bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass Loss from Stars
Authors: Pottasch S. R.
Published: July 2016

In this summary we shall attempt to evaluate the mass loss from several kinds of high luminosity stars, especially planetary nebulae, OB supergiants and M giants and supergiants. The purpose is to give an observational basis for the discussion of the mechanism of mass loss and of the consequences of stellar mass loss for the interstellar medium and for stellar evolution. For reasons which will presently be discussed, we are now certain that mass loss is occurring in all the objects mentioned, and probably to a similar extent in all high luminosity stars as well. The precise values of the mass loss rate are uncertain at present; for some objects the uncertainty will be large (two orders of magnitude) and have important influence on the consequences of the mass loss. Therefore we shall discuss in some detail how the different loss rates quoted in the literature have been obtained and what assumptions have been made (see also the Report by Boyarchuk, p. 281). On the basis of this discussion we will indicate the most probable loss rates and their consequences, always remembering the possible influence of the uncertainties.
Discussion following the Reports by Pottasch and Boyarchuk
Authors: Weymann R. , Kaplan S. A.
Published: July 2016

This Discussion contains the remarks made during the discussion after Boyarchuk's Report on Tuesday, September 16, and about half of the remarks made in the discussion after the Reports on Sunday, September 14. The other half of the latter discussion is presented in Chapter 18. At the end of the Session on Tuesday Thomas asked Busemann to comment on the interrelation between aerodynamics and interstellar gas dynamics. Busemann's response has been transferred to the Final Discussion (Chapter 27). Some general comments by Goldsworthy have been moved to Chapter 5, Section 6.
Discussion following the Reports by Greenberg and Stecher
Authors: van de Hulst H. C.
Published: July 2016

The material of this Discussion has been rearranged in five sections: 1. Grain Orientation; 2. The Diffuse Galactic Light; 3. The Extinction Curve in the Far UV; 4. Formation and Destruction of Grains; 5. The OH Molecule. Except for rearranging, very few changes have been made.
The Neutral Hydrogen Distribution in Spiral and Irregular Galaxies
Authors: Davies R. D.
Published: July 2016

An investigation of several nearby and irregular galaxies shows significant changes in the neutral hydrogen distribution with morphological type. M31, an Sb, has a central hole while M33, an Sc, has relatively a much smaller hole or no hole at all and NGC 6822, an irregular galaxy, is centrally concentrated. The Hii regions in all these morphological types are found in the regions of highest neutral hydrogen density.
Do Galaxies Evolve Along the R – ω Sequence?
Authors: Saslaw William C.
Published: July 2016

The stellar contents of Sb and Sc galaxies do not appear to be related to their rotation properties. This lack of correlation suggests that the position of a galaxy on the R – ω sequence is determined to a large extent by the environment in which the galaxy formed, rather than by subsequent evolution.
Classification of Compact Objects: QSS, QSOs, N-Type and Compact Galaxies, Seyfert and Galactic Nuclei
Authors: Morgan W. W.
Published: July 2016

Some methods currently in use for the classification of the optical forms of the ‘compact’ galaxies and quasi-stellar objects are reviewed. It is shown that the category ‘Seyfert Galaxy’ is basically a spectroscopic (rather than a form) classification.

An optical form-classification is described which is, in principle, identical with published classification criteria for QSO, N-type, and compact objects. The importance of maintaining rigid form-standards is emphasized.
Astrophysical Statistics of 745 Compact Galaxies Near the Galactic North Pole
Authors: Richter L. , Richter N. B. , Schneller P.
Published: July 2016

A brief description is given of methods used to find 745 compact galaxies in a 36 sq deg-field around M3. These constitute 24–40% of all galaxies in this area, brighter than 18.5 magnitude in B. Significant clustering found is related to Zwicky clusters of compact galaxies. Photographic 3-color photometry has been carried out. There seems to be no physical difference between cluster and field objects. The catalogue is to be published elsewhere, together with finding charts and detailed discussion of the photometry and statistics.
Optical Spectra of Compact Objects
Authors: Burbidge E. M.
Published: July 2016

On the basis of their optical spectra, compact objects are divided into 3 classes according to the probable nature of their energy sources, as follows:

(1)

Non-thermal: This class includes Seyfert nuclei, most N-type radio galaxies, and also very luminous Zwicky compact objects. The existence of high-velocity clouds, and a wide variety of densities and temperatures appear to be common characteristics of these objects. QSOs are considered to be related, with similar but more extreme properties.

(2)

Hot, massive stars: This class includes some small galaxies, parts of galaxies or appendages to galaxies, which are usually much less luminous than class (1) objects.

(3)

Stellar: Some compact galaxies having only absorption line spectra fall into this class.

A variety of morphological forms exists amongst class (1) and (2) objects.

