bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Polarization Measurements of Pulsars
Authors: Wagner Stefan J. , Seifert W.
Published: July 2016

We investigate the polarization characteristics of optical emission from young pulsars. In a first attempt we search for polarization in images without time resolution in order to select suitable candidates for time-resolved studies. Polarization information constrains the nature of the faint optical emission of pulsars and will eventually allow to derive the topology of the field in those areas were optical radiation is emitted. We determine the polarization of the time-integrated optical emission of the SMC pulsar B0540-69 and the Vela pulsar B0833-45. We identify a new candidate optical counterpart for the young pulsar B1509-58 and find that the old candidate is unpolarized. The polarization of these three sources is rather high in view of the assumption that averaging over a putative swing of the polarization angle through 180 degrees will lead to depolarisation in the pulse-averaged signal.

We also detect high degrees of polarization in the synchrotron nebula surrounding the LMC pulsar B0540-69, indicating even further similarity to the Crab.
X-ray emission characteristics of pulsars and their nebulae
Authors: Becker Werner
Published: July 2016

Recent X-ray observatories like ROSAT, ASCA, RXTE, BeppoSAX and Chandra have achieved important progress in neutron star and pulsar astronomy. The identification of Geminga as a rotation-powered pulsar, the discovery of X-ray emission from millisecond pulsars and the identification of cooling neutron stars are only few of the fascinating results. In the following I will give a brief review on the X-ray emission properties of rotation-powered pulsars and their wind nebulae.
RXTE Observations of the Vela Pulsar: The X-ray-Optical Connection
Authors: Harding Alice K , Strickman Mark S. , Gwinn Carl , McCulloch P. , Moffet D.
Published: July 2016

We report on our analysis of a 300 ks observation of the Vela pulsar with the Rossi X-Ray Timing Explorer (RXTE). The double-peaked, pulsed emission at 2 - 30 keV, which we had previously detected during a 93 ks observation, is confirmed with much improved statistics. There is now clear evidence, both in the spectrum and the light curve, that the emission in the RXTE band is a blend of two separate components. The spectrum of the harder component connects smoothly with the OSSE, COMPTEL and EGRET spectrum and the peaks in the light curve are in phase coincidence with those of the high-energy light curve. The spectrum of the softer component is consistent with an extrapolation to the pulsed optical flux, and the second RXTE pulse is in phase coincidence with the second optical peak. In addition, we see a peak in the 2-8 keV RXTE pulse profile at the radio phase.
The Superluminal Model of Pulsars
Authors: Ardavan H.
Published: July 2016

Salient features of the pulsar emission are all consequences of a single property of the source of this radiation: the superluminal nature of the phase speeds with which the outer parts of the distribution pattern of the emitting electric current rotate. Here we outline the principles underlying the superluminal model of pulsars, on which this claim is based, and describe a ground-based experiment currently being built that will be capable of testing,inter alia, the validity of this model.
The Statistics of Radio Pulsars: A Spark Model
Authors: Cheng K.S. , Fan G.L.
Published: July 2016

We investigate pulsar statistics based on theoretical model of radio emission of Ruderman-Sutherland (1975) and the revised spark model of Gil et al. (1999). In the present approach the intrinsic luminosity is no more given by observed relationship betweenLrandP,. Our studies show that R-S & spark model can explain the statistical properties of radio pulsars reasonably well.
A low energy-model for coherent radio emission — the three-liter-pulsar
Authors: Lesch Harald , Kunzl Thomas , Jessner Axel
Published: July 2016

We present a new model for the coherent radio emission of pulsars that succeeds in reproducing observed luminosities at emission heights of 50-100 pulsar radii. Based on energy conservation and propagation effects we apply the concept of a free electron maser (FEM) to the creation of coherent radio emission. With the characteristic frequencyν≃γ2νpe(νpedenotes the plasma frequency andγis the Lorentz factor of the emitting particles) we find that even for the lowest frequencies at which the highest degree of coherence is required only low energy particles (γ≃ 10) with Goldreich-Julian-density are necessary. Because of its low energy budget we call itthree-liter-pulsar.
On the nature of optical emission from radio pulsars
Authors: Malov I.F. , Machabeli G.Z.
Published: July 2016

There are more than one thousand known radio pulsars, but only 9 of them have detected optical emission (Caraveo 1999). A part of optical emission can be caused by thermal radiation from the hot surface of the neutron star. We shall try to describe the non-thermal component (Kurt et al. 1980) on the base of the synchrotron mechanism, using one-dimensional distribution function of emitting electrons.

