bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of the Cluster X-Ray Luminosity Function
Authors: Perrenod Stephen C. 
Published: July 2016

I predict the evolution of the X-ray luminosity function of clusters of galaxies. Predominantly, I treat the assumption that galaxies form first, then cluster purely due to gravitation. I show that the richness distribution of Abell clusters favors this scenario, rather than the protocluster hypothesis. The luminosity function is produced by combining a generalized (for all Ω) Press-Schechter evolutionary mass function for clusters (derived herein) with a power law X-ray luminosity-mass relation; a power law relation is supported by observations of low-redshift clusters.I find very steep evolution in the luminosity function, and thus in the source counts, for large Ω, and moderate evolution for small Ω. For a variety of models for the gas supply rate to the intracluster medium, the evolution of the luminosity function does not vary greatly. Thus it appears that the Ω, dependence will dominate and that number counts of X-ray clusters will yield cosmological information. The power of a test of Ω with an evolving luminosity function is considerably enhanced relative to a test which involves solely global cosmological effects on a non-evolving population. This occurs because of the well-known result that, at late times, clustering tends to proceed slowly for universes of small Ω and rapidly for large Ω.
Non-Static Structure of the Chromosphere-Corona Transition Region
Authors: Delache Philippe 
Published: July 2016

The emission measure Ne2 dh, which is so useful in reducing XUV as well as radio data, is redefined as f(T) dT where f(T) is called ‘thermal emission measure’. Theoretical predictions for f(T) on the basis of a simple, one dimensional, steadily expanding atmosphere are presented. Depending upon the boundary conditions, and essentially upon the mass flux, two very different behaviours show up.(1)With a mass flux compatible with an extrapolation of the solar wind flux, f(T) would correspond to a transition region controlled by a constant conductive flux. It can be fitted, as was shown e.g. by Athay (1966), with the XUV observations of the integrated disk for lines formed at temperatures higher than about 2 × 105 K.(2)But only with a mass flux enhanced by a factor of 50 to 100, can we interpret the radio spectrum and the XUV observations of lines formed at temperatures less than 2 × 105 K.The suggestion is made that a single model can reconcile both behaviours: below 2 × 105 K the emitting region is squeezed so that it covers 1–2% of the surface that it occupies at higher temperatures where all structures begin to merge, filling the whole corona. This variation with height compares with usual models derived from spatially resolved observations; as usual the underlying magnetic field is expected to support this channelling.
The U.S. Naval Observatory Parallax Program
Authors: Strand K. Aa. , Harrington R. S. , Dahn C. C. 
Published: July 2016

The U.S. Naval Observatory program on trigonometric stellar parallaxes with the 61-in. astrometric reflector has been in progress since 1964. To date 201 definitive and 8 preliminary negligible parallaxes have been published, including the UBV photometry of these stars. Data for an additional 35 stars are still unpublished.The mean error in position for an image of unit weight is 1.2 μ or 0″.016, of which 0.8 μ originates from the measuring error of the automatic measuring machine.An error of the parallax of 0″.004 can usually be obtained with 40 or fewer plates and with an average parallax factor of 0.7.A statistical investigation of the derived parallaxes shows that they are free from significant internal systematic errors.
On the Project of a New Fourfold Coverage of the Northern Hemisphere
Authors: de Vegt Chr. 
Published: July 2016

The fully inherent information of the AGK 2 plate material, covering the northern hemisphere down to δ= −2.5° with homogeneous epoch and limiting magnitude has not been used to establish the AGK2 catalogue. A new measurement will provide positions for all stars with at least mpg=2 in the FK4 system, yielding an estimated accuracy of σ = 0″.14.In March 1973 a newly developed zone astrograph for the yellow spectral-region has been set in operation at the Hamburg observatory which would be available about 1975 for a new fourfold coverage of the northern hemisphere. A technical description of the instrument is given. Details of the fourfold plate coverage and the observing program are discussed. As a suitable reference star system the AGK3R catalogue, updated with recently derived proper motions to that epoch, is adopted. A final positional accuracy σ = 0″.11 of the new catalogue is expected. The available epoch difference of 45 years up to that date will then provide proper motions in the FK 4 system with an estimated accuracy of at least 0″.005/a for all stars of the northern hemisphere down to mpg=2.
The Origin of Commensurabilities in the Satellite Systems
Authors: Dermott S. F. 
Published: July 2016

