bluuebunny/crossref_metadata_2025 huggingface dataset:
13. The Polarization of Radiation from White Dwarfs
Authors: Angel J. R. P. , Landstreet J. D.
Published: July 2016

During the course of two observational programs to search for magnetic fields in white dwarfs (Angel and Landstreet, 1970a; Kemp, 1970), it was discovered by Kemp and Swedlund (Kemp et al., 1970b) that the continuum optical radiation from the λ4135 type white dwarf Grw + 70° 8247 is circularly polarized. This circular polarization was measured in a broad band from about 4000 to 7000 Å a number of times; in this band the circular polarization does not appear to vary from its mean value of 3.29% with an amplitude of more than about 0.1% (or 3% of the measured mean polarization) on any time scale from 24 seconds to 2 weeks (Angel and Landstreet, 1970b).
18. Model Atmospheres for Hydrogen-Deficient White Dwarfs
Authors: Bues I.
Published: July 2016

The determination of atmospheric parameters for non-DA white dwarfs is investigated with the computed helium-rich model atmospheres by Bues (1970). Only poor predictions are possible from UBV colors alone for DB and DC stars. From uvby colors a determination of effective temperature is possible within 1000 K. Profiles of lines in different parts of the spectrum are necessary for better results.

A deficiency of metal abundances for the cooler non-DA stars is obtained.
19. Convection Zones and Coronae of White Dwarfs
Authors: Böhm K. H. , Cassinelli J.
Published: July 2016

Outer convection zones of white dwarfs in the range 5800 K ≤ Teff ≤ 30000 K have been studied assuming that they have the same chemical composition as determined by Weidemann (1960) for van Maanen 2. Convection is important in all these stars. In white dwarfs Teff < 8000 K the adiabatic temperature gradient is strongly influenced by the pressure ionization of H, HeI and HeII which occurs within the convection zone. Partial degeneracy is also important.

Convective velocities are very small for cool white dwarfs but they reach considerable values for hotter objects. For a white dwarf of Teff = 30000 K a velocity of 6.05 km/sec and an acoustic flux (generated by the turbulent convection) of 1.5 × 1011 erg cm−2 sec−1 is reached. The formation of white dwarf coronae is briefly discussed.
On the Motion of the Equator and the Ecliptic
Authors: Fricke Walter
Published: July 2016

A report is given on work in progress on the available observational evidence for an excess secular change of the obliquity of the ecliptic. Some of the recent determinations suggested that the conventionally adopted value of the secular change requires a correction of the order of per century. Since an error of this size in the adopted motion of the ecliptic must be ruled out, the observed corrections may indicate either a rotation of the equatorial plane with respect to an inertial system about an axis passing through the equinox or the existence of systematic errors of the observations. In following Aoki's suggestion of a real motion of the equator, the averaged proper motions in the systems FK4 and N30 yield a rotation of the galaxy with an angular velocity of 43.6 km s−1 kpc−1 near the Sun and a positive gradient of the circular velocity in the galaxy near the Sun. If the distance of the Sun from the galactic center is 10 kpc, the circular velocity of the galaxy would be 436 km s−1. Should, however, the circular velocity be less than 300 km s−1, the distance of the Sun from the galactic center would have to be smaller than 7 kpc.

For the following reasons such far reaching conclusions are not well founded:

(1) Fundamental observations of the stars, the Sun and the planets carried out before about 1900 show appreciable systematic deviations from the average of the observations carried out after 1900. The excess secular change of the obliquity is suspected to be the consequence of systematic errors of older observations.

(2) The determinations of individual values of Δɛ from observations of the Sun and the planets show a steep decrease of Δɛ from about 1780 to 1900; the individual values of Δɛ derived from observations after 1900 do not deviate significantly from zero and do not show a significant secular decrease. On the other hand, a small secular decrease cannot be excluded.

(3) The first results of determinations of Oort's constant B from proper motions of stars with respect to galaxies do not indicate significant deviations from the results derived on the basis of proper motions measured in the fundamental system.

This investigation, which is not yet completed, concentrates on an analysis of fundamental observations of stars, the Sun and planets. From the systematic errors of observations which have contributed to the formation of the FK4 it can already be stated that modern observations cannot exclude the possibility of an excess secular change of the obliquity within the limits of per century and, consequently, the possibility of a real motion of the equatorial plane within these limits. It appears, therefore, that Aoki's suggestion deserves further attention, but that its effect on galactic rotation is smaller than was originally assumed.
On the Correlation between Earthquake Occurrence and Disturbances in the Path of the Rotation Pole
Authors: Chinnery Michael A. , Wells Fred J.
Published: July 2016

The hypothesis that earthquakes may be the principal excitation of the Chandler motion of the rotation pole is examined in the light of recent theoretical and observational developments. There is some doubt about the amount of excitation by a large earthquake necessary to maintain the Chandler Wobble, but it appears to be about 10 ft. Theoretical calculations for the Alaskan Earthquake (M = 8½) give available excitations in the range 1–5 ft, but there are considerable uncertainties in these calculations. Earthquakes may be able to provide all of the required excitation, or only a small portion (10% or less). The problem is confused by observational studies, which show differences between various sets of data on polar motion which seem to be larger than the expected error in each set. The earthquake hypothesis, though reasonable, is still very much open to debate.
On Some Natures of the Excitation and Damping of the Polar Motion
Authors: Sekiguchi Naosuke
Published: July 2016

