bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic Approach
Authors: Gail H.-P.
Published: July 2016

A general formalism for describing the radiation transfer in a medium with arbitrary velocity fields is presented. It is demonstrated that classical microturbulence and mesoturbulent models based on Markov processes can be considered as the two lowest order members within a hierarchy of model equations with an increasing degree of approximation to reality. Some preliminary results concerning the relevance of low order model equations are presented.
The Application of Mesoturbulence to Stellar Atmospheres
Authors: Sedlmayr E.
Published: July 2016

For realistic stellar atmospheres the equations describing mesoturbulent line formation are solved numerically. The general dependence of theoretical line profiles and equivalent widths on the correlation length 1 and the mean square turbulent velocity a is demonstrated. Also empirical relations between the basic parameters of the micro-macroturbulence description (vmic, vmac) and the fundamental mesoturbulence parameters (1,σ) are derived.
Some Effects of Strong Acoustic Waves on Strong Spectral Lines
Authors: Gouttebroze Pierre , Leibacher John
Published: July 2016

We have studied the formation of optically thick lines in time dependent, nonlinear hydrodynamic model of the solar chromosphere. Models of the 200 second, chromospheric oscillation indicate that the emission peaks of self-reversed profiles such as those of Mg II and Ca II are formed at very different depths depending on the phase of the oscillation, while the central absorption feature is emitted at a very nearly constant mass depth. The figure shows the Mg II k line emitted by the mean atmosphere, including “microturbulence” (triangles) and the mean profile (squares). In addition to the substantial intensity increase interior to the emission peaks, one should note that the peaks are broadened only towards line center; i.e. the intensity fluctuations are symmetric outside of the peaks and strengthen more than they weaken within the peaks. A more detailed version has been submitted to the Astrophysical Journal.

J.L. wishes to acknowledge support by NASA contracts NASA-3053 and 5-23758.
The Solar Chromospheric Microturbulence and the Emission Observed at Eclipse
Authors: Cuny Y.
Published: July 2016

For a long time there was not a clear interpretation of the fact that the emission observed at eclipse is systematically too high compared with predictions based on disk observations. This discrepancy has been attributed to the hydrogen density, the atomic abundances, or the multiplet excitation temperatures, the physical cause being assumed to be some inhomogeneities. We have shown (Liege 1978, under press) that it can be attributed to the microturbulence. The radiative energy absorbed in the doppler width of the absorption profiles of lines, produces high excitation temperatures. The relative abundances of Ba II, Sr II, Ti II with these excitation temperatures are in agreement with the photospheric abundances.

Assuming photospheric abundances, we get the hydrogen density versus the altitude while the observations give ne ne/Te3/2. The solution of these two equations, taking account of non-LTE for hydrogen but without the assumption of hydrostatic equilibrium, gives a chromospheric model. The model obtained is very near the usual quiet chromospheric models based on disk data.

This work confirms the validity of our assumption of the influence of microturbulence on the chromospheric emission observed at eclipse.
On the Structural and Stochastic Motions in the Solar and Stellar Atmospheres
Authors: Mogilevsky E.I.
Published: July 2016

Existence of discrete structures of velocity and magnetic field in stellar atmospheres follows from the Vlasov’s integral equation

where is a statistical function of the distribution of the elements of matter having masses and velocities, v, dT is elementary phase volume, F is functional which arrange the ties between macrovelocity, magnetic field, temperature, etc., providing self containment of cosmic plasma.
On the Establishment of Internally Consistent Abundance-Oscillator Strength Scales
Authors: Gurtovenko E.A. , Kostik R.I.
Published: July 2016

The method of establishing of internally consistent abundance-oscillator strength scales by using solar fraunhofer lines is elaborated and investigated.

The error of internal accuracy should not exceed 0.05 - 0.06 dex. The absolute accuracy depends on the accuracy of “reference” gf-values.

The oscillator strengths for about 800 Fe I lines are obtained. The comparison of the results for 19 lines common in our and Blackwell et al. (1976) investigations gives the difference log gfblack - log gfauth = Δ = -0.044 ± 0.010. The accidental part of the difference actually determines the internal accuracy of the obtained oscillator strengths.

The Kurucz and Peytremann (1975) oscillator strengths for Fe I lines are analysed. Large systematic errors depending on gf and excitation potential are revealed and investigated. For some lines those errors may change the true values of gf by two orders of magnitude.
Improved Secular Stability Limits for Rotating White Dwarfs
Authors: Durisen R. H. , Imamura J. N.
Published: July 2016

In the special case of the Maclaurin spheroids, it has been known for some time that the m = 2 barlike modes become secularly unstable for t ≡ T/IWI ≥ 0.1376 where T is the total rotational kinetic energy and W is the total gravitational energy of the spheroid. “Secular” here means that the instability depends on dissipative processes and grows on a long dissipative time scale. In particular, the Dedekind-like bar mode, which has zero eigenfrequency at t = 0.1376 as viewed in the nonrotating frame, is unstable due to gravitational radiation (Chandrasekhar 1970).
Evolution of a Degenerate Component in a Close Binary System
Authors: Ergma E.V.
Published: July 2016

