bluuebunny/crossref_metadata_2025 huggingface dataset:
Astrometric and Photometric Area-Scanner Measurements of Double Stars
Authors: Kreidl Tobias J.
Published: July 2016

Accurate magnitudes and colors of individual components of binaries are needed to provide valuable information on stellar evolution. Using an area scanner, accurate magnitudes, as well as good astrometric data, can be obtained for close pairs. A summary is given for the first major data set.
L’Astronomie des Etoiles Doubles face a la Mission Astrometrique du Satellite Hipparcos
Authors: Dommanget J.
Published: July 2016

The Hipparcos satellite is described as well as the scanning process of the sky by its optical design, as a consequence of the satellite’s motion. From these data, the possibilities of the mission is deduced and applied in the case of the binaries.

Discussion is made of what may be expected for different double star categories including spectroscopic, astrometric, close visual and wide pairs. Information are given on how proposals should be made for lists of binaries that should be observed.
Reduction of Astrometric Binaries for Low Mass Companions
Authors: Russell Jane L.
Published: July 2016

Described is the plan of a study just underway to assess the progress so far in the astrometric search for low mass companions. The range of periods which would be discernible, based on the obsprvations’ distribution in time, and the range in amplitude of the detectable orbits, based on careful analysis of the accuracy of the observations, can be used to determine the confidence level of any perturbations as well as to specify what possible companions and orbits for a given star have been ruled out. This study, when completed for several nearby stars, should yield the first comprehensive progress report for the search for astrometric companions.
Long Period Variables in the Magellanic Clouds: the OGLE/MACHO/2MASS/DENIS view
Authors: Groenewegen Martin
Published: July 2016

I present a brief analysis of K-band period-luminosity relations for AGB stars in the SMC based on OGLE, 2MASS and DENIS data. I also present, for a selected sample of SMC and LMC stars, a comparison between the analysis of respective MACHO and OGLE data and a method to combine the data from the two surveys.
NGC 6822: short period variable stars, stellar population and distance scale
Authors: Baldacci Lara , Rizzi Luca , Clementini Gisella , Held Enrico V.
Published: July 2016

Results are presented on a study of the short period variable stars in the dwarf irregular galaxy NGC 6822. We observed an almost uniformly populated classical instability strip from the Horizontal Branch up to the Classical Cepheid region. The main goal we achieved from the analysis of the faint sample is the first detection of RR Lyrae stars in this galaxy.
An application of Bayesian statistics to the extragalactic Cepheid distance scale
Authors: Barnes Thomas G. , Moffett Thomas J. , Jefferys W.H. , Forestell Amy D.
Published: July 2016

We have determined quasi-geometric distances to the Magellanic Clouds, M31 and M33. Our analysis uses a Bayesian statistical method to provide mathematically rigorous and objective solutions for individual Cepheids. We combine the individual distances with a hierarchical Bayesian model to determine the galactic distances. We obtain distance moduli 18.87 ± 0.07 mag (LMC, 12 stars), 19.14 ± 0.10 (SMC, 8 stars), 23.83 ± 0.35 mag (M33, 1 star) and 25.2 ± 0.6 mag (M31, 1 star) – all uncorrected for metallicity. The M31 and M33 distances are very preliminary. If the PL relations of the LMC, SMC and Galaxy are identical, our results exclude the metallicity effect in the V, (V – R) surface brightness method predicted by Hindsley & Bell (1989) at the 5σ level. Alternately, if Hindsley & Bell’s prediction is adopted as true, we find a metallicity effect intrinsic to the Cepheid PL relation requiring a correction Δ(V – Mv) = (0.36 ± 0.07)Δ[A/H] mag. The latter has the opposite sign to other observational estimates of the Cepheid metallicity effect.
The kinematics and zero point of the log P –〈MK〉 relation for galactic field RR Lyrae variables via statistical parallax
Authors: Dambis A.K. , Vozyakova O.V.
Published: July 2016

The kinematical parameters of the local field RR Lyrae population and the zero point of the log P –〈MK〉 relation for these variables are inferred by applying the statistical parallax (maximum-likelihood) technique to a sample of 379 RR Lyrae stars with known periods, radial-velocities, metallicities, K-band photometry, and absolute proper motions on the ICRS system. Hipparcos, Tycho-2, SPM, UCAC1 and NPM1 were used as the sources of proper motions. The K-band magnitudes were adopted from the 2MASS All-Sky Data Release. The parameters of the velocity distribution are found to be (U0 = −13 ± 9, V0 = −41 ± 7, W0 = −19±4) kms−1, (σU = 66±9, σV = 47±7, σW = 23±5) km s−1 and (U0 = −11±10, V0 = −224±8, W0 = −8±6) km s−1 (σU = 158±9, σV = 95±5, σW = 88±5) km s−1 for the thick-disk (the purest disk sample, 56 stars) and halo (the purest halo sample, 264 stars) objects, respectively. The zero point of the infrared PL relation of Jones et al. (1992 – based on the results obtained using the Baade-Wesselink method) is confirmed: we find 〈MK〉 = −2.33⋅log PF−0.89±0.09, which is only brighter than found using the Baade-Wesselink method (Jones et al. 1992). A conversion of the resulting log P –〈MK〉 relation to V-band luminosities yields the metallicity-luminosity relation 〈MV〉 = +1.12 + 0.18 ⋅ [Fe/H] ± 0.10. Our results imply a solar Galactocentric distance of R0 = 7.8±0.4 kpc and an LMC distance modulus of DMLMC = 18.17 ±0.10 (cluster RR Lyraes) or DMLMC = 18.10±0.10 (field RR Lyraes), thereby favoring the so-called short distance scale.
g-mode pulsations in slowly pulsating B stars
Authors: De Cat P. , Daszyńska-Daszkiewicz J. , Briquet M. , Dupret M.-A. , Scuflaire R. , De Ridder J. , Niemczura E. , Aerts C.
Published: July 2016