Emission line spectra of QSOs are reviewed, and related to the physical conditions in the emitting regions.
The Luminosity-Volume Test for Quasi-Stellar Objects
Authors: Longair M. S.
Published: July 2016

(Abstract of a paper by M. S. Longair and P. A. G. Scheuer (1971))
Intergalactic Matter and Radiation
Authors: Burbidge G. R.
Published: July 2016

This paper presents a critical discussion of our present knowledge of intergalactic matter and radiation as it relates to cosmology. While there have been some observational successes and much theoretical speculation, studies of intergalactic matter and radiation have still not allowed us to draw certain conclusions about the origin and evolution of the universe.
On Establishing an International Service for Cometary Observations and Ephemerides
Authors: Candy M. P.
Published: July 2016

I agree entirely that there is a need for such a service. As the proposal has come from the Institute for Theoretical Astronomy, is it intended that the service should be organized from there? Consideration should be given to having subsidiary centres with identical information available on request – as for the double-star service.
The Motions of Bodies Close to Commensurabilities with Jupiter
Authors: Sinclair A. T.
Published: July 2016

The theory of the libration motion of a body close to a commensurability in mean motions with Jupiter is briefly described, and the importance of such motions in that they enable the body to avoid close approaches to Jupiter is discussed. By means of numerical integrations of the equations of motion some of the work that has been done on librations in orbits of low eccentricities is extended to higher eccentricities, so that the results can be applied to cometary orbits. By making some approximations the results are expressed in a very simplified form which makes it possible to compare the sizes of libration regions. This is done for six interior commensurabilities, namely the 3:1, 2:1, 5:3, 3:2, 7:5 and 4:3 commensurabilities.
On the Differential Correction of Nearly Parabolic Orbits
Authors: Herget P.
Published: July 2016

The differential correction of nearly parabolic orbits was discussed by the author (Herget, 1939) in the era of lead pencil computing. The Gauss-Marth method is the best one to use whenever the appropriate conditions exist, i.e., |E| < 64° and e nearly unity. The crucial point in the above-cited discussion is the use of the first differences from the Gauss-Marth tables in order to simplify the computation of the partial differential coefficients, namely dB/dA, dC/dA, and dD/dA.
Investigation of the Motion of Periodic Comet Giacobini-Zinner and the Origin of the Draconid Meteor Showers of 1926, 1933 and 1946
Authors: Evdokimov Yu. V.
Published: July 2016

Orbital elements of P/Giacobini-Zinner have been obtained from 577 observations at the eight apparitions 1900 to 1965 by linking apparitions in pairs. By this technique we established that the comet has a nongravitational secular deceleration amounting, on the average, to 0.081 day/(period)2. As a result of the comet's approach to Jupiter in 1969, a return of the Draconid meteor shower is possible on 1972 October 8d15h45m UT. The 1946 meteor shower was due to meteoroids ejected forward along the orbit of the comet in 1940 with velocities of 14 m s- 1. The meteor showers of 1933 and 1926 were apparently produced by meteoroids ejected in 1900 with velocities of 15.0 m s- 1 forward and 14.5 m s- 1 backward, respectively.
The Motion of Periodic Comet Pons-Brooks, 1812–1954
Authors: Herget P. , Carr H. J.
Published: July 2016

The orbit of P/Pons-Brooks has been studied using the observations of 1812, 1883–1884 and 1953–1954. A curious deviation of the residuals has been established during the last two months of observation in April and May 1884, but no discontinuity in the orbit due to an impulsive action on the comet has been found. The observations covering two complete revolutions cannot be fitted into one single orbit.
Investigation of the Motion of Periodic Comet Stephan-Oterma
Authors: Shmakova M. Ya.
Published: July 2016

The orbit of P/Stephan-Oterma has been determined using 128 observations at the two apparitions (1867 and 1942) and taking into account perturbations by Venus to Neptune. The evolution of the comet's orbit has been studied over the interval 1660–2060.
Determination of Planetary Masses from the Motions of Comets
Authors: Klepczynski W. J.
Published: July 2016

A brief survey is given of past determinations of the masses of the principal planets from analyses of the motions of comets. Some numerical experiments using comets which have close approaches to Jupiter are made. As a result of these experiments, it is concluded that the conventional least squares solution for the correction to the mass of Jupiter is inadequate for comets which have a close approach to Jupiter. It is further concluded that perhaps, in some cases, the apparent presence of nongravitational forces is merely a manifestation of the failure of the conventional orbit correction process to adjust correctly the orbits of objects which undergo very large perturbations, and it also may be a consequence of errors in the adopted planetary masses. It is suggested that the use of partial derivatives obtained through the numerical integration of the variational equations may overcome the difficulties.
The Determination of Jupiter's Mass from Large Perturbations on Cometary Orbits in Jupiter's Sphere of Action
Authors: Kazimirchak-Polonskaya E. I.
Published: July 2016

Necessary and sufficient conditions are formulated for determining the mass of Jupiter from large perturbations induced in cometary orbits in the sphere of action of Jupiter. A procedure for the investigation has been developed and programmed for an electronic computer. Comparison of heliocentric and jovicentric computations shows that the perturbations on P/Wolf could be determined with great accuracy when this comet passed through Jupiter's sphere of action in 1922. The first attempt has been made to determine the mass of Jupiter using this passage and the observations of the comet in 1925. The resulting value for the reciprocal mass is 1047.345.
Some Remarks on the Liberation of Gases from Cometary Nuclei
Authors: Levin B. Yu.
Published: July 2016

