bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of PSR 1641–45 Using Specialized Capabilities of the S2 VLBI Correlator
Authors: Rizzo D.A. Del , Carlson B.R. , Petrachenko W.T. , Everett J. E. , Cordes J. M.
Published: July 2016

The pulsar PSR 1641-45 was observed using the S2 VLBI Recording System at 1.6 GHz with radio telescopes at Tidbinbilla and Narrabri in Australia, and at Hartebeesthoek in South Africa. The data were correlated with the Canadian S2 VLBI Correlator using the ‘fast-dumping’ mode in conjunction with two independent pulsar gates. The high time and spectral resolution capabilities of this correlator permit a detailed examination of dispersion and dispersion-removal effects on individual pulses, and a comparison of these effects from pulse to pulse over the duration of the observation. We give a brief summary of the pulsar processing capabilities highlighted by examples from the PSR 1641-45 data.
PuMa, the new Dutch PulsarMachine
Authors: Kouwenhoven M.L.A. , van Haren P.C. , Driesens D. , Langerak J.J. , Beijaard T.D. , Voûte J.L.L. , Stappers B.W. , Ramachandran R.
Published: July 2016

PuMa is a fully digital PulsarMachine the operation at the Westerbork Synthesis Radio Telescope (WSRT). Its design is based on the use of Digital Signal Processors. It has two modes of operation: a baseband recording mode and a digital filterbank mode.
Unpulsed Optical Emission from the Crab Pulsar
Authors: Golden Aaron , Shearer Andy , Beskin Gregory
Published: July 2016

Using the high speed 2-d TRIFFID photometer, we have obtained phase resolved photometry of the Crab pulsar inUBVthat allows us to flux the unpulsed light curve component. Following de-extinction, weighted least-square fitting indicates a power-law exponent ofα= −0.62 ± 0.49. This is steeper than that reported for the peak components and its origin remains unclear with respect to contemporary magnetospheric theory.
Detection of Pulsed X-ray Emission from The Fastest Millisecond Pulsar PSR B1937+21 with ASCA
Authors: Takahashi Motoki , Shibata Shinpei , Torii Ken’ichi , Saito Yoshitaka , Kawai Nobuyuki , Hirayama Masaharu , Dotani Tadayasu , Gunji Shuichi , Sakurai Hirohisa
Published: July 2016

We report the first detection of the pulsed X-ray emission from the fastest millisecond pulsar known PSR B1937+21 (P=1.558msec) with ASCA. The pulsar is detected as a point source above ∼ 1.7keV, with no nebulosity indicated. The source flux in the energy band 2–10keV is found to bef= 4.3 × 10−13erg s−1cm−2, which corresponds to the luminosity ofLx= 4πD2f≈ 6.6 × 1032(D/3.6kpc)2erg s−1, whereDis the distance, and correspond to ≈ 6 × 10−4of the rotation power of the pulsar. The pulsation is found at the period predicted by the radio ephemerides with very narrow primary peaks, the width of which is about 1/16 phase ≈ 100μs near the time resolution limit (61μs) of the observation. The pulsed luminosity within the primary peak (1/16 phase interval) is found to befp= 4.0 × 10−12erg s−1cm−2. Although there may be a secondary peak, its statistical significance is too low to identify. Spectra of the whole source region and the primary peak are fitted by power law models to give photon indices of about unity for both.
Gamma Ray Pulsar Luminosities
Authors: McLaughlin Maura , Cordes James
Published: July 2016

We apply a likelihood analysis to pulsar detections, pulsar upper limits, and diffuse background measurements from the OSSE and EGRET instruments to constrain theγ-rays pulsar luminosity law. We find a steeper dependence on period and magnetic field at OSSE than at EGRET energies. We also find that pulsars may be an important component of the OSSE diffuse flux, but are most likely not important for EGRET. We estimate that as many as half of the unidentified EGRET sources may beγ-rays pulsars. Furthermore, we predict that GLAST will detect roughly 1000γ-rays pulsars, only 100 of which are currently known.
Energy Loss of Radio Pulsars
Authors: Beskin V.S. , Rafikov R.R.
Published: July 2016

Two-fluid effects on the radial 2D outflow of relativistic electron–positron plasma are considered. It is shown that when the longitudinal electric current is smaller than the Goldreich–Julian one, almost all electromagnetic energy is transformed into the energy of particles in the narrow boundary layer near the light surface |E| = |B|.
Beaming Due to Comptonisation in X-ray Pulsars
Authors: Galloway D.K. , Wu K.
Published: July 2016

Comptonisation may play an important role in determining beam patterns and hence pulse profiles in X-ray pulsars. We describe a Monte Carlo simulation used to investigate the spectra and pulse profiles emitted by two semi-infinite homogeneous cyclindrical accretion columns diametrically located on the surface of a ‘canonical’ neutron star.
Possible re-acceleration regions above the inner gap and pulsar gamma-ray emission
Authors: Hong B.H. , Qiao G.J. , Zhang B. , Han J.L. , Xu R.X.
Published: July 2016

We propose that the violent breakdown of the Ruderman-Sutherland type vacuum gap above the pulsar polar cap region may produce copious primary particles and make the charge density above the gap in excess of the Goldreich-Julian density. Such an excess residue of charge density may arise some re-acceleration regions above the gap due to the space-charge-limited flow mechanism. Such re-acceleration regions, if exist, may accelerate particles to carry away more spin-down energy, and may have some implications for pulsar γ-ray emission.
Charge Densities above Pulsar Polar Caps
Authors: Jessner A. , Lesch H. , Kunzl Th.
Published: July 2016