One of the possible reasons of observed pulsar emission is the cyclotron instability developed in an anisotropic plasma (Sagdeev & Shafranov 1960). To generate transversal (t) waves with the spectrum

the condition of the cyclotron resonance (Kazbegi et al. 1992)

must be fulfilled. Hereis the Lorentz-factor of resonance particles,is the drift velocity of particles,ρis the curvature radius of field lines.
On the Nature of the Geminga Pulsar
Authors: Khechinashvili D. , Melikidze G. , Gil J.
Published: July 2016

The model provided that Geminga is an almost aligned pulsar, which is supported by the low-frequency observations. The model explains successfully most of the peculiarities of Geminga radio emission. In the frame of the same geometry we propose a mechanism for the recently detected optical pulsation from that pulsar.
Model of pulse separation in the gamma light curve of the Vela pulsar
Authors: Dyks Jaroslaw , Rudak Bronislaw
Published: July 2016

Within the framework of a single polar cap model we calculate the energy dependence of phase separation between two peaks in the gamma-ray lightcurve of the Vela pulsar. Results are confronted with EGRET data (Kanbach 1999).
The Pulsar Pair Plasma
Authors: Asseo Estelle , Riazuelo Alain
Published: July 2016

The anisotropic and relativistic features of the pulsar pair plasma are adequately modelled using relativistic one-dimensional Jűttner-Synge distribution functions. The dispersion relation for wave propagation in such a plasma involves coefficients that specifically depend on the distribution function of its particles. An analytical determination of these coefficients allows us to obtain characteristics of quasi-longitudinal waves together with the conditions for the unstable interaction of ultrarelativistic beam and plasma. Similar derivations concern electromagnetic waves.
The Crab pulsar echoes
Authors: Smith F. Graham , Lyne A.G.
Published: July 2016

Observations over an eight month period from July 1997 to March 1998 show echoes following the radio pulses, and unusual changes in dispersion measure. We interpret this remarkable and complex event as refraction and dispersion in an ionised shell in the outer part of the Crab Nebula. The shell is remarkably compact; it has a electron density of about 103– 104cm−3and a thickness of about 3 × 1011m. Similar events have been noticed on several other occasions during the continuous monitoring of the Crab pulsar over the past 25 years.
Bow Shocks from Radio Pulsars: Observations of the Guitar Nebula
Authors: Chatterjee Shami , Cordes James M.
Published: July 2016

We present optical observations and radio non-detections of the bow shock nebula associated with the pulsar B2224+65 (the “Guitar Nebula”), and fit an analytic model to the observed bow shock to estimate its inclination and constrain other parameters (distance, pulsar velocity, ISM density). We also test scaling laws for bow shock parameters.
Physical Connections Between Pulsar Outer Magnetospheres and Pulsar Nebulae
Authors: Chiueh Tzihnong
Published: July 2016

The spin-down luminosity together with the morphology of pulsar nebula, such a the Crab, have long been known to imply that the pulsar wind be practically unmagnetized immediately before it impinges onto the nebula. In fact, the condition of low wind magnetization can be shown to further imply that the pulsar outer magnetosphere be strongly distorted, where the toroidal field exceeds the conventionally-assumed dipole field by nearly two orders of magnitude in the outer magnetosphere; the current needed requires the plasma density to exceed the Goldreich-Julian charge density by several orders of magnitude. Such a physical condition can certainly impose a constraint on the candidate mechanisms of non-thermal radio emission, and may also place a constraint on the high-energy, electrode-gap emission mechanisms.
Transient radio emission from PSR B1259–63
Authors: Ball Lewis , Melatos Andrew , Johnston Simon , Skjæraasen Olaf
Published: July 2016

The unique binary pulsar system PSR B1259–63, comprising a radio pulsar in an eccentric orbit about a hot, massive companion star, has been extensively monitored at radio frequencies between 843 MHz and 8.4 GHz during its 1994 and 1997 periastron passages. Unpulsed radio emission was detected for about 100 days around each periastron, varying on time scales as short as a day. We argue that the emission is synchrotron radiation generated as the pulsar passes through the Be-star’s excretion disk just before and just after periastron.
Constraints on Interstellar Plasma Turbulence Spectrum from Pulsar Observations at the Ooty Radio Telescope
Authors: Bhat N. D. Ramesh , Gupta Yashwant , Rao A. Pramesh
Published: July 2016

Refractive Interstellar Scintillation (RISS) effects on pulsar signals are powerful techniques for discriminating between different models that have been proposed for the power spectrum of plasma density fluctuations in the Interstellar Medium (ISM; e.g. Rickett 1990). The nature of the spectrum is considered to be a major input for understanding the underlying mechanism of interstellar plasma turbulence. Data from our long-term pulsar scintillation observations using the Ooty Radio Telescope (ORT) at 327 MHz are used to investigate the nature of the spectrum in the Local Interstellar Medium (LISM; region within ∼ 1 kpc of the Sun). Dynamic scintillation spectra were obtained for 18 pulsars in the DM range 3–35 pc cm−3at ∼10–100 epochs spanning ∼100–1000 days during 1993–1995 (Bhat et al. 1999). From these observations, various scintillation properties and the ISM parameters are estimated with accuracies much better than that which has been possible from most earlier data. The time series of parameters,viz., decorrelation bandwidth (vd), scintillation time scale (τd) and the drift slope of intensity scintillation patterns, and pulsar flux density are used to study various observable effects of Interstellar Scintillation, based on which the spectral form is inferred over the spatial scale range ∼ 107m to ∼ 1013m.
Extreme scattering of pulsars
Authors: Walker Mark A.
Published: July 2016