According to modern data water ice is the main constituent of cometary nuclei. The rate of its evaporation determines the rate of liberation of other constituents, including those that determine the photometric properties of comets. The estimates of the total mass loss per perihelion passage seem to give values about one order of magnitude smaller than those necessary to explain the nongravitational forces as due to the reactive force of material leaving the nuclei. Thus the conventional explanation of the nongravitational forces deserves further study from the point of view of the physical theory of comets.
Laboratory Simulation of Icy Cometary Nuclei
Authors: Kajmakov E. A. , Sharkov V. I.
Published: July 2016

The problems of laboratory simulation of cometary phenomena are discussed. Results are given of experimental investigations of the thermodynamic parameters of H2O ice and of frozen mixtures of electrolytes during sublimation under conditions of high vacuum and low temperature. At a distance of 1 AU from the Sun the equilibrium temperature of H2O ice is shown to be about −75 °C. Conditions are determined for the formation and disintegration of dust matrices during the sublimation of ices containing small dust particles. Dust particles are shown to leave the surface of the ice in the form of conglomerates of primary particles. The outflow velocities of the particles are found to be as high as several metres per second. The results obtained are discussed in relation to cometary phenomena.
Ejection of Bodies from the Solar System in the Course of the Accumulation of the Giant Planets and the Formation of the Cometary Cloud
Authors: Safronov V. S.
Published: July 2016

The theory of planetary accumulation leads quite definitely to the conclusion that the formation of Oort's cometary cloud is the result of ejection of bodies to the outermost parts of the solar system due to encounters with the giant planets during their growth. Uranus and Neptune could have grown to their present dimensions only if the initial mass of solid material in their zones were substantially larger than that of these planets. The relative velocities of the bodies were increased through perturbations by the planetary embryos, and on reaching the escape velocity they would start to be ejected. Our concept of this process differs from that suggested by Öpik by the assumption that Jupiter and Saturn accreted hydrogen, not in solid but in gaseous state, and by the introduction of a more effective mechanism for the interaction with several embryos. In their final stages the embryos ejected amounts of mass an order of magnitude higher than the amounts accreted. Most of the mass was ejected into interstellar space by Jupiter, but the cometary cloud was created mainly by Neptune. The mass of the cloud is estimated to be about three times that of the Earth.
Diffusion of Comets from Parabolic into Nearly Parabolic Orbits
Authors: Shtejns K. A.
Published: July 2016

It is assumed that the accumulation of small, independent, random perturbations in the reciprocal semimajor axis of the orbit of a comet follows a normal distribution law whose standard deviation is a function of the inclination and perihelion distance and that for nongravitational forces it is a function of perihelion distances only; it is also assumed that secular accelerations do not change into decelerations, and vice versa. The standard deviations given by diffusion theory are in good agreement with the mean values of nongravitational impulses obtained from calculations from short overlapping arcs. The mean lifetime of a comet is found to be one hundred revolutions. To explain why many more near-parabolic comets are actually discovered than are theoretically expected the existence of comets of very short lifetimes must be accepted.
The Origin and Evolution of the Comets and Other Small Bodies in the Solar System
Authors: Vsekhsvyatskij S. K.
Published: July 2016

It has become evident that comets and other small bodies are indications of eruptive evolution processes occurring in many of the planetary bodies of the solar system. The total number of near-parabolic comets moving in the solar system is 1011 to 1012, but as many as 10 to 15 percent of them are leaving the solar system with hyperbolic velocities. Taking into account also the number of short-period comets that degenerate into asteroids and meteor streams, we have estimated the total number of comets formed during the lifetime of the solar system as 1015 to 1016 (and total mass 1029 to 1031 g). The investigation of comets and other small bodies enables us to evaluate the scale of the processes of cosmic vulcanism and the tremendous internal energy of the planets, that energy being derived from the initial stellar nature of planetary material.
Évolution séculaire des orbites de particules météoriques
Authors: Delcourt J.
Published: July 2016

We study the secular evolution of the orbit described by a meteoric particle moving under the influence of planetary perturbations and the Poynting-Robertson effect. Using a simplified model, this study is made with only one disturbing planet. We present preliminary results on the long-term variation of the osculating elements of the orbit.
Statistics of the Orbits of Meteor Streams and Comets
Authors: Lebedinets V. N. , Korpusov V. N. , Sosnova A. K.
Published: July 2016

From radar observations carried out during 1967–1968 a catalogue of 20000 orbits was obtained. A method has been developed for identifying meteor streams and associations, and the orbits of the meteors recorded during January–April 1968 have been analysed. Among them 163 streams have been identified, and these contain 33.5% of the total number of orbits. Comparison with the orbits of the short-period comets of q <1.1 AU shows considerable differences.
On the Dividing Line between Cometary and Asteroidal Orbits
Authors: Kresák L.
Published: July 2016