A simplified model provided the framework for our investigation into the distribution of energy and charge densities above the polar caps of a rotating neutron star. We assumed a neutron star withm= 1.4M⊙,r= 10km, dipolar field |B0| = 1012G,B||Ω and Ω = 2Π · (0.5s)−1. The effects of general relativity were disregarded. The induced accelerating electric fieldE||reachesE0= 2.5 · 1013V m−1at the surface near the magnetic poles. The current density along the field lines has an upper limitnGJ, when the electric field of the charged particle flow cancels the induced electric field: At the polesnGJ(r=rns,θ= 0) = 1.4 · 1017m−3.The work function(surface potential barrier)EWis approximated by the Fermi energyEFof magnetised matter. Following Abrahams and Shapiro (1992) one needs to revise the surface density from the canonical 1.4 · 108kg m−3down toρFe = 2.9 · 107kg m−3. Withwe obtain a value ofEF=Ew= 417eV. There are two relevant particle emission processes:Field (cold cathode) emissionby quantum-mechanical tunneling of charges through the surface potentialandthermal emissionwhich is a purely classical process. In strong electric fields it is enhanced by the lowering of the potential barrier due to the Schottky effect. The combined Dushman-Schottky equationwithtells us, thatat temperatures> 2 · 105K the the Goldreich-Julian current can be supplied thermal emission alone. The surface temperature however has a lower limit in the order of 105K due to the rotational braking. Therefore, in most cases a sufficient supply of charges for the Goldreich-Julian current is available and the electrical field accelerating the particles will be quenched as a result of their abundance. Otherwise a residual equilibrium electric field Eeqremains with:and hence the equilibrium density is:n=nfieid(Eeq,EW) +nDS(Eeq,EW,T) For a temperature just below the onset of thermal emission (T= 1.85 · 105K) the charge density is found to vary almost linearly with the work functionEWfor values ofEWbetween 0.3 and 2 keV. At the chosen value forEWof 417 eVthe residual electric field amounts to only 8.5% of the vacuum value. Even in the residual electric field the particles are rapidly accelerated to relativistic energies balanced by inverse Compton and curvature radiation losses.
Emission of particles and photons in the pulsar polar cap
Authors: Tsygan A. I.
Published: July 2016

We study emission of particles and photons from a pulsar polar cap. The Goldreich-Julian model for the regime of free emission of charged particles from the neutron star surface is used. In this case the electric field is generated due to the general relativistic effect of dragging of inertial frames. The spectra and shapes of gamma-ray pulses, the parameters of the electron-positron plasma and the intensity of X-ray emission from hot spots in the polar region of radio pulsars are discussed. The effect of non-dipole magnetic field on X-ray emission of polar caps is considered. It is shown that the increase of magnetic line curvature leads to much smaller temperatures and X-ray luminosities of the polar caps as compared with the purely dipole field.
High-energy accelerators above pulsar polar caps
Authors: Xu R. X. , Qiao G. J. , Zhang B.
Published: July 2016

Similar to the terrestrial collision accelerators of e±, another kind of accelerator is above a positively or negatively charged pulsar polar cap. In the case of pulsars with magnetic axis parallel (anti-parallel) to rotational axis, relativistic e+(e−) with Lorentz factorγ~ 106hit the electrons in the polar caps. These scenarios are investigated both for pulsars being BSSs (bare strange stars) and for pulsars being NSs (neutron stars). Such a study may be valuable to differentiate NSs and BSSs observationally.
A full polar cap cascade model: pulsar γ-ray and X-ray luminosities
Authors: Zhang Bing , Harding Alice K.
Published: July 2016

We propose a full polar cap cascade model which includes the curvature and inverse Compton emission of the primary particles, and both synchrotron radiation and inverse Compton of the higher generation pairs. Such a full cascade model can reproduce both theLγ∝ (Lsd)1/2and theLx~ 10−3Lsddependences observed from the known spin-powered pulsars.
A VLBI Search for a Pulsar Nebula in SN1993J in the Galaxy M81
Authors: Bartel N. , Bietenholz M. F. , Cannon W. H. , Rupen M. P. , Beasley A. J. , Graham D. A. , Altunin V. I. , Venturi T. , Umana G. , Conway J. E.
Published: July 2016

Twenty consecutive VLBI images of supernova 1993J in M81 from the time of explosion to the present show the dynamic evolution of the expanding radio shell of an exploded star. No clear sign of a pulsar nebula, expected to have a spectral luminosity 10 to 1,000 times larger than that of the Crab, has yet been seen. The upper limit on the brightness at 8.4 GHz in the center of the shell in one of the latest images is 0.15 mJy per beam of 0.4 mas2, corresponding to a spectral luminosity of that of the Crab. Any nebula that may have formed in the center is probably still obscured by the surrounding thermal matter with no substantial filamentation having yet occurred in the latter.
Pulsar distance measurements using interstellar scintillation data
Authors: Smirnova T.V. , Shishov V.I.
Published: July 2016