In this paper, we give an updated overview of the observed characteristics of g-mode pulsations in slowly pulsating B stars. These characteristics are based on the combined results of linear nonadiabatic analysis of the oscillations and a photometric and spectroscopic mode identification for a sample of 13 members. For 4 stars, at least one mode is stable in all the considered theoretical models.
Pulsating stars in the open cluster NGC 1817
Authors: Arentoft T. , Freyhammer L.M. , Bouzid M.Y. , Sterken C. , Frandsen S.
Published: July 2016

We report on new CCD observations of the open cluster NGC 1817, obtained as part of a program to search for pulsating stars in clusters. In a previous study, several δ Sct stars were found in NGC 1817 and our observations confirm that NGC 1817 is a special cluster, as we detected 19 variable stars. Twelve of these are most likely δ Sct stars of which 11 seem to be cluster members. One is also an eclipsing binary.
Short-term instabilities in γ Velorum: a search for strange modes in variable stars
Authors: Bentley John , Cottrell P.L.
Published: July 2016

Strange mode instabilities in Wolf-Rayet stars have been proposed as the cause of clumping in the stellar wind. This, in turn, is suggested as a cause of line profile variations found on short time scales. High-frequency, short-duration, time-series spectroscopy was performed on the Wolf-Rayet star γ Velorum and analysis confirmed the results of a previous study of γ Velorum’s stellar wind which showed that the wind is indeed clumped, most likely from the predicted strange mode pulsations.
First results of Mercator observations of variable A and F stars
Authors: De Ridder J. , Cuypers J. , De Cat P. , Uytterhoeven K. , Schoenaers C. , Davignon G. , Raskin G. , Vanautgaerden J. , Broeders E. , DeMeester W. , Van Malderen R. , De Ruyter S. , Vandenbussche B. , Maas T. , Kolenberg K. , Reyniers M. , Decin G. , Acke B. , Ausseloos M. , Aerts C. , Van Winckel H. , Waelkens C.
Published: July 2016

We report on the first results from observations of 31 variable A and F stars, obtained with the new Mercator telescope (La Palma). Besides confirming the γ Dor nature of known bonafide and candidate γ Dor stars, we also present new candidate γ Dor stars. In addition, we found a new short-period variable star.
Spectra of RV Tauri stars in the Large Magellanic Cloud
Authors: Evans Tom Lloyd , Pollard Karen R.
Published: July 2016

Low-resolution (0.6 nm) spectra of 24 RV Tauri stars in the LMC shows that most are of intermediate Preston type, hence intermediate metal deficiency. Two belong to Preston’s class B, with enhanced CH and CN. Higher resolution spectra of the carbon star MACHO 47.2496.8 show that the 12C/13C ratio is high and that the Ball lines at 455.4 and 493.4 nm are enhanced. This suggests that the star has undergone the third dredge-up of helium-burning products on the thermally-pulsing AGB and is now in a post-AGB stage of evolution. JHK photometry from the 2MASS catalogue confirms and extends earlier findings that only moderate infrared excesses occur among this sample of RV Tauri stars.
Period Changes in Miras
Authors: Koen Chris , Lombard Fred
Published: July 2016

A brief rationale for the use of a period test statistic based on the periodogram is given. Results of its application to 380 Mira datasets are summarised.
An overtone Cepheid variable in an LMC eclipsing binary
Authors: Lepischak D. , Welch D.L.
Published: July 2016

Eclipsing binary systems potentially allow the direct and precise determination of the important properties of their component stars. An eclipsing binary containing a Cepheid variable which is also a double-lined spectroscopic binary would allow, for the first time, the direct measurement of the absolute luminosity and mass of the Cepheid. The MACHO Project LMC database contains five systems whose light curves show variations due to both eclipses and pulsation but only one has been clearly identified as an intermediate-mass, Population I object. This object, MACHO 81.8997.87 (= OGLELMC_SC16 119952) is a 2.035-d overtone Cepheid in an 800.4-d binary system with an M-type companion. Here we present the results of the analysis of the light curve of this system, the implications for its evolutionary history and discuss the prospects for future observations.
A spectroscopic study of southern binary Cepheids
Authors: Petterson O.K.L. , Albrow Michael D. , Cottrell P.L. , Fokin A.
Published: July 2016