A simplified form of the Jacobi integral in the three-body system Sun-Jupiter-comet or asteroid provides an excellent method for discriminating between cometary and asteroidal orbits. Omitting the librating bodies, unambiguous separation is obtained for all known objects with reliable orbital data, i.e., about 600 comets and 1800 asteroids. The only exception is the peculiar asteroid 944 Hidalgo – which is presumably a comet. The intermediate region is occupied exclusively by bodies revolving in resonance with Jupiter, and the value of the libration argument yields a sharp secondary criterion in these cases. Besides the direct perturbational capture of long-period comets from high-eccentricity orbits into Jupiter's family, a ring of nearly circular orbits between Jupiter and Saturn is suggested as another significant source of short-period comets. For these comets the subsequent operation of nongravitational effects gives a better chance of injection into small orbits of the Apollo type and for the formation of short-period meteor streams. Some phenomena (the outbursts of P/Schwassmann-Wachmann 1, the probable recent splitting of one parent body into P/Whipple and P/Shajn-Schaldach) give reasons for speculation about the population of this region, too distant for the discovery of typical asteroids or comets, by interplanetary particles up to sizeable solid bodies.
Dynamics of the Crab Nebula
Authors: Trimble Virginia
Published: July 2016

Studies of the proper motion of many filaments in the Crab Nebula show that the expansion centre does not coincide with the present position of the pulsar NP 0532. Possible reasons for this difference are discussed. Estimates of the turbulent velocity within the nebula indicate that it lies in the range 100 to 300 km sec-1. An analysis of the present expansion rate of the nebula indicates a convergence at 1140 ± 10 AD. The acceleration implied in this result could arise from magnetic or relativistic electron pressure.
The Electromagnetic Spectrum of the Crab Nebula
Authors: Baldwin J. E.
Published: July 2016

I shall discuss observations of the spectrum of the integrated emission from the Crab Nebula. The radio data with accurate calibrations lead to a flux density spectral index of −0.26. Discrepancies in the published fluxes at millimetre wavelengths can be resolved if appropriate angular dimensions are used. In the optical range the spectral index has increased to a value of −0.9 if 1m.0 of absorption is used. At X-ray wavelengths the spectral index has increased further to −1.2.
Upper Limit of the X-Ray Polarization of the Crab Nebula
Authors: Novick R. , Angel J. R. P. , Wolff R. S.
Published: July 2016

A rocket-borne X-ray polarimeter was flown to search for polarization in Taurus X-1. Although a result consistent with zero polarization was obtained, the statistics were such that X-ray polarization comparable in magnitude and direction to that of radio and optical continuum emission cannot be excluded.
Equilibrium Problem in a Rotating Convection Zone
Authors: Vandakurov YU. V.
Published: July 2016

Taking into account effects produced by the convective motions, the equilibrium problem for a rotating star becomes greatly complicated. We consider this problem for the case of slow rotation in the following approximations.

We treat the convection zone as a medium with turbulent viscosity and turbulent thermal conductivity. However, we take into account the nonlinear effects produced by the most rapidly growing perturbations. The corresponding nonlinear terms are calculated by using the solution of linear perturbed equations. Each independent convective mode is supposed to have initially the same amount of kinetic energy.

In the limit of small turbulent viscosity, we show that unstable convective perturbations produce a mean azimuthal force due to which rigid rotation appears not to be in the equilibrium. For the case of small-scale perturbations and latitudinal differential rotation, this force is analogous to the viscous force, but the coefficient of viscosity is negative.

We suggest that such a force maintains the differential rotation of the solar convection zone. Note that in the case under consideration the latitudinal dependence of the solar heat flux is small. However, difficulties arise due to different conditions at different depths in the convection zone. In this connection, a hypothesis is put forward that magnetic fields are also necessary to get balance in full. A model of the solar cycle is discussed which is similar in some respects to the well-known Babcock model. We propose, however, that the field reversal takes place in the lower layers of that zone where fields are intensified.
Dynamo in the Presence of Differential Rotation
Authors: Vainshtein S. I.
Published: July 2016

It is well know that the ‘dynamo’ theory has a number of vetoes; e.g. axisymmetric, two-dimensional, central-symmetric, etc. dynamo are impossible. In principle, the problem is essentially three-dimensional in any coordinate system. This is the main difficulty of both the theory itself and its possible applications. In fact, one prefers to believe that, for example, a non-rigid body-rotating star or convection in the Earth's nucleus possesses axis symmetry. However, due to the above vetoes one has to add finer effects (Coriolis strength, density, inhomogeneity) to create asymmetrical convection. On the other hand, the authors try to find the most simple movements with minimum deviations from axial symmetry. Thus, the Herzenberg's dynamo (Herzenberg, 1958) is realized by two rotating cylinders, axes of which are parallel to each other (see also Galaitis, 1973; Galaitis and Freinberg, 1974), the Lortz's dynamo-spiral movement (Lortz, 1968; Ponomarenko, 1973). Nevertheless, the mentioned vetoes possess a common feature, the assumption regarding the symmetry extends both to the movement and to the field. Hence, it makes sense to raise a question whether symmetric movements are able to generate an asymmetric field. A positive answer to this question, in particular, is given by Tverskoy's model (Tverskoy, 1966) – the toroidal vortex. The latter possesses axial symmetry. Nevertheless, the toroidal vortex is a complex motion; we will proceed along the path of a minimum simplification.
On Fast Magnetic Field Reconnection
Authors: Priest E. R. , Soward A. M.
Published: July 2016

The first model for ‘fast’ magnetic field reconnection at speeds comparable with the Alfvén speed was put forward by Petschek (1964). It involves one shock wave in each quadrant radiating from a central diffusion region and leads to a maximum reconnection rate dependent on the electrical conductivity but typically of order 10-1 or 10-2 of the Alfvén speed. Sonnerup (1970) and Yeh and Axford (1970) then looked for similarity solutions of the magnetohydrodynamic equations, valid at large distances from the diffusion region; by contrast with Petschek's analysis, their models have two waves in each quadrant and produce no sub-Alfvénic limit on the reconnection rate.