We evaluate the distance to pulsars and the location of the effective scattering layer of turbulent medium along the line of sight on the base of analysis diffractive and refractive scintillation of pulsars. In some cases our estimations of distances to pulsars as more than 3 times differ from the values quoted in the TML pulsar catalog.
Recycling NSs to ultrashort periods: a statistical analysis of their evolution in the μ – P plane
Authors: Possenti Andrea , Colpi Monica , Geppert Ulrich , Burderi Luciano , D’Amico Nichi
Published: July 2016

We investigate the statistical evolution of magnetic neutron stars recycled in Low Mass Binary (LMB) systems, simulating synthetic populations. Irrespective to the details of the physical models, we find to be significant the fraction of neutron stars spinning close to their mass shedding limit relative to the millisecond pulsar population. The simulated neutron stars show a tail in their period distribution at periods shorter than 1.558 ms, the minimum detected so far. Crustal magnetic field decay models predict also the existence of massive rapidly spinning neutron stars with very low magnetic moment.
HST Observations of PSR J2051–0827: Asymmetry, Variability and Modelling
Authors: Stappers B. W. , van Kerkwijk M. , Bell J. F.
Published: July 2016

Using the Hubble Space Telescope we have successfully detected the ”dark” side of the optical companion to the eclipsing millisecond pulsar J2051–0827. These data were obtained over a number of system orbits and clearly show that there is variability in the optical flux, particularly at orbital phases after maximum light. Comparison with phases before maximum light suggests this variation is due to an additional component. The data are modelled by a gravitationally-distorted low-mass secondary star which is irradiated by the impinging pulsar wind. The quality of the model fits are however limited by the variability.
Are there Strange Stars in the Universe?
Authors: Bombaci Ignazio
Published: July 2016

Strange stars could represent a new class of stellar compact objects, where a new phase of dense matter (deconfined strange quark matter) comes into play. Here, we discuss some possible observational evidence for their existence.
Studying pulsars with the SKA and other new facilities
Authors: Bell Jon
Published: July 2016

The Square Kilometre Array (SKA) is a proposed next generation radio telescope. Between now and 2005 this project is in a technology development and prototyping phase, with construction likely to begin in ~ 2010. This paper describes what the SKA may be like, its key features, the motivation for building it and where you can access more details about it. Its is important to see any new facility in context, so other new facilities are also discussed. Avenues for future extensibility of the SKA other telescopes are covered, with some emphasis on multiple beam systems. Some suggestions for useful pulsar experiments and pulsar searches strategies are summarised. A conclusion is that the SKA may not be the most cost effective way to search for pulsars and that a 128 beam receiver system on an Arecibo like telescope working between 1 and 5 GHz may be a more cost effective approach.
Detecting Gravitational Waves from Quasi-Continuous Sources: the German-British Project GEO 600
Authors: Rüdiger Albrecht
Published: July 2016

At five sites, laser-interferometric detectors, with armlengths ranging from 0.3 to 4 km, are being built. By using advanced optical technologies early on, the German-British project GEO 600, although only intermediate in size (600 m), has good chances for a competitive sensitivity. Particularly the use of the so-calledsignal recyclingtechnique will allow a search for faint sources of only slowly varying frequency (pulsars, close binaries). First science runs of GEO 600 are expected in the year 2001.
Browsing through the Observing Books of Carloforte
Authors: Uras S. , Poma A. , Calledda P.
Published: July 2016

The history of the Carloforte ILS Station is also the history of all the people who have spent part of their life working there. Table 1 shows the names of these people from the beginning of the service till its end.

Running our eyes through the pages of the Carloforte ILS Station Observing books, we can read, beyond the cold figures that refer to the star transits, a lot of notes and comments that allow us to understand the high degree of humanity, scientific reliability and self-abnegation of the observers. Many of them, after their experience at Carloforte, had continued their activity as researchers in other fields of the Astronomy; just as an example, we may cite Bianchi, Volta, Martin, Righini, that respectively became Directors of the Astronomical Observatories of Brera, Turin, Trieste, Arcetri. We also may cite Camera, Cecchini, Nicolini, that played important roles in the Central Bureau of ILS when this one was awarded to Italy. A few on the list were just temporary observers, and their history outside of the Observatory remains unknown for us.
Survey of Observational Techniques and Hipparcos Reanalysis
Authors: Vondrák Jan , Ron Cyril , Pešek Ivan
Published: July 2016

Polar motion and Universal Time have been regularly determined since 1899 and 1956, respectively, at a number of observatories all over the world. Before the International Earth Rotation Service (IERS) was established in 1988, the classical astrometry instruments such as visual zenith-telescopes, PZTs, transit instruments, astrolabes etc. were used. The survey of all these instruments and the methods of observation used is described. The values of instantaneous latitude and UT0-UTC made at a set of selected observatories and based on individual star observations have been collected at the Astronomical Institute in Prague during the past years. They were recalculated using the most recent astronomical standards and the Hipparcos Catalogue, and used to determine the Earth orientation parameters (polar motion, celestial pole offsets and Universal Time). The most recent solution, based on about 4.5 million observations with 47 different instruments at 33 observatories, is described and the results of polar motion presented.
The Markowitz Wobble
Authors: Poma A.
Published: July 2016

