this paper we discuss some of the difficulties and review the not inconsiderable progress which has been made in this area of astrophysical research.
The Absolute Flux Distribution of Sirius
Authors: Davis J. , Webb R. J.
Published: July 2016

The angular diameter of a star, combined with observed stellar fluxes in absolute units, allows the absolute fluxes emitted at the surface of the star to be calculated and thus provides a stringent test of model atmosphere predictions. Furthermore, if the flux distribution is observed at all wavelengths contributing significantly to the net flux, an empirical effective temperature can be found. Sufficient data are now available for Sirius (αCMa) to be studied in this way.
Non-linear Convection at High Rayleigh Number
Authors: Borght R. Van Der
Published: July 2016

The numerical solution of the basic equations for non-linear steady convection in the weak-coupling approximation is exceedingly difficult. In astronomical applications the Rayleigh number R will be of the order of1012, and we wish to report here some results obtained in the case of high Rayleigh numbers with the use of an asymptotic method.
Line Interactions in Saturated Masers
Authors: Bromley A. G.
Published: July 2016

Two important problems have emerged from observations of 18 cm OH emission sources that remain substantially unanswered by existing theories. The first is the problem of the origin of the high degree of circular polarization that is frequently observed. The second is what I have called the ‘problem of variety’: is it necessary to invoke a number of different physical mechanisms to explain the variety of qualitatively different behaviours observed, or can these different behaviours be explained by variations of one basic physical process?
Observations at 408 MHz of Supernova Remnants in the LMC
Authors: Clarke J. N.
Published: July 2016

There are three non-thermal sources in the Large Magellanic Cloud which are recognized as supernova remnants. They are N49, N63A and N132D in Henize’s catalogue; a summary of their observing history is given by Westerlund and Mathewson (hereinafter referred to as ‘WM’). They are rather important to our knowledge of supernovae, as there are only four galactic supernova remnants (Cas A, the Crab, the Cygnus Loop and Vela) whose distances are known approximately from independent evidence. Since the distance to the LMC is well-known, the distance to sources in it is also known quite accurately.
Non-linear Convection with Free Boundaries at High Rayleigh Number
Authors: Murphy J. O.
Published: July 2016

It has been suggested, for example by Wilson and Spiegel, that the results from the study of convection in incompressible fluids may provide a basis for the study of the solar convection zone. In fact Wilson’s models contain temperature fluctuation maxima, a feature exhibited by the results obtained from the convection problem for large values of the Rayleigh number.
Non-linear Convection with Hexagonal Planform
Authors: Murphy J. O.
Published: July 2016

Observations of the solar surface indicate a cellular structure, photospheric granulation, which, as suggested by Wilson and others, could arise from a shallow convection layer. The basic observed granulation pattern has been likened to a hexagonal cell type structure.
Coronal Broadening of the Crab Nebula 1969-71: Observations
Authors: Blesing R. G. , Dennison P. A.
Published: July 2016

A description was given in a previous paper of the first observations of the two-dimensional image of the Crab Nebula as it became broadened by the solar corona in June 1969. In this paper we describe further observations at 80 MHz during 1970 and 1971, again using the CSIRO Radioheliograph at Culgoora, N.S.W., and we discuss the derived values for radial and tangential broadening in relation to previous work at various phases of the solar cycle. Other methods of observing angular broadening have generally employed two or three interferometers at different position angles, and only the simplest model for the image could be assumed in interpreting the results. The radioheliograph, however, has the advantage of recording the complete two-dimensional image and also, simultaneously, the surrounding background.
Astrophysics at the University of Otago (N.Z.)
Authors: Edwards P. J.
Published: July 2016

The Physics Department at the University of Otago, Dunedin, New Zealand, has over the past three years commenced a research and teaching programme in astronomy and astrophysics. Observing facilities now include two metric wave meridian transit telescopes at a site 6 km from Dunedin and a 16-inch optical telescope, formerly at Mt John, which is now sited 4 km from Dunedin at the Signal Hill observatory built by the University’s Surveying Department for geodetic work.
Synchrotron Radiation Spectra
Authors: Gleeson L. J. , Westfold K. C.
Published: July 2016

In this paper we give an account of the corrections that must be made to the formula for the emissivity ηf due to a power-law energy distribution of ultrarelativistic charged particles in a uniform magnetic field B0 in directions well away from the field lines when the effects of upper and lower cut-off values E2 and E1 in the energy distribution are not negligible.
Giant Cells and the Solar Cycle
Authors: Wilson P. R.
Published: July 2016