High-resolution spectroscopic observations have been made of a number of southern binary Cepheids to determine their dynamical masses. The stars are part of a long-term programme to observe southern variable stars for which a valuable long-term database has been obtained. The most recent radial velocities have a precision of ~300ms−1, allowing the detection of velocity differences of ~l kms−1 with confidence. Masses were determined for three systems: the 9-day Cepheid S Mus (6.0±0.4M⊙), the double-mode Cepheid Y Car (4.5±1.8M⊙) and the 5-day Cepheid V350Sgr (6.0±0.9M⊙). For five Cepheids (YZCar, AX Cir, V636 Sco, W Sgr and T Mon) new or improved orbital solutions were found. Line level effects have been observed in several species of lines. Most Cepheids were observed to show the same progression of line level effects. Using non-linear radiative hydrodynamical models, we have compared the results of these models with our observations. These have shown that AX Cir and YZ Car have the following properties: L = 2050 L⊙, M = 4.8 M), Teff = 5900 K and L = 9350 L∩, M = 7.7M∩, Teff = 5590 K. Our models show no strong Shockwaves being produced. Good agreement was found between the observed and modelled spectral lines Fe I 5576Å, Si II 6347Å, Ba II 5853Å and Ca II 8542Å.
Seismic Tests of Accretion in Central Stars of Planetary Systems
Authors: Bazot Michaël , Vauclair Sylvie
Published: July 2016

Central stars of extra-solar planetary systems are metal-rich. Planet accretion or initial high metallicity are two models proposed to explain this observational fact that can be tested with asteroseismology. We calculate two stellar models, one with accretion and one with high initial metallicity, in order to obtain the same external parameters for both of them. We then compare their internal structures and their oscillation frequencies.
The effect of metallicity on the Cepheid period-luminosity relation
Authors: Romaniello Martino , Primas Francesca , Mottini Marta , Groenewegen Martin
Published: July 2016

We present preliminary results of an observational campaign devoted to establishing the influence of chemical composition on the Cepheid Period-Luminosity relation. The data are in good agreement with theoretical predictions based on non-linear convective models, suggesting a fairly strong dependence of the Period-Luminosity relation on metallicity in the sense of more metal rich stars being intrinsically fainter than otherwise expected. Our data indicate that the error on the inferred distance can be as large as 10% if the role of metallicity is neglected.
The chemical composition and circumstellar environment of the variable star QY Sge
Authors: Goswami Aruna , Kameswara Rao N. , Lambert D.L.
Published: July 2016

Chemical composition studies of the variable star QY Sge show abundance anomalies suggestive of the pattern exhibited by the warmer RV Tau variables. Abundance analysis indicates a near-solar atmosphere with highly condensable elements depleted by several factors. Evidence of broad Na D emission features in its spectrum, a characteristic feature of R CrB stars taken at minimum, however, raises the question of its spectral classification. We address this question through a comparative analysis of its spectrum with those of γ Cyg 89 Her and R CrB taken at minimum, in addition to abundance analysis. We also discuss a possible physical scenario of the circumstellar environment accounting for the characteristics of the distinct spectroscopic features.
Does Extreme Mixing Improve Frequency Agreement for δ Scuti Stars?
Authors: Guzik Joyce A. , Austin Benjamin A. , Bradley Paul A. , Cox Arthur N.
Published: July 2016

δ Scuti stars that have been observed intensely by the Delta Scuti Network and other campaigns exhibit fewer modes than predicted in the observed frequency range. In addition, some modes are difficult to match by the most likely observable l = 0, 1, and 2 modes, especially considering available spectroscopic mode identifications. Here we examine frequency predictions for stellar models for FG Vir and 4 CVn with extensive core mixing, well beyond the plausible limits of such mixing from convective core overshooting. We find that mixing has the potential to substantially improve frequency agreement, and deserves further investigation.
Structure and Evolution of the Milky Way Galaxy
Authors: Gilmore Gerard , Wyse Rosemary F.G.
Published: July 2016

The combination of chemical abundance, kinematic, and age data for stars near the sun provides important information about the early evolution of the Galaxy. We review available data, with some new analysis, to show that the sum of all available information strongly suggests that the extreme population II subdwarf system formed during a period of rapid collapse of the proto-Galaxy. This subdwarf system now forms a flattened, pressure-supported distribution, with axial ratio ∼2:1. The thick disk formed subsequent to the subdwarf system. At least the metal-poor tail of the thick disk is comparable in age to the globular cluster system. The thick disk is probably kinematically discrete from the Galactic old disk, though the data remain inadequate for robust conclusions.
Type I Intermittent Chaos in Hydrodynamic Pulsation Models
Authors: Aikawa Tohsiki
Published: July 2016

We investigate the cause of the transition from limit cycles to chaotic oscillations in pulsation of less-massive supergiant stars. For this purpose, we examine one of the models which has a limit cycle but is very close to the transition to the type I intermittency (Aikawa 1988, Astrophys. & Space Sci., 139, 214). It is shown that the pulsational driving by the hydrogen ionization with the M type ionization front, which becomes very effective at amplitudes beyond the limit cycle, is responsible for the existence of another unstable fixed point beyond the limit cycle (see Aikawa, 1988, in press Astrophys. & Space Sci.) A merging process of these two fixed points makes the transition.
Double Mode Pulsating Stars and Opacity Changes
Authors: Andreasen G.K.
Published: July 2016

