bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toward an Empirical Theory of Pulsar Emission
Authors: Rankin Joanna M. 
Published: June 2019

Polarized, pulsar profiles consist of two distinct types of emission units, core and conal components. Various configurations of these two basic units then underlie the 5 principal species of profile: conal and core single, conal double, triple, and multiple (5 comp.) profiles. Conal single profiles typically evolve through bifurcation into conal double forms at low frequency; whereas core single profiles evolve into triple forms at high frequency by adding pairs of conal “outriders”. Conal components and outrider pairs exhibit polarization properties compatible with a hollow-conical emission zone which spreads weakly at low frequency. The central core components in each profile species, by contrast, often exhibit circular polarization of symmetrically alternating sense. The triple profile is then most generally prototypical of pulsar emission, and the physical distinction between its outriding conal components and its central core emission feature are primary–implying two distinct corresponding radiation mechanism. (Ap. J. 274, 333/359).The isolated core components of stars with core single profiles exhibit little ordered modulation, nor do they null or evince of any sort of mode changing; many have featureless fluctuation spectra, while others exhibit low-frequency (P3 = 15–50 periods/cycle) features with which no orderly “drift” is apparently associated. The core components in triple, double (“saddle” region), and multiple profiles also exhibit these stationary, low-frequency fluctuations. “Drifting” subpulses are then an exclusively conal phenomenon. Systematic subpulse modulation (P3 = 2–15 periods/cycle) is associated with the conal components of stars with double, triple, and multiple profiles, but progressive, orderly drifting is observed only in conal single stars. The ensemble P3 values associated with the conal components of the various profile species seem indistinguishable, again suggesting that these species are geometry-specific manifestations of a single physical configuration. Mode changing and pulse nulling are exclusively associated with neither core nor conal emission, but rather connect the two. Mode changing is typically manifest as a reorganization of the conal constituents of emission about the profile's core component. Finally, pulse nulling is not so closely associated with spindown age as has been thought. Pulsars which null are members of older profile species to be sure, but within a given species, those stars which null are no older than those that do not. (1986 Ap. J. 301, 901)
Inverse Compton Scattering in Strong Magnetic Fields: Applied to the Radiation Mechanism of PSR 0531+21
Authors: Chen H. , Wu X.J. , Qiao G.J. 
Published: June 2019

In strong magnetic field near pulsar's surface, the quantum effect for electrons is quite complicated. The classical approximation may lose resonance feature, which gives much smaller cross-section.In this paper, we performed numerical integrations to get the total cross-section and the power spectrum of single electron. Thus considering the resonance, the inverse Compton scattering could be an efficient mechanism in strong magnetic fields. We have carefully calculated the power spectrum of single electron travelling through the isotropic thermal fields.
Production and Interaction of High Energy Neutrinos in Close X-ray Binaries
Authors: Harding A. K. , Barnard J. J. , Stecker F. W. , Gaisser T. K. 
Published: June 2019

Reports of air showers with E > 1015 eV from Cygnus X-3, LMC X-4, Vela X-1 and Hercules X-1 have been interpreted as requiring production of neutral secondaries by cosmic rays accelerated by the compact partner in these systems. If neutral pions are the source of photons that produce the observed air showers, then charged pions must also be produced, and they will give rise to neutrinos. We consider limits that may be placed on binary systems like Cygnus X-3 in which a neutron star is a strong source of ultra-high energy (UHE) particles that produce photons, neutrinos and other secondary particles in the companion star through nuclear interactions. The highest energy neutrinos (> 1 TeV), which have the largest interaction cross sections, are absorbed deep in the companion. From a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star, we estimate the neutrino production spectrum from an isotropic flux of monoenergetic 1017 eV protons and we estimate the resulting neutrino absorption in the stellar core. In the case of Cyg X-3 and LMC X-4, the cosmic-ray luminosities required to produce the observed gamma rays would result in energy deposition from neutrino absorption exceeding the intrinsic stellar luminosity of the companion. Over a timescale of 104−105 yr, the star would absorb its own binding energy and be disrupted. On shorter timescales, the energy deposition will cause significant expansion of the star, perhaps leading to quenching of high-energy signals from the source. From these results, we conclude that systems requiring intense UHE proton fluxes are either very young or the companion star is not the site of observed gamma-ray production. Alternatively, if the gamma-ray source is highly variable, the proton flux requirements would be lower, providing some relaxation of the above constraints.[See Gaisser et al. 1986, Ap. J. (Oct. 15), in press].
Ice Mantle Formation in the Envelopes of OH/IR Stars
Authors: Charnley S.B. , Smith R.G. 
Published: June 2019

