bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dust-Embedded AGN in Unusually Warm IRAS Galaxies
Authors: Vader J. P. , Frogel J. A. , Gillett F. C. , de Grijp M. H. K. 
Published: June 2019

The IRAS Point Source Catalog contains only 61 sources identified as galaxies whose energy distribution peaks at 60 mμ. The scarcity of such galaxies has prompted a search for possible common properties. This sample of ‘60 mμ peakers’, 21 of which are previously identified galaxies, partially overlaps with that of warm IRAS galaxies studied by de Grijp et al. (1987) and contains similar percentages of Seyfert (65%) and starburst galaxies on the one hand, and of strong and weak radio sources on the other hand. A remarkable characteristic is, however, that about half of the 60 mμ peakers seem to be early-type galaxies. The fact that such galaxies are rarely IRAS sources and, if so, have FIR energy distributions peaking at 100 mμ similar to those of spirals, implies that we are sampling active or nuclear starburst early-type galaxies with a very large success rate. The observational data accumulated so far further show that:
(i)objects with smaller FIR to near-IR flux ratios have redder J-K colors and warmer 60 to 25 mμ colors, i.e., an infared spectrum dominated by warmer dust and/or a nonthermal source (Figs. 1a,b);(ii)out of 32 objects with radio data, the 5 compact radio sources with luminosities intermediate between those af radio-quiet and radio-loud AGN have among the warmest 60 to 25 mμ colors (Fig. 2). Such warm FIR colors are not a common characteristic of radio galaxies and quasars (Golombek et al. 1987, Neugebauer et al. 1986).(iii)the 60 mμ luminosities range from 109 to 1012 L0, and are largest for Mkn 231, 2306+0505 (Hill et al. 1987) and 2046+1925 (Frogel et al. 1988). The latter 2 objects, along with 0052-7054 (Frogel and Elias 1987) which also belongs to our sample, are Seyfert 2 galaxies with evidence for the presence of a dust-obsured broad line region.
Precollapse Evolution of Globular Clusters
Authors: Spitzer Lyman 
Published: June 2019

The dynamical evolution of a cluster in which N, the number of stars, is large, results primarily from encounters between pairs of stars; these tend to modify the system so that it approaches a more probable configuration. In statistical equilibrium, the distribution of stars among states of different energy, Ei, per unit mass would be determined to a first approximation by the probability Pi, wherehere giis the statistical weight of each state, proportional to the amount of phase space available, and B is a constant. Evidently dynamical evolution tends a) towards stellar states which are more tightly bound by their mutual gravitational attraction and have a correspondingly lower Ei, and b) towards the free state, where the volume of available phase space is very large. The only relatively stable state for an isolated cluster is one in which a central, non-evolving massive configuration (a compact object, or tight binary, or a hierarchical multiple system) has all the initial binding energy of the cluster and all other stars have escaped.
Libration of the Moon: shape of the Earth and motion of the ecliptic plane
Authors: Moons M. 
Published: June 2019

Very accurate theories of the libration of the Moon have been recently built by Migus (1980), Eckhardt (1981, 1982) and Moons (1982, 1984). All of them take into account the perturbation due to the Earth and the Sun on the motion of a rigid Moon about its center of mass. Additional perturbations (influence of the planets, shape of the Earth, elasticity of the Moon, …) are also often included.We present here the perturbations due to the shape of the Earth and the motion of the ecliptic plane on our theory which already contains planetary perturbations. This theory is completely analytical with respect to the harmonic coefficients of the lunar gravity field which is expanded in spherical harmonics up to the fourth order. The ELP 2000 solution (Chapront and Chapront-Touzé, 1983) supplies us with the motion of the center of mass of the Moon.
Connection Between Optical Outbursts and Superluminal Motion in the Milliarcsecond Radio Structure of the Extragalactic Objects
Authors: Babadzhanyants M.K. , Belokon E.T. 
Published: June 2019