The basic physical properties of double mode Cepheids and double mode δ Scuti stars are still highly controversial. Based on results of very recent opacity calculations a detailed consistent, possible solution of the problem of the nature of double mode variable stars has been developed. Extensive studies have been performed to establish the rules governing the morphology of the period ratio diagrams. An ideal reproduction of the period ratio data for both stellar types are obtained assuming an increase of the Cox-Steward opacity by a factor of about 2.5 in the temperature range from 1.5 X 105K to 8.0 X 105K. Consequences for the mass calibration of Petersen diagrams are evaluated.
Secular Changes in the Light Curve of the Short-Period Cepheid EU Tau
Authors: Matthews J.M. , Gieren W.P.
Published: July 2016

UBVRI photometry and radial velocity measurements of EU Tau obtained during three weeks in November/December 1987 have been used to (1) confirm the period, P = 2.1025 days, and epoch established by Fernie (1987, P.A.S.P.,99, 1093) and earlier observers, and (2) investigate apparent phase and/or amplitude discrepancies in the light curve first reported by Gieren and Matthews (1987, A.J.,94, 431). Comparison of these new data with photometry collected by different observers covering over two decades suggests that the light curve of EU Tau undergoes short-lived (less than about 2 pulsation cycles) changes which appear to occur with a period of roughly 19 – 21 days. Various possible sources of modulation – including binarity, double-mode beating and nonradial pulsations – are considered and rejected as unsatisfactory.
Statistics of Pulsating Variables
Authors: Novikova M.F. , Fadeyev Yu.A.
Published: July 2016

Classification of pulsating variables is based on a number of properties but the most important of them are the period and amplitude of the light variation. These quantities also play an important role in understanding the evolutionary status of the pulsating stars since the pulsation period is related to the mass and radius through the period--mean density relation while the amplitude of the light curve characterizes the efficiency of the mechanism responsible for the pulsational instability. In the present study we considered the period--frequency and light amplitude--frequency distributions for ten types of the most numerous pulsating variables from the fourth edition of the General Catalogue of Variable Stars. The following types of pulsating variables were considered: DSCT, DSCTC, DCEP, RR, RRAB, RRC, CWA, CWB, RV and M. Using these distributions we estimated the upper and lower limits of the period and light amplitude within which 95% and 99% of the pulsating stars of a given type are contained.
The Binary Cepheid S Sagittae Revisited
Authors: Slovak Mark H. , Barnes Thomas G. , Evans Nancy R. , Welch Douglas L. , Moffett Thomas J.
Published: July 2016

A new orbit has been derived for the binary Cepheid S Sagittae = HD 188727 = BD+16°4067, using both extant data and new radial velocities derived from radial velocity spectrometer observations at McDonald Observatory and the Dominion Astrophysical Observatory. We deconvoled both the pulsational and orbital components from the observed velocities in order to fit a truncated Fourier series to the pulsation velocities and to derive orbital elements respectively. We confirm the orbital elements given in Herbig and Moore (1952) and speculate that the secular trend evident in the orbital (O-C) diagram may be interpreted as evidence for a third component. (See Evans, Slovak and Welch, this volume, for IUE observations supporting this interpretation.)
Emission Lines From Hot Astrophysical Plasmas
Authors: Raymond John C.
Published: July 2016

The spectral lines which dominate the X-ray emission of hot, optically thin astrophysical plasmas reflect the elemental abundances, temperature distribution, and other physical parameters of the emitting gas. The accuracy and level of detail with which these parameters can be inferred are limited by the measurement uncertainties and uncertainties in atomic rates used to compute the model spectrum. This paper discusses the relative importance and the likely uncertainties in the various atomic rates and the likely uncertainties in the overall ionization balance and spectral line emissivities predicted by the computer codes currently used to fit X-ray spectral data.
Recent Advances in Atomic Modeling
Authors: Goldstein W. H.
Published: July 2016

Precision spectroscopy of solar plasmas has historically been the goad for advances in calculating the atomic physics and dynamics of highly ionized atoms. Recent efforts to understand the laboratory plasmas associated with magnetic and inertial confinement fusion, and with X-ray laser research, have played a similar role. Developments spurred by laboratory plasma research are applicable to the modeling of high-resolution spectra from both solar and cosmic X-ray sources, such as the photo-ionized plasmas associated with accretion disks. Three of these developments in large scale atomic modeling are reviewed: a new method for calculating large arrays of collisional excitation rates, a sum rule based method for extending collisional-radiative models and modeling the effects of autoionizing resonances, and a detailed level accounting calculation of resonant excitation rates in FeXVII.
X-ray Lines From Mg VIII and Si X Ions and Their Diagnostic Use
Authors: Dwivedi Bhola N.
Published: July 2016