Despite the success of the Babcock-Leighton model in explaining some phenomena of the solar cycle, e.g. Hale’s polarity law and Maunder’s butterfly diagram, it has recently encountered a number of observational and theoretical difficulties. The observational difficulties are centred around the different behaviour of bi-polar magnetic regions (BMRs) and uni-polar magnetic regions (UMRs). Babcock explains BMRs as the surface eruptions of toroidal fields wound by the differential rotation and it is clear that in their subsequent evolution and decay they are obviously influenced by this effect. However, UMRs display a sector structure in which the boundaries between regions of opposite polarities appear to be quite unaffected by the differential rotation but closely related to the interplanetary field sectors. Another feature of solar activity unexplained by the Babcock theory is the tendency of sunspots, flares, etc. to reappear at the same latitude during a cycle. Warwick has observed that proton flares show a preference for particular latitudes which may extend over several cycles. Again Bumba et al. have observed that new cycle fields tend to appear in longitude regions where old cycle fields are still visible.
A Numerical Method for the Inversion of a Single Line Profile
Authors: Holt J. N.
Published: July 2016

Established techniques for inverting observed solar spectra rely on the use of centre to limb observations.
The Temperature and Continuum of the N Stars
Authors: Bessell M. S. , Youngbom Lee
Published: July 2016

On the basis of (R — I) colours it has been suggested that the N stars (the cool carbon stars) occupy a very restricted region in the Mb01 — log Te diagram (Te = 3300 to 3500 K) Mb01 ~ —3), falling on the normal giant sequence, but hotter than the M variables. This appeared somewhat puzzling in view of the variability of many of the carbon stars and their large range of periods, which suggested that the N stars ought perhaps to have similar temperatures to the variable M stars. In order to compare the continua of the M stars and N stars within the range of the R and I filters, and also to determine the continuum between the molecular bands, photometric observations were made of 20 M and N stars at carefully chosen wavelengths with 30Å resolution.
The Search for Cen X-3
Authors: Perry M. E. , Peterson B. A. , Wickramasinghe D. T. , Vidal N. V.
Published: July 2016

Cen X-3 was first discovered by Chodil et al. Since then, observations using the UHURU satellite have shown it to be an X-ray pulsar, and it must now have become one of the most searched for objects in the sky. It is both an X-ray pulsar (P~4.8 secs) and an X-ray eclipsing binary (P~2.08712 days).
Hyperfine Structure in the Radio Spectra of Jupiter
Authors: Ellis G. R. A.
Published: July 2016

Observations of the Jupiter radio emissions have established that the radiation is normally received as bursts with two quite different time scales. The L bursts mostly have durations of 1-10 seconds, although extended bursts up to 100 seconds are sometimes observed. The S bursts on the other hand have time scales of milliseconds and fractions of a millisecond. Dynamic spectrographic observations have shown that both types are structured in the frequency-time plane although the frequency and time resolution used so far has been insufficient to investigate detail smaller than 50 KHz and 10 msec respectively.
On the Regularity of Motions of the Pole
Authors: Abraham H. J. M.
Published: July 2016

This paper suggests reasons why certain forms and frequencies are found in librations of the pole. The period is about 27 years, but there is also a shorter period which was found empirically to vary with the inverse of the amplitude of the Chandler nutation. It had been found also that the pattern of the motions would sometimes become reversed.
National Mapping’s Astro-Geodetic Complex
Authors: McK. Luck J. , Miller M. J. , Morgan P. J.
Published: July 2016

The Division of National Mapping has received, on long term loan from NASA and in co-operation with the Smithsonian Astrophysical Observatory, a Lunar Laser Ranging instrument consisting of a gigawatt pulsed ruby laser, a 150 cm aspheric Ritchey-Chretien telescope, and associated electronic equipment. The instrument was formerly operated by the Air Force Cambridge Research Laboratories at Mount Lemmon in Arizona. Its principal use by National Mapping will be direct determination of the distance between the telescope and any of the three retro-reflector arrays placed on the Moon at Hadley’s Rille, Fra Mauro and Mare Tranquillitatis by Apollo astronauts. Full scale operation in conjunction with similar instruments well separated in latitude and longitude, in particular at Mount McDonald in Texas and Mount Haleakala in Hawaii, will permit determination of Earth rotation and polar motion, lunar ephemeris and libration, and tectonic plate movement or continental drift, which justifies its use in a geodetic environment.
A Plasma Hypothesis for Anomalous OH Emission
Authors: Melrose D. B.
Published: July 2016

Although the maser hypothesis for anomalous OH emission encounters difficulties it has not been seriously questioned because, as pointed out by Turner, no alternative has been available. The following ideas might suggest that there is an alternative hypothesis for anomalous OH emission.
The Relevance of Bipolar Type I Storm Structures to the Theory of Mode Coupling in the Solar Corona
Authors: Melrose D. B.
Published: July 2016