The analysis of the optical variability of 3C 345 along with the apparent superluminal motions in the milliarcsecond jet suggests a connection between these forms of activity.The optical variability of the quasar 3C 345 is presented including our 18-year photographic observations and all published data by 1984. The extrapolated moments of ejection of milliarcsecond jet components from nucleus coincide with the initial phases of the “slow” optical flares. The prediction about the arising of a new radiocomponent based on such treatment was confirmed later on. Some evidence of similar connection for the N-galaxy 3C 120 is given.It has been discovered in recent years that some extragalactic objects have apparent superluminal motions in their milliarcsecond jets. It is obvious that independently of the concrete physical interpretation of this phenomenon it represents an evidence of nuclear activity. Consequently this phenomenon may be connected with the variability of the optical continuum source. The object most suitable for studying such a relationship is the quasar 3C 345. This superluminal object is the best-observed both by VLBI technique and by several optical monitoring programs which revealed very high degree of its optical variability ( in the B-band).
Internal constitution and oscillation spectrum of Procyon
Authors: Demarque P. , Guenther D. B. 
Published: June 2019

In a previous paper on Procyon A, we analyzed the best available observational data (summarized here in Table 1), discussed its evolutionary status in terms of theoretical evolutionary tracks, and evaluated on the basis of these models its expected characteristic p-mode frequency spacing (Demarque and Guenther 1986). We reached the following conclusions:
(1)that the published astrometric mass of Procyon A is inconsistent with stellar models and seems too large by about 15 per cent.(2)that evolutionary models have too high effective temperatures unless convective overshoot at the edge of the convective core, of the order of a tenth of a pressure scale height, is taken into account.(3)that the p-mode characteristic frequency spacing for Procyon A should be in the range 25–30 μHz.The aim of this paper is to explore theoretically the potential ability of the p-mode and g-mode non-radial oscillation spectrum to throw light on two fundamental problems raised by our first study: Procyon A's evolutionary status, and its mass-luminosity relation.
The non linear dynamic of the ZZ Ceti variable GD 66
Authors: Auvergne Michel , Baglin Annie , Vauclair Gérard 
Published: June 2019

We present here a new method for analysing stellar variability: a geometrical study of the attractor associated with a variable star. In contrary to Fourier analysis, which focuses on times scales, this approach attemps to define the shape of the attractor in its phase space. It presents the advantage of being almost unsensitive to gaps in the data as long as uninterrupted sequences contain several tens of characteristic times. But, its noise sensitivity calls for very accurate photometry (10−4), still extremely difficult to perform up to now.A preliminary test has been done on the variable white dwarf GD 66 on data obtained by classical photometry from the ground.
Thermal processes in molecular gas
Authors: Chièze J.P. , de Boisanger C. 
Published: June 2019

The dynamics of the cold atomic and molecular gas, on which we focus here, is strongly affected by non equilibrium heating and cooling processes. We give two different examples, in which the breaking of the thermal balance is due respectively to variations of the incident ultraviolet radiation flux, and non equilibrium abundances of H2 molecules in molecular clouds envelopes. Fluctuations of the ultraviolet radiation flux in clumpy molecular cloud envelopes result in the formation or the destruction of dense regions. Large density contrasts, greater than one order of magnitude, are easily achieved in cloud regions of moderate visual extinction. Condensation or expansion develop on quite short time scales, of the order of a few tenth of million year, and induce collective motions which can feed turbulence.Another example of the importance of out of equilibrium thermochemical processes is furnished by the study of the H — H2 transition layers in molecular clouds envelopes. They turn out to be unstable against convection-like motions, driven by the energy released by H2 photodestruction. The gas velocities involved in these motions are, again, typical of the observed turbulent velocity in clouds envelopes.
Global properties of star formation in Taurus
Authors: de Castro Ana I. Gomez , Pudritz Ralph E. 
Published: June 2019