Several decades ago Markowitz was the first to report the existence of fluctuations in the motion of the Earth’s axis with a period of about twenty-four years. This empirical term was often considered not real but only an artifact due to local effects. In this paper long-term variations and the relationship between the 30-yr Markowitz wobble and changes in the Earth’s rotational speed are briefly discussed.
ILS Polar Motion Results at Interannual Time Scales
Authors: Li Z.X. , Pâquet P.
Published: July 2016

From a comparison between the ILS interannual polar motion and that calculated from the ILS latitude data but with different combinations of the ILS stations, the ILS polar motion has been studied at interannual time scales. It has been concluded that the interannual polar motion reduced from the ILS observations is influenced by an unknown phenomenon of the Earth; the obtained polar motion is reflecting, at interannual time scales, the real motion of the pole at certain epochs only.
Free Frequencies for a Three Layered Earth Model
Authors: Escapa Alberto , Getino Juan , Ferrándiz J.M.
Published: July 2016

The Hamiltonian formalism is applied to the treatment of the free motion of a three layered Earth model, where the effects of the pressure coupling, centrifugal deformation as well as gravitational and viscous-electromagnetic torques, are considered. Analytical expressions of the four normal modes of this dynamical system are derived.
Mathematical Theory of Motion of Revolving Axes on the Surface of Planets
Authors: Kozhanov T.S. , N. Nizyarov
Published: July 2016

Let a planet perform translational and rotational motions in the field of solar attraction. Let’s assume that the observer on the surface of the planet, knows (even approximately) an orbit and variations of orientation. It is necessary to clarify the motion of the instanteous rotation axis on the planet’s surface from the observer’s point of view on the planet’s surface.

1. The coordinate system, to describe the translational and rotational motions of planets around the Sun we shall take into account the properties of orbits of solar system planets, namely:

1)

All planets move in the same direction as the Sun revolves.

2)

At the present time, from June until December the Earth’s inhabitants see the north pole of the Sun and during the second half of year the southern one (Beleckei 1975, Menzel 1959).
The Magnetic Variable Stars
Authors: Wolff Sidney C.
Published: July 2016

The peculiar A stars were first noted as peculiar because they exhibit anomalously strong lines of one or more of the elements Si, Cr, Mn, Sr, and Eu. These diverse objects are all called Ap stars because their assigned spectral types fall predominantly in the range B9-F0. Recent studies have suggested, however, that the Ap stars should be subdivided into two groups. The stars characterized by enhanced lines of Mn, and usually Hg as well, differ from the remaining Ap stars in composition and binary frequency; there are no confirmed spectrum, photometric, or magnetic variations in any Hg-Mn stars; and the upper limit on the magnetic field strengths of the Hg-Mn stars is about 200 gauss. Because of these differences, many observers (e.g. Sargent and Searle 1967; Preston 1971b; Wolff and Wolff 1974) have suggested that the Hg-Mn stars are fundamentally different in their properties, and possibly in their origin and evolution, from the SiCrEuSr stars. We shall be concerned today only with this latter group of stars, and in the review that follows only members of the SiCrEuSr class of stars will be referred to as Ap stars.
Cepheid Pulsation Theory and Multiperiodic Cepheid Variables
Authors: Cox A. N. , Cox J. P.
Published: July 2016

In this review of the situation with regard to the multiperiodic Cepheid variables, our subject matter is divided into four parts. The first discusses general causes of pulsation of Cepheids and other variable stars, and their locations on the H-R diagram. For this section we draw upon the work during the past 10-15 years of J. P. Cox, Baker, Kippenhahn, A. N. Cox, King, Christy, Castor, Stobie, Stellingwerf, Davey, Iben, and Tuggle, mostly with the small amplitude linear nonadiabatic radial pulsation theory. In the second section we review the linear adiabatic and nonadiabatic theory calculation of radial pulsation periods and their application to the problem of masses of double-mode Cepheids. Contributions discussed are by Cogan, J. P. Cox, King, Stellingwerf, Petersen, Hansen, and Ross. Periodic solutions, and their stability, of the nonlinear radial pulsation equations for Cepheids and RR Lyrae stars are considered in the third section. This research has been done by Stellingwerf with previous development of methods by Baker and von Sengbusch and current work by A. N. Cox and Davey at Los Alamos. In the last section we give the latest results on nonlinear, nonperiodic, radial pulsations for Cepheids and RR Lyrae stars. This work has been done by Stellingwerf, King, A. N. Cox, J. P. Cox, and Davey.
On the Solution of the Exterior Boundary Value Problem with the Aid of Series
Authors: Petrovskaya M. S.
Published: July 2016

The exterior gravitational field depending on the Earth’s non-sphericity is usually determined from the analysis of satellite data or by the solution of the exterior boundary value problem. In the latter case some integral equations are solved which correlate the exterior potential with the known vector of gravity and the shape of the Earth’s surface (molodensky problem). In order to carry out the integration the small parameter method is applied. As a result, all the quantities which involve the equations should be expanded in powers of a certain small parameter, among these being the heights of the Earth’s surface points as well as the inclination α of the Earth’s physical surface. Since the angle α can be significant, especially in mountains, and in fact does not depend on any small parameter then the solution of integral equations is possible only for the Earth’s surface which is smoothed enough.
New Formulation of De Sitter’s Theory of Motion for Jupiter I-IV. I. Equations of Motion and the Disturbing Function
Authors: Aksnes K.
Published: July 2016