Values of the Chandlerian period and the damping coefficient of the polar motion are calculated for every ten years from 1900.0 to 1970.0, using a method developed by Sekiguchi (1966). The damping coefficient is variable between 0.074 and 0.008 (yr)−1 through this period, and correlative with the variation of the Chandlerian period, as Sekiguchi (1961) theorized.
O and Of Stars
Authors: Conti Peter S.
Published: July 2016

My intention here is to discuss the ‘high temperature’ portion of this symposium and call attention to those stars that are called Of. There are some similarities in spectral appearance to WR stars, e.g. emission lines. I should first like to define what I think are the essential differences among four groups of hot stars;

O stars: Stars that have only absorption lines in the visible spectrum. Type O is distinguished from type B by the presence of He ii 4541 at MK dispersion. It may be that some (supergiants) O stars will have emission lines in the rocket UV region but this description will be primarily concerned with ground based observations.

Of stars: These are O type stars that also have λλ 4634,40 N iii in emission above the continuum. In addition to normal O star absorption lines and N iii emission, they may also have other lines in emission. I will discuss this further below.

Oe stars: These are O type stars that have emission in the hydrogen lines (or at least at Hα), but with no emission in N iii or in other lines. I personally think that this small class of objects is related to the Be stars in their evolutionary status and in their emission mechanism.

WR stars: These stars are primarily characterized by emission lines. The only absorption lines seen are violet shifted (P Cyg type). Although in some cases emission lines appear which are similar to those found in some Of stars, the latter types always have some unshifted absorption lines present. Several Of stars have P Cyg profiles in some lines.
Spectral Classification Studies of Cepheids Using a Small Telescope with an Image Tube Spectrograph
Authors: McCarthy M. F.
Published: July 2016

Most of the results reported thus far of image tube spectroscopy as applied in astronomy have been concerned with emission features and have been the result of a combination of the largest available light gathering power of large telescopes with the improved sensitivity of image intensifiers. We consider here the application of image tube techniques to moderate sized telescopes; concretely, we describe the first program of spectral classification using absorption features as carried out with the image tube spectrograph of the Vatican Observatory attached to the Zeiss 60-cm reflector at Castel Gandolfo. Treanor (1970) has described the optical design, construction and the first tests of this instrument. The receiver is an RCA cascaded image tube loaned to the Vatican Observatory by the Carnegie Image Tube Committee.
Spectral Classification of Some Long-Period and Semiregular Variables Near Times of Maximum
Authors: Simon L. W. , Buscombe W.
Published: July 2016

Spectra of 60 M-type long-period and semiregular variables, obtained near the time of maximum at Siding Spring Observatory in Australia, from 1965–1967, have been classified on the Keenan system.
On the Accuracy of Spectral Classifications of Main-Sequence Stars
Authors: Gliese W.
Published: July 2016

By examining the observed dispersion in (colour, spectral type) relations, classification errors have been derived from the data of nearby stars. The comparisons of the colour deviations observed in spectral regions of large variations of colour with type with the deviations in regions of small variations give the following standard errors in units of a tenth of a spectral class: For K dwarfs ±0.6 (MK), ±1.2 (Mt. Wilson), ±0.7 (Kuiper); for early M dwarfs ±0.9: (MK), ±0.7 (Mt. Wilson), ±0.5: (Kuiper); and for late M dwarfs ±0.7 (Kuiper).
Objective Prism Spectral Classification at the Stockholm Observatory
Authors: Nordström B. , Sundman A.
Published: July 2016

As a result of the spectral survey at the Stockholm Observatory finding lists are prepared for early and late type stars in the Southern Milky Way. In order to make the lists more useful we present the principles of the stellar classification.
Automatic Classification of Objective Prism Spectra
Authors: West R. M.
Published: July 2016

Methodological problems and hardware/software requirements of efficient automatic classification of objective prism stellar spectra are described on the basis of experience from ‘microphotometer-computer’ classification. Significant advances in hardware (two-dimensional scanners, on-line computers) as well as in software (image processing techniques) have now brought high-speed, exhaustive, automatic classification within reach. Some astronomical implications of automatic spectral surveys are discussed.
Applications of the UB1B2V1G Photometric System
Authors: Golay M.
Published: July 2016

This photometric system which was described for the first time in 1963 by Golay has been in use at the Geneva Observatory since 1959. We are involved in a long term observational programme having as objective the study of cluster stars, peculiar stars and interstellar extinction. This research aims at the determination of physical parameters such as effective temperature, gravity, abundance, or those of spectral type, absolute magnitude, [Fe/H]. To permit such an analysis the photometric effects of rotation, of multiplicity and of interstellar extinction were given particular attention. Attempting to attain the above mentioned purposes, we have had to give great care to the precision of the measurements during their acquisition as also during their reduction. Finally, in view of allowing a valid comparison between observations and the theory of stellar atmospheres, particular care had to be given to the maintenance of the pass-bands and to the knowledge of their form.