Investigation of evolution of a degenerate component (helium or carbon-oxygen dwarf) in a close binary system is rather important. Such dwarfs may be candidates for nova or supernova stars. The first possibility has been studied by several authors (see review paper by Starrfield et al., 1976) and it has been shown that explosive hydrogen burning with enriched CNO abundance in the degenerate envelope of a massive carbon-oxygen dwarf may explain nova phenomena.
Metal Abundances in Hot White Dwarfs: Predictions of the Diffusion Theory
Authors: Vauclair Gérard , Vauclair Sylvie
Published: July 2016

In the course of an exploration of the diffusion processes in white dwarfs, the role of the radiative acceleration has been investigated in detail and found to be quite important in hot white dwarfs (Vauclair, Vauclair and Greenstein, 1979; hereafter referred to as V2G). In view of the increasing interest accorded to hot white dwarfs which become accessible to observations in the ultraviolet owing to satellites like IUE, it appeared quite relevant to obtain theoretical predictions of the effect of the diffusion of metals in hot white dwarfs. This short note is a summary of the results presented in more detail elsewhere (V2G).
Metal Abundances in Cool White Dwarfs and the Diffusion Theory
Authors: Vauclair Gérard
Published: July 2016

In this theoretical review about cool white dwarfs, I will restrict myself to the problem of the metallic content in white dwarf outer layers. The first section will be a short review of what we know about the metal abundances. The hottest presently known white dwarf showing metal in its spectrum is the DB GD 40 (Te = 15 000 K). This temperature will be considered here as the hot boundary of the “cool” white dwarfs. Many efforts have been recently devoted to the understanding of these metal abundances. Section 2 will be a summary of recent calculations of diffusion time scales in both hydrogen and helium white dwarfs. It will be seen that diffusion is so efficient in white dwarf conditions that the convection zone which develops in the envelope as the effective temperature decreases along the cooling sequence is never deep enough to bring back to the surface the metals which had previously diffused downwards. A discussion of the carbon white dwarfs, also called λ 4670 stars, will be presented in section 3. Recent calculations show that the convective mixing between a helium envelope and a carbon core would produce λ 4670 composition for only very special conditions and for this reason we believe that this is an improbable explanation for this type of white dwarfs. We clearly need another physical mechanism to compete with diffusion and to maintain an observable amount of metals in some cool white dwarf atmospheres. We discuss in section 4 the competition between diffusion and accretion. This seems a very promising mechanism in spite of the fact that considerable improvements are still needed in the theory of accretion. Substantial progress has to be made in this direction. A few problems related to this model are invoked in the conclusion.
Spectrum Analysis of the Cool White Dwarfs G 128-7 and G 165-7
Authors: Wehrse R. , Liebert J.
Published: July 2016

The cool white dwarf stars G 128-7 and G 165-7 have a quite different character: While the line spectrum of G 165-7 is the richest of all white dwarfs known, G 128-7 shows only a strong Hα line (Wλ ≈ 5.5 Å) and a much weaker Hβ line (Wλ ≈ 1 Å).
Statistical Investigations of the Luminosity Distribution of the Spectroscopic White Dwarf Sample
Authors: Sion Edward M.
Published: July 2016

In the nine years since Symposium No. 42 at St. Andrews, Scotland, the number of spectroscopically identified white dwarfs has grown from 285 then to over 750 spectroscopic degenerates now. Significant increases in the number and quality of faint star parallaxes and the multichannel spectrophotometry at the 5.1m Hale reflector by Jesse Greenstein has made possible a major breakthrough in the color-luminosity relation for white dwarfs. Of the present sample only ninety-one stars lack measured colors. Over 300 white dwarfs have multichannel colors while over 200 have Strömgren photometry due primarily to Graham (1972), Eggen and Bessell (1978), Wegner (1979), and Green (1977, 1979). Green’s north galactic pole survey of hot white dwarfs will present Strömgren colors for each of several hundred stars in his sample. At the time of this writing it is anticipated that Green’s blue survey will add 500 – 700 new white dwarfs with spectra and measured colors. Thus by the first half of 1980 the spectroscopic white dwarf sample will number between 1300 and 1500 stars.
Four Color Photometry of DB White Dwarfs
Authors: Wegner Gary
Published: July 2016

Observations of 22 DB stars using the uvby photometric system are discussed. In the [(b–y),(u–b)] diagram, these objects define a relatively tight sequence, but the interpretation is hampered by the lack of a precise knowledge of atmospheric element abundances in these stars. The recent models of Koester (1979) show a larger gravity separation for the DB’s using Strömgren photometry and appear to fit the observations better than earlier theoretical results. Due to the tightness of the DB sequence at the hot and cool ends, respectively, there appears to be evidence for restricted ranges in log g and the atmospheric hydrogen abundance.
The Eclipsing Binary System LB3459
Authors: Kilkenny D. , Lynas-Gray A.E. , Hilditch R.W.
Published: July 2016

The extremely blue foreground LMC star LB3459 (= HDE 269696) was reported by Kilkenny, Hilditch and Penfold (1978) to be an eclipsing binary system with a period of 6h17m. Preliminary analysis of uvby photometry and data obtained with the University of Cape Town highspeed photometer (Nather 1973) indicated that the system was composed of two degenerate stars, probably 0-type subdwarfs.
Hydrogen and Helium Burning in the Degenerate Envelopes of C–O Dwarfs
Authors: Ergma E.V. , Tutukov A.V.
Published: July 2016