Our approach has been, like Yeh and Axford, to look for solutions valid far from the diffusion region, but we allow only one wave in each quadrant, since the second is externally generated and so unphysical for astrophysical applications. The result is a model which qualitatively supports Petschek's picture; in fact it can be regarded as putting Petschek's model on a firm mathematical basis. The differences are that the shock waves are curved rather than straight and the maximum reconnection rate is typically a half of what Petschek gave. The paper is a summary of a much larger one (Soward and Priest, 1976).
On the Dipole-Like Progressive Wave in the Photosphere
Authors: Csada I. K.
Published: July 2016

Statistical analysis of the photospheric magnetic field averaged over 27 day time intervals shows periodical variations. The results of such an analysis are usually considered to be a pure mathematical representation of the observation material and additional analysis is necessary to infer the physical meaning of the results. Some ideas for this analysis are given by the mathematical method of the ‘non-axisymmetric dynamo’ theories which suggest the representation of the field by the series

i.e. the field variation is equivalent to the interference of progressive wave moving parallel to the equator with velocity

If n = 1 the variation is equivalent to a progressive dipole field circulating over the photosphere by a time 2π/Ω and this period can be derived from the 27-day averages. The superimposition of the circulation to the rotation will result in the apparent ‘field rotation’ being observable as recurrence time of the largest magnetic areas. Observational evidences are found for a progressive dipole circulating in a great circle with a period of 4⅙ yr.

The higher multipole field components (if n ≥ 2) have no characteristic variations but their mean effect results in statistical spread in the ‘multipole field rotation’.
Ultraviolet Spectrophotometry of Early-Type Stars
Authors: Nandy K. , Thompson G. I. , Humphries C. M.
Published: July 2016

The ultraviolet spectra of B stars obtained with the sky scan telescope in the TD1 satellite have been used to obtain narrow-band magnitudes at several wavelengths. These photometric bands have an effective half-width of 100 Å. We have proposed a two-dimensional classification scheme based on ultraviolet colours, and some preliminary results are presented.
Abundances in the Galactic Clusters of Hyades and M 67
Authors: Foy R.
Published: July 2016

Two Hyades dwarfs and two giants in the old galactic cluster M 67 have been carefully analyzed from 7 å mm−1 taken at OHP with an electronic camera. Measurements of weak lines lead to € the conclusion that both these clusters have a solar chemical composition, although they have very different ages.
Molecules in star formation
Authors: Shu F.H.
Published: July 2016

We review current ideas and models in the problem of star formation from molecular cloud cores that are relatively isolated from the influences of other forming stars. We discuss the time scales, flow dynamics, and density and temperature structures applicable to each of the four stages of the entire process: (a) formation of a magnetized cloud core by ambipolar diffusion and evolution to a pivotal state of gravomagneto catastrophe; (b) self-similar collapse of the pivotal configuration and the formation of protostars, disks, and pseudo-disks; (c) onset of a magnetocentrifugally driven, lightly ionized wind from the interaction of an accretion disk and the magnetosphere of the central star, and the driving of bipolar molecular outflows; (d) evolution of pre-main-sequnce stars surrounded by dusty accretion disks. For each of these stages and processes, we consider the characteristics of the molecular diagnostics needed to investigate the crucial aspects of the observational problem.
Mixing layers in flows in star forming regions
Authors: Raga A. C. , Cantó J.
Published: July 2016

There are now many observations of high velocity, molecular emission associated with outflows from young stars. This emission might come from molecules that are formed in the outflowing material, or from entrained, ambient molecular gas. The present paper explores the latter possibility, describing the efforts that have been made to model the “lateral entrainment” that occurs in the turbulent mixing layer formed along the edges of a jet-like flow (or, equivalently, at any interface between a fast moving flow and the surrounding environment). A simple, analytic approach based on model equations is used to provide a qualitative picture of the dynamical, thermal and chemical structure of such a turbulent mixing layer. Finally, a review of the efforts up to date of modelling the dynamics and chemistry of turbulent mixing layers is presented.
Photon-dominated and X-ray dominated regions
Authors: Sternberg A. , Yan Min , Dalgarno A.
Published: July 2016

A brief account is presented of the chemical characteristics of regions controlled by the absorption of X-rays. Recent studies of the infrared emission from molecular hydrogen and time-dependent effects in evolving photon-dominated regions are summarized.
Dark cloud observations: Problems and progress
Authors: Minh Y. C.
Published: July 2016

Interstellar dark clouds have provided a laboratory which has been successfully used to identify a number of species, perform high resolution spectroscopy, and characterize the processes in the interstellar medium. We have successfully solved a number of problems and achieved significant progress through dark cloud observations. With the improvement of observing techniques and theories, however, we are now having new problems and are waiting for further progress. The dark clouds, because of their quietness and large column densities, still provide a very useful testing ground of many uncertain interstellar processes. Here we summarize some of the recent progress made in dark cloud observations and discuss related problems. We focus especially on the importance of nearby objects, possible signs of gas-grain interactions in dark clouds, and further sensitive observations.
Reactions between neutral species at low temperatures: Laboratory results and astrophysical modelling
Authors: Smith Ian W.M.
Published: July 2016