The distribution of orbits in the satellite systems of the major planets is definitely nonrandom as there is a marked preference for commensurability among pairs of mean motions in these systems. If this preference is not the result of a formation process then it follows that since the time of satellite formation dynamical evolution has occurred. In this paper (a full version of which is to be submitted to another journal) I show that there is a bulk of evidence in favour of the hypothesis that orbital evolution has occurred as the result of tidal dissipation in the planets. This evidence can be listed as follows:(i) In a tidally evolved satellite system there should be a linear correlation between log (orbital radius) and log (satellite mass). The expected correlation is observed among the inner satellites of Saturn and Uranus, the slope of the log-log plots being consistent with an amplitude and frequency independent Q (the tidal dissipation function). The correlation in Saturn's system must be largely due to either a formation process or possibly an early amplitude and frequency dependent tidal process, but certainly the present satellite distribution is completely consistent with the tidal hypothesis.(ii) If Q is amplitude- and frequency-independent then the Mimas-Tethys and Enceladus-Dione resonances are stable under the action of tidal forces. This is an important result as it indicates that the necessary tidal dissipation occurred in the solid parts of the planets. Whether or not these planets have any solid parts at present is a matter of dispute.(iii) The tidal hypothesis can account for the formation (capture into libration) of the Mimas-Tethys and Enceladus-Dione resonances.(iv) If it is allowed that the age of the Mimas-Tethys resonance is not small (> 108 yr) in comparison with that of the solar system and that orbital evolution since the time of satellite formation has been appreciable then it can be shown that tidal forces (with Q amplitude- and frequency-independent) can account for the present large amplitude of libration of this resonance.(v) If tidal evolution in the satellite systems of Jupiter and Saturn has been appreciable then from the present orbits of Io and Mimas it can be deduced that Q (Jupiter) ~1.1 × 105 and Q (Saturn) ~1.2 × 105. As the masses of the two satellites differ by a factor ~2000 and the amplitudes of the tides they raise on their respective planets differ by a factor ~ 5000 this agreement in the Q-values is somewhat remarkable. But as the stability of the Mimas-Tethys and Enceladus-Dione resonances demands that Q is amplitude- and frequency-independent and as the chemical compositions and structures of Jupiter and Saturn are probably similar then one should expect the Q's of these planets to be similar and thus the result supports the tidal hypothesis.(vi) Finally, as the values of Q are so very high it would be remarkable if tidal evolution had not taken place.
On the Disappearance of Isolating Integrals in Dynamical Systems with More than Two Degrees of Freedom
Authors: Froeschlé C. , Scheidecker J.-P. 
Published: July 2016

We continue to study the number of isolating integrals in dynamical systems with three and four degrees of freedom, using as models the measure preserving mappings T already introduced in previous papers (Froeschlé, 1972; Froeschlé and Scheidecker, 1973a).Thus, we use here a new numerical method which enables us to take as indicator of stochasticity the variation with n of the two (respectively three) largest eigenvalues - in absolute magnitude - of the linear tangential mapping Tn∗ of Tn. This variation appears to be a very good tool for studying the diffusion process which occurs during the disappearance of the isolating integrals, already shown in a previous paper (Froeschlé, 1971). In the case of systems with three degrees of freedom, we define and give an estimation of the diffusion time, and show that the gambler's ruin model is an approximation of this diffusion process.
Solar Activity Observed in X-Rays and the EUV from OSO 7
Authors: Thomas Roger J. 
Published: July 2016