In our previous papers (Tutukov, Ergma, 1979; Ergma and Tutukov, 1979) we have proposed a simple analytical method to investigate the thermal evolution of shells accreted onto the surface of a neutron star. We have used this method for investigation of thermal evolution of shells accreted onto the surface of a carbon-oxygen white dwarf.
On the Time-Scale for Turn-Off of a Nova After the Outburst
Authors: Starrfield Sumner
Published: July 2016

It is now generally accepted that a nova outburst is caused by a thermonuclear runaway (TR) in the accreted hydrogen rich envelope of a carbon white dwarf. Over the past few years we have studied the evolution of such runaways and have shown that the calculated evolutionary sequences are in substantial agreement with the observations (Starrfield, et. al. 1978; Sparks, et. al. 1978). In the published work we have varied the white dwarf mass, the envelope mass, the accreted envelope mass, and the chemical composition in the envelope (Starrfield, et. al. 1976; Gallagher and Starrfield 1978). In all cases we find that a TR results in mass ejection and the luminosity variations of this ejected material can reproduce the observed light curves of the fast and slow novae.
“Two New States” of VV Puppis
Authors: Visvanathan N. , Wickramasinghe D. T.
Published: July 2016

VV Puppis, a dwarf-nova binary with a 100 min period (Herbig 1960) was observed on two occasions. On 2nd February 1979, VV Puppis was in a faint inactive state. On the other hand it was bright and active on 14th June 1979. Spectral and polarimetry observations were made on both these occasions using IDS (modified as polarimeter) at the f/15 Cassegrain focus of the 4 meter Anglo-Australian Telescope. Spectral range covered was from 3600 Å to 7000 Å with a resolution of 10 Å. The star and sky apertures both were of size 3 × 4 sec of arc and 40 sec apart.
Absorption by Cyclotron Harmonics in the Optical Spectrum of VV Puppis
Authors: Stockman H.S. , Liebert James , Bond Howard E.
Published: July 2016

Most theoretical models of the AM Her variables (AM Her, AN UMa, W Pup and 2A0311-22) rely on strong cyclotron emission at the fundamental cyclotron frequency and higher harmonics to produce the observed, strongly-polarized optical continuum (e.g. Lamb and Masters 1979). The cyclotron lines, which presumably originate in the hot, isothermal accretion shock at the surface of the white dwarf (kT ≳ 10 keV, h/R* ≲ 0.1), should be blurred into a continuous spectrum by both optical depth effects and electron Doppler broadening. Thus the lack of even weak cyclotron features in the optical spectra of these objects is still compatible with a cyclotron origin.
The Location of the ZZ Ceti Stars on the Hertzsprung-Russell Diagram
Authors: Cox John P. , Hansen Carl J.
Published: July 2016

By means of a simple analysis, it is shown that the combination of long periods and relatively high effective temperatures in ZZ Ceti variables may be made consistent with each other if the driving region for instability occurs at a temperature of (1–2) × 105K. Since this temperature does not coincide with the zone of He+ ionization, the driving mechanism is then not the same as for the Cepheid variables and the linear extension of the Cepheid strip down to the ZZ Ceti white dwarfs may be regarded as a coincidence. A Stelllngwerf “bump” type mechanism may be more appropriate for the latter. However, it is also shown that the short period modes computed by Dziembowski and found to be unstable, are consistent with the Cepheid mechanism. A special plea is made for further opacity calculations at temperatures of ~105 K and densities within a few orders of magnitude of unity — a ρ-T region of considerable interest for the envelopes of ZZ Ceti variables.
Theory and Observations of Accretion Disc Spectra
Authors: Mayo S.K. , Wickramasinghe D.T. , Whelan J.A.J.
Published: July 2016

Theoretical continua (3000 ≲ λ (Å) ≲ 20000), UBV colours and Balmer absorption line profiles (Hα – Hδ) have been computed for the optically thick parts of steady-state accretion discs around white dwarfs as a function of mass flow rate, mass of white dwarf and inclination angle. The uncertainties due to disc z-structure and outer radius and viscosity are considered.

The theoretical results for continua and UBV colours are compared with the theoretical results of Schwarzenberg-Czerny and Rózyczka (1977) and Herter et al. (1979) and with results obtained using black bodies instead of stellar atmospheres (e.g. Lynden-Bell 1969). Where models can be directly compared the quantitative agreement is good.
IUE Ultraviolet Spectra of V Sagittae
Authors: Koch Robert H. , Javad Siah M. , Fanelli Michael N.
Published: July 2016

V Sge is a short period, double-line spectroscopic and eclipsing close binary which is also intrinsically variable through a range of at most 3 mag in visual and photographic light. Almost all modern insight is founded upon the interpretation by Herbig, et al. (1965), who developed the evidence for the binary nature of the star, evaluated the nearly 0.5 day Keplerian period, studied the short-term Doppler and intensity variations of the spectrum, and obtained a limiting representation of the intrinsically noisy ultraviolet light curve. The orbital plane view of the binary, as developed by these authors, shows patchy distributions of 0 IIIf1 and 0 VI emissions and mass loss from the system as a whole.
Theoretically Inferred Masses of the White Dwarf Components of Common Nova Systems
Authors: Truran James W.
Published: July 2016