Bipolar structures are discernible in three categories of solar radio emission: the slowly varying component (S-component), microwave bursts and metre-wavelength type I storms. Piddington and Minnett, discussing the S-component, showed that when coupling between the magneto-ionic modes along the ray path is ignored the emission from a regular dipolar field should have two specific polarization properties. These properties (see Figure 1) are that both feet of the bipolar structure should be similarly polarized, i.e. both left-hand (LH) or both right-hand (RH), and that this handedness should reverse on central meridian passage (CMP). (Reversal of the handedness at CMP had been suggested earlier by Martyn.) These arguments should apply also to microwave bursts and to type I storms.
The Effect of a Magnetic Field on Individual Convective Cells
Authors: Murphy J. O.
Published: July 2016

The darkness of sunspots has been attributed by many authors (Biermann 1941; Danielson 1961) to the inhibition of the normal solar convective processes by the presence of strong magnetic fields. Observations of the solar photospheric granulation pattern have also shown that a weak longitudinal field exists outside the activity regions. Although these observations have not revealed any close association between the magnetic field and individual granules, nor the exact reasons for the darker cell boundaries, it must be accepted that, overall, the role of the magnetic field must be such as to influence the cell structure and reduce the normal heat transfer by convection.
The Spectrum of Smc X-1
Authors: Peterson B. A. , Vidal N. V.
Published: July 2016

The variable X-ray source in the direction of the Small Magellanic Cloud (SMC), SMC X-1 (2U 0115-73) was discovered by Leong et al. (1971). X-ray eclipses with a period of 3.8927 ± 0.0010 days were subsequently reported by Schreier et al. (1972). Identification of the X-ray source with SK 160, star number 160 in the list of Sanduleak (1968), was proposed by Webster et al. (1972) on the basis of the similarity of its spectrum with that of the optical counterpart of Cyg X-1.
A Comment on X-Ray Source Identifications
Authors: Thomas R. M. , Davison P. J. N.
Published: July 2016

The third Uhuru catalogue of X-ray sources (Giacconi et al. 1974) contains X-ray source positions given to a much higher precision than was previously available and this fact has given considerable impetus to the search for optical and radio counterparts. Many such identifications have now been made and confirmed, e.g. by discoveries of correlated variability.
Modulation of Cosmic Ray Intensity Underground Associated with the Planet Jupiter
Authors: Jacklyn R. M. , Cini-Castagnoli G.
Published: July 2016

Evidence has recently been put forward that Jupiter might be modulating the intensity of cosmic radiation observed at the earth (Pizzella and Venditti 1973; Cini-Castagnoli et al. 1973). It therefore seemed worthwhile to analyse underground meson data in Jovian time for any evidence of an effect at the higher energies over a complete orbital period.
Sidereal Cosmic Ray Variations Observed Deep Underground
Authors: Fenton A. G. , Fenton K. B.
Published: July 2016

In recent years, cosmic-rays have become part of the study of astrophysics and the search for information as to their origin has assumed considerable importance. The question of the origin of the rays is linked with questions concerning their acceleration and propagation through interstellar space. The main problem facing the cosmic-ray astrophysicist in attempting to elucidate these questions observationally arises from the fact that most particles are electrically charged, causing their paths to be curved by the magnetic fields of the Earth and interplanetary and interstellar space.
The U.K. 48-inch (1.2 metre) Schmidt Telescope and the SRC IllaJ Survey
Authors: Cannon R.D.
Published: July 2016

The U.K. Schmidt telescope is one of three independent ‘observatories’ now on Siding Spring Mountain near Coonabarabran, and is operated by the United Kingdom Science Research Council. The telescope has been fully operational since September 1973. So far we have taken about 800 astronomical plates, about half being for the main IllaJ Survey and half for other scientific programmes. The latter have mostly been taken when the moon or mediocre seeing have prevented us working on the Survey.
The Parkes 408 MHz Southern Survey
Authors: Haslam C.G.T. , Wilson W.E. , Cooke D.J. , Cleary M.N. , Graham D.A. , Wielebinski R. , Day G.A.
Published: July 2016

In recent years two 408 MHz surveys of the northern sky have been made to study the large-scale, low-surface-brightness features of the galactic background such as the loops and spurs (Haslam et al. 1970; Haslam et al. 1974). These surveys were designed to make maps down to the confusion limits of the telescopes used and to provide as far as practicable accurate calibration of the temperature scale and zero level for large-scale features. This work is complementary to the work of the large array telescopes; these telescopes can provide high resolution detail but they have lower surface brightness sensitivity, and have problems in determining the low-order terms which define the large-scale structure. The Parkes 408 MHz sourthern survey continues this work using the 64-m telescope to complete the coverage of the sky to the south pole. The project is a joint venture between the Max-Planck-Institut and CSIRO. For the southern survey it was felt desirable to measure the linear polarization distribution, besides making an accurate average temperature map in left-hand circular polarization (which is insensitive to variations of ionospheric Faraday effects). The previous surveys did not include linear polarization measurements.
Can the Peculiarities of HD 101065 be Explained by Fission of Transuranium Elements?
Authors: Przybylski A.
Published: July 2016