We intend here to give the main bibliographical references relative to the articles which present the general properties of the system, its applications and the catalogues.
Narrow Band Photometry of Supergiant Stars
Authors: Mendoza V. E. E.
Published: July 2016

At the National Astronomical Observatory in San Pedro Mártir, B. C. (Mexico), we have performed photoelectric photometry for 31 stars in a narrow-band system. The system allows the measurements of total absorptions of neutral oxygen at 7774 Å through three interference filters (20–25 Å half-width), one for the OI lines and two for the continuum.

The preliminary results are very encouraging: Supergiant stars, ranging in spectrum from the later subdivisions of type B to early G, can be clearly separated from other luminosity classes. The total absorptions depend strongly on the stellar luminosity and, to a lesser degree on the effective temperature (spectral type) of the star. The system may be improved by using narrower filters and detectors with a higher quantum efficiency, already in existence.
Some Blue Stars of Peculiar Type in the Region of the South Galactic Pole
Authors: Graham J. A. , Slettebak A.
Published: July 2016

uvby photometric observations have been used in conjunction with slit spectra to classify 90 stars which were noted as peculiar by Slettebak and Brundage in a recent objective prism survey of the South Galactic Pole region. In this paper, we review the photometric classification criteria and identify in the Slettebak-Brundage list, 8 subdwarf O stars, 10 subdwarf B stars, 10 horizontal branch stars, 1 white dwarf star and 26 late subdwarf stars. Three stars with outstanding peculiarities are SB (Slettebak-Brundage) 58 which is a helium subdwarf O star, SB 319 (CD–38°245), a late type star with extremely weak metal lines and SB 845 (BD–13°6465), an A type star with a very small Balmer discontinuity.
Two Dimensional Spectral Classification of Early Type Stars by Low Dispersion Spectrophotometry
Authors: Gutiérrez-Moreno A. , Moreno H.
Published: July 2016

Spectrophotometric data of early type stars (spectral intensity distributions from 3100 to 6000 Å and equivalent widths of Hβ, Hγ and Hδ) have been analysed, looking for the best parameters for a two dimensional spectral classification. It was found that the best correlation with MK classification is given by the equivalent width of Hβ and the Balmer discontinuity.

The classification scheme is well defined for stars from B0 to A1 of luminosity classes V to III. No stars of luminosity class II were observed. Luminosity class I is clearly separated from the less luminous stars, but the number of supergiants observed is too small to give a clear separation of spectral types.
A Study of Interstellar Reddening at High Galactic Latitudes
Authors: Philip A. G. Davis
Published: July 2016

A series of finding lists of A stars in regions at high galactic latitudes has been published in the last few years. Strömgren four-color and Hβ measures have been made of stars in five of the regions, allowing the interstellar absorption in each to be calculated. The two most important regions are the North Galactic Pole and the South Galactic Pole where color excesses of EB_V=0.00 and EB_V=0.02 were found respectively. An area in front of the Large Magellanic Cloud has a color excess of EB_V=0.04.
Discussion of Observations of the Flow of Matter Within Binary Systems
Authors: Batten Alan H.
Published: July 2016

Observational determinations of density, dimensions, temperatures, and velocities of circumstellar features are surveyed and discussed, with a view to establishing limiting values that could be useful in any theoretical treatment of circumstellar structure. Densities of the order of 1013 particles cm-3 are found for streams and disks, although there is evidence for regions of much lower density in many systems, and some systems may have much denser circumstellar matter.

Dimensions of disks seem to be remarkably constant (fractional radius ∼ 0.3) in a wide variety of systems. The total mass of circumstellar matter is always a small fraction of the mass of the system. Temperatures are usually similar to the temperatures of the stars in the system, although hot spots certainly exist in some systems, and ‘flare’ activity is evidence of localized very high temperatures. On the other hand, some systems may contain solid circumstellar matter. Observed velocities are usually several hundred km s-1. The empirical relation between the velocity of rotation of disks and the orbital period is described. Finally, the stability of these features is briefly discussed.
Evolutionary Aspects of Circumstellar Matter in Binary Systems
Authors: Plavec Miroslav
Published: July 2016

Several groups of close binary stars are considered in an attempt to explain their present state as a consequence of a large-scale mass transfer or mass loss in the past: Algol-like semidetached binaries, some shell stars (AX Mon), some binary X-ray sources (Cen X-3, Her X-1), the recurrent nova T CrB, helium-rich binaries v Sgr and KS Per, and the symbiotic variables.

Algol-like binaries like U Sge cannot be products of a conservative case A of mass transfer; rather, mass loss from system and/or a temporary contact stage must be invoked. Nova T CrB as well as the symbiotic variables probably contain a mass-losing giant and a helium star, which again may be a product of a previous mass transfer of type B. Similarly, some of the X-ray sources may actually be binaries undergoing a second process of mass transfer. The systems v Sgr and KS Per may contain helium stars expanding to the right of the helium main sequence, while the other component may be a rather inactive main-sequence star. Some shell stars may be products of mass transfer. Mass loss from convective envelopes is also discussed.