A brief discussion is given of the basic features of de Sitter’s theory. The main advantage of his theory is that it contains no small divisors, thanks to the use of elliptic rather than circular intermediate orbits in the first approximation. A 50-year extension of the satellite observations available to de Sitter makes it desirable to rederive the elements of his intermediate orbits, whose perijoves have a common retrograde motion. Furthermore, the theory suffers from a convergence problem, which can be avoided by reformulating the theory in terms of canonical variables, a task that is begun here. We adopt a formulation in Poincaré’s canonical relative coordinates rather than, as customary, in ordinary relative coordinates or in the Jacobian canonical coordinates. By means of the generalized Newcomb operators devised by Izsak, the disturbing function is expanded in a form that is very convenient for use with the modified Delaunay variables, G, L – G, H – G,l+ ω + Ω,l, and ω and their associated Poincaré variables.
Solar Perturbations in Saturnian Satellite Motions and Iapetus-Titan Interactions
Authors: Kozai Yoshihide
Published: July 2016

Solar perturbations in Saturnian satellite motions are computed with accuracy of 10-5 to try to analyze observed data of orbital elements for Titan. Perturbations due to Iapetus in Titan’s orbit are also developed by taking into account the motion of the orbital plane of Iapetus. Then the mass of Iapetus is determined by the motion of the orbital plane of Titan. Also oblateness parameters of Saturn and the mass of Rhea are determined by seven secular motions for six satellites. It is also found in the analysis that G. Struve’s values for the semi-major axes adopted in almanacs differ from the computed values by using the new data.
Gravitational Restricted Three-Body Problem: Existence of Retrograde Satellites at Large Distance
Authors: Benest Daniel
Published: July 2016

In the frame of the gravitational restricted three-body problem, we study by numerical simulation the retrograde satellites -and their stability-at large distance. In the circular plane case, the stable satellites mostly surround (in the phase-space X°-V°) the characteristic of a family of single-periodic orbits where this family is stable, and librates (in the physical space) around a curve which corresponds to the nearest (in the phase-space X°-V°) periodic orbit. An analytical analysis of this libration is made for Hill’s case. The beginning of the study of the three—dimensional orbits is presented.
Periodic Orbits of the First Kind in the Restricted Three-Body Problem When the More Massive Primary is an Oblate Spheroid
Authors: Sharma R.K.
Published: July 2016

The existence of periodic orbits of the first kind using Delaunay’s canonical variables is established through analytic continuation in the planar restricted three-body problem when the more massive primary is an oblate spheroid with its equatorial plane coincident with the plane of motion.
The Infrared HR Diagram - The IRAS Two-Colour Diagram of AGB Stars and Its Evolutionary Explanation
Authors: Shi-yang Jiang
Published: July 2016

In recent years several people have used the IRAS data to produce ([25] - [60]) / ([12] - [25]) two-colour diagrams of late type stars (Van der Veen and Habing 1988; Qing-Quan 1988). The distribution of all these AGB stars are concentrated in a limited area, and any special series of stars are limited on a definite curve which can be represented by an exponential equation like.
Photospheric Models for Cool Giant Stars
Authors: Bessell M.S. , Scholz M.
Published: July 2016

Models for M and C giant stars differ from those for hotter stars by having complicated state equations and opacities dominated by lines from diatomic and polyatomic molecules. In addition many cool giants have atmospheres which are extended, and which cannot therefore be adequately modelled using a plane-parallel approximation. Mira variable stars have atmospheres which are even more extended due to the regular passage of shock waves through their atmosphere. In this review we will discuss recent modelling of such atmospheres and show comparisons with observations of variable and non-variable M stars.
BD-21.3873: An Heavy Element-Rich Symbiotic?
Authors: Jorissen A.
Published: July 2016

The recent discovery (Jorissen and Mayor, 1988) that not only Ba II but also S stars appear to belong predominantly to binary systems with periods of several hundred days raises the question of the similarity between these peculiar red giants and symbiotic stars. That question has been addressed by looking whether symbiotics have enhanced s-element lines in their spectra. In most cases, definite conclusions are hampered by the composite nature of such spectra. Nevertheless, in the case of the “yellow symbiotic” BD -21.3873, the spectral classification criteria provided by Keenan and Wilson (1977) allow to assign without ambiguity the type GIII-II to BD -21., 3873, the symbiotic nature of that star being apparent only through weak Fe II emission lines. Some heavy element lines (such as Sm II λ4220.7, λ4221.1 and λ4566.3) are clearly enhanced. Comparison with a spectrum of a G3Ib supergiant ensures that luminosity is not responsible for that effect. Moreover, some of these spectral features are also enhanced in Barium stars, as seen on a comparison spectrum of a Barium Star.
Comparison of Blanketing in a 3000 K, Oxygen Rich, Spherically Symmetric Model with the Blanketing in Non-Mira, M Giant Stars
Authors: Augason G.C. , Brown J.A. , Alexander D.R.
Published: July 2016