We have computed ice column densities for a sample of O-rich late-type stars.Water ice is observed in the outflows from several late-type stars (e.g. Smith et al. 1988) and it is of some observational and theoretical importance to understand how common ice mantles may be and how their formation depends upon the physical conditions in the envelope, such as the radial distributions of density and temperature. We have developed a simple theory of the gas-grain interaction in circumstellar shells (Jura & Morris 1985; Charnley et al. 1992) and used it to compute ice column densities (Nice) and mantle thicknesses (d) for a sample of well-studied OH/IR stars (Herman & Habing 1985). The models are most sensitive to the dust and gas mass loss rates, as well as to the inner radius of the envelope, Ri, which is poorly determined. Representative results are presented in the Table below where Ri was estimated according to the prescription of Herman et al. (1986).
On the Evolution of Proto-Planetary Nebulae
Authors: Hu J.Y. , Jiang B.W. , Slijkhuis S. 
Published: June 2019

The ages of PNNe in our sample (Hu et al., 1990) were derived from the inner radius of the dust shell using the radiative transfer model fitting with SED and expansion velocities of envelopes obtained from radio molecular lines observations (if without radio data a Vexp of 15 km/sec was assumed). The objects are classified into the following groups:
1.invisible;2.M-type;3.F (or G)-type; and4.F (or G)-type with Ra emission.
Analysis of Hipparcos Measurements: Positions, Proper Motions, Parallaxes
Authors: Walter H.G. , Froeschlé M. , Falin J. L. , Hering R. , Kovalevsky J. , Lenhardt H. 
Published: June 2019

Using the first 12 months of HIPPARCOS mission data already reduced, a synthesis solution was obtained by both CERGA and ARI teams. The reduction includes two steps. In the first one the origins of individual reference circles are determined, thus constituting the HIPPARCOS celestial reference frame. This solution uses a subset of some 30 000 bright and evidently single stars in order to minimize possible corruptive effects on the system. In the second step, the abscissa measurements of all observed stars are substituted in the system and then processed star by star in a least squares adjustment providing the astrometric parameters (positions and parallaxes).The results of sphere solution and astrometric parameter determination are discussed. In this context error ellipses and internal errors are calculated. External errors are derived by comparison with suitable astrometric catalogues. Especially, for estimating the external errors of the HIPPARCOS measured FK5 stars the instrumental system was tied to the FK5 system by rigid rotations followed by comparisons of the positions with those of FK5. The mean internal errors of the HIPPARCOS positions of FK5 stars is 1.5 milliarcseconds (mas) while the standard deviation of the differences HIPPARCOS minus FK5 reaches 90 mas. For the 5022 measured parallaxes the mean internal and external errors are 3.8 mas and 16.7 mas, respectively. — The results of precision and comparisons with external data show that the accuracy predicted for the final catalogue can be reached.
The Mark IV VLBI Data-Acquisition and Correlation System
Authors: Whitney Alan R. 
Published: June 2019

Modern VLBI observations for both astronomy and geodesy continue to demand the utmost in sensitivity. Of the methods potentially available for increasing the sensitivity of continuum VLBI observations, increasing the recorded bandwidth is generally the most cost effective.Over the past two years a broadly-supported program has been underway at Haystack Observatory to increase the sensitivity of the Mark IIIA VLBI system by more than a factor of 2. The result is an upgrade to the existing Mark IIIA data-acquisition system, dubbed Mark IV, which increases the maximum data rate to 1024 Mbits/sec, more than quadrupling the maximum data-rate of the Mark IIIA.A new correlator, based on a new custom VLSI correlator chip is also being designed to support the 1 Gbit/sec data rates from the Mark IV data-acquisition-system. An international collaborative effort is being mounted to help defray the high costs of development.
Summary of a contribution on “the Magellanic Clouds”
Authors: Feast M. W. , Thackeray A. D. , Wesselink A. J. 
Published: June 2019