A careful analysis of the data available in the literature has been carried out to determine the global properties of star formation in Taurus. Three main trends arise in the data:
(1)the magnetic field in Taurus is distorted in the direction of the proper motions of the T Tauri Stars (TIS) (see below).(2)the groups with different proper motions seem to have different stellar contents. An analysis of the stellar population based on the equivalent width of Hα, W(Hα), shows that groups I and III (Jones and Herbig, 1979) have approximately the same population (TTS show either large or small W(Hα)). However in group II (central part of the cloud) there are also a large number of stars with intermediate W(Hα) (Gomez de Castro and Pudritz, 1990).(3)the mass function of the NH3 cores (thought to be "protostellar cores") is dN/dM< M∝ with α=−1.5, in contrast with the IMF of the TTS given by Cohen and Kuhi (1979), α=−2.5.
Only point (1) will be outlined in this contribution.
Polarization of background starlight and the structure of the interstellar magnetic field
Authors: Goodman Alyssa A. , Myers Philip C. , Bastien Pierre 
Published: June 2019

We discuss the use of polarization maps of background starlight in studying the structure of the interstellar magnetic field. We make the assumption that the polarization observed is due to magnetically aligned dust grains associated with interstellar clouds along the line of sight, and that the position angle (ΘE) of polarization observed gives the direction (modulo 180°) of , the plane-of-the-sky projection of the (line-of-sight-averaged) magnetic field.There are two basic points in this paper. (1.) Out of context, the projected orientation of an elongated dark cloud may appear special (e.g. roughly "parallel" or “perpendicular”) in relation to the local (plane-of-the-sky) field direction given by polarization observations, but, when the view is expanded to include an entire complex of dark clouds, the shape and orientation of clouds within a complex often appears unrelated to the field structure. (2.) the dispersion in the postion angle of polarization observed in a region of the sky contains information about the ratio of the strength of the uniform (straight) component of the local magnetic field as compared to the dispersion (nonuniform component) in the field. Furthermore, in a region where Zeeman measurements covering the same region as polarization observations have been made, the uniform-to-nonuniform ratio deduced for the field from polarization data, can be combined with information about the line-of-sight field and an estimate of the correlation length of the field, to describe the magnetic field in three dimensions. We discuss the results of such an analysis for the dark cloud Lynds 204 (L204).
Comparison of turbulence in HII regions and molecular clouds
Authors: O'Dell C. R. 
Published: June 2019

Both the HII Regions and the Molecular Clouds show broadening of their emission lines beyond that expected from thermal motion and this is ascribed to turbulence. Turbulence in molecular clouds generally agrees with a model where the velocity of motion is determined by the Alfv én velocity.Turbulence in Galactic HII Regions and Giant Extragalactic HII Regions can also be studied by the width of the emission lines. The magnitude of the turbulent velocities in these regions are characteristically about 10 km/s. There is a general increase in turbulent velocity with the size of the HII Region, and this relation is close to but different from the one third power dependence expected from the most naive application of Kolmogorov theory. When a detailed study is conducted of each Galactic HII Region by means of the structure function, one finds that there is not agreement with Kolmogorov theory.The Size-Turbulent versus Velocity relation for Galactic HII Regions differs slightly from the better defined velocity relation for Giant Extragalactic HII Regions. This difference is probably due to the fact that the larger extragalactic objects are probably complexes of multiple individual HII Regions. There is no evidence that broadening of extragalactic HII Regions is due to motion about a common center of mass.
Synthetic linemaps for hierarchial clouds
Authors: Stenholm L. G. 
Published: June 2019

Molecular clouds are characterized by large density contrasts and pronounced internal motions. Some information on their internal physics has been acquired through relatively simple data analysis and through theoretical modelling, mainly hydrodynamical calculations. More detailed radiative transfer models have been limited to spherical cloud models.A related but less recognized problem is the classification of molecular clouds, or otherwise stated, can we compress the information in the observed two-dimensional maps for various line parameters in such a way that the physical differences are retained, while the random component has been removed? This is a more fundamental formulation of the special problem of comparing the appearance of two molecular clouds, or of the problems of quantifying the velocity correlation within the clouds.
Examples of Gas Motion and Certain Hypotheses on the Mechanism of Stellar Outbursts
Authors: Sedov L. I. 
Published: June 2019