Questions concerning the origin and evolution of cataclysmic variables continue to be the subject of considerable inquiry and debate. Significant boundary conditions upon theoretical models may be imposed by our increasing knowledge of the characteristics of specific systems. It is the purpose of this contribution to argue that, within the framework of the thermonuclear runaway model, the classical novae are most reasonably interpreted as systems characterized by relatively massive white dwarf components.
SS 433 – The Ultimate Cataclysmic Variable?
Authors: Faulkner John , Gilliland Ronald L. , Kemper Edward
Published: July 2016

Several authors (Begelman et al. 1979; Martin and Rees 1979; Bandwagon 1979) suggest that the precessing relativistic gas jets observed in SS 433 (Abell and Margon 1979) arise from de Sitter and/or Lense-Thirring precession of one member of a close binary system. For a semi-detached system of a few solar masses, we find the mean density of the lobe-filling secondary, ρ̄2 ∽ 3 × 104 gm cm-3. The secondary may thus be a low mass white dwarf, transferring material to the vicinity of its companion at a supercritical rate because of gravitational radiation losses.
Interpretation of Radio Observations of FH Serpentis
Authors: Friedjung M.
Published: July 2016

Seaquist and Palimaka (1977) interpreted the radio observations of this nova according to a “Hubble flow” model, in which all gas was ejected at the same time, and for which the velocity of any point in the shell at a given time is proportional to its radial distance. Their model involving a thick shell contradicts observations made in other parts of the spectrum of this and other novae, so in the present study other possibilities have been examined.
He3 as the Recurrent Nova Trigger Mechanism
Authors: Shara M.M.
Published: July 2016

Observations of recurrent novae (Warner 1976) imply the presence of a red giant (RG) in most, if not all, cases. Giant secondaries in nova systems are otherwise known or suspected only in the peculiar slow novae RR Tel and RT Ser. Bath and Shaviv (1978) showed quantitatively that only a red giant can transfer enough hydrogen-rich mass (~10-5M⊙) to a white dwarf (WD) companion rapidly enough (in ∽30 years) to yield a recurrent nova.
Radiation Pressure in Nova Ejecta
Authors: Younger James W.
Published: July 2016

The main features of the spectral evolution of novae consist of: 1. An overall increase in absorption line velocities and emission line widths as a function of time past maximum light. 2. The subsequent appearance of an absorption line system at roughly twice the velocity of the previous absorption line system. 3. Some absorption line systems apparently consist of multiple absorption components at different velocities.
The Effect of a Close Binary Companion on a Nova Outburst
Authors: MacDonald Jim
Published: July 2016

We compare two hydrodynamic calculations of thermonuclear runaways in material accreted by a 1M⊙ white dwarf of initial luminosity 10−3L⊙. In both cases the CNO abundances are taken to be near solar (ZCNO = 0.014). The only difference between the calculations is that in one sequence of models (seq.B) the additional energy generation due to the interaction between the expanding nova envelope and a close red dwarf companion is allowed for, using a simple model based on that of Paczynski (1976).
Extreme and Far Ultraviolet Astronomy from Voyagers 1 and 2
Authors: Holberg J.B.
Published: July 2016

The instrumental characteristics, observational capabilities and scientific results of the Voyager 1 and 2 ultraviolet spectrometers are reviewed. These instruments provide current and ongoing access to low resolution spectra for a wide variety of astronomical sources in the 500 to 1700 Å band. Observations of the brightest OB stars and hot subluminous stars as faint as V = 15 mag. are possible. In the EUV, at wavelengths shortward of 900 Å, several new sources have been detected and a host of potential sources ruled out. In the Far UV, particularly at wavelengths between 900 and 1200 Å, Voyager is capable of observing a wide range of stellar and non-stellar sources. Such observations can often provide a valuable complement to IUE and other data sets at longer wavelengths. The Voyager spectrometers have proved remarkably stable photon counting instruments, capable of extremely long integration times. The long integration times, relatively large field of view, and location in the outer solar system also provide an ideal platform for observations of sources of faint diffuse emission, such as nebulae and the general sky background.
Röntgen Satellite
Authors: Trümper J.
Published: July 2016

The ROSAT launch on June 1, 1990 happened to be after the IAU Colloquium No. 123 before the deadline for submitting manuscripts. I therefore take the liberty to deviate grossly from the manuscript of my talk and give a short up to date mission summary. A more complete description of the mission can be found in References 1 and 2.