Since 1971 the Goddard X-ray and EUV spectroheliograph aboard OSO 7 has been measuring the spatial distribution and time-variations of localized temperature and density features in solar active centers and flares. In some cases the sizes, shapes, orientations and locations of emitting plasmas at temperatures ranging from 104 K (Hα) to as high as 2 × 107 K (Fe xxv) have now been measured simultaneously. Our observations of active regions are consistent with the coronal structure being made up of nested systems of arches with footpoints in areas of opposite magnetic polarity. Temperatures seem to increase for arches nearer the center and also towards the top of any given magnetic arch, the innermost loops having the highest temperature gradients. There is also some evidence for electric current flow along such loops. Radiative cooling is significant for the region's hot central core which therefore must be maintained by a more or less continuous injection of energy.A nested arch structure is also indicated for XUV flares of the two-component type, which likewise may require continuous energy input since conduction cooling should otherwise be very rapid. Multiple spikes during the impulsive phase seem to represent the consecutive triggering of different sources within the region and may occur outside of any detectable pre-existing coronal feature. Comparison of spatial distributions at several wavelengths during various stages of flare events provides information on interactions between the wide range of atmospheric levels involved. We have evidence for polarization of about 20% in a number of X-ray bursts, continuing throughout the decay phase. At least for some flares, our measurements seem to contradict the model of electron beams being radially injected into the chromosphere.
Interpretation of the X-Ray Spectra of Solar Active Regions
Authors: Walker Arthur B. C. 
Published: July 2016

This paper presents a review of recent analytical studies of the coronal X-ray spectrum below 25 Å. The techniques used to compute the theoretical coronal spectrum, and the currently available atomic rate constant data are reviewed first. Spectroscopic techniques which have been proposed for the determination of coronal temperature and density structure, and the results derived from their application to coronal spectra are also reviewed.A number of coronal models based on X-ray observations have been developed recently, and the coronal temperature structure and composition predicted by these models is discussed, and compared with models of the corona and transition region derived from studies of the solar EUV spectrum.
Flare-Like Ultraviolet Spectra of Active Regions
Authors: Brueckner G. E. 
Published: July 2016

SummarySome characteristic features of UV spectra which can be seen in flares (Brueckner, this Symposium, p. 135) can also be detected in active regions without the presence of typical other flare phenomena like X-ray enhancement. Another distinct difference between these ‘flare-like’ spectra and flare spectra is the absence of very high temperature ions like Fe XXI in the ‘flare-like’ spectra. They occur in small areas and can be detected as ‘fluctuating Hα bright points’ in broad band Hα. Simultaneously, a strong UV brightening can be seen. As reported by the Skylab crews, these brightenings occur more frequently and quasi-periodic prior to flares. Their spectra show the very broad transition zone lines and often strong line shifts toward the blue or red. Figure 1 shows a selection of typical spectra. One notices a very asymmetric Lα profile in one case. Spectra prior to, during, and after a flare are reproduced in Figure 2. One recognizes that the transition zone instability started intermittently prior to the flare and could be seen during short time intervals long after the flare had ceased.
Studies of the Dynamic Structure and Spectra of Solar X-Ray Flares
Authors: Kahler S. W. , Krieger A. S. , Silk J. K. , Simon R. W. , Timothy A. F. , Vaiana G. 
Published: July 2016

SummaryData from the AS & E X-ray spectrographic telescope on Skylab were used for a preliminary study of two solar flares on 1973, August 9 and September 5. Photographic images taken through broad band filters during the early flare onsets and subsequent evolution of the flares were analyzed by microdensitometry and subsequent conversion to energy maps of the flare areas.
Determination of the Height of Hard X-Ray Sources in the Solar Atmosphere by Measurement of Photospheric Albedo Photons
Authors: Brown John C. , Van Beek H. F. 
Published: July 2016