Loss of mass and of angular momentum from many binary systems must be anticipated. Behavior of the mass-accreting stars may often be decisive for the appearance and evolution of the system.
Variational Method for Dense Systems
Authors: Pandharipande V. R.
Published: July 2016

The variational method for calculating energy of quantum fluids, and its applications to the Bose liquid 4He, Fermi neutron gas, and liquid 3He are discussed. The correlation functions are parameterized by their healing distance, and can depend on the states occupied by the correlated particles in the model wave function. They are calculated by constrained variation of lowest order contributions. The healing distance has a prescribed value in lowest order calculations, whereas it is sufficiently large in hopefully exact energy calculations. The direct many-body cluster diagrams are summed with successive approximations of an integral equation. The contribution of exchange diagrams is shown to decrease rapidly with the number of exchanges, and their sums are truncated after the energy has converged to within a few percent.
A Simple Equation of State of Matter at Super-Nuclear Densities
Authors: Leung Y. C. , Wang C. G.
Published: July 2016

The qualitative features of the equation of state of matter at supernuclear densities are deduced through a careful examination of the nature of particle interactions at short distances and by the introduction of an ‘effective mass spectrum.’ it is found that the equation of state begins to take on a particularly simple form (the ‘asymptotic form’) at a relatively low matter density of 1017 g cm−3. A brief review of various approaches to calculate the equation of state for a neutron star is also given.
Superfluidity in Neutron Stars
Authors: Greenstein George
Published: July 2016

We present a short Cook's tour of the possible effects of rotation coupled with superfluid properties of neutron star interiors. A suggestion is made to take advantage of forthcoming lunar occultations of the Crab Nebula in order to search for blackbody X-ray emission from the Crab pulsar.
Supernovae and Neutron Stars
Authors: Colgate Stirling A.
Published: July 2016

The formation of a neutron star and the event observed as a supernova are presumed by most astrophysicists to be simultaneous. The theoretical difficulty of understanding this is compounded by a hierarchy of conflicting phenomena dominated by the possibility of effective neutrino transport of the heat of the neutron star formation to the outer envelope. A thermonuclear detonation of a carbon core may take place at just the right density such that both neutron star formation and neutrino assisted envelope ejection can occur together.
Hadron Star Models
Authors: Cohen Jeffrey M. , Börner Gerhard
Published: July 2016

The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as ∼ 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.
Differential Rotation in Degenerate Stars
Authors: Van Horn H. M.
Published: July 2016

The problem of the development of the angular velocity distribution during the final phase of gravitational contraction of a star immediately prior to the onset of degeneracy and during the subsequent cooling phase is surveyed. Processes that may affect this distribution are discussed at some length, and estimates of the timescales for redistribution of the angular momentum are given for each process. Possible effects on the evolution and observable consequences are briefly considered.
Polarized Radiation from White Dwarfs and Atoms in Strong Magnetic Fields
Authors: O'Connell R. F.
Published: July 2016

We present the recent results of our continuing program of investigation of the behavior of matter in strong to super-strong magnetic fields (B ∼ 106−1012 G). This work was motivated by the discovery of strong magnetic fields (B ∼ 107 G) in some white dwarfs and the likely existence of super-strong fields (B ∼ 1012 G) in pulsars. Magnetic white dwarfs were discovered from observations of the continuous spectrum and one of the most intriguing challenges for the theorist is to provide an explanation for the observed wavelength dependence of the fractional circularly and linearly polarized radiation. Our initial response to this question was the determination of an exact solution of Kemp's harmonic oscillator model. These results are used as input to the ATLAS model atmosphere program and then comparison is made with observations. The disparities still existing between theory and observation convince us of the necessity for developing a new model of the continuum radiation, two likely possibilities being photoionization and free-free absorption. This leads us to present a general formulation of radiation absorption and emission processes in a magnetic field. Next we calculate the cross section for the photoionization, correct to first order in B. For the purpose of obtaining exact results for this cross section, the effect of a magnetic field on the energy spectrum and wave functions of hydrogen, helium, etc. must be obtained. The results for hydrogen are presented here. They will be useful also in determining accurate values for the displacements due to the quadratic Zeeman effect in the line spectra of DA stars, particularly for the higher excited states.
Simultaneous X-Ray, Optical and Radio Observations of Galactic X-Ray Sources
Authors: Hiltner W. A.
Published: July 2016

Simultaneous observations of the X-ray source Sco X-1 are reviewed and discussed. Several conclusions can be drawn from the observations. (a) There is no correlation of the radio intensities with either the optical or X-ray intensities. (b) The X-ray intensity is high and variable only when the blue optical magnitude is brighter than 12.6–12.7. (c) There is often correlation of X-ray and optical flares, but the relationship is not one to one.

Attention is called to the paucity of simultaneous observations of other identified X-ray sources.
Structure and motions in the interstellar medium (Introductory Report)
Authors: van Woerden Hugo
Published: July 2016

This review summarizes information obtained from studies of dark matter, of optical interstellar absorption lines, and of the 21-cm line observed in absorption and in emission.