The eighth magnitude star HD 101065 has an extremely peculiar spectrum dominated by very numerous lines of the rare earths (with only the one possible exception of ytterbium, whose lines are difficult to identify). Besides the rare earths only strontium, yttrium and zirconium could be found in substantial quantities, while calcium though present is highly underabundant. The most surprising feature of the star is the absence of iron peak elements in its spectrum.
Convective Overshooting in Main Sequence Models
Authors: Cogan Bruce C.
Published: July 2016

In calculating models of stellar interiors convection is almost always treated by assuming that it is present if and only if the Schwarzschild criterion is satisfied. It seems possible that this oversimplifies the actual situation. In particular convective motions may overshoot beyond the formal boundary of the convective core, as given by the Schwarzschild criterion. The principal result of such overshooting would be the mixing of additional material into the core. This sort of additional mixing has been considered by Maeder (1974) and by Prather and Demarque (1974) in relation to the evolution of stars away from the main sequence in old open clusters.
Three-frequency Radioheliograph Observations of Solar Continuum Events
Authors: Magun A. , Stewart R.T. , Robinson R.D.
Published: July 2016

To date the Culgoora radioheliograph has recorded seven continuum bursts simultaneously at its three operating frequencies of 160, 80 and 43 MHz. In every case the radio emission is found to originate from stationary sources whose heights increase with decreasing frequency. The implications of these new observations are discussed below.
Evidence for Large Scale Cosmic Ray Electron Gradients in the Galaxy
Authors: Webber W. R.
Published: July 2016

In recent years observations of γ-ray emission from the disk of the galaxy have provided a new opportunity for research into the structure of the spiral arms of our own galaxy. In Figure 1 we show a map of the structure of the disk of the galaxy as observed for γ-rays of energy > 100 MeV by the SAS-2 satellite (Fichtel et al. 1975). The angular resolution of these measurements is ~ 3°, and besides two point sources at l = 190° and 265° several features related to the spiral structure of the galaxy are evident in the data. Most of these γ-rays are believed to arise from the decay of π° mesons produced by the nuclear interactions of cosmic rays (mostly protons) with the ambient interstellar gas. As a result, the γ-ray fluxes represent a measure of the line of sight integral of the product of the cosmic ray density NCR and the interstellar matter density N1
Molecular Astronomy
Authors: Robinson B. J.
Published: July 2016

At the first A.S.A. meeting in 1966 radio astronomers knew of only the 21 cm line of hydrogen, a handful of hydroxyl lines and some radio recombination lines. The number of molecular lines now known in the radio spectrum is close to 220, so radio spectroscopy has become a fully fledged subject. I shall not discuss here the recent ultraviolet studies of H2, HD and CO molecules that have been reviewed by Spitzer and Jenkins (1975).
Extensions to the Fleurs Synthesis Telescope
Authors: Christiansen W. N.
Published: July 2016

Four years ago a Table was shown in which the sensitivity of the Fleurs Synthesis Telescope (F.S.T.) was compared with that of three other radiotelescopes of similar resolving
power (Christiansen 1972). At that time the high sensitivities quoted for the F.S.T., like those for all but one of the comparison telescopes were only theoretical since only the eastwest array of the F.S.T. was in operation and low noise r.f. amplifiers had not been installed. Now the telescope is in operation with characteristics close to those given in the Table quoted. Sources are mapped separately with the eastwest and north-south arrays and the two maps are combined. The combination produces maps with a resolution that is
approximately the same in declination and right ascension. This is unique amongst existing rotational synthesis telescopes. Some of these maps will be shown in papers now in preparation.
The Pitch Angles of Electrons in Jupiter’s Radiation Belt
Authors: Roberts J. A.
Published: July 2016

The radio emission from Jupiter in the frequency range from ∽ 50 MHz to ∽ 5 GHz is mainly synchrotron emission from electrons in the intense radiation belt which surrounds Jupiter out to several planetary radii. Information about the pitch angles of these electrons can be derived both from the radio observations and from the Pioneer space probe observations. In this communication we discuss the pitch angle distribution inferred from the radio data and the apparent conflict with the Pioneer data.
Line Profiles of the β Cephei Stars
Authors: Stamford P. A. , Watson R. D.
Published: July 2016