Over the past few years, rate coefficients (k) have been measured for neutral-neutral reactions at low (down to 80 K) and ultra-low (down to 13 K) temperatures (T). The experimental methods and the results which have been obtained are reviewed. A surprisingly large number of reactions become faster at lower temperatures and have rate coefficients close to the collisional value below ca. 50 K. The factors which influence the form of k(T) are briefly discussed and proposals are made as to how rate coefficients might be estimated for use in astrochemical models.
Microprobe two-step laser mass spectrometry as an analytical tool for meteoritic samples
Authors: Clemett Simon J. , Zare Richard N.
Published: July 2016

Microprobe two-step laser mass spectrometry (μL2MS) is a new mass spectrometric method in which the two essential steps of any mass spectrometric analysis, vaporization and ionization, are carried out using two independent laser sources. In the first step, the output of a pulsed infrared laser is focused on the sample to cause rapid heating in the spot area illuminated, which is typically 40 μm by 40 μm. In the second step, the output of a pulsed ultraviolet laser causes (1+1) resonance-enhanced multiphoton ionization (REMPI) of those desorbed neutral molecules that (1) are able to absorb this UV wavelength and (2) whose ionization potential is less than the energy of two photons of this UV wavelength. The resulting ions are then mass analyzed in a reflectron time-of-flight apparatus. Under suitable conditions fragmentation can be avoided in both the vaporization and ionization steps so that μL2MS can be applied to the analysis of a mixture of molecules. Applications of μL2MS to meteorite samples are presented as a means of detecting trace amounts of certain organic molecules present in complex materials without prior sample preparation, extraction, purification, and separation steps. Moreover, this analysis can be carried out with micrometer spatial resolution so that in favorable cases the presence or absence of certain molecules can be correlated to mineralogical features of the sample.
Detection of thermal water vapor emission from W Hydrae
Authors: Neufeld David A. , Chen Wesley , Melnick Gary J. , De Graauw Thijs , Feuchtgruber Helmut , Haser Leo , Lutz Dieter , Harwit Martin
Published: July 2016

We have detected four far-infrared emission lines of water vapor toward the evolved star W Hydrae, using the Short Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). This is the first detection of thermal water vapor emission from a circumstellar outflow.
ISO LWS spectra of AGB and post-AGB objects
Authors: Cox P.
Published: July 2016

We present ISO Long Wavelength Spectrometer (LWS) grating spectra of AGB and post-AGB stars. The LWS instrument and the calibration procedures are described by Clegg et al. (1996) and Swinyard et al. (1996).
Abundant, hot water toward young stellar objects
Authors: Helmich F.P. , Van Dishoeck E.F. , Black J.H. , De Graauw Th.
Published: July 2016

The large amount of water vapour in the Earth's atmosphere makes it extremely difficult to observe water in interstellar space, except under unusual conditions (e.g., masers). The Short Wavelength Spectrometer (SWS; de Graauw et al. 1996) on board the Infrared Space Observatory (ISO) provides an unique opportunity to study the ro-vibrational fundamental bands of water in absorption against bright infrared continuum sources. Such absorption line data have several advantages over emission observations. For example, only a pencil beam to the infrared source is probed, which minimizes the complications due to the small-scale physical and chemical heterogeneity of star-forming regions. In addition, lines from all rotational levels are present within a vibrational band, so that the complete spectrum yields a direct estimate of the level populations and excitation temperature along the line of sight. Other molecules, such as CO, HCN and C2H2, can be observed with the same technique, leading to accurate relative abundances. The main limitation of the ISO-SWS grating is its low spectral resolving power, λ/Δ λ ≈ 1350 at 6 μm, since the lines are intrinsically much narrower. This limits the sensitivity, so that only high column densities can be detected, and complicates the interpretation because detectable lines are often saturated. The low spectral resolution also blends the lines, making it difficult to determine the equivalent widths unambiguously. The ISO-SWS is therefore particularly sensitive to molecules in warm gas with relatively large line widths (Δ V > 3 km s−1).
Theoretical models of diffuse clouds
Authors: Spaans Marco
Published: July 2016

Two-dimensional model calculations for inhomogeneous diffuse and translucent clouds are presented which include line and continuum radiative transfer, thermal balance and chemical equilibrium. The effects of an inhomogeous density distribution on the abundances of chemical species and line maps are discussed. Additional calculations are presented for the fluorescently pumped H2 visual and infrared lines which emanate from spherical diffuse clouds. The results indicate that these lines yield sensitive probes of the ambient cloud density when combined with co-spatial HI observations.
The neutral envelopes around AGB and post-AGB objects
Authors: Olofsson H.
Published: July 2016

The circumstellar gas/dust envelopes of stars on and beyond the asymptotic giant branch harbor an impressive number of different molecular species and their isotopic variants. Some of these molecules are of photospheric origin, but the majority have been produced through various chemical processes in the envelope. This chemistry depends primarily on the chemical composition of the gas (i.e., C/O<1 or >1), but the conditions also change as the central star evolves. In this review we present circumstellar molecular abundance and isotope ratio estimates, and discuss how they can be used in the study of the late evolution of stars, which in extreme cases may become heavily obscured.
Physical properties and kinematics of the molecular gas near galaxy nuclei
Authors: Tacconi L.J.
Published: July 2016