Combined spectroscopic and photo-electric observations of bright stars in the two Magellanic Clouds show that:
1)There is no marked difference between the stars observed in the two Clouds when compared with each other or with normal galactic supergiants, as judged by:
(a)direct spectroscopic comparison,(b)Hertzsprung-Russell diagram,(c)U, B, V plot.2)Stars observed in both Clouds suffer a small amount of absorption, the precise amount depending on the intrinsic colours adopted. How much of the absorption takes place within the Clouds remains to be determined.3)A reddening path has been determined by comparison of Cloud stars (little reddened) and galactic supergiants (heavily reddened). The observations are consistent with a single reddening path and have not yet suggested any difference in the absorbing properties of dust in the Clouds and in the Galaxy. A conclusion on this latter point must await observations of heavily reddened stars in the Clouds.
Summary
Authors: Tremaine Scott 
Published: June 2019

This is the first IAU symposium devoted specifically to elliptical galaxies. I would like to congratulate the organizers for initiating a symposium on such a well-defined topic with so many interesting puzzles. I have been impressed at this meeting by the great strides made in this subject over the last ten years, both in the quality and quantity of data and in the sophistication of the theoretical models. In addition, I'm sure that I express the sentiments of the great majority of the participants when I say what a pleasure it was to attend a meeting on galaxies in which there was not a single paper on spiral structure!Rather than attempting to give a general summary, I have chosen to concentrate on four specific topics which reflect some of my personal impressions of the meeting.
Direct IR Determination of the Stellar Luminosity Function to 0.2 M⊙ in Elliptical Galaxies
Authors: Gilmore G. , Arnaud K. 
Published: June 2019

SummaryWe present a determination of the stellar luminosity function in luminous elliptical galaxies which includes all stars more massive than 0.15 M⊙. This limit corresponds to masses beyond the maximum in the solar neighbourhood stellar mass function, and therefore includes effectively all the luminous mass. Galaxies with X-ray evidence for current massive star formation, also show no evidence for enhanced low mass star formation in their central regions. All elliptical galaxies studied to date have stellar luminosity functions for masses above 0.15 solar masses which do not differ significantly from that in the solar neighbourhood. Elliptical galaxies have stellar bolometric mass-to-light ratios of 2.5< M/L <5.0.
Shells around Tumbling Bars: The Mass Distribution Around NGC 3923
Authors: Dupraz Ch. , Combes F. , Prieur J.-L. 
Published: June 2019

In previous articles (Dupraz & Combes, 1985, 1986a), we showed that shells form with different geometries around prolate and oblate galaxies. However, theory and observations suggest that some ellipticals could be tumbling bars (Miller & Smith 1980; Müllenhoff & Marenbach 1986). Here we simulate the accretion of a small galaxy by a tumbling bar; the tumble period T& is kept free. Let Tp be the typical period of motion of a particle in the potential of the elliptical galaxy. Then we find (Dupraz & Combes, 1986b):a) When Tt > 3TP (Figure l a), shells form with the geometry of a static prolate potential, i.e., aligned with the major axis.When Tb < 3Tp (Figure lc), the particles feel the time-averaged potential, which is oblate: the shells display the typical oblate geometry. But there is no confusion with a static oblate shell galaxy, because the tumbling bars must be seen edge -on for the shells to appear.c) When Tb ~ 3Tp (Figure lb), the outer shells form with the oblate geometry, the inner shells with the prolate geometry. In between, no shells form, because particles follow resonant (non-radial) motions.
Numerical Investigation of the Density Distribution of Stars and the Dispersion of Velocities in Spiral Galaxies
Authors: Zhou Hong-Nan 
Published: June 2019

We use a three-component model of a spiral galaxy, given by (Huang et al., 1979):
1.An outer halo with a gravitational potential of the form

where R2 = x2 + y2 + z2, M1 = 1.2 × 1011M⊙ and b1 = 1.1 Kpc.2.A nucleus, with a gravitational potential given by

where M0 = 1.1 × 107M⊙, and b0 = 0.61 × 10−2 Kpc.3.A self-gravitating disk containing N stars. The density distribution in the z-direction is assumed to be:

where α = 2.1 Kpc−1 is the equivalent semi-thickness of the galaxy, and σ(r) is the surface density. We consider three different initial expressions for σ(r):
i.A Toomre (1963) disk.ii.A uniform distribution.iii.An exponential distribution.
Gas Dynamics in the Galactic Centre: Gravity vs. Magnetism
Authors: Pudritz Ralph E. 
Published: June 2019