A flux curve has been computed using a preliminary, spherically symmetric model for a 3000 K, oxygen rich, giant star. The model was computed using the opacity sampling method with an improved frequency set, improved molecular equilibrium data and an improved set of opacities. In addition, a continuum flux curve is computed using the same model and only continuum opacity sources. The relative and to some extent the absolute blanketing used to compute both the model and the flux curve derived from the model may be illustrated by dividing the normal flux curve by the continuum flux curve. This same procedure is used to illustrate the blanketing in an observed star by dividing the observed flux curve by the continuum flux curve. When this is done, the blanketing in an observed flux curve may be compared with the blanketing in a model. When this comparison is made, it is obvious that the treatment of blanketing in the “new” flux curve, computed using the spherically symmetric model and using new parameters, is superior to the flux curves based on earlier models. This is especially true in the regions of the fundamental, the first overtone and the second overtone of Co. Also, the new water vapor opacity is much improved. The new water vapor opacity is based on actual measurements of high temperature water vapor. Correct representation of water vapor opacity is extremely important for oxygen rich stars because it forms a psuedo continuum because of its many lines. The TiO opacity does not fit the observations well. When the spherically symmetrical model flux curve is compared directly to an observed flux curve, the new flux curve gives a better fit than do flux curves computed from previous models. There is still (at least for the non-Mira stars) a serious flux excess in the model flux curves at 1.6 microns in the region of the H minus b-f and f-f crossover. However, this excess is not as great for the spherically symmetric model as it is for earlier plane parallel models. It is not determined if this improvement is due to spherical symmetry or due to the new model parameters.
The Role of Binarity in the Evolution of Peculiar Red Giants
Authors: McClure R.D.
Published: July 2016

There are several types of Peculiar Red Giants (PRG's) which have enhanced s-process elements and/or carbon, but which cannot be explained by mixing during helium shell-flashing in the late stages of Asymptotic Giant Branch (AGB) evolution. These are the Ball, CH, sgCH, and the hotter R-type carbon stars. All these PRG's have absolute magnitudes which range down to zero and fainter. The Ball stars (Bidelman & Keenan 1951) are G-K giants whose spectra have strong CN and CH bands, and in extreme cases bands of C2 become noticeable. In addition they have strong lines of s-process elements such as Ball and SrII. The CH stars (Keenan 1942) are Population II equivalents of the Ball stars, and show similar spectral features, but with weaker metal lines, and usually stronger carbon bands. Bond (1974) introduced a new class of late F and G stars named the CH subgiants, which he suggests are fainter than the classical CH and Ball stars. They appear to be of mixed population (Luck & Bond 1982), and they are probably subgiants which will eventually evolve up the giant branch to become classical CH and Ball stars. The R-type carbon stars, at least the hotter (R0-R4) ones, differ from many of the other peculiar red giants in that they do not show enhanced s-process element abundances. The R stars have strong carbon bands, but relative to the N-type carbon stars they have less blue and ultraviolet absorption in their spectra. They range in absolute magnitude from near zero, similar to the Ball stars, up to several magnitudes brighter than this.
Red Giant Mass Loss and Planetary Nebula Formation
Authors: Huggins P.J. , Healy A.P.
Published: July 2016

It is generally believed that red giant mass loss plays some role in the formation of planetary nebulae (PNe), but the connection is not clearly understood. To investigate this issue we have undertaken an extensive search for molecular gas in PNe, which is likely to be remnant material of the red giant wind not yet ionized by the central star. The search has been carried out with the NRAO 12 m telescope in the 1.3 mm line of 00 which is widely observable in the molecular winds of red giants.
Neutron Nucleosynthesis in a Low-Mass, Low-Metallicity AGB Star
Authors: Hollowell David , Iben, Icko
Published: July 2016

Stellar evolution calculations confirm that semiconvection will occur below the convective envelope of a low-mass, low-metallicity AGB star, after a thermal pulse. These calculations show how semiconvection leads to the creation of a “13C layer” in the star, which can provide a potent source of neutrons (via the 13C[a, n]160 reaction) in a convective shell during later evolution. The rate at which neutrons are released is largely determined by the rate at which the 13C layer is introduced into the convective shell. The 13C neutron source maintains neutron densities of 109-1010 n/cm3 for ∼ 10 years. This provides a neutron exposure r=0.15 mb“1 during most of the pulses calculated. Because of the strong filtering effect by light elements, only 10—20% of the neutrons produced will be captured by iron-seed nuclei, each such nucleus capturing 4–5 neutrons per pulse.
IRAS 21282+5050: A Transitional Planetary Nebula
Authors: Likkel L. , Morris M. , Omont A. , Forveille T.
Published: July 2016

IRAS 21282+5050 is very compact planetary nebula with a substantial molecular shell. It is carbon-rich and exhibits infrared features attributed to PAH molecules. It has a far infrared color temperature higher than almost all other planetary nebulae, with IRAS flux ratios similar to low color temperature evolved stars. We present VLA images of IRAS 21282 at wavelengths of 2 and 6 cm (with FWHM beamsizes of 0.5” and 0.9”, respectively).
Observations of Long Period Variable Stars
Authors: Evans T. Lloyd
Published: July 2016

The study of long period variable stars has been transformed in recent years by two observational developments. Large samples of stars have been observed at infrared wavelengths, providing knowledge of the intrinsic properties of the star as well as of circumstellar dust shells, and these observations have been extended to the variables in well defined stellar systems to allow their properties to be studied in relation to the stellar population to which they belong. Spectroscopic determinations of chemical composition have also provided several crucial insights.
Another Look at the RV Tauri Period-Luminosity Relation
Authors: Wahlgren Glenn M.
Published: July 2016