During the last decade there have been enormous steps forward in our understanding of the molecular gas properties of other galaxies, due to the huge increase in sensitivity and spatial resolution of instruments in the millimeter and submillimeter wavelength ranges. In particular, the emphasis has shifted from trying to detect CO in a variety of objects to studying the gas distributions and kinematics in a variety of species and transitions. For nearby galaxies, we are now able to study the physical and chemical processes occurring in the molecular gas over GMC size scales. Here I discuss a few examples of progress made in the study of galaxy nuclei.
Flare Colours and Luminosities
Authors: Cristaldi S. , Rodonò M.
Published: July 2016

Flare colours determined from simultaneous UBV observations made at Catania Observatory and from sequential UBV observations made at McDonald Observatory are presented. They fit fairly well with the theoretical colours computed according to the Gurzadian's (1970) non-thermal model. Only part of the observed flare colours are consistent with the solar type models by Gershberg (1967) and Kunkel (1970).

From a B-band patrol of UV Cet-type stars carried out from 1967 to 1972, some quantitative estimates of flare frequencies and luminosities and of their average contribution to the stellar radiation are given.

The corresponding parameters for the Sun, which were estimated from ‘white light’ flare activity, are also given for comparison. The Sun and V 1216 Sgr can be regarded as low-activity flare stars of the type found by Kunkel (1973).
The R Coronae Borealis Type Variables
Authors: Feast M. W.
Published: July 2016

A general review of the RCB stars is given. The available observations (spectra, photometry (including infrared) and polarization) seem most easily explained by a model in which a cloud of dust is ejected towards the observer at times of deep minima. The large radius changes in the pulsation cycle of RY Sgr suggest a high luminosity. This is also indicated by the RCB stars in the LMC. Theoretical work on RCB stars is briefly reviewed. The possible relation of the variables to the planetary nebulae and the novae is mentioned.
The So-Called Antiflare Stars
Authors: Pugach A. F.
Published: July 2016

There seems to exist a small subgroup of irregular variables with light curves similar to R CrB stars but with a shorter time scale. These stars have small-amplitude light variations around a ‘normal brightness’, but this is interrupted by Algol-like minima of about to at irregular intervals. The duration of the minimum phase is several percent of the total time. While at minimum the variables also show rapid light variation of greater amplitude. Moreover, RZ Psc shows a flare activity, which strongly resembles that of UV Cet stars. The minimum phase is followed by a rapid recovery to the ‘normal brightness’.
Some Statistics of Southern R Coronae Borealis Variables
Authors: Sherwood Vicki E.
Published: July 2016

UBV observations of RCB stars with δ⩽30° were made at La Silla, Chile in the summer of 1972. Of 26 stars, 5 were below maximum brightness, including R CrB and RY Sgr. On the basis of a comparison of the dispersion in observations of the RCB stars and nearby non-variable comparison stars, 9 RCB stars were found to show significant variation at maximum brightness. They are W Men, UX Ant, UW Cen, DY Cen, AE Cir, S Aps, RT Nor, RZ Nor, and V CrA. The amplitude of these variations ranges from to and tentative periods from 19 to 54 days and > 90 days for S Aps. Similar variations at maximum are already known for R CrB, RY Sgr and XX Cam. Of the 5 stars which showed no significant variation at maximum, DZ And, Z Cir and V 973 Oph (see Orlov and Rodriguez, and Feast, this Symposium) are not RCB stars and SY Hyi is a questionable RCB star; only Y Mus is listed as a definite RCB variable.

4 RCB stars in the Large Magellanic Cloud were observed: W Men, SY Hyi, HV 5637, and HV 12842. Absolute magnitudes at maximum of and respectively were derived. When plotted on a colour-colour diagram, most of these stars show an UV-excess for average colours at maximum. In the H-R diagram, they fall in a region where one would expect to find stars which are losing mass.
On the Structure of the Envelope of Nova Delphini 1967 in the Nebular Stage
Authors: Tylenda Romuald
Published: July 2016

The analysis of line profiles in the spectrum of Nova Del 1967 in the nebular stage shows that the polar axis of the envelope is longer than the equatorial one. The polar caps are probably cooler and thinner than the equatorial rings.
Nova Delphini 1967: Radial Velocities and Excitation Potentials of Lines
Authors: Szumiejko E. , Jarzebowski T. , Bartl E.
Published: July 2016

Radial velocities were derived from absorption lines of various excitation potentials; there seems to exist a small dependence on this potential.
Spectroscopic Observations of Nova Cephei 1971
Authors: Rosino L.
Published: July 2016

Spectroscopic observations of Nova Cep 1971 in the visual and infrared regions were carried out at Asiago from July to December 1971. The spectra were characterized at first by the presence of wide emission bands of moderate excitation (H, OI, NI, FeII) accompanied by two absorption systems with mean radial velocity −1300 km s−1 and −2200 km s−1. The velocity was increasing with time. The absorption spectrum disappeared in September and soon the nova entered the nebular stage. The HeI flash was observed in mid-September. In the following months the degree of excitation was steadily increasing. The nebular [OIII] lines became outstanding, even stronger than Hα and the spectrum was characterized by forbidden and permitted lines of relatively high ionization potential (O II, O III, N II, N III, He II).