This contribution is a summary of an impromptu and extremely interesting discussion on the nature of the forces acting on gas in the galactic centre. The origins of the gas motions in the central few parsecs are crucial for clarifying many important problems about galactic nuclei. Some of the many gas dynamics issues that were raised include: 1. are there explosive events in the galactic centre which produce outward moving gas clouds (see Heyvaerts, these proceedings)? 2. are the streamers of gas due to the tidal disruption of molecular clouds that stray in too deep in the galactic centre's tidal field (see Serabyn, these proceedings)? 3. is there circular gas motion which would be important in constraining the nature of the mass distribution inside scales of a few pc (see review by Townes, these proceedings)?The discussion centered on gas dynamics in the molecular torus and ionized gas streamers on the 2–5 pc scale. Because reliable measurements of the magnetic field strength in the galactic centre are not yet available, several of the key points of contention will not be finally settled until the data are in. Be this as it may, the discussion boiled down to the issue of whether gravity or magnetic fields were responsible for the structures and morphology on this scale. Accordingly I will label the arguments of the two relevant camps by G (for gravitational fields as the predominant shaper of things) and M (for magnetic fields as the important agents).
Multi-Array λ2 and 6cm Radio Continuum Observations of Sgr A West
Authors: Yusef-Zadeh F. , Morris Mark , Ekers Ron 
Published: June 2019

Sub-arcsecond (down to 0.1″ × 0.2″) radio continuum observations using the VLA2 in a number of configurations have been carried out in order to investigate the fine-scale morphological details of the ionized gas and the distribution of spectral index along the triskelian-shaped figure of Sgr A West. In addition to finding a number of isolated patches of thermally-emitting gas and an absorbing feature at λ6cm within three arcminutes of the Galactic center, we have observed:1) radio continuum emission from IRS-7, implying that the stellar wind from this supergiant is externally ionized. An improved position for this object was obtained.2) the circular mini-cavity located along the east-west bar of Sgr A West. This feature has a diameter of 2-arcseconds and may have been created by a spherical wind, the source of which is yet to be identified; the seemingly most plausible candidate, IRS-16, is offset by 3″ from the center of the cavity.Spectral index maps having a resolution of 0.7″ × 0.3″ were made from scaled array observations at λ2cm and 6cm. They show that the eastern arm has a spectral index near −0.1, while the northern arm and the bar have positive spectral indices, indicating perhaps a partial opacity effect. The spectral index of IRS-7 is +0.6, consistent with that expected from a completely ionized stellar wind.
Subfuors in Orion association
Authors: Gasparian L.G. , Melkonian A.S. , Ohanian G.B. , Parsamian E.S. 
Published: June 2019

Results of spectral and photometric observations of Sugano star = V1143 Ori in brightness minimum and near it are given. Emission lines of HI, CaII, FeI, TiI, TiII and TiO absorption bands are detected. The appearing envelope is observed also in minimum. A brightness increase of Shanalstar V1118 Ori is observed. In its spectrum lines of HI, CaII, FeI, FeII are found, testifying to formation of an envelope.During the last ten years data on T Tau type stars which have fuor-like outburst-subfuors were obtained. Two such stars were found in Orion association. These are V1118 Ori [1] and V 1143 Ori [2,3]. In recent years, in Byurakan observatory observations of these stars have been made.
Formation of Twin Clusters in a Galactic Tidal Field
Authors: Theis Christian 
Published: June 2019