In connection with the problem of the explanation of stellar outbursts exact solutions for gas flows with spherical symmetry can be given in the following three cases.1. Propagation of detonation waves from the interior to the surface of a star, accompanied by an output of nuclear energy on the wave front. Effects of the increase of detonation velocity depending upon the law of density decrease from the center to the outer layer (failure of Chapman-Jourguet's rule) are investigated. As a result of a sufficiently rapid density decrease one obtains a complete dispersion of the detonation products with the formation of a vacuum near the center. Similar solutions are obtained for the spherical problem of the propagation of a rarefaction jump, accompanied by an energy output (a jump of flame front type) through a gas at rest.2. Perturbed gas motion due to an explosion caused by a sudden large output of energy inside a star. The energy is transferred to the surface together with the shock wave. Exact automodel solutions of the equations for adiabatic time-dependent gas motion, accompanied by the formation of a vacuum when γ=Cp/Cv = 4/3 and without it, are given, gravitation being taken into account. Some solutions for larger values of y are studied.3. Examples of dynamically unstable equilibrium states disturbed by an explosion followed by the development of a shock wave, propagating through a gas at rest with density gradient. A motion without energy output develops. The energy of the disturbed motion at any time is equal to the initial energy in the equilibrium state.
Variations in the Line Spectrum of A-Type Supergiants
Authors: Buscombe William 
Published: June 2019

Attention is drawn to a group of stars of luminosity class Ia, in which variation of radial velocity has long been known in semi-regular cycles of 5 to 30 days. The interval of approximate repetition appears to be positively correlated with the luminosity of the star.Recent spectrophotometry of the absorption lines, especially by Rosendhal, Aydin, Groth, and Buscombe shows a considerable variation in the strength of Balmer lines (with emission components detected at H∝), as well as those of metallic ions. The microturbulence parameter derived from curves of growth for Fe ii varies by a factor of two or more during some cycles.
On the Binary Nature of the Slow Nova, RR Telescopii
Authors: Webster B. L. 
Published: June 2019

Those novae known to be binaries generally have orbital periods of the order of hours, exceptions being the atypical recurrent novae T CrB and RS Oph, which have giant companions and probably much longer periods. Since the orbital period in a semi-detached system relates to the mechanism of current mass exchange and also to the extent to which the primary evolved before mass exchange took place at an earlier stage, it is of interest to see if any classical novae are in more widely separated systems.This communication concerns the star RR Telescopii, which has all the characteristics of a slow nova – a range in amplitude greater than seven magnitudes, a spectral type at maximum of F, and a decline through a nebular stage of increasing ionization level (e.g. Thackeray, 1955). RR Tel was seen as a variable before outburst, but little is known about this variable apart from its period of 387 days, although doubts have been expressed about its being a red variable (Payne-Gaposchkin, 1957). Dr Thackeray has Radcliffe spectrograms of RR Tel from soon after maximum to the present. On some of the more recent of these, bands of TiO have become visible, presumably as the hot star has faded, and Dr Thackeray and I interpret these as meaning that the original variable is still there and is an M giant. Thus RR Tel is in a binary system containing a giant M star and a hot companion and such a system cannot have an orbital period of hours like the classical novae mentioned above.In 1972, Dr Glass and I examined RR Tel in the infrared between 1.2 and 20 µ. The energy distribution does not resemble the cool star that might be expected, but is exactly like that of free-free radiation over the whole wavelength range. The puzzle is that the infrared is two orders of magnitude stronger than we would predict from the optical spectrum for free-free radiation.
A Search for ℓ = 2 Asymmetries in Bison Data
Authors: Chaplin W.J. , Elsworth Y. , Isaak G.R. , McLeod C.P. , Miller B.A. , New R. 
Published: June 2019