Great improvements in the velocity resolution of interstellar lines (Section 4) are making possible a detailed analysis of their component structure, and determination of the internal motions in the clouds. The 21-cm absorption spectra of strong radio sources (Section 5) have yielded statistics of the optical depths and the internal velocity dispersions of absorbing clouds. Studies of the 21-cm line in emission (Section 6) supply a wealth of data on internal motions in the clouds. Comparisons of Gaussian component parameters at neighbouring positions allow delineation of cloud boundaries on the sky, but estimates of size and mass depend on (usually unknown) distance. The Green Bank telescope has revealed the existence of ‘cloudlets’ containing a few solar masses within a volume of about 5 pc diameter.

Structural details in the interstellar medium show a wide variety of size, density and mass. Recent studies tend to emphasize the smaller and thinner structures. The external cloud motions are best approximated by an exponential velocity distribution, with a root-mean-square velocity of 7 km/sec in one coordinate. Internal motions within the clouds probably have Gaussian distributions, with velocity dispersions ranging from o·6 to possibly 7 km/sec; part of these may be due to non-thermal mass motions.
On Petschek's mechanism for dissipating interstellar magnetic fields
Authors: Wentzel Donat G.
Published: July 2016

Petschek's solution for the hydromagnetic flow at a magnetic neutral plane is applied to the interior of interstellar clouds. The stationary flow between the opposed magnetic fields involves a streaming speed of about 3 km/s and a gas density of roughly 102atoms/cm3. At most one-tenth of all the gas resides in these streams, but their low temperatures should make them observable in absorption at 21 cm; they may even dominate the interstellar absorption lines of Ca+and of Na, since the abundance of these absorbing ions, proportional to the recombination rate of the dominant ions with electrons, depends on the square of the gas density. Optical and 21-cm lines may, therefore, represent somewhat different samples of the interstellar velocity and density distributions.

In analogy to the geomagnetic field, which is separated from the interplanetary field, interstellar clouds may be separated from the general galactic magnetic field. Such magnetic bubbles can move through the galactic field without twisting it, but they can maintain their identity only if they contain a twisted magnetic field. This field leads to the operation of Petschek's Mechanism and makes these clouds prominent in the optical absorption lines. A full evaluation of Petschek's Mechanism must involve some plasma instability to reconnect the lines of force.

Details of this work have appeared elsewhere (Wentzel 1966).
Direct transformation of magnetic-field energy into energy of fast particles
Authors: Syrovatskii S. I.
Published: July 2016

There are two distinct but as it seems strongly connected problems. The first is the surprisingly rapid dissipation of magnetic fields which is observed in the Sun's atmosphere and must be supposed for some other objects as well. The second problem is the acceleration of fast particles in magnetized cosmical plasma.
The Maryland-Green Bank galactic 21-cm line survey
Authors: Westerhout Gart
Published: July 2016

A strip of 2° width along the galactic equator is being surveyed with an angular resolution of 0°·2 and velocity resolution of 2 km/sec.
Narrow-band observations of neutral hydrogen in galaxies
Authors: Davies R. D.
Published: July 2016

From a survey with 50 kHz bandwidth, a correlation between H 1 and H 11 regions in M 31 is suggested; the SW companion appears connected to the main body of the system. In M 33 the distribution of hydrogen is asymmetric with respect to the major axis.
Ionized hydrogen in the Galaxy and in other galaxies
Authors: Burbidge E. Margaret
Published: July 2016

This review summarizes data obtained by various methods, both optical (in particular: slit spectroscopy and filter photography, including interferometric techniques) and radio-astronomical (continuum studies as well as those of the recombination lines). It deals with the space distribution of H 11 regions, in terms of: degree of concentration to a galaxy's center, spiral pattern, layer thickness, correlation with dust, and treats their total mass and average size. It further discusses velocities of ionized hydrogen in comparison with those of neutral hydrogen, and with special attention to departures from circular motion. Finally, it considers the various determinations of electron temperature and their discrepancies. These items are discussed for both galactic and extragalactic H 11 regions, and distinctions are made according to galaxy type.
A radio method of searching for fine structure in H 11 regions
Authors: Slee O. B.
Published: July 2016

Fine structure with a scale size of about 10-3pc in the galactic ionized hydrogen may scatter the low-frequency radio emission of extragalactic sources with intrinsically small angular diameters, thus making them apparently large. For example, application of the Chandrasekhar scattering formula to a path length of 100 pc through an H 11 region with an average electron density of 0·1 cm-3, and structure of scale size 10-3pc filling 1% of the volume, results in a scattering to half-brightness points of 8″ (arc) at 38 MHz. Radio sources with apparent angular sizes of this amount should be partially resolved by an interferometer with an effective baseline of about 10 000 wavelengths.
Interstellar gas in the central region of the Galaxy
Authors: Kerr F. J.
Published: July 2016

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.

Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.
Upper limits on the galactic halo at 234 MHz
Authors: Burke B. F.
Published: July 2016

Preliminary analysis of a survey at galactic latitudes -20°, -30°, and -40° indicates an upper limit of 30° K (antenna temperature) for the halo.
Supernova remnants
Authors: Minkowski R. L.
Published: July 2016

The brightness distribution of the remnant of Tycho's Nova, which Baldwin has shown in Paper 56 (Figure 6), and the distance of 5000 pc determined by Menon and Williams (unpublished), establish beyond doubt a diameter of 10·8 pc and an average velocity of 13 300 km/sec. The initial velocity must have been higher. The light-curve leaves no doubt that Tycho's Nova of + 1572 was a supernova of type I; for this type velocities of expansion of 20 000 km/sec or more are indeed suggested by the appearance of the spectra around maximum. The faintness of the optical remnant is easily understood as a consequence of the temperature of the order of 1010°K, which must reign behind a shock-front moving with a velocity of the order of 20 000 km/sec. Application of Sedov's similarity solution for a strong explosion gives a total initial energy of about 3 × 1051erg. If one third of this was kinetic energy, the ejected mass was 0·25 solar masses.
Radio-frequency emission from supernova ejecta
Authors: Colgate S. A.
Published: July 2016

A new mechanism is proposed for non-thermal radio emission, which depends upon the scattering of photons within an unstable counter-streaming plasma. This mechanism may play a dominant role in several phenomena:

(i)

the short-wave emission from quasi-stellar sources;

(ii)

the emission from symmetric supernova nebulae in the early stages of the nebular expansion;

(iii)

maintenance or modification of the 3 °K black-body background radiation of the Universe.
On the nature of the galactic halo
Authors: Biermann L.
Published: July 2016

The physical arguments for the existence of a galactic halo, as reviewed by Ginzburg in Paper 61 and by Ginzburg and Syrovatskij in Paper 71, have changed little in recent years. The observational evidence, according to the reports at this Symposium (Baldwin, Paper 56, Section 4; Burke, Paper 59; Mills, Paper 60; Discussion, Paper 63), has become more ambiguous than it appeared to be in the years following Baldwin's first work. While some observers still find indications for a halo not too different from the one originally proposed, others see little evidence in their data for its existence. In this situation it is natural to turn to other galaxies of similar type, of which some dozens have been observed with the necessary resolution. Of these, only M 31 shows enhanced emission (possibly of spotty character) out to distances comparable with its radius, while in a number of other galaxies no evidence for such emissions has been found so far.
The Effect of Silicon and Carbon opacity on ultraviolet stellar spectra
Authors: Gingerich Owen , Latham David
Published: July 2016

Silicon and especially carbon bound-free absorptions considerably reduce the emergent flux in the ultraviolet for stars near spectral type A0 (Teff = 10000 K). An overabundance of silicon and/or an underabundance of carbon can affect the Balmer discontinuity and the Paschen continuum by a few per cent at most. However, the abundances of these ultraviolet absorbers will have little effect on the temperature distribution calculated for a star if the model is chosen to match the visual spectrum. An examination of the ultraviolet spectrum of Sirius shows that still more opacity is needed; part of this absorption can be supplied by line blanketing.
On ultraviolet fluxes, bolometric corrections and effective temperatures of late B to F stars
Authors: Davis John , Webb Robert J.
Published: July 2016

Observed ultraviolet fluxes have been compared with the predictions of line blanketed model atmospheres for stars of spectral type later than B5. The comparison reveals significant differences which increase towards later spectral type and which lead to differences between empirical and theoretical bolometric corrections. Empirical bolometric corrections for the spectral range B8–F5 have been computed from a combination of ultraviolet, visual and infrared observational data. These have been used to derive empirically based effective temperatures for five A and F type stars for which angular diameter measurements are available.
Preliminary note on the astronomical satellite Kosmos 215
Authors: Dimov N.
Published: July 2016

The astronomical satellite Kosmos 215 was launched in April 1968 to examine ultraviolet and X-ray stellar radiation. During a period of 40 days the spectral region from 1250 Å to 2700 Å was recorded by 7 photon-counters and photomultipliers mounted in the focal planes of similar telescopes with apertures of 70 mm, fields of view 1° and focal ratios about ⅓. The optical axes of all the telescopes were parallel. The satellite was not stabilized but special damping was used to reduce the rotational velocity to 0°.12 sec−1. The optical telescopes scanned the sky and recorded all stars which crossed their fields of view.
Interstellar molecular hydrogen
Authors: Solomon Philip M.
Published: July 2016

The dominant photodissociation process for H2 under interstellar conditions is absorption in the lines of the ultraviolet Lyman bands at 912 Å < λ < 1108 Å and re-emission into the continuum at λ ~ 1600 Å. It is shown that 40% of all upward transitions in this band lead to emission into the continuum of the ground state and therefore dissociation of the molecule. The photodissociation rate is calculated and the theory is developed for the abundance of interstellar H2. It is shown that interstellar space will be divided into atomic and molecular regions in a manner analogous to the division between Hii and Hi regions. The molecular regions will exist only where the rate of formation of H2 is sufficiently great to build up a self-shielding layer. This is expected in cold clouds with number densities greater than 100 atoms cm−3. Normal regions of interstellar space will have an extremely small abundance of molecular hydrogen.
The chemical composition of the atmosphere of Venus
Authors: Vinogradov A. P. , Surkov Yu. A. , Andreichikov B. M. , Kalinkina O. M. , Grechischeva I. M.
Published: July 2016

