bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New View on Young Pulsars in Supernova Remnants: Slow, Radio-quiet & X-ray Bright
Authors: Gotthelf E. V. , Vasisht G. 
Published: July 2016

AbstractWe 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

AbstractDuring 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

AbstractAmong 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

AbstractAstronomy 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

AbstractVLBI 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

AbstractSince 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

AbstractThe 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

AbstractVariations 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.
The CEP and Geophysical Interpretation of Modern Earth Rotation Observations
Authors: Brzeziński Aleksander 
Published: July 2016

AbstractThe 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

AbstractWe 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.
The Asteroidal Planet as the Origin of Comets
Authors: Van Flandern Thomas C. 
Published: July 2016

AbstractRecently, 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

AbstractA 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.
New Orbits for Enceladus and Dione Based on the Photographic Observations
Authors: Jefferys W.H. , Mulholland J.D. , Ries L.M. 
Published: July 2016

AbstractA 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

AbstractA 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

AbstractA 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.
Peculiar Red Giants in External Galaxies
Authors: Richer Harvey B. 
Published: July 2016

AbstractStudy 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.
The Role of Technetium in the Evolution of Red Giants
Authors: Little-Marenin Irene R. 
Published: July 2016

AbstractTc 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.
s-Process Enrichment in Low-Mass Agb Stars
Authors: Gallino R. 
Published: July 2016

AbstractAfter a brief description of the developments of the theory of s-process nucleosynthesis, the difficulties recently encountered in envisaging reliable astrophysical conditions for obtaining a solar-system distribution of s-isotopes are discussed. In particular, while the reaction 22Ne(α, n)25Mg may account for the nucleosynthesis of the weak s-component in massive stars, it fails to reproduce the main s-component in intermediate mass stars. The efficiency of the alternative reaction 13C(α, n)160 occurring in low mass stars during recurring thermal instabilities of the He shell is then analyzed. It is shown that, contrary to previous expectations, the 13C source well reproduces the main component, provided that realistic physical conditions are assumed for the temporal behaviour of the pulse and the effect of the light n-absorbers (especially 12C) is properly taken into account. The results satisfactorily compare with the constraints of the classical s-analysis. Key observational evidences also appear to be in agreement with this scenario.
Molecular Radio Line Observations of Mass Loss From Red Giants
Authors: Olofsson H. 
Published: July 2016

AbstractThe number of molecules detected at radio wavelengths in envelopes around red giants stands presently at 36. Among these OH and CO have proven to be the most useful for the study of the physical characteristics of a circumstellar envelope. The mass loss rate of the central star can be relatively accurately estimated and it appears possible to trace its evolution with time. Also fascinating objects in transition from the red giant phase to the planetary nebula phase are becoming observationally accessible.
Possible Proto-Planetary Nebulae
Authors: Parthasarathy M. 
Published: July 2016

AbstractIRAS data for high-galactic-latitude F supergiants, a few luminous F-G stars, and a few peculiar (forbidden) emission-line stars reveal they have dust shells with characteristics similar to those observed in planetary nebulae. The objects described here appear to have experienced severe mass loss in the recent past on the AGB. These stars are most likely post-AGB stars or evolving from the tip of AGB towards the left in the H-R diagram and may be described as possible proto-planetary nebulae. From the IRAS data we find ten additional possible proto-planetary nebulae. From the IRAS data of HD 56126, -53° 5072, HD 168625 and -59° 6723 the luminosities, temperatures and masses of the dust shells are derived. HD 56126 (F5I), HD 168625 (B8Iae), and -59° 6723 (B8Iae) appear to be in an evolutionary stage (post-AGB) similar to that of HD 161796 and HR 4049.
IRAS Observations of Symbiotic Stars
Authors: Parthasarathy M. , Bhatt H.C. 
Published: July 2016

AbstractOf the 129 symbiotic stars in Allen's (1984) catalogue, 42 were found to be IRAS sources. Of these 42 IRAS sources, 22 are D-type (symbiotic Miras), 5 are D'-type (yellow symbiotics) and 15 are S-type. The separation of S, D and D’ types into three distinct groups is clearer in the log[fλ(25μm)/fλ(12μm)] versus (H-K) diagram. The IRAS fluxes of S-type symbiotics are consistent with that observed from normal M giants. This result suggests that mass-loss rate from most of the S-type symbiotics is similar to that from normal M giants. The IRAS data of D-type symbiotics shows evidence for the presence of dust envelopes. The masses of the dust envelopes (10-6 to 10-7 Mo) around Miras in D-type symbiotics are similar to that observed in field Mira variables. These results suggest that mass-loss rates in symbiotic Miras are similar to those from field Mira variables and also that the mass loss from symbiotic Miras is pulsationally driven similar to that found in field Mira variables by Whitelock, Pottasch and Feast (1987). Analysis of IRAS data of yellow symbiotics Ml-2, AS201, Cnl-1, Wray 157. and HD149427 suggests that they are young planetary nebulae containing a binary nucleus. Ml-2, AS201 and Cnl-1 show evidence for the presence of evolved hot companions. The evolutionary stage of the late type (F-G) companions is not clear.