Extreme Scattering Events are radio-wave lensing events caused by AU-sized concentrations of ionised gas. Although they were discovered more than a decade ago we still have no clear picture of the physical nature of the lenses. To discriminate between the various models, we need to amass more information on multiple imaging phenomena. Pulsars are perfect targets for such studies: they offer six- to ten-times the information content of quasar observations, and their small angular sizes make them sensitive to distant lenses. In addition, small source-size means that multiple imaging can be studied even when there is little change in the total source flux, because the (weak) secondary images interfere with the primary and create periodic fringes in the spectrum.
Search for Single Scattering Events
Authors: Ramachandran R. , Deshpande A. A. , Stappers B. W.
Published: July 2016

Radio signals, during their passage through the intervening medium, are scattered due to irregularities in the density of free electrons in the interstellar medium. Signals from distant sources undergo, most often,strong & multiple scatteringwhile the signals from nearby sources may be onlyweakly scatteredeven at meter wavelengths. It is likely that the scattering of signals from some nearby sources is possibly non-multiple in nature and hence may show a distinct signature ofsingle or discrete scattering events. In such a situation we receive, along with the direct unscattered signal, only a few discrete delayed versions of the signal. In such a case, it appears possible to probe the properties (such as the size and the density contrast) of the discrete density-irregularities responsible for the scattering, if the associated delays can be measured.
Neutron Star Populations at the Millenium
Authors: Cordes James
Published: July 2016

Identified neutron star (NS) classes evidently are determined by several intertwined features: kinematics of NS at their formation (spin and translational); magnetic field strength; and binary membership. I discuss the well-known classes of isolated and accreting NS while keeping in mind recent discoveries of magnetars, anomalous X-ray pulsars, and long-period radio pulsars. I summarize the results of several likelihood analyses on radio pulsars, which yield information on the velocity distribution, luminosity function, and birth rate of high-field radio pulsars. I review the evidence for the occurrence of momentum kicks at the time of NS birth. Discerning the relationship of the classic radio pulsars to the more exotic classes probably requires careful comparison of magnetic fields, kinematics and birthrates, a program for the next millenium. Exciting discoveries of classic pulsars will also be made: sub-millisecond pulsars, massive binaries in fast orbits and truly hyper-velocity pulsars that shed light on core-collapse processes in supernovae.
Theoretical Implications of the 47 Tuc Pulsars
Authors: Rasio Frederic A.
Published: July 2016

Twenty millisecond radio pulsars have now been observed in the globular cluster 47 Tuc. This is by far the largest sample of radio pulsars known in any globular cluster. These recent observations provide a unique opportunity to re-examine theoretically the formation and evolution of recycled pulsars in globular clusters.
New Direct Observational Evidence for Kicks in SNe
Authors: Tauris T. M. , Heuvel E. P. J. van den
Published: July 2016

We present an updated list of direct strong evidence in favour of kicks being imparted to newborn neutron stars. In particular we discuss the new cases of evidence resulting from recent observations of the X-ray binary Circinus X-1 and the newly discovered binary radio pulsar PSR J1141–6545. We conclude that the assumption that neutron stars receive a kick velocity at their formation is unavoidable (van den Heuvel & van Paradijs 1997).

This assumption explains a large variety of observations, ranging from direct observed properties of individual binary pulsars and Be/X-ray binaries to the observed birth rates and dynamical properties of the populations of LMXBs, binary recycled pulsars as well as the motion and distribution of single pulsars. Below we give an updated list in favour of kicks based on the compilation given by van den Heuvel & van Paradijs (1997) – see references therein for details.
On the Existence of an Universal Spin-down Equation for Pulsars
Authors: Alvarez César , Carramiñana Alberto
Published: July 2016

The Taylor expansion of the generalized spin-down equation= −f(v), derives into the multipolar equation= −gv5–rv3−sv), which is used here to study pulsar evolution. The coefficientsg,rand s can be physically associated to gravitational radiation, magnetic dipolar radiation and particle aceleration. The multipolar expansion with constant coefficients cannot describe theP Ṗdiagram in a consistent manner and therefore it is unlikely a generalized equation of the form= −f(v;t) can be used to describe pulsar evolution. A more general form,= −f(v;t) can be investigated giving to the coefficientsg,rand s time dependence. We consider some explicit functional forms forg(t),r(t) ands(t) which are consistent with observational and theoretical constraints.
Heat and charge transport in envelopes of weakly and strongly magnetized neutron stars
Authors: Potekhin Alexander
Published: July 2016

Thermal and electrical electron conductivities are calculated for a broad range of physical parameters typical for envelopes of neutron stars. An appropriate effective electron-ion scattering potential is used, based on calculations involving modified ion structure factors suggested recently for the treatment of the transport problems in dense Coulomb plasmas. These results are applied to calculation of the thermal structure of neutron-star envelopes.
Non-LTE effects in neutron star atmospheres
Authors: Werner K. , Deetjen J.
Published: July 2016

We present the first non-LTE model atmospheres for neutron stars (NS). We study their structure and NLTE effects on the emergent thermal radiation of old isolated NS.
The Temperature and Cooling Age of t h e White-Dwarf Companion to the Millisecond Pulsar PSR B1855+09
Authors: Bell Jon , van Kerkwijk Marten , Kaspi Vicky , Kulkarni Shri
Published: July 2016