The chemical composition sensors on the Venera-4, -5, and -6 spacecraft are described. The mixing ratio by volume of carbon dioxide is determined to be 97 (+3, −4)%; nitrogen, less than 2%, oxygen, less than about 0.1%; and water vapor at the 25 °C temperature level, on the order of 10 mg/l, an amount large enough to imply that the clouds of Venus are composed of condensed water.
Some consequences of critical refraction in the Venus atmosphere
Authors: Snyder Conway W.
Published: July 2016

Mariner V and the three successful Venera probes have shown the density of the atmosphere of Venus to be so high that critical refraction occurs at an altitude near 35 km. Somewhat bizarre optical effects are to be expected in such an atmosphere. Using a spherically symmetric model based upon the measurements of the refractivity at the top of the atmosphere by the Mariner V S-band occultation experiment, the Venera 4 data in its altitude range, and adiabatic extrapolation to the surface, calculations of a variety of ray paths have been made with a double-precision computer program. Phenomena discussed include the magnification of the planet, the elevation of the horizon, the apparent motion and distortion of the sun, and the possibility of ‘seeing’ completely around the planet.
Ultraviolet polarization measurements of Mars and the opacity of the Martian atmosphere
Authors: Ingersoll Andrew P.
Published: July 2016

Ground-based polarimetric data taken near maximum elongation are presented. These data are analyzed assuming an optically thin, Rayleigh scattering atmosphere, and a surface whose polarization varies inversely as the surface albedo. The best fit to the data yields an optical depth for Rayleigh scattering corresponding to a surface pressure of 6 ± 1 mb, if carbon dioxide is the principal constituent. There is no need to postulate the existence of fine dust in the Martian atmosphere. This method is potentially capable of resolving elevation differences on the Martian surface.
An interpretation of the Mars spectrum taken by the Connes
Authors: Kaplan L. D. , Gray Young L. D.
Published: July 2016

Lines of the 2-0 and 3-0 bands of carbon monoxide and (many) bands of carbon dioxide appear prominently in the Connes' Mars spectrum [1]. Five carbon dioxide bands were measured to construct a curve of growth for CO2 lines formed in the Martian atmosphere [2]. A similar curve of growth was constructed for the 2-0 band of carbon monoxide. From these curves, we have computed the rotational temperature of the atmosphere, the surface pressure, and the abundance of CO and CO2. The surface pressure is found to be approximately equal to the CO2 partial pressure, i.e. ps ~ 5 mb. The CO concentration by volume was found to be slightly less than one part per thousand.
The spectroscopic search for water on Mars: A history
Authors: Schorn Ronald A.
Published: July 2016

The discovery of water on Mars is a lot like the discovery of America. Both were done many times by many different people. In both cases many of the ‘discoveries’ were either fictitious or difficult to verify. Regarding the discovery of America, a grammar school teacher of mine once pointed out that Columbus was the effective discoverer of America. After he did it, people believed it was so. More importantly, people began to act on the basis of his discovery.
The latitude variation of water vapor on Mars
Authors: Tull Robert G.
Published: July 2016

Spectra of Mars, centered on the 8200 Å band of H2O, have been obtained using the coudé spectrograph of the 107-inch telescope at McDonald Observatory with reciprocal dispersion of 1.9 Å/mm. The plate scale (4.4 arc sec/mm) and angular resolution (3″–6″) were sufficient to measure the strength of the Doppler-shifted H2O lines at 5 points across the disk.

The spectra were obtained in March and April 1969, when the apparent diameter of Mars was 10″ to 16″ during mid-summer of the northern hemisphere; the Doppler shift at 8200 Å varied from –0.42 Å to –0.28 Å. On the first plate, obtained on March 27, 1969 the abundance reached a maximum of about 48 μ precipitable H2O at 30° to 40° north latitude and decreased to about 20 μ at 30° south latitude. The second plate, taken on April 28, 1969 showed the same north-south decrease in abundance but the total amounts were about two-thirds of the March abundances.
CO2+dayglow on Mars and Venus
Authors: Dalgarno A. , Degges T. C.
Published: July 2016

Quantitative calculations are presented of the intensities of the CO2+bands present in the dayglows of Mars and Venus and it is argued that fluorescent scattering by CO2+ions and photoionization of CO2are the main sources of excitation. An estimate is made of the intensity of 3914 Å emission that would arise if the atmosphere contained N2.
Phase behavior of light gas mixtures at high pressures
Authors: Streett William B.
Published: July 2016

If solid surfaces exist beneath the visible clouds of the major planets, they may be expected to exist at depths and pressures at which the component gas mixtures solidify under their own weight. The elucidation of phase behavior in mixtures of light gases at very high pressures is therefore essential to the solution of the problem of deep atmosphere structures in these planets. Available experimental evidence suggests several possible extrapolations of the H2-He phase diagram to high pressures. These have been used to develop a structural model for a H2-He atmosphere. In this model, gravitational separation of coexisting phases results in a layered structure, and it is shown that masses of H2-rich solid can exist in dynamic and thermodynamic equilibrium with a fluid layer of equal density but higher He content. This model forms the basis of a new hypothesis for Jupiter's Red Spot.
Estimate of the H2 abundance in the atmosphere of uranus from the pressure induced spectrum
Authors: Poll J. D.
Published: July 2016