The launch of the Delta II rocket was perfect and the orbital parameters reached are very close to nominal: height 580 km, inclination 53°. The predicted satellite’s lifetime in this orbital is at least 10 years. The switch-on of the spacecraft and instrument subsystems could be completed without any losses. All systems are in good health.
The Gamma-Ray Observatory
Authors: Kniffen Donald A.
Published: July 2016

The Gamma-Ray Observatory (GRO), a Shuttle-launched free-flying Observatory is currently scheduled for launch in November 1990. The mission provides nearly six orders of magnitude in spectral coverage, from about 50 KeV to about 30 GeV, with a sensitivity over the entire range over an order of magnitude greater than that of previous observations. The 16,000 kilogram Observatory contains four instruments on a stabilized platform. The mission duration is expected to be from six to ten years. A Science Support Center has been established at the Goddard Space Flight Center for the purpose of supporting a vigorous Guest Investigator Program.
First – Far Infrared and Submillimetre Space Telescope
Authors: Frisk U. O.
Published: July 2016

First is an element of the ESA long term science program. Currently in a detailed study phase it is foreseen as a large (4.5–8 m) diameter passively cooled telescope equipped with a combination of photometer/camera and very high resolution spectrometers. The spectrometers will utilize both direct detection and heterodyne techniques to cover the wavelength band 85–600 micron. The photometers will have both bolometer and photoconductor detector arrays. FIRST is foreseen to be launched shortly after the year 2000 and will be operated as a facility open to the wide scientific community.
SOHO – an Observatory to Study the Solar Interior and the Solar Atmosphere
Authors: Poland A.I. , Domingo V.
Published: July 2016

The Solar and Heliospheric Observatory, Soho, is a joint venture of ESA and NASA. The main objectives of Soho are: a) the study and understanding of solar coronal phenomena; and b) the study of the solar structure and interior dynamics from its core to the photosphere. The primary goals of the coronal and solar wind studies are to understand the coronal heating mechanism and its expansion into the solar wind.

These goal will be achieved both by remote sensing of the solar atmosphere with high resolution spectrometers and telescopes and by “in situ” measurement of the composition and energy of the resulting solar wind and the energetic particles that propagate through it. The structure and interior dynamics will be studied by helio-seismological methods and the measurement of solar irradiance variations. The Soho spacecraft will be three-axis stabilized and located in a halo orbit around the L1 Lagrangian point (approximately 1% of the distance from the Earth to the Sun). It is currently scheduled for launch in July 1995.
The Broad Band X-Ray Telescope (BBXRT) on Astro-1
Authors: Serlemitsos P.J.
Published: July 2016

BBXRT is one of four pointed instruments comprising NASA’s Astro-1 mission, currently scheduled for a 9–10 day flight in May 1990 on board the Space Shuttle Columbia. X-ray Spectra of over 150 sources will be obtained in the energy range 0.3 to 12 keV, with energy resolution of ~100 eV FWHM and timing resolution of 64 μS. BBXRT’S large throughput, broad band mirrors, coupled to segmented cooled Si(Li) detectors, give us the first opportunity to study in detail X-ray spectral features, from oxygen to the iron K band. In developing this instrument, we have made extensive use of detector background reduction techniques in order to be able to observe the many faint extra-galactic sources discovered with the Einstein observatory. Sources in our observing plan have been selected to give us in a 2–4 ks observation < 103 net counts with negligible background. Specific scientific objectives range from refinements of spectra previously obtained at lower resolution, such as a search for relativistic line shifts in compact objects, to observations of faint extragalactic sources for which spectral information is, at best, sketchy, viz. elliptical galaxies and distant quasars. High on our priorities are a search for emission from SN1987A and the first simultaneous observations in the UV and X-ray band of selected sources such as cataclysmic variables and late-type stars.
Future Deep Space Propulsion Systems
Authors: Stuhlinger Ernst
Published: July 2016

Among several potential future deep space propulsion systems, the two which are closest to realization are selected for closer consideration: solar-electric, and nuclear-electric propulsion. In particular, the paper describes a manned Mars mission using a particle bed reactor and Brayton cycle converter as power source. Technical details of the design and the mission profile of a 4-astronaut expedition to Mars, and a proposed course of action for project implementation are presented.
Relative Merits of Low-Earth, Eccentric, Geosynchronous, and Interplanetary Orbits and Sites in Space
Authors: Taylor B.G.
Published: July 2016

One criterium for the best orbit (or site) for an observatory has to be “that which is both scientifically and cost-effective”. Perhaps the worst orbits are those offered by “infrastructures”, which were not designed with astronomy as their primary driver, yet have to be used “because they are there”. The ESA astronomy programme currently tends to favour highly eccentric or geostationary orbits (e.g. COS-B, IUE, EXOSAT, HIPPARCOS, ISO), as these appear to satisfy the above criterium. However, depending on the scientific mission to be accomplished and the availability of funds, other orbits are not ruled out priori.
Astrophysics from The Moon
Authors: Mumma Michael J.
Published: July 2016

The moon offers mixed blessings as a site for astronomical observatories, and some of these are presented in Tables I and II (see the paper by Smith for a more complete discussion). The advantages are so strong that they make the moon a unique site for certain kinds of observatories, particularly those which feature very large telescopes or interferometric arrays of large dimensions, and those that require a presence beyond the screening effect of the earth’s magnetic field. More than one hundred scientists gathered at Annapolis, Maryland for a Workshop on Astrophysics from the Moon (Feb. 5-7, 1990), and discussed these questions in considerable detail (Mumma and Smith 1990). The objective was to examine the astrophysical frontiers of the 21st century, and to identify those which require the presence of astrophysical observatories on the moon for their successful address. The scope of the Workshop was defined to include all areas of space astronomy. It was assumed that the base program of space astronomy will have been completed prior to the emplacement of lunar-based observatories, thus that the four Great Observatories, the Solar and Heliospheric Observatory, the Orbiting Solar Laboratory, the Coronagraphic Imaging and Astrometric Telescope Facility, and the Earth-Orbital Planetary Telescope will all have been accomplished. The Workshop participants tried to look beyond the scientific objectives to be addressed with those Earth-orbiting facilities to the next generation of scientific frontiers, which are associated with the very small, the very distant, and the very faint. This paper summarizes some of the ideas presented there, but these are presented in much greater detail in the published Proceedings (Mumma and Smith 1990).
Evolution of the Unsolved Problems
Authors: Oda Minoru
Published: July 2016