The solar X-ray emission lines from Mg VIII and Si X ions have been studied. The variation of theoretical line intensity ratio I(λ 75.03)/I(λ 74.86) from Mg VIII and I(λ 50.69)/I(λ 50.52) from Si X as a function of electron density is found to be good density monitors of the emitting regions of solar plasma. The computed values of line intensity from these ions based on Kopp and Orrall model have been used to derive electron density of the quiet Sun and coronal holes. The electron densities of 109 cm-3 and 4.6 × 108 cm-3 are estimated at the electron temperatures of 8 x 105 K and 1.6 x 106 K for the quiet Sun whereas the respective values of 5.4 x 108 cm-3 and 1.7 x 108 cm-3 are obtained for the coronal holes. The line intensity ratios studied here are independent of temperature variation and are therefore excellent candidates for electron density diagnostics. However, observational data with improved spectral resolution is needed for using X-ray line pairs studied for their diagnostic use.
Measurement of Carbon Ion Photoabsorption Cross Sections Using Laser Plasmas
Authors: Wargelin B. , Kahn S.M. , Craig W. , London R.
Published: July 2016

Laser plasmas are well-suited to studies of ionic photoabsorption because they can provide highly ionized, low temperature plasmas of high column density, as well as bright, compact continuum X-ray sources which can illuminate the plasma under study. In our experiment, continuum X-rays from a gold laser plasma are partially absorbed as they traverse a carbon plasma and are then dispersed by a grazing incidence reflection grating. An X-ray imaging camera records both the absorbed and unabsorbed spectra simultaneously for later computer analysis to determine the photoabsorption cross sections for each carbon ion species.
The Effect of Magnetic Fields Upon Cosmic X-ray Spectra
Authors: Mészáros P.
Published: July 2016

The effect of strong magnetic fields (B ≳ 1011Gauss) upon various atomic line emission mechanisms in the X-ray range is considered, in particular for H and H-like or He-like ions, and a discussion of the detectability and significance of possible measurements is given. The cyclotron mechanism, the one- and two-photon scattering and the bremsstrahlung effects in a strong B are reviewed, as well as the role they play in determining X-ray spectra. These considerations are applied to typical models of X-ray pulsars and Gamma-ray bursters, contrasting observations of magnetic related features to the present theoretical understanding of these objects.
Effect of Vacuum Polarization in a Strong Magnetic Field and Spectral Features of X-Ray Source Emission
Authors: Gnedin Yu. N.
Published: July 2016

In strong magnetic fields of neutron stars electron-positron vacuum behaves as an anisotropic medium. Vacuum influences the generation and propagation of electromagnetic radiation in plasma and changes the spectrum of radiation. As a result the change of cyclotron lines shape and appearance of specific “vacuum lines” should be observed in X-ray spectra of accreting neutron stars.
High Resolution Spectroscopy and Plasma Diagnostics of Supernova Remnants
Authors: Canizares Claude R.
Published: July 2016

The MIT group has used data from the Focal Plane Crystal Spectrometer on the Einstein Observatory to perform plasma diagnostics of four supernova remnants (SNRs), the Cygnus Loop, Puppis A, N132D, and Cas A. The ratio of luminosities of the forbidden line to resonance line of He-like ions of oxygen and neon allow us to show that all four SNRs depart from ionization equilibrium in that they are under-ionized for their electron temperatures. Thus despite the fact that their ages range from 300 yr to 20,000 yr, all four SNRs are still ionizing and, in that sense, are still young. We derive values of ionization time and electron temperature for one or more components in each remnant. The agreement between these values and those deduced by others using entirely different means (e.g. broad-band spectroscopy or imaging) gives us confidence in the reliability of the diagnostics. Two of the SNRs, Puppis A and N132D, show evidence for an overabundance of oxygen by factors of three or more. These results, based on a handful of weak lines, show the great promise of the much more powerful future spectroscopy missions for revealing detailed information about astrophysical plasmas.
Signatures of Cooling Flows
Authors: Fabian A.C.
Published: July 2016

The evidence for cooling flows in clusters of galaxies is discussed. Peaked X-ray surface brightness profiles and the presence of soft X-ray spectral components are characteristic signatures of cooling flows. The best available data are consistent with gas cooling at a rate of ~ 100M⊙yr-1 and depositing cooled matter over a radius of 100 – 200 kpc. The same rate is obtained from observations of gas cooling over a range of temperatures and thus a range of cooling times covering less than 3 × 107 yr to more than 3 × 109 yr. It appears that cooling flows are both steady and long-lived. Some indirect optical evidence for distant cooling flows (0.5 < z < 1) is presented.
The X-ray Astronomy Satellite SAX
Authors: Butler R.C.
Published: July 2016

The SAX satellite is forseen for launch at the end of 1992 to study the X-ray emission from galactic and extra-galactic sources in the energy range 0.1-200 keV. The payload consists of four concentrator/spectrometer systems (3 units 1-10keV, 1 unit 0.1-10keV), a high pressure gas scintillation proportional counter (3-120keV), a phoswich scintillation counter (15-200keV), and two wide field cameras (2-30keV). Together these instruments will perform the following:-

- Broad band spectroscopy (E/ΔE=12) in the energy range 0.1-10 keV with imaging resolution of 1 arcmin

- Continuum and cyclotron line spectroscopy (E/ΔE=5-20) in the wide energy range 3-200 keV