The profiles of the emission bands were complex from the beginning, with a strong central peak. Later, most of the bands split into two separate components, with radial velocities ± 1360 km s−1.

The light curve was that of a relatively fast nova. The minimum, B∼ 17.5, was attained in the first half of 1973.
Some Photometric Peculiarities of Symbiotic Stars
Authors: Belyakina T. S.
Published: July 2016

The results of UBV photoelectric observations of 12 symbiotic stars have been considered. It must be noted that their light-curves are very different (irregular, regular, of Mira Ceti type) and, in the two-colour diagram (B – V)–(U – B), all these stars are located rather far to the right from the main sequence. The photometric peculiarities of symbiotic stars just mentioned can be explained by assuming that they are binary systems.
Symbiosis in Radio Stars with Infrared Excess
Authors: Ciatti F. , Mammano A.
Published: July 2016

An outline is given of the observing programme of peculiar radio stars with combination spectrum at the Asiago Observatory.
Circular Polarization of Cyg X-1, Sco X-1 and 3C 273
Authors: Severny A. B. , Kuvshinov V. M.
Published: July 2016

An attempt is made to detect polarization from Cyg X-1, Sco X-1 and 3C273.
A Search for Rapid Variables and RR Lyrae Stars in the LMC on ESO Schmidt Plates
Authors: Geyer E. H.
Published: July 2016

This is a very preliminary report about a search for rapid variables in extended fields of the Large Magellanic Cloud.
On the Eclipsing Binaries in the Globular Clusters NGC 3201 and NGC 5139
Authors: Geyer E. H.
Published: July 2016

V 65 is not a member of NGC 3201; there is no certainty about the membership of V 78 to NGC 5139 (ω Cen).
The Period-Luminosity Relation for Red Variables in Globular Clusters
Authors: Russev R. M.
Published: July 2016

Recent data for red pulsating variables in globular clusters are discussed. There seems to exist a period-luminosity relation in the near-by infrared but not in the visual magnitude.
Variable Quasi-Stellar Sources with Particular Emphasis on Objects of the BL Lac Type
Authors: Kinman T. D.
Published: July 2016

The optically variable quasars tend to have steep optical spectra and to show variable polarization; they tend to be associated with compact radio sources which have flat radio spectra at GHz frequencies. Objects are known which have continuous spectra (like BL Lac and OJ 287), but whose other properties closely parallel those of the variable quasars and N galaxies; in fact no sharp distinction can be drawn between them. The variation in the visibility of emission lines in quasars and N galaxies could be due to variations in the strength and spectral index of the radiation from the non-thermal source and from the differences in the amount and disposition of the material around it; it does not seem unlikely that a combination of these factors accounts for the observed range in emission line strength. The systematic difference in optical spectral index between continuous-spectrum objects (and OVV variables) on the one hand and those with emission lines on the other will produce a difference in K term between them, which may be expected to affect their relative distributions with respect to apparent magnitude.
A Survey of Hα in the Brighter Northern Be Stars
Authors: Bidelman William P. , Weitenbeck Anthony J.
Published: July 2016

Hα observations have been made of the stars brighter than mv = 7.5 and north of δ = −30° contained in the three classical Be-star catalogues of Merrill and Burwell. At least one observation of each star was made at each of the two epochs 1958/9 and 1970/2 at the Lick Observatory and at the Warner and Swasey Observatory respectively. The dispersions used were 88 Å mm−1 at Lick and 66 Å mm−1 and 18 Å mm−1 (with image tube) at Warner and Swasey.

Results were as follows: The total number of objects observed was 215. Of these, 32 were supergiants and will be discussed later. Another 16 stars were deemed abnormal in some manner (helium and/or forbidden emission, composite spectrum, markedly violet-displaced Hα emission component: an interesting group of five stars including the nebular variable AB Aurigae). Thirteen of the stars showed no emission at either epoch. Of the 154 presumably normal low-luminosity stars showing emission, 70 displayed shell structure in Hα at one or both epochs, though in over half of these cases the shell absorption was considered ‘weak’. Thirty of the 70 stars varied in their shell characteristics between the two epochs. The total number of stars whose Hα line varied in some respect was 43, or 26 percent of the 167 normal low-luminosity stars observed. Quite a number of the stars observed have been reported to show shell characteristics by others but were not so noted by us.

Eight additional Be stars not contained in the Merrill-Burwell catalogues have also been observed. Seven of these are shell stars; the other is the unusually high latitude object HD 127617.

It is a pleasure to acknowledge that many of the Lick observations were made by Dr Jack E. Forbes, a graduate student at the time in the Department of Astronomy at the University of California, Berkeley.
Rapid Variations of Hα in Be Stars
Authors: Bahng J. D. R.
Published: July 2016

Photoelectric spectrum scans of Be stars were analysed to study the short-term variations of Hα emission strengths. In ζ Tau, α Col, PP Car, and δ Cen, definite variations of a few percent with time scales of 1 to 3 minutes were found. These variations do not exhibit any periodicity.