An in-depth discussion of the analysis presented here can be found in an up-coming paper (Chaplin et al., 1997).The presence of a magnetic field will raise the degeneracy in ℓ of the resonant p-mode oscillations, via perturbations resulting from the Lorentz force. These degeneracyraising effects will give rise to asymmetric mode-multiplet structures. Both Gough & Thompson (1990). and Dziembowski & Goode (1997) have addressed the implications and potential complications that might result from such phenomena. Here, in an attempt to reveal the presence of an asymmetric frequency structure in the low-degree ℓ = 2 modes, i.e. to measure the asymmetries
Excitation of Oscillations - An Update of Bison Data
Authors: Chaplin W. J. , Elsworth Y. , Isaak G. R. , McLeod C. P. , Miller B. A. , New R. 
Published: June 2019

BiSON is a 6-station, world-wide network of instruments which observe low-degree solar oscillations.Theory (Goldreich & Keeley, 1977) predicts that the probability distribution of the mode powers is expected to follow negative exponential statistics under the condition that the interval of time for which the modes are averaged is less than the lifetime of the mode. Simulations (Chaplin et al, 1997) confirm this. The first publication of such an analysis for real data (Elsworth et al., 1995) showed that the oscillations largely follow the predictions with a small excess of the very largest power in the modes. In this paper we extend the previous observations of BiSON data to 80 months of data taken during the declining phase of the solar cycle. The data span the period January 1990 to August 1996. The data have been analysed using Fourier transforms each about 1/2 day in length. The minimum data fill accepted in any one period was 0.7 (Elsworth et al, 1995). Below this fill the data were discarded. The resolution of such short transforms is insufficient to distinguish between the components of the even and odd mode pairs. The mode powers are calculated for mode pairs ℓ = 0 & 2 and ℓ=1&3.Comparison with theoretical predictions show that, as seen previously, there is still an excess of very high excitations which can be seen throughout the 80 months.
Asteroseismology of δ Scuti Stars: Observations
Authors: Breger Michel 
Published: June 2019

We review recent observational developments which provide important asteroseismological tools. Extensive multisite campaigns of individual δ Scuti stars show that 24 or more pulsation modes with ℓ = 0 to 2 can be detected photometrically. Spectroscopically, also about 30 modes have been detected, and these can be identified with modes of ℓ values up to 20. Since each technique favors the detection of specific types of modes, hundreds or thousands of modes must be excited in δ Scuti stars.We examine the quantities which can be matched between observations and theoretical models specifically computed for each star. Recent progress in tbe mode identification of multiple pulsation modes is illustrated by presenting an application of the phase shift method for the two stars, FG Vir and 4 CVn, recently measured by the Delta Scuti Network.
Theory of Formation of Massive Stars via Accretion
Authors: Yorke Harold W. 
Published: June 2019

The collapse of massive molecular clumps can produce high mass stars, but the evolution is not simply a scaled-up version of low mass star formation. Outflows and radiative effects strongly hinder the formation of massive stars via accretion. A necessary condition for accretion growth of a hydrostatic object up to high masses M ≳ 20M⊙ (rather than coalescence of optically thick objects) is the formation of, and accretion through, a circumstellar disk. Once the central object has accreted approximately 10 M⊙ it has already evolved to core hydrogen-burning; the resultant main sequence star continues to accrete material as it begins to photoevaporate its circumstellar disk (and any nearby disks) on a timescale of ∼105 yr, similar to the accretion timescale. Until the disk(s) is (are) completely photoevaporated, this configuration is observable as an ultra-compact Hii region (UCHii). The final mass of the central star (and any nearby neighboring systems) is determined by the interplay between radiation acceleration, UV photoevaporation, stellar winds and outflows, and the accretion through the disk.Several aspects of this evolutionary sequence have been simulated numerically, resulting in a “proof of concept”. This scenario places strong constraints on the accretion rate necessary to produce high mass stars and offers an opportunity to test the accretion hypothesis.