The β Cephei variables are a group of short period pulsating variables of early spectral type for which no satisfactory physical driving mechanism has yet been discovered. Further it is not clear what form of pulsation these stars are undergoing. The existence of a beat phenomenon and a phase of spectral line broadening is well established in some of these stars. This extends to observed spectral line doubling in three stars, BW Vul, σ Sco and 12 Lac. Because of the difficulty in explaining these phenomena with purely radial oscillations, Ledoux (1951) first suggested the possibility of non-radial oscillations. Other stars in the group, γ Peg, δ Cet, #x03BE;’ CMa and β Cep have approximately sinusoidal velocity and light curves with little indication of spectral line broadening. For these there is probably no a priori observational need to look beyond purely radial oscillations. It is of course conceivable that different modes of oscillation are present in different members of the β Cephei group. However, if line profiles are calculated for various proposed oscillation modes and compared with the observations, it may be possible to eliminate some suggestions and hence limit the search for an instability mechanism.
The Velocities of 6cm Recombination Line Emission originating near the Galactic Nucleus
Authors: Gardner F. F. , Whiteoak J. B.
Published: July 2016

Although it is well known that HII regions are present in the innermost regions of the Galaxy their kinematics are still not fully understood. In one study Pauls et al. (1976) surveyed with a beamwidth of 3′ arc the 10 GHz recombination line emission in directions within 15′ arc of the nuclear radio source Sgr A. They found that the emission velocities varied from position to position within the range -50 to + 50 km s-1but appeared to lack any overall pattern. In contrast, we have recently observed the recombination line emission from the galactic centre region with a beamwidth of 4′.5 arc, and find strong evidence of ordered motions near the galactic nucleus.
The Effect of a Magnetic Field on the Onset of Thermal Convection when Constant Flux Boundary Conditions Apply
Authors: Murphy J. O.
Published: July 2016

The energy passing through the boundaries of a convective zone in a star, in an outward radial direction per second, must in total be equal to the luminosity of the star, provided of course that this zone does not encompass nuclear energy producing regions. If, in an endeavour to establish the nature of the convective motions in this zone, a section of the zone is modelled by considering steady cellular convection in a horizontal layer of Boussinesq fluid, it is on the basis of an average energy flux being imposed. Moreover, the sum of the conductive and convective heat fluxes is represented by the Nusselt number, which is specified and constant for the zone.
A Semitheory for Semiconvection
Authors: Stevenson D. J.
Published: July 2016

Semiconvection is the name given to a situation that arises in the evolution of large-mass main-sequence stars and lower-mass horizontal-branch stars, in which a layer forms where almost all of the heat flux is transported by radiation, but where slow convection is required to redistribute a stably stratified solute (e.g. helium). For a general discussion on semiconvection, see Spiegel (1969). The main problem is to determine the correct relationship between the solute distribution and the temperature gradient in the inhomogeneous layer. Ledoux (1947) and Schwarzschild and Harm (1958) have proposed two very different prescriptions. Since theory and experiment indicate that the Schwarzschild-Harm (SH) prescription is correct for the onset of convection (in the form of overstability), Spiegel (1969) has proposed that SH are correct. However, neither observation (oceanographic or laboratory) nor theory precludes a substantial deviation from the SH prescription as applied to finite amplitude semiconvection. The observational evidence is only readily applicable to stars if Pr≳, 1, where Pr is the Prandtl number of the fluid. In fact, Pr≪ 1 in stars. It is shown below that if one could have stars in which Pr ≳ 1, then the SH prescription would probably be wrong, and the Ledoux criterion might then be nearer to being correct. In the real situation (Pr≪ 1), observations or experiments are lacking and theory alone does not provide an unequivocal answer to the problem. This paper does not attempt a complete discussion of the problem, and a more detailed report will be submitted elsewhere. Some aspects of the problem have already been discussed in the context of the giant planets (Stevenson and Salpeter 1977).
Immiscibilities in cold, degenerate Stars
Authors: Stevenson D. J.
Published: July 2016

The deep interiors of cold, degenerate stars consist of a mixture of elements, either because of primordial inhomogeneities or because of incomplete nuclear burning. However, most existing calculations for the cooling of such bodies (subsequent to any nuclear burning) assume that the only source of luminosity is the heat content of the star. An additional (and potentially much larger) energy source is available if the elements have limited mutual solubility below some temperature. The resulting differentiation and gravitational settling can dramatically decrease the rate of cooling, enhance the number of (potentially) observable low luminosity bodies, and may deplete the atmosphere of heavy elements (if substantial mixing between the atmosphere and deep interior occurs). The observational evidence for these phenomena is equivocal at present.
Numerical Experiments on Planetesimal Aggregation during the Formation of the Solar System
Authors: Hourigan K.
Published: July 2016