- Variability studies of bright source energy spectra on time scales from milliseconds to days and months

- Systematic long term source variability studies in selected regions of the sky down to a source intensity of 1 mCrab.
Isotopic Ratios in Comets
Authors: Vanysek V.
Published: July 2016

The isotopic abundances depend on the universal evolution of elements and on the individual history of particular objects. Since it is believed that unprocessed material of the solar nebula is preserved in comets, the data concerning the abundance of stable isotopes in these primitive bodies are of some importance in the cosmological context. The present status of this problem is reviewed. The reliability of results for nuclear species with cosmological and cosmogonical implications, such as D/H, C 12/13, N 14/15, O 16/18, and Mg 24/25/26, is discussed. Significant variation is found for the isotopic abundance of carbon, depending upon which carbon reservoir is sampled. Deuterium is probably enhanced relative to the interstellar ratio. For other isotopes, the ratios are close to those of the terrestrial data. The tendency of the D/H ratio to be at higher values indicates a low temperature in the environment of the comet’s formation, and, together with similar effects in the outer planets, suggests that there were two different primordial reservoirs of deuterium in the solar system. The 12C/13C ratio inferred from in situ mass spectrometry of the dust, as well as from the ground-based optical spectra of the Swan band, tends to be approximately equal to the average terrestrial ratio (89) or larger. Recent results obtained from the CN band provide a significantly lower value (about 65), which corresponds to the carbon isotopic ratio in the diffuse interstellar clouds. The enhancement of deuterium and the possible differences of the carbon isotopic ratio in different species and refractory material are indicative of chemical fractionation processes in the protosolar nebula.
The Hydrogen Clouds of Comets
Authors: Shimizu Mikio
Published: July 2016

In a cometary coma, various hydrogen compounds, especially water, that are photodissociated by solar ultraviolet radiation form a gigantic hydrogen cloud with a radius of several million kilometers around the cometary nucleus. These cometary hydrogen clouds have been observed by a number of spacecraft outside the terrestrial atmosphere and in interplanetary space. For instance, the hydrogen cloud of Comet Halley was a good target for the ultraviolet photometers and spectrometers on board the International Ultraviolet Explorer (IUE), Suisei, Pioneer Venus, DE-1, and sounding rockets. Hydrogen cloud activity could be used as a good measure of cometary activity, but some problems remain to be explored in the future.
The Forest and the Trees
Authors: Whipple Fred L.
Published: July 2016

Some 24 points are made concerning the author’s understanding of the cometary nucleus as developed in this colloquium. Comparisons with an earlier report are noted, and most of the earlier advances in concept are substantiated. The mean density of the Halley nucleus may have been underestimated. The dust/gas ratio apparently needs to be increased by as much as two times, perhaps to unity or higher. The nature of the rotation remains puzzling. CHON grains now appear to be more important sources of gas than thought earlier. A very low temperature at, and subsequent to, the formation of the nucleus continues to receive support, as does a solar-system composition. The 12C/i:3C ratio may, however, be lower than expected.
Source-noise in radio synthesis images
Authors: Anantharamaiah K.R. , Deshpande A.A. , Radhakrishnan V. , Ekers R.D. , Cornwell T.J. , Goss W.M.
Published: July 2016

We discuss the distribution of source- and receiver- noise in radio synthesis images and show that the source-noise is maximum at the position of the source but also appears in the off-source region because of the sidelobes. Analytical expressions are derived for the rms noise at any location of both “total-power” and “correlation” images. We show that under certain conditions, deconvolution can remove the source noise from the off-source region in snap-shot images. Some of the results are verified experimentally.
The design of high frequency antennas
Authors: Delannoy J.
Published: July 2016

The conceptual guidelines in designing mm radio-telescope antennas are enlightened by some recent progress in their mechanical construction, and opto-radio-geometrical adjustment. This paper reviews concepts, illustrated in many existing solutions, including the new “phaseretrieval” holography for single dish adjustment (D.Morris, IRAM, 1982): 2 amplitude only maps at focus and out of focus, with enough dynamic range and signal to noise ratio, give surface errors within hours.
The use of optical fibres in radioastronomy
Authors: Young Alan C.
Published: July 2016

Optical fibres have been used extensively within the Australia Telescope to carry IF data, LO reference, timing signals and computer communications. This paper discusses the various options considered in the design of a system which should assist similar projects in making the best use of optical fibres.
Direct Imaging Digital Lens for Transient Radio Source Survey
Authors: Daishido Tsuneaki , Asuma Kuniyuki , Nishibori Kazuhiko , Nakajima Junichi , Yano Motoko , Otobe Eiichiro , Watanabe Naoki , Tsuchiya Akira , Iwase Seiichiro
Published: July 2016

FFT based 2D Dygital Lens is discussed comparing with Fourier synthesis. The sensitivity of constructing Large Array will be 50mJy. Precise manipuration of the radiation field is possible in it.
Phase Control in the Digital Lens
Authors: Asuma Kuniyuki , Iwase Seiichiro , Nisibori Kazuhiko , Nakajima Junichi , Otobe Eiichiro , Tuchiya Akira , Watanabe Naoki , Daisido Tsuneaki
Published: July 2016