SummaryThe importance and difficulties of determining the height of hard X-ray sources in the solar atmosphere, in order to distinguish source models, have been discussed by Brown and McClymont (1974) and also in this Symposium (Brown, 1975; Datlowe, 1975). Theoretical predictions of this height, h, range between and 105 km above the photosphere for different models (Brown and McClymont, 1974; McClymont and Brown, 1974). Equally diverse values have been inferred from observations of synchronous chromospheric EUV bursts (Kane and Donnelly, 1971) on the one hand and from apparently behind-the-limb events (e.g. Datlowe, 1975) on the other.
Population Inversion and Suprathermal Excitation in Carbon Monoxide
Authors: Köppen J. , Kegel W. H. 
Published: July 2016

We have investigated under which physical conditions (kinetic temperature, H2 density, CO column density) the CO molecule shows suprathermal excitation and population inversion. The computations are based on a model in which the excitation is basically due to collisions with H2 molecules. The collision cross-sections were taken from Green and Thaddeus (1976). The radiative transport in the molecular lines is treated in an on-the-spot approximation (see e.g. Kegel 1979)J = S(1 - e-τ) + Ibge-τin order to keep the computing time low enough to permit the investigation of a wide range of parameters. Our approximation of the radiative transfer is mathematically equivalent to a formalism involving an escape probability β = e-τ. This escape probability arises from the fact that the radiative transfer in the line wings is neglected.
Role of Grains in the Drift of Plasma and Magnetic Field in Dense Interstellar Clouds
Authors: Umebayashi Toyoharu , Nakano Takenori 
Published: July 2016

The magnetic flux through an interstellar cloud or through a part of the cloud must decrease considerably by the drift of plasma and magnetic field in order that stars form in the cloud. Because most grains are negatively charged in dense clouds (Elmegreen 1979; Umebayashi and Nakano 1980), they retard magnetic flux leakage in addition to ions (Elmegreen 1979). We investigate this effect for different situations and obtain the following results (for details, see Nakano and Umebayashi 1980):
1.For nearly spherical clouds of mass ≳ 103M⊙ sustained by magnetic force the friction of grains is efficient at nH⊙ ≳ 105 cm−3, and the magnetic flux leakage time tB is greater than a few million years at any density. Grains drift as fast as ions and electrons.2.For spherical clouds of smaller mass and disk-shaped clouds, tB becomes much smaller and the drift of grains is much slower than ions and electrons at nH ≳ 106 cm−3.3.Thus magnetic flux leakage occurs mainly in the condensations described in 2, and the abundance of heavy elements in stars deviates little from that of the parent clouds because of small grain drift.
A New Kind of Gamma Ray Burst?
Authors: Pizzichini G. 
Published: July 2016

One of the most recently detected (Cline et al., 1980) Gamma Ray Bursts (GRB) appears to have very unusual properties.We recall here briefly the main features of the time history and of the spectral data, as given by Cline (19 79). The time history has a very fast initial rise, less than 200 usee , a smooth, large but very short initial peak, with a maximum intensity of several × 10−3 ergs cm−2 sec−1 and a 150 msec duration, followed by an oscillating decay phase, with at least 22 compound 8 second pulses. The spectrum of the initial phase of the event; corresponds to a steep power law with possibly a line at 420 keV. The total spectrum of the decay phase is even steeper and shows no lines (Mazets and Golenetskii, 1979), The location of the wait (Evans et al., 1980) corresponds to N49, a supernova remnant in the Large Magellanic Cloud, which gives a total (isotropic) emission of ≈ 1045 erg, one half of it in the initial spike, the rest in the decay phase. Three later events, apparently with no special properties, are attributed to the same source (Mazets and Golenetskii, 1979), with increasing delays (0.6, 29 and 50 days) and decreasing peak intensities (3%, 1% and 0.5% of the first event), because their locations are all consistent with the much smaller March 5 error box.
A VLBI Study of GHz-Peaked-Spectrum Radio Sources
Authors: Stanghellini C. , O'DEA C.P. , Baum S.A. , Dallacasa D. , Fanti R. , Fanti C. 
Published: July 2016