The formation of globular clusters is still an unsolved problem. Though most scenarios assume a massive molecular cloud as the progenitor, it is unclear how the cloud is transformed into a star cluster. Here a scheme of supernova (SN) induced cluster formation is investigated. In this scenario the expanding SN shell accumulates the mass of the cloud. This is accompanied by fragmentation resulting in star formation in the shell. If this stellar shell expands sufficiently slowly, its self-gravity leads to a recollapsing shell, thus forming one or several stellar clusters.In this paper N-body simulations of collapsing shells moving on circular orbits in a galactic potential are presented. It is shown that typical shells (105 M⊙, 30 pc) evolve to twin clusters in the galactocentric distance range between 3 and 11 kpc. Their masses show a strong radial trend: on orbits inside 5 kpc both clusters have almost equal mass. Outside 5 kpc the more massive twin cluster contains about 55% of the shell's mass, whereas the mass of the smaller decreases linearily to 15% at 11 kpc. Outside 11 kpc the collapsing shells end up in a single cluster. Inside 3 kpc the shells are tidally disrupted and only fragments substantially less massive than the initial shell survive.
Tycho Astrometry from 30 Months of Satellite Mission
Authors: Høg E. 
Published: June 2019

The Hipparcos satellite's star mapper gives photon counts in two spectral channels simultaneously, close to Johnson B and V. The transit times and the signal amplitudes for each star across two groups of four slits are derived and used for astrometry and photometry, respectively, and this constitutes the Tycho project. The present paper describes results of Tycho astrometric data processing, leading from the transit times to the astrometric parameters of the Tycho stars.Some 30 months of Tycho observations, i.e. about 80 percent of the Hipparcos-Tycho mission, have been used to produce a working catalogue of Tycho positions, proper motions and parallaxes of a million stars. The external errors of this preliminary catalogue have been determined by comparison of 98 000 stars common with a preliminary, but much more accurate Hipparcos catalogue. External systematic errors of positions and annual proper motions are less than 0.5 milliarcsecond (mas) and the accidental errors per star are about 30 mas rms at V = 10.5 mag, the median magnitude of the catalogue. It is concluded that a satisfactory accuracy has been achieved.
Astrometry with the HST Planetary Camera
Authors: Girard T. M. , Li Y. , Van Altena W. F. , Nunez J. M. , Benedict G. F. , Duncombe R. L. , Hemenway P. D. , Jefferys W. H. , McArthur B. , McCartney J. , Nelan E. , Shelus P. , Story D. , Whipple A. L. , Franz O. G. , Wasserman L. W. , Fredrick L. W. 
Published: June 2019

The astrometric capability of the Hubble Space Telescope Planetary Camera (WF/PC1) is investigated, motivated by a study of the internal velocity distribution of globular clusters. The astrometric accuracy of the HST PC will be determined ultimately by 1) the accuracy to which the aberrated images can be ‘centered’, and 2) the accuracy to which the distortions across the PC field can be modeled. A series of overlapping exposures of two clusters, NGC 6752 and M15, are utilized to examine these issues.We have made use of maximum-likelihood image reconstruction to address the first issue, with good success. Reconstruction improves both the detectability and precision of the image centers. A preliminary exploration of the second issue, that of modeling the distortion across the PC field, is also presented, using positions derived from the multiple overlapping exposures.
HST in Search of Binaries among Faint Members of the Hyades Cluster
Authors: Franz O. , Kreidl K.J. , Wasserman L.H. , Bradley A.J. , Benedict G.F. , Duncombe R.L. , Hemenway P.D. , Jefferys W.H. , McArthur B. , Nelan E. , Shelus P.J. , Story D. , Whipple A.L. , Fredrick L.W. , Van Altena W.F. 
Published: June 2019

The HST Astrometry Science Team is using the Fine Guidance Sensors (FGS) in the Transfer Function (TF) Scan mode to search for binaries among the faint members of the Hyades cluster. To date (March 1994), nine binaries have been discovered among 24 stars examined. The closest pair (total V=13.5) has a separation of 0.051 arcsec; the faintest (sep=0.287 arcsec) has magnitudes V=15.0 and 16.5; neither object posed a challenge to the capabilities of FGS. For another pair, two observations 152 days apart show a 13 deg change in position angle, indicating rapid orbital motion. One decade should suffice to define the orbit with angular dimensions of sub-millisecond of arc accuracy.Clearly, this work will soon permit mass determinations for low-luminosity members of the Hyades cluster. Moreover, information on the frequency of binaries will provide insight into the role of duplicity in star formation and in the dynamic evolution of the cluster. To be truly useful, a census of binaries in the Hyades (and other clusters) must ultimately reach cluster members fainter than those currently under investigation, requiring astrometry with sub-millisecond of arc accuracy at near-infrared wavelengths.