Phase and amplitude is controlled by manipulating the digitized radiation field. Application to the phase switching, and the calibration of phase and amplitude is discussed.
A Portable Holographic Antenna Measurement System
Authors: Shaffer David B. , Gipson John M.
Published: July 2016

Interferometrics has developed a portable holographic antenna measurement system. The system is comprised of a small interferometer which uses satellite signals to measure the complex beam pattern of the antenna under test. A PC controls all aspects of data collection and analysis. The system produces maps of surface profile errors and the illumination power in reflector antennas.
The NRAO Millimeter Array Site Survey
Authors: Owen Frazer N.
Published: July 2016

The measurements being made to pick a site for the NRAO Millimeter Array are described. The instruments, techniques and preliminary results are discussed, along with the strategy for picking the final site for the array.
The use of beam-sets in the Analysis of wide-field maps from the CLFST
Authors: Waldram Em
Published: July 2016

The Cambridge Low Frequency Synthesis Telescope (CLFST) has baselines which are offset from the E-W direction by about 3°. The wide-field mapping problem has been overcome by the use of beam-sets, or artificial maps consisting of grids of synthesized beams, which incorporate the effects of both the geometric and chromatic aberration. By appropriate interpolation we can find a good approximation to the beam-shape at any point on a map.
State-of-the-art VLBI imaging: 3C345
Authors: Wehrle Ann E. , Unwin Stephen C.
Published: July 2016

Most VLBI images have low dynamic range because they are limited by instrumental effects such as calibration errors and poor u, v-coverage. We outline the method used to make a new image of the bright quasar 3C345 which has very high dynamic range (peak-to-noise of 5000:1) and which is limited by the thermal noise, not instrumental errors. Both the Caltech VLBI package and the NRAO AIPS package were required to manipulate the data.
VHF Radio Interferometry of Lightning
Authors: Krehbiel P.R. , Shao X.M. , Thomas R.J. , Rhodes C.T. , Hayenga C.O.
Published: July 2016

Lightning discharges radiate strongly at radio frequencies, and studies of the radiation provide valuable information on lightning breakdown processes. Interferometric techniques can be used to locate the numerous radiation events as a function of time during a discharge and to generate images of the developing lightning channels inside a storm, where they are obscured from view at optical wavelengths.
A Dynamical Systems Approach to Nonlinear Stellar Pulsations
Authors: Buchler J. R.
Published: July 2016

Over the last decade we have seen the application of novel techniques to the old problem of nonlinear stellar pulsations. Together with numerical hydrodynamics this approach provides a more fundamental understanding of the systematics of the pulsational behavior. For weakly nonadiabatic pulsations, whether regular or multi-periodic, dimensional reduction techniques lead to amplitude equations and to a description in terms of modal interactions and resonances. In particular they shed new light on the bump progression in the classical Cepheids. In more dissipative stars numerical hydrodynamical modelling has uncovered the existence of irregular variability, both in radiative and in convective models. An application of modern dynamical systems techniques has shown that this behavior occurs according to well understood routes from regular to chaotic behavior. The mechanism is very robust and represents the first nonad hoctheoretical explanation of irregular stellar variability. Finally, we discuss how a comparison with observations of irregular variability shows the need for more suitable observations, on the one hand, and of better techniques of signal processing, on the other.
An Overview of Stellar Pulsation Theory
Authors: Saio H.
Published: July 2016

In this paper I will give overview of the stellar pulsation theory. Starting with basic equations I will discuss modal properties of oscillations and excitation mechanisms. I also mention briefly the effects of rotation.
Nonlinear Expansion Triggered by Magnetic Stress in Accretion Flow onto a Black Hole
Authors: Yokosawa M.
Published: July 2016

The paper is an investigation of the magnetohydrodynamics (MHD) of the quasi-radial accretion onto a rotating black hole. It is demonstrated that the nonlinear effects in the accretion flow accelerate the rate of expansion of the Alfven mode. The accretion flow becomes unstable at the weak strength of magnetic field which is about one-thirtieth of the expected value by the linear theory.
Spatial Pattern Formation of Interstellar Medium
Authors: Tainaka K. , Fukazawa S. , Nishimori H. , Yokosawa M. , Mineshige S.
Published: July 2016

Population dynamics of multi-phased interstellar medium (ISM) is investigated by using the lattice model in position-fixed reaction. Interactions between three distinct phases of gas, cold clouds, warm gas, and hot gas give rise to cyclic phase changes in ISM. Such local phase changes are propagated in space, and stochastic steady-state spatial pattern is finally achieved. We obtain the following two characteristic patterns:

(1)

When the sweeping rate of a warm gas into a cold component is relatively high, cold clouds associated with warm gas form small-scale clumps and are dispersively distributed, whereas hot gas covers large fraction of space.

(2)

When the sweeping rate is relatively low, in contrast, warm gas and cold clouds are diffusively and equally distributed, while hot gas component is substantially localized.
Low Amplitude New Type Variable Stars in Globular Clusters
Authors: Bao-An Yao , Chung-Sheng Zhang , Dao Qin , Jian-Hua Tong
Published: July 2016

Rapid progress in the stellar pulsation research has presented many new challenges to traditional pulsation theory. The following progress made by us should belong to one of the new challenges:

1)

There are many variable stars located at the Horizontal Branch (HB) but outside the instability strip with amplitude larger than 0.02 mag.