A major area of difficulty in the cosmogony of the solar system is understanding how a large number of small planetesimals, which have condensed from the primordial gas, can aggregate into the ordered planetary system present today. Theories involving aggregation within a gaseous disc [e.g. Cameron (1973)] suffer the common difficulty that the particles, once condensed, are no longer supported by the radial gas pressure gradient and spiral rapidly in towards the Sun. Most of the planetesimals are dragged in to the central body in times several orders of magnitude less than would be required for larger bodies to accrete (Goldreich & Ward 1973).
Hydromagnetic Waves in Magnetic Flux Tubes
Authors: Wilson P. R.
Published: July 2016

In discussions of the non-radiative propagation of energy through stellar atmospheres hydromagnetic waves, or in their more specialized form Alfven waves, have played an increasingly important role. Parker (1974) has suggested that they provide the cooling mechanism for sunspots, while Piddington (1974) has attempted to explain the flare energy supply in terms of hydromagnetic energy transport. While most analyses assume a homogeneous magnetic field extending to infinity in a compressible but unstratified atmosphere, it is important to remember that most astrophysical plasmas are gravitationally stratified and that the magnetic fields are highly inhomogeneous, exhibiting a variety of different structures.
On the Relative Importance of Radiative, Mechanical and Magnetic Energy Release of Flares
Authors: McLean D. J. , Dulk G. A.
Published: July 2016

For many years we have had evidence from solar radio bursts of violent mass motions in the solar corona: type II bursts reveal the passage of shock waves through the solar corona, and moving type IV bursts show that plasma and magnetic field travel to great distances without any sign of slowing down.
Evidence for the Existence of a Low-Velocity Molecular Cloud near Sgr A
Authors: Whiteoak J. B. , Gardner F. F.
Published: July 2016

In the wide complex profiles of OH, H2CO and CO spectra observed in directions towards the galactic centre, only the features at radial velocities near + 40 km s-1 are generally believed to originate in the molecular clouds nearest the galactic nucleus. The features at other velocities are associated with clouds or spiral features that can be traced over larger ranges of galactic longitude, implying locations which are more distant from the nucleus. In particular, the features near zero velocity have been traditionally associated with molecular clouds within 1-2 kpc of the Sun. However, H2CO observations with high velocity resolution provide evidence that one cloud with velocity near zero is probably near the galactic nucleus.
The Tilt of the LMC
Authors: Gascoigne S. C. B. , Shobbrook R. R.
Published: July 2016

It has been accepted since the mid-1950’s that the LMC is a flat rotating body, with its plane inclined at an angle of about 27° to the line of sight and so nearly face on, and its line of nodes running 10° west of north (de Vaucouleurs and Freeman 1972). The inclination is inferred from the ellipticity of the outermost optical and radio isophotes but there has been no convincing way to fix its sense — whether the E or W side is nearer. Some years ago the late Dr David Thackeray suggested to one of us (SCBG) that this could be done by comparing the magnitudes of cepheids on the extreme E and W sides of the Cloud. With the discovery of the Magellanic Stream and the great increase of interest in the spatial geometry and dynamics of the Clouds and Galaxy complex, the sense of the tilt of the LMC has become a matter of importance, and we decided to go ahead with the project.
Isothermal Clusters of Galaxies
Authors: Lewis B. M.
Published: July 2016

A departure from an isothermal mass distribution in a rich cluster is expected if the genesis involves a coherent recollapse phase. The character of this departure is calculated and looked for in the data available for the Comma Cluster. No significant deviation from an isothermal mass distribution is found for r < 360’.
Infrared Spectroscopy in Australia
Authors: Jones Terry Jay
Published: July 2016

Infrared spectroscopy is a relatively new field in astronomy. When the study of celestial sources at wavelengths longer than 1μm underwent a major spurt of growth in the mid-sixties, it was natural for astronomers to concentrate on broad band measurements. As detectors and instrumentation have steadily improved and the broad band characteristics of stellar sources in the IR have become better known, there has been a natural trend to higher spectral resolution. To date there has been sufficient work in IR spectroscopy to warrant several reviews on the subject. Although Australia has been late in entering this exciting and expanding field, the quality of work has more than made up for the delay. In this review I will briefly describe several projects involving IR spectra performed in Australia. Special emphasis will be placed on those experiments thatcannotbe done by any means other than IR spectroscopy. Also presented is a description of Australia’s next generation of spectroscopic instrumentation for the IR.
Optical Identification of the Strong Radio Source PKS 0511-48
Authors: Robertson J. G. , Smith R. M.
Published: July 2016