We report on Keck and HST observations of the binary millisecond pulsar PSR B1855+09. We detect its white-dwarf companion and measuremF555W= 25.90 ± 0.12 andmF814W= 24.19 ± 0.11 (Vega system). From the reddening-corrected color we infer a temperatureTeff= 4800 ± 800 K. The companion mass is known accurately from measurements of the Shapiro delay of the pulsar signal,. Given a cooling model, one can use the measured temperature to determine the cooling age. The main uncertainty in the cooling models for such low-mass white dwarfs is the amount of residual nuclear burning, which depends on the thickness of the hydrogen layer surrounding the helium core. For PSR B1855+09, such models lead to a cooling age of ∼10Gyr, which is twice the spin-down age of the pulsar. It may be that the pulsar does not brake (n=3.0) like a dipole rotatingin vacuo. For other pulsar companions, however, ages well over lOGyr are inferred, indicating that the problem may lie with the cooling models. There is no age discrepancy for models in which the white dwarfs are formed with thinner hydrogen layers (< 3 × 10−4M⊙). See van Kerkwijk et al. ApJ (submitted) for more details.
Evolution of the Magnetic Field of a Neutron Star During Polar-Cap Accretion
Authors: Melatos A. , Phinney E. S.
Published: July 2016

Neutron stars that have experienced episodes of mass transfer exhibit lower magnetic dipole momentsμthan other neutron stars, e.g. binary radio pulsars with high-mass (μ∼ 1028G cm3) and low-mass (μ∼ 1027G cm3) companions, isolated millisecond pulsars (μ∼ 1026G cm3), and accreting objects in low-mass X-ray binaries (μ< 1027G cm3). Indeed, theμ-versus-orbital-period andμ-versus-age relations for low-mass and high-mass binaries imply thatμdecreasesmonotonicallywith accreted massMa(Taam & van den Heuvel 1986; van den Heuvel & Bitzaraki 1995). Simple Ohmic field decay cannot be responsible given the existence of cold and therefore old white-dwarf companions (Kulkarni 1986). Alternative mechanisms include accretion-induced heating of the crust (Konar & Bhattacharya 1997) and fluxoid-vortex interactions in the stellar interior (Srinivasan et al. 1990).
Magnetars
Authors: Thompson Christopher
Published: July 2016

I summarize recent observational and theoretical advances in the understanding of the Soft Gamma Repeaters and the Anomalous X-ray Pulsars. Several direct physical arguments point to very strong magnetic fields (B> 10BQED= 4.4 × 1014 G) in SGR outbursts. The connection between these two classes of neutron stars is examined. Their persistent X-ray emission and spindown behavior are interpreted in the magnetar model, where a decaying magnetic field dominates all other sources of energy for radiative and particle emission. The response of a magnetic field to the violent motions in a supernova core is also examined, with a focus on mechanisms that may impart unusually large kicks.
Bumpy Spin-Down of Anomalous X-Ray Pulsars: The Link with Magnetars
Authors: Melatos A.
Published: July 2016

It is argued that bumps in the timing histories Ω(t) of the anomalous X-ray pulsars (AXPs) IE 1048.1-5937 and IE 2259+586 are the signature of a magnetar undergoing radiative precession, wherein the hydromagnetic deformation of the neutron star couples to an oscillating component of the vacuum-dipole radiation torque to produce an anharmonic wobble with periodτpr∼ 10 yr. An analysis of Euler’s equations of motion for a biaxial magnet reproduces the amplitude and recurrence time of the bumps for IE 1048.1-5937 and IE 2259+586, predicts Ω(t) for the next 20 years for both objects, and predicts a testable statistical relation betweendΩ/dtandτprfor the AXP population overall. Radiative precession of soft gamma-ray repeaters is also discussed, together with implications for the internal (e.g. viscosity) and magnetospheric (e.g.e+e−pair currents) properties of magnetars.
New ASCA Observations of two Anomalous X-ray Pulsars
Authors: Paul B. , Kawasaki M. , Dotani T. , Nagase F.
Published: July 2016

NewASCAobservations of two anomalous X-ray pulsars (AXP) 4U 0142+61 and 1E 1048.1-5937, made in 1998, when compared to earlier observations in 1994 show remarkable stability in the intensity, spectral shape and pulse profile. The energy spectra consist of two components, a power-law and a blackbody emission from the neutron star surface. In IE 1048.1-5937, we have identified three epochs with different spin-down rates and discuss its implications for the magnetar hypothesis of the AXPs. We also note that the spin-down rate and its variations in IE 1048.1-5937 are much larger than what normally can be produced by an accretion disc with very low mass accretion rate corresponding to its low X-ray luminosity.
A New View on Young Pulsars in Supernova Remnants: Slow, Radio-quiet & X-ray Bright
Authors: Gotthelf E. V. , Vasisht G.
Published: July 2016