The Period-Luminosity (P-L) relation for the RV Tauri variables (DuPuy 1973) contradicts those of other variables in the instability strip as it predicts lower luminosity at longer pulsational periods. It is based primarily upon three globular cluster variables. DuPuy determined secular and statistical parallaxes from 23 field variables, defining a simple P-L relation with a slightly negative slope.
Grains of Meteorites, Originating in Cool Carbon Stars
Authors: Jørgensen Uffe G.
Published: July 2016

The bulk of meteorites consist of material that condensed out of the primitive solar nebula, and their isotopic composition is therefore similar to that of the sun. Unfractionated meteorites (carbonaceous chondrites), nevertheless, contain a small fraction of inclusions that have a distinctly different isotopie composition of carbon, xenon, krypton and other elements (Zinner et al., 1987). These inclusions are therefore believed to be of pre-solar origin, and their composition and mineralogical structure carries information about the place where they were born.
Current Status of the Astrometric Capabilities of the Hubble Space Telescope Fine Guidance Sensors
Authors: Jefferys W.H. , Benedict G.F. , Duncombe R.L. , Franz O.G. , Fredrick L.W. , Gerard T. , Hemenway P.D. , McArthur B. , McCartney J. , Nelan E. , Shelus P.J. , Story D. , van Altena W. , Wasserman L. , Whipple A. , Whitney J.
Published: July 2016

The Fine Guidance Sensors (FGSs) are the instrument of choice for most astrometric measurements with the Hubble Space Telescope (HST). The observed amount of spherical aberration in the Ritchey Chretien optical system does not affect positional measurements with perfectly aligned FGSs because they are interferometers. The FGSs combine wavefronts from points in the exit pupil with other points which are at the same radial distance from the optical axis. Asymmetric aberrations such as coma and astigmatism do affect the measured positions. The current knowledge of the HST wavefront error, the FGS operation and the implications for milliarcsecond relative astrometry are discussed. It is still planned to use the HST to tie the HIPPARCOS and VLBI Reference Frames together at the few milliarcsecond level.
Procedure for VLBI Estimates of Earth Rotation Parameters Referred to the Nonrotating Origin
Authors: Capitaine N. , Gontier A.M.
Published: July 2016

This paper investigates the practical use of the nonrotating origin (NRO) (Guinot 1979) for estimating the Earth Rotation Parameters from VLBI data, which is based on the rotational transformation between the geocentric celestial and terrestrial frames as previously derived by Capitaine (1990). Numerical checks of consistency show that the transformation referred to the NRO is equivalent to the classical one referred to the equinox and considering the complete “equation of the equinoxes” (Aoki & Kinoshita 1983). The paper contains the expressions for the partial derivatives of the VLBI geometric delay to be used for the adjustment of the pole coordinates, UT1 and deficiencies in the two celestial coordinates of the Celestial Ephemeris Pole (CEP) in the multiparameters fits to VLBI data. The use of the NRO is shown to simplify the estimates of these parameters and to free the estimated UT1 parameter from the model for precession and nutation.
The Organization of Space: Frames, Systems and Standards
Authors: Eichhorn Heinrich
Published: July 2016

The term “frame of reference” or “reference frame” has long been established in physics. The recent emergence of the use of this very term in astronomy to denote “a catalogue of the adopted coordinates of reference points that serves to define, or realize, a particular coordinate frame” is misleading because “a catalogue of adopted coordinates” must necessarily consists of estimates which cannot uniquely define a coordinate system.
Permanent Milliarcsecond Link of Celestial and Terrestrial Reference Systems
Authors: Feissel M.
Published: July 2016

The celestial reference system and the terrestial reference system of the International Earth Rotation Service (IERS) are realized on the basis of observation programs in Very Long Baseline radio Interferometry and laser ranging to the Moon and artificial satellites. The celestial frame is materialized by the equatorial coordinates of radio sources observed in VLBI; the terrestrial frame is materialized by the cartesian coordinates of the terrestrial sites monitored by the three techniques. Series of the Earth Orientation Parameters are derived from the same observations. These series provide a permanent link between the celestial system and the terrestrial system at the level of 0.001”.

The global adjustment in which the reference systems are defined and realized is described, and the metrological properties of the frames and of the derived EOP are evaluated.
The Transformation from FK4 To FK5 and the Definition of UT
Authors: Xu B.X , Xia Y.F , Huang T.Y. , Han C.H.
Published: July 2016

The different procedures of the transforation from FK4 to FK5 are reviewed. With these procedures some numerical examples for selected FK4 stars are given. Basing on the original work of Fricke (1985), we prefer to select the procedure developed by Standisti (1982). One of the main reasons for the procedure of Aoki et al. (1983) is to consist with the new definition of UT. Since the corrections “FK5 - FK4” for many stars are significant, even if adopting this procedure, it is still impossible to avoid the effect of the right ascension discontinuities on UT.
Dynamical Reference Frame and Some Astronomical Constants from Planetary Observations 1769–1908 YY
Authors: Krasinsky G.A. , Pitjeva E.v. , Sveshnikov H.L. , Chunayeva L.I.
Published: July 2016

Modern planetary theory may be considred as a carrier of 4-dimensianal dynamical reference frame which is to be canfronted with stellar (or quasar) based fundamental frame. Of most interest is the problem of existence of secular trends between the above systems. We investigated the problem by discussing a vast set of planetary observations of different types.
The Use of the Nonrotating Origin in the Computation of Apparent Places of Stars for Estimating Earth Rotation Parameters
Authors: Capitaine N. , Chollet F.
Published: July 2016