The radio source PKS 0511-48 is among the hundred strongest southern sources at low frequencies. It was catalogued in the Parkes survey (Ekers 1969) and mapped with the Molonglo Cross at 408 MHz by Schilizzi and McAdam (1975) with a resolution of 2′ .6 arc. It appeared in that work as a complex source, with an integrated flux density of 8.8 Jy. A search for optical identifications was made by Tritton and Schilizzi (1973), but none were found to a level of B ~ 19. We have inspected the field on the ESO B survey film, and find a group of ~ 20 faint galaxies (approximately 19-20 mag).
Cook’s Model and Linewidths of OH Masers
Authors: White Stephen
Published: July 2016

Two outstanding problems in the interpretation of OH masers are their narrow linewidths, and the rare occurrence of Zeeman pairs (Reid and Moran 1981). On discovery, the narrow but intense features of OH sources suggested unsaturated maser action (Perkins et al 1966). However the features are often so bright that saturation must be involved, and in saturated growth the features should rebroaden to about the thermal width (Goldreich and Kwan 1974). This is not observed (Reid and Moran 1981).
Theoretical Studies of Star Formation
Authors: Monaghan J. J.
Published: July 2016

There are two major difficulties associated with theoretical studies of star formation. The first of these is that the dominant physical process or processes leading to star formation have not been identified. The second is that realistic calculations at an appropriate level of accuracy have been impossible to carry out. The result has been that only minor advances have been made on the early work of Jeans (1929) and Hoyle (1953). Much greater progress can be expected in the next few years both because observations of infra-red sources have given us much more information about the site of star formation, and because access to the current generation of very fast computers is becoming more common.
Composite Analytical Solutions of the Lane-Emden Equation with Polytropic Indicies n = 1 and n = 5
Authors: Murphy J. O.
Published: July 2016

For a spherically symmetrical distribution of gaseous matter in gravitational equilibrium the total pressure, density and other physical variables are all functions of the radial distance measured from the centre.
Solar Ca II K Resonance Line Polarization
Authors: Rees D. E. , Saliba G. J.
Published: July 2016

The Ca II K line serves as an important tool in determining the physics of the photosphere-chromosphere region of the solar atmosphere (Cram 1983). To date detailed analyses have centred on the study of line intensity profiles.
Geometry of Hα Active Region Loops Observed on the Solar Disk
Authors: Chuan-le Chen , Loughhead R. E.
Published: July 2016

Plasma loops are the dominant structures, in the higher levels of the Sun’s atmosphere above active regions. Much of our knowledge of their properties has come from space observations made over the past decade or so in the EUV and X-ray regions of the spectrum and, more recently, from high-resolution, two-dimensional images of microwave sources obtained with the Very Large Array radio interferometer (VLA). On the other hand, the spatial resolution of rocket and satellite observations has so far generally failed to match that of ground-level optical observations made in Hα and other strong chromospheric lines. The latter permit one to study in much greater detail the morphology of individual loops, as illustrated for example in the recent work of Loughhead, Wang and Blows (1983). These authors addressed themselves to the task of determining the true geometrical shapes of individual loops, a problem which had hitherto received little attention.
The Distribution of 115 GHz CO Towards W33
Authors: Gardner F. F. , Whiteoak J. B. , Otrupcek Robina E.
Published: July 2016

Although the radio continuum distribution of the HII-region/molecular-cloud complex W33 (peak l = 12°.8, b = -0°.2) resembles a discrete region about 15′ arc in size, the behaviour of the recombination-line velocities (Gardner et al. 1975; Bieging et al. 1978) and molecular-line velocities (OH: Robinson et al. 1970; H2CO: Gardner and Whiteoak 1972) has been difficult to interpret in terms of a simple model. There is a difference of opinion as to whether W33 consists of two independent complexes at different distances along the line of sight or a single expanding complex (e.g. Goss et al. 1978).
Precession in the Jet of NGC 5128 (Centaurus A)
Authors: Haynes R.F. , Cannon R.D. , Ekers R.D.
Published: July 2016

NGC 5128, identified with the radio source Centaurus A by Bolton et al. (1949), is a remarkable galaxy which appears to consist of an elliptical or SO galaxy crossed by a strong dust lane. The early idea that this represented a pair of colliding galaxies (Baade and Minkowski 1954) powering the extended double radio source fell out of favour but has recently been revived (Malin et al. 1983) in the light of extensive kinematic evidence. However, the interpretation of the data is not yet complete, and it has also been suggested recently that NGC 5128 is really a spiral galaxy with a spectacularly large bulge (Marcelin et al. 1982).
Maps of Centaurus A from Molonglo and Culgoora
Authors: Slee O.B. , Sheridan K.V. , Dulk G.A. , Little A.G.
Published: July 2016