We propose a simple explanation for the apparent dearth of radio pulsars associated with young supernova remnants (SNRs). Recent X-ray observations of young remnants have revealed slowly rotating (P∼ 10s) central pulsars with pulsed emission above 2 keV, lacking in detectable radio emission. Some of these objects apparently have enormous magnetic fields, evolving in a manner distinct from the Crab pulsar. We argue that these X-ray pulsars can account for a substantial fraction of the long sought after neutron stars in SNRs and that Crab-like pulsars are perhaps the rarer, but more highly visible example of these stellar embers. Magnetic field decay likely accounts for their high X-ray luminosity, which cannot be explained as rotational energy loss, as for the Crab-like pulsars. We suggest that the natal magnetic field strength of these objects control their subsequent evolution. There are currently almost a dozen slow X-ray pulsars associated with young SNRs. Remarkably, these objects, taken together, represent at least half of the confirmed pulsars in supernova remnants. This being the case, these pulsars must be the progenitors of a vast population of previously unrecognized neutron stars.
The Future X-ray Observations of Pulsars and Isolated Neutron Stars
Authors: Trümper Joachim
Published: July 2016

During the last decade the X-ray observations ROSAT and ASCA have made it possible to distinguish between photospheric (thermal) and (nonthermal) magnetospheric radiation of single neutron stars. The next generation of X-ray satellites (Chandra, XMM and Astro-E) and the follow-up mission Constellation and XEUS- will allow spectroscopic and timing studies with much higher sensitivity and resolution. Primary future goals are to determine the chemical composition of neutron star photospheres and to measure the gravitational redshift of spectral features.
On Leonhard Euler’s Contribution to the Theory of Precession and Nutation
Authors: Abalakin Victor K.
Published: July 2016

Among the immense heritage of Leonhard Euler’s astronomical, mechanical, and mathematical works there has been particularly strong interest in those that deal with principles describing the Earth’s perturbed rotation around its axis. The outstanding meaning of the works is obvious even today, since they give a deep insight into the essence of the phenomena of precessional and nutational displacements of the fundamental coordinate planes and axes constituting astronomical frames of reference.
The Observations of Latitude Changes Measured in Prague
Authors: Šíma Zdislav
Published: July 2016

Astronomy in Prague has long been associated with Charles University, since its founding in 1348. After a long and complicated history, “The State Observatory” was established in the former Jesuit college of Klementinum. The polar height was measured at this location in the last century, during the periods 1889 – 1892, 1895 – 1899 and 1900 – 1904. The observations were made by Gerstner, Laska, Spitaler and others, under the leadership of Prof. Lad. Weinek. The measurements were performed with a transit instrument. The inspection was made in the Archive of Academy of Sciences, where practically all the observations are still preserved.
VLBI Observations of Earth Orientation
Authors: Ma C. , MacMillan D.S.
Published: July 2016

VLBI has been used for high precision EOP measurements since 1980. The typical formal error for current routine monitoring of polar motion is ~80 µas. A program for continuous EOP observations using VLBI is being incrementally implemented. There are unexplained differences between EOP values derived from simultaneously observing networks.
Astrolabe Solar Observations
Authors: Andrei A.H. , Laclare F. , Penna J.L. , Jilinski E.G. , Puliaev S.P. , Delmas C.
Published: July 2016

Since 1978 at the Calern Observatory-France and from 1996 at the Observatório Nacional (O.N.)-Brasil solar observations have been carried out, aiming primarily to study the solar diameter. The ensemble of these two series is noteworthy by the length of Calern’s, which spans about two solar cycles, and by the high density of O.N.’s, with typically 20 observations per day, on each side of the meridian, all year around. The precision of a single measure is 015 for the northern hemisphere observations and 02 for the southern hemisphere observations.

The characteristics of the combined series enabled detailed searches for anomalous trends (e.g., from atmospheric origin) and systematic bias (e.g., from instrumental origin). The analysis show the series robust for either. Thus there is a possiblity to investigate the variable time of transit of the solar disc across the almucantars of observation.

The apparent solar time, defined by the actual diurnal motion of the Sun, shows variations because of the varying rate of motion of the Sun in hour angle. That is, due to the inequalities in the annual motion along the ecliptic and to the inclination of the ecliptic to the equator.

In this work we detail the series characteristics and discuss the determination of the hour angle of the true Sun, as exemplified by the equation of time. The accuracy of the determination varies with the solar declination and the length of the observed apparent orbit. Typical precisions follow those for the semi-diameter determinations.
The TOCAMM Project
Authors: Bo M. Del , Lattanzi M.G. , Massone G. , Porcu F. , Salvati F. , Deiana G.L. , Poma A. , Uras S.
Published: July 2016

The TOCAMM (TOrino CAgliari Measuring Machine) project undertaken jointly between Torino and Cagliari Astronomical Observatories aimed to convert the old measuring machine ASCORECORD into an automatic and impersonal one. This program is intended to contribute to the link of the HIPPARCOS Catalogue to the ICRS through the determination of precise position of optical counterparts of 80 extragalactic radiosources taken from the IERS list and to investigate the astrometric accuracy of the Guide Star Catalog (version 1 and 2). The calibration test phase, carried out first at the Astronomical Observatory of Torino and after at Cagliari Observatory, where the machine has been now installed, indicate that the available positional accuracy is about 0.5 microns in both x and y coordinates.
Atmospheric Excitation of Polar Motion
Authors: Salstein David
Published: July 2016