I would like to trace the evolution of the major problems or questions since the 1950’s by showing several diagrams (Fig. 1a-e) based on my own recollections. As for the coordinates of the diagrams, the latitude towards North indicates the magnitude of surprise and that towards the South indicated is the deepening of our knowledge. Of course such a visual approach is incomplete and is full of personal prejudices, and many important subjects and considerations may be missing.

I will not go into detail of the interpretation of the diagram. But from the series of the diagram we may see that unification and diversification of the questions alternate as one of our co-panelists, Freeman Dyson, pointed out in one of his inspiring books.

In the 1970’s to the 1980’s we had good hopes that GUT would develop and in its evidence mono-poles and Proton-decay’s would be discovered and that proposed candidates of the dark matter may also be discovered from fairly reasonable particles to much more exotic particles.
The Stellar X-Ray Polarimeter for the Spectrum-X-Gamma Mission
Authors: Kaaret P. , Novick R. , Martin C. , Shaw P. , Fleischman J.R. , Hamilton T. , Sunyaev R. , Lapshov I. , Silver E. , Ziock K. , Weisskopf M. , Elsner R. , Ramsey B. , Chanan G. , Manzo G. , Giarrusso S. , Santangelo A. , Costa E. , Piro L. , Fraser G. , Pearson J.F. , Lees J.E. , Perola G.C. , Massaro E. , Matt G.
Published: July 2016

We describe an X-ray polarimeter which will be flown on the SPECTRUM-X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a Cesium Iodide photocathode. These three processes allow polarization measurements over an energy band of 0.3 keV to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will allow us to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.
Project of a Three Reflection Telescope for Wide Field Ultraviolet Observations
Authors: Amoretti A. , Badiali M. , Preite-Martinez A. , Viotti R.
Published: July 2016

We present a project of a three-reflection 1.5 m f/3 aplanatic wide-field telescope, in view of a small-satellite mission for the all-sky survey in the Ultraviolet.
Low Frequency Radio Astronomy from Earth Orbit
Authors: Weiler Kurt W. , Kassim Namir E.
Published: July 2016

Low frequency radio astronomy for the purpose of this discussion is defined as frequencies ≲100 MHz. Since the technology is fairly simple at these frequencies and even Jansky’s original observations were made at 20.5 MHz, there have been many years of research at these wavelengths. However, though radio astronomers have been working at low frequencies since the first days of science, the observing limitations and the move of much of the effort to ever shorter wavelengths has meant that most areas still remain to be fully exploited with modern techniques and instruments. In particular, the possibilities for pursuing the very lowest frequencies by interferometry of ground to space, in Earth orbit, or from the Moon promises a rebirth of work in this wavelength range.

We present concepts for space-ground VLBI and a fully space-based array in high Earth orbit to pursue the astrophysics which can only be probed at these frequencies. An Orbiting Low Frequency Radio Astronomy Satellite (OLFRAS) and a Low Frequency Space Array (LFSA) are two concepts which will open this last, poorly explored area of astronomy at relatively low cost and well within the limits of current technology.
High-Resolution Imaging Spectroscopy at Terahertz Frequencies
Authors: Brown Robert L. , Kerr Anthony R. , Thompson A. Richard , Schwab Frederic R.
Published: July 2016

HISAT, a multi-element heterodyne interferometer attached to Space Station Freedom, will provide spectroscopic images with unprecedented detail of those submillimeter lines of C,O and C+ which are critical diagnostics of UV excitation in the Galaxy. With the arcsecond angular resolution achievable from the space station, HISAT will reveal:

– The distribution of sources of ultraviolet radiation in the Galaxy;

–The effective temperature of the UV radiation as a function of galactocentric radius;

– The chemical and isotopic enhancement of atomic carbon and oxygen with galactic radius;

– The propagation of UV radiation in molecular clouds and its stimulative, or inhibitive, effect on star formation;

– The density structure, dumpiness or fragmentation, of molecular clouds throughout the Galaxy. HISAT has been selected by NASA for a concept-phase study.
Structure of Radiatively Cooled Jets
Authors: Kondo Masa-Aki
Published: July 2016

Radiative cooling strongly affects the thermal structure of dense jet, such as in SS433, through free-free emission. From the dynamical aspect, the beam width of a cooled jet does not expand, unlike from an adiabatic jet. From the thermal aspect, cooling efficiency determines the ratio of X-ray region of high temperature to optical one of low temperature. However, this ratio is influenced by the heating due to contained high-energy particles, which produce synchrotron radiation in the tail of the jet.