While Centaurus A (NGC 5128) is not a particularly powerful radio galaxy, its proximity (˜ 5 Mpc) permits us to obtain linear resolution an order of magnitude better than can be obtained for the more powerful, distant radio galaxies. Thus one can hope to make meaningful comparisons between the morphologies seen over the electromagnetic spectrum from γ-rays to metre waves. This should lead to a more complete understanding of the energy production mechanisms and evolutionary histories of these objects.
A New Underground Telescope at the Mawson Cosmic Ray Observatory
Authors: Jacklyn R.M. , Duldig M.L.
Published: July 2016

For many years now, large plastic scintillator and geiger counter muon telescope systems have been used underground for studies of the small variations of the cosmic ray particle intensity that occur at primary energies around 1011 – 1012 eV. Although long-term deterioration in telescope counting efficiency is liable to take place it has been possible to take care of it sufficiently well to allow accurate observations to be made of the important daily variation and of transient events such as the Forbush Decrease and the solar flare increase.
UBV Photometry for 31 Galactic Globular Clusters
Authors: Hanes David A.
Published: July 2016

For many reasons, it is important to have a sound body of reliable photometry for the globular clusters in the Milky Way galaxy. Given the striking appearance of the globular clusters and their historical and astrophysical interest, it is perhaps surprising that the available photoelectric photometry for globular clusters is of mixed quality (see Harris and Racine 1979). Here I present a homogeneous body of photometry through a single aperture and in the UBV system for 31 globular clusters south of declination +12°.
The International Halley Watch From Australia
Authors: Candy M. P.
Published: July 2016

The original concept of the International Halley Watch was presented by Louis Friedman to NASA in 1979. The intent was to maximise the scientific value of ground-based and space studies of Comet Halley. This initial suggestion met with a very positive response and has developed into a smooth organization, principally concerned with rapid communication and promoting co-operation between scientists in a wide range of disciplines. The main aim here is to put the IHW in perspective; further details of its origin and evolution can be found in Newsletter No. 1, from which the following three diagrams are taken: To quote from Newsletter No. 1 ‘The most important elements in the IHW are the Professional Observers and the Discipline Specialist Teams. Without the Observers, there can be no Halley Watch, and without the Discipline Specialists, there would be no co-ordination of observations.’ If there are any professional observers who have not yet been contacted by a Discipline Specialist it is recommended that they make their interest known immediately.
Accretion onto Magnetized Neutron Stars
Authors: Kirk J. G.
Published: July 2016

Magnetic fields of about 1012 G have now been measured in several astrophysical objects (Trümper etal. 1978, Wheaton et al. 1979, Mazets et al. 1981). In the case of pulsating X-ray sources, the presence of a companion star indicates that accretion is probably the energy source for the X-rays.
Formation of the Planets and Asteroids: Some Difficulties of Accretion Theories
Authors: Komesaroff M. M.
Published: July 2016

Figure 1 is a plot of spin angular momentum, J, against mass, m, for some of the main sequence stars, the planets and the asteroids.
Titan and the Dispersal of the Proto-Saturnian Nebula
Authors: Hourigan K.
Published: July 2016

The NASA Voyager spacecraft missions to the outer planets have provided a wealth of observational data with regard to the physical and chemical properties of the attendant satellite systems. Although the gaseous nebula discs from which these satellites are suspected to have formed are no longer present, these data provide at least some basis from which the characteristics of individual nebula can be deduced.
Tidal Models of the Magellanic System
Authors: Gingold R. A.
Published: July 2016

Of the attempts to model the Magellanic system as the result of tidal interactions, only the works of Lin and Lynden-Bell (LLB 1982) and Murai and Fujimoto (MF 1981) can be considered to be successful.
The Stability of Stellar Atmospheres
Authors: Auman Jason R.
Published: July 2016

There have been extensive calculations of model atmospheres of stars over the past few decades. Almost all of these calculations have assumed radiative equilibrium. Except for convection, very little work has been done on the stability of the surface layers of stars at small optical depths. Although there has been a considerable amount of research concerning the stability of stars, this work has assumed the diffusion approximation for the transport of radiation and has been primarily concerned with the envelopes of stars rather than their atmospheres.
Photospheric Flux Changes and the MHD Approximation
Authors: Wilson P. R.
Published: July 2016

The rate of change of magnetic flux Ф contained within a closed curve C moving with the plasma velocity u, is given by

where B is the magnetic induction and S is a surface bounded by the curve C. Using the hydromagnetic equation,

where η is the magnetic diffusivity, this becomes

In many astrophysical contexts η is small and thus approximately

Since this implies that the flux within any moving closed curve does not change, the field is said to be ‘frozen into’ the plasma and moving with it.