Variations in the angular momentum of the atmosphere in the equatorial plane due to shifts in air mass distribution and changing winds impact the orientation of Earth so that motions of the pole occur on a broad range of time scales. The wind terms have notable diurnal fluctuations, which appear as a tidal signature. Subseasonal fluctuations of the pole are shown to be related to the atmospheric signal on scales as short as at least a week, according to a coherency analysis. Atmospheric mass fluctuations over certain regions, such as Eurasia and North America, appear to be more responsible for rapid polar motions than are those elsewhere, and may be related to known climate modes. On the other hand, atmospheric pressure fluctuations over the ocean are counteracted in large measure by a sea level response, due to an inverted barometer relationship. Ocean forcing from model results assist in narrowing the differences in the geodetic and atmospheric budgets. Efforts to assess dynamic forecasts of the atmospheric polar motion excitations have demonstrated positive skill out to at least 10 days for the mass term.
On Estimate of Real Accuracy of EOP Prediction
Authors: Malkin Zinovy
Published: July 2016

To estimate the real accuracy of EOP predictions, real-time predictions made by the IERS Subbureau for Rapid Service and Prediction (USNO) and at the IAA EOP Service are analyzed. Methods of estimating prediction accuracy are discussed.
The CEP and Geophysical Interpretation of Modern Earth Rotation Observations
Authors: Brzeziński Aleksander
Published: July 2016

The definition of the Celestial Ephemeris Pole (CEP) which is the pole of reference for precession and nutation, should be revised taking into account recent advances in observation and theory. This paper reviews the current realization of the CEP and discusses possible extensions of both the conceptual definition and the realization of the CEP. Attention is focused on the corresponding connections between the Earth orientation parameters describing rotational variations and the related excitation parameters expressing dynamics of the geophysical fluids.
Numerical Convolution Method in Time Domain and Its Application to Nonrigid Earth Nutation Theory
Authors: Fukushima Toshio , Shirai Toshimichi
Published: July 2016

We developed a numerical method to incorporate nonrigid effects into a nutation theory of the rigid Earth. Here we assume that the nonrigid effects are based on a linear response theory and its transfer function is expressed as a rational function of frequency. The method replaces the convolution of the transfer function in the frequency domain by the corresponding integro-differential operations in the time domain numerically; namely multiplying the polynomial in the frequency domain by the numerical differentiations in the time domain and multiplying the fractions in the frequency domain by the numerical integrations with a suitable kernel in the time domain. In replacing by the integrations, the method requires the determination of the coefficients of free oscillation. This is done by a least-squares method to fit the theory incorporated with the nonrigid effects to the observational data, whose availability is also assumed. The numerical differentiation and integration are effectively computed by means of the symmetric formulas of differentiation and integration. Numerical tests showed that the method is sufficiently precise to reproduce the analytically convolved nutation at the level of 10 nano arcseconds by using the 9-point central difference formulas and the 8-point symmetric integration formula to cover the period of 15 years with 1.5-hour stepsize. Since we only require the rigid Earth nutation theory to be expressed as a numerical table of time, this method enables one to create a purely numerical theory of nutation of the nonrigid Earth.
Cepheids
Authors: Stobie R.S.
Published: July 2016

The scope of this review will be to summarize our knowledge of Cepheids at the present time concentrating primarily on the observational results obtained but at the same time relating these to the relevant results of pulsation and evolution theory. Of the many previous reviews of pulsating stars we would mention especially Payne-Gaposchkin and Gaposchkin (1938), Ledoux and Walraven (1958), Christy (1966a) and Cox (1974) as providing an excellent background to the theoretical and observational aspects of the subject. Because of these reviews we will concentrate on the more recent results obtained in connection with Cepheids. At the end a special section is devoted to the double-mode Cepheids as they are particularly relevant to this Colloquium.
Rotation Mixing and Variability in a Stars
Authors: Baglin A.
Published: July 2016

The purpose of this paper is to contribute to answer the question : why among A stars are there variable and “constant” stars? To do this we will first review the observational properties of these stars, then discuss the theoretical models based on the interplay between microscopic diffusion and rotation, and finally discuss the “unsolved” questions !
The Asteroidal Planet as the Origin of Comets
Authors: Van Flandern Thomas C.
Published: July 2016

Recently, M. W. Ovenden has raised seemingly plausible dynamical arguments which suggest that a 90-earth-mass planet existed in the present location of the asteroid belt until 16×106 years ago, and then rapidly disintegrated. He mentions supporting evidence from the cosmic ray exposure ages of chondritic meteorites. If the long-period comets originated from the recent disintegration of such a planet, several otherwise improbable characteristics of their orbits would be predicted, including a tendency for those orbits which are least perturbed to return to the site of the original break-up. In this investigation, we compare observed characteristics of long-period comet orbits with expected characteristics, based on the missing planet hypothesis. The conclusion is that long-period comet orbits are wholly consistent with the hypothesis; indeed, certain of their characteristics are difficult to explain in any other way.
Stabilization by Making Use of a Generalized Hamiltonian Variational Formalism
Authors: Baumgarte Joachim W.
Published: July 2016

A generalized Hamiltonian formalism is established which is invariant not only under canonical transformations but under arbitrary transformations. Moreover the dependent variables, coordinates and momenta, as well as the independent variable are allowed to be transformed. This is to say that instead of the physical time t another independent variable s is used, such that t becomes a dependent variable or, more precisely, an additional coordinate. The formalism under consideration permits also to include nonconservative forces.