Theoretical values of matrix elements of the quadrupole moment (Birnbaum and Poll, 1969; Dalgarno and Allison, 1969) and of the polarizability of H2 (Birnbaum and Poll, to be published) are used to calculate the integrated intensities of a number of lines in the pressure-induced overtone spectra of molecular hydrogen. These calculated intensities are used to obtain an estimate of the H2 abundance in the atmosphere of Uranus from the equivalent width of a feature in the 4-0 pressure-induced band observed by Giver and Spinrad (1966). An estimate of the equivalent width of the corresponding bands on Jupiter is also given.
Investigation of the Power of Resolution of a Spark Chamber for Gamma-Ray Astronomy
Authors: Mayer-Hasselwander H. A. , Pinkau K. , Schenkl K. H. , Voges W. , Schneider H. J.
Published: July 2016

The registration of gamma rays in a spark chamber has been simulated by Monte-Carlo-calculation technique. The spark chamber pictures of these gamma-ray events having a known energy and direction of incidence have been analysed for determinability of direction of incidence. The values obtained for angular resolution depending on energy are compared with values derived by other authors.
Instrumentation for the Measurement of High Energy Phenomena on NASA Spacecraft
Authors: Opp Albert G. , Roman Nancy G.
Published: July 2016

High energy astrophysical observations supported by the National Aeronautics and Space Administration will be conducted primarily from the Small Astronomy Satellites (SAS) and the High Energy Astronomy Observatories (HEAO). At the present time, three Small Astronomy Satellites have been approved for flight. The first (SAS A) will carry a set of collimated proportional counters to conduct a high sensitivity, high spatial resolution, all sky survey for X-ray sources, to search for temporal variations in the source intensity, and to measure the spectral distribution of sources in the energy range 1 to 20 keV. The spacecraft will carry two collimator systems of 1 by 10 deg and 10 by 10 deg fullwidth. The proportional counters are gas-filled beryllium window tubes. SAS A is planned for launch in late 1970.
A Large Area Thomson-Scattering Stellar X-Ray Polarimeter
Authors: Novick R. , Wolff R. S.
Published: July 2016

An instrument for measuring the polarization of stellar X-ray emission has been designed, constructed, and tested. The polarization dependence of incoherent Thomson scattering in lithium metal is utilized. Means for suppression of cosmic ray background effects have been provided. The apparatus has been flown in rockets to obtain data in the polarization of X-ray sources in Sco X-1 and Tau X-1.
Rocket Prototype of An X-Ray Optical System for Surveying and Locating Cosmic X-Ray Sources
Authors: Fisher P. C. , Acton L. W. , Catura R. C. , Kirkpatrick P. , Meyerott A. J. , Roethig D. T.
Published: July 2016

The characteristics of an X-ray detection system based on an array of parabolic reflectors that provide a line-shaped focus will be described. The most recent rocket instrument has an overall length of about two meters and utilizes a pair of thin-window gas-flow proportional counters for detecting the X-rays. The variation of effective aperture with X-ray energy, the amount of scattering from the mirror surfaces, and the quality of the optical focus will be discussed. Estimates of the sensitivity of a larger set of X-ray optics used as a survey system, and when combined with a special grating to form a spectrograph, will be presented.
An Automatic Stabilized Detection System for Measuring Soft Celestial X-Rays
Authors: Den Boggende A. J. F. , Van Beek H. F. , Brinkman A. C. , Lafleur H. Th. J. A.
Published: July 2016

In order to observe celestial X-ray sources an instrument is under development to be launched in the Astronomical Netherlands Satellite (ANS) in 1974. The aim of the experiment is to measure the spectral distribution of the sources. If there is some evidence that a source should be a pulsar the instrument can be switched from the normal mode to the pulsar mode. In this latter mode the detected photons are labeled in time using an on board clock. The ANS will have a pointing mode and a slow scanning mode. The maximum observing time per orbit for one object will be about 2000 s.
The Use of Silicium Solid-State Detector in Solar X-Ray Measurements
Authors: Valniček B.
Published: July 2016

The silicium solid-state detector has been used as control-detector in the X-ray photometer system on board of the satellite Interkosmos 1.

The effectiveness of the use of such detector as control-unit for radiation-belts has been confirmed also as independent indicator of high energy X-ray quants during high levels emission of solar active regions.
Reflectors and Polarizers for the Vacuum Ultraviolet
Authors: Feuerbacher B. , Fitton B.
Published: July 2016

The reflectance of aluminium films has been determined with films free of contaminating layers (Feuerbacher and Steinmann, 1969.) It has been shown that the reflectance of smooth aluminium films is 91% at the Lyα line. The influence of the surface plasmon excitation has also been investigated. This shows up as a dip in the reflectance if the film is not perfectly smooth. It imposes stringent requirements on the polishing of mirror substrates if optimum reflectance is required in the 1200–1700 Å region, since the influence of the surface plasmon is caused by surface roughness of lateral dimensions less than 1000 Å.