Extragalactic jets can also be considered in a similar way due to other energy loss mechanisms.
Studying the Galactic Central Engine from Space Observatories
Authors: Greyber Howard D.
Published: July 2016

Three general models have been constructed for the fantastically powerful “central engine” that powers the enormous energy output from quasars and active galactic nuclei (AGN). One model assumes a rapidly rotating accretion disk around a central black hole (however the disks, thick or thin, are subject to violent instabilities). Another assumes that in some postulated circuitry energy is extracted from the rotational portion of the deepest potential hole known, a black hole. Both models appear implausible.

The third model is the STRONG MAGNETIC FIELD MODEL (SMF) in which an extremely strong gravitationally bound current loop (GBCL) is formed during the gravitational collapse that forms the galaxy or quasar, producing a very intense dipole magnetic field anchored in the nucleus. SMF, first published in 1962, thus predicted the vertical magnetic field configuration seen today at our own galactic nucleus; to some the radio arcs observed suggest a dipole magnetic field there, just as SMF predicts.
Monte Carlo Simulations of Particle Acceleration at Oblique Shocks
Authors: Baring Matthew G. , Ellison Donald C. , Jones Frank C.
Published: July 2016

The Fermi shock acceleration mechanism may be responsible for the production of high-energy cosmic rays in a wide variety of environments. Modeling of this phenomenon has largely focused on plane-parallel shocks, and one of the most promising techniques for its study is the Monte Carlo simulation of particle transport in shocked fluid flows. One of the principal problems in shock acceleration theory is the mechanism and efficiency of injection of particles from the thermal gas into the accelerated population. The Monte Carlo technique is ideally suited to addressing the injection problem directly, and previous applications of it to the quasi-parallel Earth bow shock led to very successful modeling of proton and heavy ion spectra, as well as other observed quantities. Recently this technique has been extended to oblique shock geometries, in which the upstream magnetic field makes a significant angle ΘB1 to the shock normal. In this paper, spectral results from test particle Monte Carlo simulations of cosmic-ray acceleration at oblique, nonrelativistic shocks are presented. The results show that low Mach number shocks have injection efficiencies that are relatively insensitive to (though not independent of) the shock obliquity, but that there is a dramatic drop in efficiency for shocks of Mach number 30 or more as the obliquity increases above 15°. Cosmic-ray distributions just upstream of the shock reveal prominent bumps at energies below the thermal peak; these disappear far upstream but might be observable features close to astrophysical shocks.

Subject headings: acceleration of particles — cosmic rays — shock waves
Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations of Energetic Electron Populations in Solar Flares
Authors: Kundu M. R. , White S. M. , Gopalswamy N. , Lim J.
Published: July 2016

We present comparisons of multiwavelength data for a number of solar flares observed during the major campaign of 1991 June. The different wavelengths are diagnostics of energetic electrons in different energy ranges: soft X-rays are produced by electrons with energies typically below 10 keV, hard X-rays by electrons with energies in the range 10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and millimeter-wavelength emission by electrons with energies of 0.5 MeV and above. The flares in the 1991 June active period were remarkable in two ways: all have very high turnover frequencies in their microwave spectra, and very soft hard X-ray spectra. The sensitivity of the microwave and millimeter data permit us to study the more energetic (>0.3 MeV) electrons even in small flares, where their high-energy bremsstrahlung is too weak for present detectors. The millimeter data show delays in the onset of emission with respect to the emissions associated with lower energy electrons and differences in time profiles, energy spectral indices incompatible with those implied by the hard X-ray data, and a range of variability of the peak flux in the impulsive phase when compared with the peak hard X-ray flux which is two orders of magnitude larger than the corresponding variability in the peak microwave flux. All these results suggest that the hard X-ray-emitting electrons and those at higher energies which produce millimeter emission must be regarded as separate populations. This has implications for the well-known “number problem” found previously when comparing the numbers of nonthermal electrons required to produce the hard X-ray and radio emissions.

Subject headings: Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays
Gamma-Ray Spectral Observations with Yohkoh
Authors: Yoshimori M. , Suga K. , Morimoto K. , Hiraoka T. , Sato J. , Kawabata K. , Ohki K.
Published: July 2016

We present gamma-ray observations of the 1991 October 27, November 15, and December 3 flares with the Yohkoh gamma-ray and hard X-ray spectrometers. The October 27 flare (X6.1 /3B) shows significant gamma-ray line emission, and the temporal evolution of the gamma-ray line-to-bremsstrahlung flux ratio indicates that protons and electrons were complicatedly accelerated during flare. The December 3 flare (X2.0/2B) shows a strong bremsstrahlung continuum extending to 10 MeV and indicates that electrons were preferentially accelerated to 10 MeV. A line feature at 420 keV was observed from the November 15 flare (X1.0/3B). This is most likely due to a compound of redshifted nuclear deexcitation lines of Be (429 keV) and Li (478 keV) resulting from He-He reactions. The spectral feature indicates that the accelerated He nuclei suffer strong pitch-angle scattering in the corona and form a downward-peaked distribution. Furthermore, the November 15 flare exhibits evidence of positron annihilation line at 511 keV. The positron production processes and the electron density of the annihilation region are discussed on the basis of the temporal characteristics of 511 keV line emission.