In case of Keplerian motion we propose to use the eccentric anomaly as the independent variable. By virtue of our generalized point of view a Lyapunov-stable differential system is obtained, such that all coordinates, including the time t, are computed by stable procedures. This stabilization is performed by control terms. As a new result a stabilizing control term also for the time integration is established, such that no longer any kind of time element is needed. This holds true for the usual coordinates as well as for the KS-coordinates.
A Special Perturbation Method: m-Fold Runge-Kutta
Authors: Bettis D.G.
Published: July 2016

Runge-Kutta methods of order p that utilize in derivatives of the equations of motion are presented. The results of applying these methods are compared to other special perturbation techniques for several test problems.
New Orbits for Enceladus and Dione Based on the Photographic Observations
Authors: Jefferys W.H. , Mulholland J.D. , Ries L.M.
Published: July 2016

A program is underway at the McDonald Observatory to extend the series of photographic observations of the satellites of the outer planets (Abbot, Mulholland and Shelus, A.J. 80, 1975), and concurrent theoretical studies have led to a new orbital theory for the resonant pair of satellites, Enceladus and Dione (Jefferys and Ries, A.J. 80, 1975). The construction of the new theory, using the computer software system TRIGMAN, has provided Fortran subroutines for the computation of the planetocentric coordinates of the two satellites, as well as partial derivatives for the orbit elements and certain other physical parameters of the orbit problem, including some of the harmonics of the gravitational field of Saturn. The available photographic observations for these two objects are currently being discussed with the new theory, and improved values of the orbital parameters are expected in the near future.
Long Periodic Variation of Orbital Elements of A Satellite Perturbed by Discrete Gravity Anomalies
Authors: Ananda M.P.
Published: July 2016

A method for generating long periodic variations in satellite orbital elements when perturbed by discrete gravity anomalies is presented. The method consists of developing a disturbing potential as a function of orbital and gravity anomaly parameters, and generating partial derivatives of the potential with respect to the orbital elements. The partials are averaged over the period of the satellite to eliminate the short periodic variations. The averaged partials are substituted into the variation of parameter equations to give the mean orbital rates. Classically orbital elements are used in generating gravity field and thus the method is dynamic in nature. The problem is extremely cumbersome and complex when multi-state parameters have to be estimated from a considerably large data set. However, when mean orbital rates are used, the problem reduces to a simple linear static case, where only the gravity parameters have to be estimated, and it is a simple matrix inversion problem. Thus the method developed here was utilized in reducing Appolo 15 and 16 subsatellite radio tracking data to produce a lunar gravity field represented by point masses.
Families of Periodic Planetary-Type Orbits in the N-Body Problem and Their Application to the Solar System
Authors: Hadjidemetriou J. D. , Michalodimitrakis M.
Published: July 2016

A new approach to the study of the Solar System and planetary systems in general is proposed, through the use of periodic planetary-type orbits of the general N-body problem. In such an orbit, one body (called Sun) has a large mass and the rest N-l bodies (called planets) have small but not negligible masses and it can be proved that monoparametric families of periodic orbits of the N-body problem exist in a rotating frame of reference, all being of the planetary type.

Two cases are studied in detail, N=3 and N=4. In N=3, apart from a general discussion, we present a detailed analysis of the Sun-Jupiter-Saturn system and a study is made on which configurations with the masses of these two planets, or a multiple of them, are stable or unstable. Also, part of a family is shown to represent the Jupiter family of comets. It was found that commensurabilities are not in general associated with instabilities. For N=4 we present three families of periodic orbits. The motion corresponding to a branch of one of the above families has many similarities with the actual motion of the three inner satellites of Jupiter.

It is shown that there exist many commensurable cases in the obtained periodic orbits and that the resonant orbits increase as the number of bodies increases. Based on these results, an attempt is made to explain the existence of commensurabilities in the Solar System.

Finally, it is mentioned that a periodic motion of the planetary type can be used as a reference orbit for accurate computations for the actual motions of the planets or satellites of the Solar System. In this way the small divisor difficulties existing in the classical approach will not appear.
A New Kind of Periodic Orbit: The Three-Dimensional Asymmetric
Authors: Markellos V. V.
Published: July 2016

A great deal of human and computer effort has been directed in recent decades to the determination of the periodic orbits of the restricted three-body problem and the study of their properties for well known reasons of significance and feasibility.
On Asymmetric Periodic Solutions of the Plane Restricted Problem of Three Bodies, and Bifurcations of Families
Authors: Message P.J. , Taylor D.B.
Published: July 2016