A new procedure has been devised for computing apparent places of stars in the intermediate frame (Capitaine 1990) linked to the nonrotating origin (Guinot 1979) for estimating the Earth rotation parameters (ERP) from astrometric observations. The latitude and time parameters as derived by this procedure have been compared to the parameters as derived from the classical procedure used for the reduction of Paris astrolabe observations (Chollet 1984). The consistency between the two procedures has been found to be of the order of a few 10−4ʺ, which is under the order of precision of the computations in the classical procedure. The new procedure, which is more directly related to the Earth rotation, is proposed to be used for the derivation of the ERP in the Hipparcos frame from existing astrometric observations, which is planned for the near future (IAU WG on “Earth Rotation in the Hipparcos Reference Frame”).
Digital Image Processing in the Analysis of Astrometric Plates
Authors: Garcia A.Lopez , Valdes J.L. , Orti J.A.Lopez , Machi R.Lopez. , Perez G.J.
Published: July 2016

In this paper, we display an improvement to our process of semi-automatic measuring of astrometric plates, in which the photometric sensor is substituted by a CCD system of image getting and digitalization. The advantages of this method are analyzed taking into account the possibilities of the image analysis in the space and frequency domain.
Status of the Hipparcos Data Reduction
Authors: Kovalevsky J. , Falin J.L. , Froeschlé M. , Mignard F.
Published: July 2016

HIPPARCOS is now well settled on its 10h40m eccentric orbit and the data is received by three telemetry stations that are also transmitting commands: Odenwald (F.R.G.), Perth (Australia) and Goldstone (California). Although during about 80 to 90% of the time, data are recovered, in practice only the observations made from higher than the outer Van Allen belt are usable. Sometimes even at that height, on-board attitude determination does not converge due to the noise that covers the star mapper signal. Finally, about between 55 and 65% of the mission time is usable for reduction. The actual routine data recovery started on November 27, 1989.
The Approach of Improvement to Stellar Coordinate
Authors: Ma W.Z.
Published: July 2016

This article presents a new method for observing minor planets. The observation is operated with a photo–electronic imaging devise CCD and a lower latitude meridian circle.

The CCD is mainly used except it is during the favourable opposition of the minor planet when the meridian circle is mainly used in this method. The method can improve precision of observation of planetary position and enlarge scope of observation of planetary orbit. Therefore, the measured precision of zero point of stellar coordinate could be increased. The key of succeeding is that more precise result is got using the CCD.

The experiment in this article indicates that this method is a good way:While a minor planet and calibration stars locate in the same image of the CCD, the measured precisions of the minor plant are

σα = ±0″.03, σ´ ±0″.035;

While the minor planet and calibration stars are located in different images of the CCD, the precisions are

σα = ±0″.06, σδ = ±0″.08.
Comparison of the FK5 Proper-Motion System with a Kinematic Distribution Function
Authors: Ratnatunga Kavan U. , Warren Wayne H.
Published: July 2016

A model for the kinematic distribution function of our Galaxy can be used as an independent confirmation that a reference system is free of Earth motions and retains the true kinematics of the stars. Maximum likelihood can simultaneously estimate the parameters required to calibrate distances to the stars, represent the kinematic distribution function, and check on residual Earth rotations in the proper-motion system. The global maximum-likelihood analysis uses all available information: photometry, trigonometric parallax, proper motion, and line-of-sight velocity for a well-defined catalog of stars. Awaiting observations from HIPPARCOS, preliminary testing of the algorithm on available ground-based observations is discussed.
Consistent Relativistic VLBI Theory with Picosecond Accuracy
Authors: Soffel M. , Müller J. , Wu X. , Xu C.
Published: July 2016

The accuracy of Very Long Baseline Interferometry (VLBI), representing one of the most important space techniques of modern geodesy, especially for the determination of the Earth’s rotation parameters and baselines, is steadily increasing. Presently, delay residuals are of the order of 30 - 50 ps, corresponding to an uncertainty in length of about 1 centimeter e.g. in the determination of baselines or the position of the rotation pole. As has already been stressed by many authors, at this level of accuracy a relativistic formulation of the VLBI measuring process is indispensable (e.g. the gravitational time delay for rays getting close to the limb of the Sun amounts to 170 ns!). Starting with the work by Finkelstein et al. (1983) a series of papers has meanwhile been published on a relativistic VLBI theory (Soffelet al., 1986; Hellings, 1986; Zeller et al., 1986; Herring, 1989). However, possibly apart from Brumberg’s treatment in his new monograph (Brumberg, 1990) all of these theories have one fatal drawback: they are not based upon some consistent theory of reference frames, which relates the global, barycentric coordinates, in which the measuring process is primarily formulated and in which positions and velocities of the bodies of the solar system are computed, with the local, geocentric coordinates, comoving with the Earth, in which the geodetically meaningful baselines are defined. Furthermore, none of these theories (including Brumberg’s (1990) treatment) have the accuracy of one picosec which seems desirable with respect to the achieved residual values.
Astrometric and Geodetic Goals for the chinese VLBI Network Project
Authors: Shuhua Ye , Zhihan Qian
Published: July 2016

This paper briefly introduces the current status of the Chinese VLBI Network (CVN) Project and its astrometric and geodetic goals.