Subject headings: line: identification — Sun: flares — Sun: X-rays, gamma-rays
Weightiness of the Dispersive Rate in Stochastic Acceleration Processes
Authors: Pérez-Peraza J. , Gallegos-Cruz A.
Published: July 2016

We present analytical solutions to the transport equation of the accelerated particles that are valid over the entire energy range (nonrelativistic, transrelativistic, and ultrarelativistic) for the time-dependent and equilibrium cases. On the basis of these overall spectra, we have studied the relative importance of the term of average (systematic) energy increase and the term of diffusion (spread) in energy that define the evolution of accelerated particles within the frame of a simplified diffusion-convection transport equation, when the particle distribution functionN(E, t) is assumed to be independent of spatial pitch-angle diffusion (isotropic). Since in some astrophysical works, only the term of average energy increase in the simplified transport equation in energy space is considered to be leading directly to a power-law-type spectrum, we have established the conditions under which such an approximation may be justified. The analysis is illustrated for acceleration by two different kinds of turbulence: MHD and Langmuir waves. The omission of the term of energy spread leads, in general, to an important depletion or overproduction of the accelerated particle flux that must be seriously considered in any calculation of the flux of secondary radiation produced by the accelerated particles. The presented analytical spectra may be of particular relevance to gamma-ray, neutron, and pion production in solar flares as well as in other astrophysical sites.

Subject headings: acceleration of particles — MHD — Sun: general — turbulence — wave motions
Particle Orbits, Trapping, and Acceleration in a Filamentary Current Sheet Model
Authors: Kliem Bernhard
Published: July 2016

Test particle orbits in the two-dimensional Fadeev equilibrium with a perpendicular electric field added are analyzed to show that impulsive bursty reconnection, which has been proposed as a model for fragmentary energy release in solar flares, may account also for particle acceleration to (near) relativistic energies within a fraction of a second. The convective electric field connected with magnetic island dynamics can play an important role in the acceleration process.

Subject headings: acceleration of particles — MHD — plasmas — Sun: corona — Sun: flares
Radio Evidence for Nonthermal Particle Acceleration on Stars of Late Spectral Type
Authors: Lang Kenneth R.
Published: July 2016

Radio evidence for nonthermal particle acceleration on stars of late spectral type (G, K, and M) is reviewed, including the pre-main-sequence T Tauri stars, the dwarf M flare stars, and the RS CVn binary stars. Both the long-lasting radio emission and the transient radio flares can be attributed to nonthermal electrons accelerated in magnetically confined coronae, radiating by either incoherent gyrosynchrotron radiation or by coherent processes. Related observations of the Sun provide the framework for interpreting the radio emission of late-type stars. We review recent VLBI observations of single and binary stars, observations of rapid acceleration and dynamic spectra of dwarf M flare stars, and models for long-lasting radio emission from dwarf M flare stars and RS CVn stars. The VLBI data provide evidence for nonthermal particle acceleration in large-scale magneto-spheres several times larger than the stellar radius for T Tauri and RS CVn stars. In contrast, rapid radio flares on dwarf M stars require sources much smaller than the visible star in size, and this is consistent with the VLBI data.

Dynamic spectra suggest particle acceleration by relativistic electron beams on dwarf M stars. The long-lived radio radiation of dwarf M stars and RS CVn stars requires more-or-less continuous particle acceleration over periods of hours, perhaps by persistent low-amplitude flaring.

Subject headings: acceleration of particles — binaries: close — radio continuum: stars — stars: flare — stars: late-type — stars: pre-main-sequence
Pulsar Studies with Comptel
Authors: Bennett K. , Busetta M. , Carramiñana A. , Diehl R. , Lichti G. , Schönfelder V. , Strong A. , Hermsen W. , Kuiper L. , Connors A. , Ryan J. , Buccheri R.
Published: July 2016

The Compton Gamma-Ray Observatory (C-GRO) has completed a full-sky survey during which the number of known γ-ray pulsars has more than doubled. COMPTEL has observed the classical pulsars Crab and Vela on several occasions and has derived detailed pulse patterns and spectral parameters in the 0.7-30 MeV energy interval. The new C-GROγ-ray pulsars have different properties in terms of energy spectra and light-curve shapes, and, in fact, only the Crab is seen by all four C-GRO instruments. This raises intriguing questions about the particle acceleration processes and beaming taking place in the neutron magnetosphere. We have examined the COMPTEL data to add information on these objects in the 0.7-30 MeV energy interval and present evidence for the detection of one of them, PSR B1509-58. We have also undertaken a search for candidate radio pulsars whose ephemerides are well defined. The results of these analyses are presented.

Subject headings: gamma rays: observations — pulsars: general
Gamma-Ray Burst Theory: Back to the Drawing Board
Authors: Harding Alice K.
Published: July 2016

Gamma-ray bursts have always been intriguing sources to study in terms of particle acceleration, but not since their discovery two decades ago has the theory of these objects been in such turmoil. Prior to the launch of Compton Gamma-Ray Observatory and observations by BATSE, there was strong evidence pointing to magnetized Galactic neutron stars as the sources of gamma-ray bursts. However, since BATSE the observational picture has changed dramatically, requiring much more distant and possibly cosmological sources. I review the history of gamma-ray burst theory from the era of growing consensus for nearby neutron stars to the recent explosion of halo and cosmological models and the impact of the present confusion on the particle acceleration problem.

Subject headings: acceleration of particles — gamma rays: bursts