The GHz-Peaked-Spectrum (GPS) radio sources are powerful (Lradio ≈ 1045 erg sec–1) and compact (10–100 mas, 10–1000 parsecs) sources characterized by a simple convex spectrum which peaks near 1 GHz (O'Dea et al. 1991 and references therein).Optical and radio observations lead to the conclusion that GPS sources are formed when the radio source is confined to the narrow line region (or an even smaller scale) by a dense and clumpy medium. This could lead to 2 different evolutionary scenarios: as first suggested by Phillips and Mutel (1982) GPS radio sources could be classical double radio sources at the very first stage of their life, or alternatively they will never become as large as the classical doubles since the dense and turbulent environment is able to confine and trap the radio emitting region on the scale of the NLR (Baum et al. 1990).
High Radio Frequency Studies of Equatorial and Southern AGN
Authors: Tornikoski M. , Valtaoja E. 
Published: July 2016

The Swedish-ESO Submillimetre Telescope (SEST) has been used for the high radio frequency observations of our group's AGN monitoring projects since the end of 1987.Our SEST results from October 1987 until June 1994 will be published in A&AS (in press); the data will be available electronically. The data set consists of 155 sources with the signal-to-noise -ratio of at least one observation (at 90 or 230 GHz) ≥ 4.
High-Energy Gamma and Radio Variability of Blazars in the Model of Non-Stationary Jets
Authors: Romanova M.M. , Lovelace R.V.E. 
Published: July 2016

A model has been developed for impulsive VLBI jet formation and gamma ray outbursts of Blazars. Propagation of newly expelled matter in the old channel of a jet is calculated supposing that the main driving force is the electromagnetic field. The new outflowing matter overtakes the old matter and forms double, fast or slow magnetosonic shock fronts. In the region of the fronts, the number of particles and their energy increase continuously with propagation time from the central object (Romanova and Lovelace, 1995). Accelerated electrons and positrons in the front interact with a diffuse field of UV photons (inverse Compton scattering), with the magnetic field (synchrotron radiation), and with synchrotron photons (SSC processes), thus creating radiation in a very wide range of bands. The self-consistent relativistic equations for the number of particles, the momentum, energy, and magnetic flux in the front are derived and solved numerically (Lovelace and Romanova, 1995). The time-dependent apparent luminosities in the radio to gamma ray bands are calculated taking into account the Doppler boost of the photons. The model predicts a short outburst of radiation in gamma rays (weeks or so) connected with Compton processes, a sharp (less than a day) outburst in the X-rays with a smooth decrease of the luminosity connected with SSC processes, and synchrotron radiation changing from infrared to radio bands (Fig. 1A). The lepton distribution function was taken as fl = K1/γ2 in the main energy containing range, γ1 ≤ γ ≤ γ2, steeper distribution fl = K2/γ3 for γ2 ≤ γ ≤ γ3, and even steeper for γ ≥ γ3. For γ < γ1, fl is assumed negligible as a result of synchrotron self-absorption. The lowest frequency f(syn1), determined by self-absorption, corresponds initially to the infrared band, and later - to the radio band. From Fig.1B, one can see that radio at 3 mm may start to appear after 2 weeks after outburst. But its maximum may correspond to much later times (months), because f(syn1) decreases slowly with time. The appearance of the new VLBI component in QSO 0528+134, which approximately coincides with the strong gamma-ray flash and with the beginning of the strong mm radio outburst (Krichbaum, et al. 1995; Pohl, et al. 1995), supports the proposed model.Both authors were supported in part by NSF grant AST-9320068. MMR is grateful to RFBR and Organizers of the Symposium for the partial support.
Improved Method for Orbital Elements Differential Correction
Authors: García A. López , Ortí J. A. López , Machí R. López 
Published: July 2016

As was pointed out by IAU in 1976, an important problem in fundamental astronomy is the improvement of the vernal equinox and equator positions. To this aim, it is necessary to know the accurate values of minor planets orbital elements. The classical methods of orbital elements differential corrections are based on linking the observations at different epochs considering equal derivatives respect to the initial and osculating elements.In this paper we present an improved method in which the least squares matrix coefficients is calculated from the integration of the Lagrange planetary equations and its derivatives.