Previous work on the plane circular restricted problem of three bodies (Message 1953, 1959, 1970, and Fragakis 1973) has shown the existence, in association with each of the commensurabilities 2:1 and 3:1 of the orbital periods, of a pair of families of asymmetric periodic solutions, branching from the stable series of symmetric periodic solutions of Poincaré’s second sort associated with that commensurability. (Each solution of either family is the mirror image, in the line of the two finite bodies, of a member of the other family of solutions associated with the commensurability.) The stability is transferred at the bifurcation to the two series of asymmetric orbits, each of which is therefore stable. Recent numerical integrations carried out by one of us (P.J.M.) have found such asymmetric periodic orbits associated also with the 4:1 commensurability, and quantities describing orbits of one of the two series are given in Table 1, showing the run of such orbits up to a second bifurcation with the same series of symmetric periodic orbits from which it sprang. Quantities describing some members of this series of symmetric orbits are given in Table 2. It is seen that stability is transferred back to the symmetric series at the second bifurcation. (The unit of distance is the distance between the two finite bodies, the unit of speed is the speed, of their relative motion, and the initial conditions given (x°, ẋ°, ẏ°) are for a crossing of the line of the two finite bodies, this line being taken as axis of “x” in a rotating Cartesian frame in the usual way. The mean values of the major semi-axis and eccentricity are denoted by ā and ē, respectively, C is Jacobi’s constant, and ȳ2 is the mean value of the critical argument ȳ2 = 4λ – λ′ – 3ω. The mass ratio used is 0.000954927, T is the period of the solution in units of the period of the motion of the two finite bodies, and 2π c/T is the non-zero characteristic exponent.)
Regions of Escape on the Velocity Ellipsoid for the Planar Three Body Problem
Authors: Bozis George
Published: July 2016

The notion of the velocity ellipsoid for the planar three body problem is given. Using the sufficient conditions for escape of one member of a triple system, given by Standish (1971), a region is found on the velocity ellipsoid for which escape is guaranteed.
Peculiar Red Giants in External Galaxies
Authors: Richer Harvey B.
Published: July 2016

Study of the late-type stellar content in external galaxies provides numerous clues for the theory of stellar evolution, for star-formation scenarios in galaxies, and for proper models of the luminosity evolution of galaxies which are then used in cosmological studies. In addition, these late-type stars can be used as distance indicators themselves and yield a local value of the Hubble constant consistent with recent Cepheid determinations.
Spectroscopy and Photometry of the Southern R Stars
Authors: Evans T. Lloyd
Published: July 2016

UBVRI photometry and 1-2Å resolution spectra have been used to classify 85 stars listed as type R by various authors. Some are N stars, including a few characterized by strong NaD, weak C2 and enhanced 13C which are distinct from the cooler counterparts of the strong-banded 13C rich stars which are the most numerous of the R stars. The latter are also distinguished from non- C rich stars by having redder V-I at given B-V in the bifurcated distribution in the B-V, V-I diagram.
A Photometric Monitoring of Barium Stars
Authors: Jorissen A. , Manrfroid J.
Published: July 2016

An uvby photometric monitoring of a sample of 19 Ba II stars has been performed since July 1984 at ESO on the Danish and ESO 50 cm telescopes, as part of the “Long Term Program for Variable Stars” (Sterken, 1983). The sample contains southern Ba II stars with variable radial velocities (from McClure, 1983 and Jorissen and Mayor, 1988) as well as Ba II stars already monitored by Landolt (1983). The observations are done differentially, using two comparison giants of the same spectral type located within a few degrees of the Ba II star. The reduction to the standard uvby system is performed using the algorithm described in Manfroid and Heck (1983), taking into account all the measurements performed on the considered telescope since the beginning of the monitoring. With such a reduction procedure, the scatter in the magnitude difference between two comparison stars (of magnitude 5 to 7) can be as low as 0.003-0.004 mag rms.
Photometric Classification of Carbon-Rich Stars
Authors: Straizys V.
Published: July 2016

The Vilnius seven-color photometric system with the mean wavelengths of bandpasses at 345, 374, 405, 466, 516, 544, and 656 nm is intended for photometric determination of spectral classes, absolute magnitudes, and metallicities of stars and the amount of interstellar reddening. At the same time, different reddening-free diagrams of the system make it possible to recognize stars with different peculiarities. Carbon-rich stars are among these types of objects. For separation of carbon, barium, and CH stars from normal stars, the diagram Q (345, 374, 466, 544), Q (405, 516, 656) is the best. Its merit is based on sensitivity of the 405 magnitude to the violet depression and of the 374 magnitude to the absorption of the C3, SiC, and CN bands, This diagram can be used to estimate the C/0 abundance ratio with corresponding calibration at hand.
The Role of Technetium in the Evolution of Red Giants
Authors: Little-Marenin Irene R.
Published: July 2016

Tc is detected in many AGB stars providing unambiguous proof that recent nuclear s-processing and mixing (the third dredge-up) has taken place. During this evolutionary episode the atmospheres of AGB stars are progressively enhanced with helium burning products (primari ly l2C) and s-process elements as they evolve from M->MS->S->SC->C stars. The increase in s-process elements can be traced most easily by the presence and increasing strength of the Tc I lines accompanying this progression. We also find that the third dredge-up phase is accompanied by an increase in the amplitude of light variation since no non-variable or low amplitude variable M, MS, SC, or S (with one exception) have Tc lines. M star Mira variables show Tc if P > 300d (low mass Pop I stars). No Pop II star is known to have Tc. Nor do supergiants show Tc I lines. The significant fraction of MS, S and C stars that do not show Tc, are surmised to be cooler analogues to the Ba II stars, i.e. binaries. The source to provide the neutrons for the s-process is most likely the 13C(a, n)16O reaction since most of the stars in which we observe Tc are thought to have masses less than 3 solar masses.