Maybe some astronomers have already doubted of the 1950’s conclusion-the RR Lyrae stars are confined to the narrow instability strip in the C-M diagram, the boundaries of the gap are extremely sharp and definite, beyond the edges no light variations occur with ranges greater than 0.02 mag. We are changing the conclusion by observations. Here we do not mean the microvariability. We still raise the question from the classical viewpoint. We want to show that there are variable stars outside the strip with peak to peak amplitudes larger than 0.02 mag.
Stellar Pulsation: (I) Analysis of Stability of Envelope
Authors: Zhi-Yao Yu
Published: July 2016

The life-time of the star on AGB is approximately 6 × 104 yr. We divide it into front half and back half of AGB (including to optical Mira variable and OH/IR star) according to their evolution character. The observations show that the star has non-pulsation, but constant mass loss rate (~ 5 × 10−7M⊙ yr−1) on front half of AGB. Its circumstellar envelope is formed. When the star has pulsation on back half of AGB, its mass loss rate is relative with time, and increases gradually. In this time the star is on the stage of optical Mira variable. When the mass loss rate reaches the value of ~ 3 × 10−6M⊙ yr−1, the star evoluted from the stage of optical variable into the stage of radio bright OH/IR star. On the end of AGB the mass loss rate reaches ~10−4M⊙ yr−1. (Band and Habing 1983, Hermen and Habing 1985).
Stellar Pulsation: (II) Multiple Distinct Shells
Authors: Zhi-Yao Yu
Published: July 2016

We can find the conclusion with our analysis for VLA observation of OH maser and CO (2–1) emission line that they are distributed on some different distinct shells in the circumstellar envelope, respectively.
Nonlinear, Nonradial Pulsation in Rapidly Oscillating Ap Stars
Authors: Kurtz D. W.
Published: July 2016

The rapidly oscillating Ap stars pulsate in high-overtone, low degree p-modes with their pulsation axes aligned with their oblique magnetic axes. They show non-linearity in their pulsation in three ways:

1)

The harmonics of the basic pulsation frequency are detectable.

2)

The pulsation phase seems to vary stochastically on a time scale of days to years depending on the star.

3)

The form of the nonradial surface distortion is not constant with time.

These three effects are illustrated with HR 3831, the best studied of the roAp stars. HR 3831 pulsates in distorted dipole mode which can be modelled as a linear sum of axisymmetric l = 0, 1, 2, and 3 spherical harmonics aligned with the magnetic axis. This gives rise to a 7-frequency multiplet split by exactly the rotation frequency. The form of the distortion shows small changes on a time-scale of years. HR 3831 shows a 5-frequency rotationally split first harmonic multiplet, a 3-frequency rotationally split second harmonic multiplet, and a single third harmonic frequency has probably been detected at an amplitude of 0.065 mmag. The first harmonic has changed its form significantly over the last 10 years. A technique for decomposing the fundamental frequency septuplet into its component spherical harmonics is used to fit the pulsation phase as a function of rotation phase. This allows a unique O-C to be defined for any length of light curve. The long term behaviour of the O-C diagram cannot be modelled adequately with a combination of periodic (Doppler shift) and quadratic (evolution) terms; there seems to be a significant stochastic component. The direction of the pulsation phase reversal at rotational phase 0.747 is indeterminate; sometimes it is a positive-going reversal, sometimes negative-going. At present it is not known whether this is a numerical artifact, or a physical effect in the star. If it is a physical effect, it means that small non-periodic differences in pulsation amplitude between the bipolar hemispheres have been detected.
Double-Mode Stellar Pulsation
Authors: Kovács G.
Published: July 2016

The current observational and theoretical status of the double-mode variables is reviewed. Focusing mostly on the RR Lyrae stars, we address the question of the observational evidence of modal stability. The problem of stationarity is a crucial issue in the modelling of these stars.

We mention past efforts in hydrodynamical and analytical modelling together with a detailed discussion of some very recent results. It is suggested that stochastic forcing due to turbulent convection may play a crucial role in exciting some marginally stable modes in the limiting pulsation. The latest hydrodynamical results first demonstrate that purely radiative models are able to show permanent double-mode behavior in the relevant period regime of RRd stars. The reason for the previous lack of double-mode behavior is attributed to the large dissipation, i.e. artificial viscosity, generally used in the codes to ensure numerical stability and to obtain amplitudes comparable to the observed ones.

We think that better models should include some physical dissipation, most probably turbulent convection, and a more accurate numerical treatment of the radiative hydrodynamics.
An Oscillator Model for Stellar Variability
Authors: Nakahara T. , Tanaka Y.
Published: July 2016

The dependence of coupling constants in a coupled oscillator model is examined with simplified methods. The Lyapunov exponents are preliminary introduced for the model. The behaviors of oscillator model are examined in a parameter plane. So-called the Arnold’s tongues for phase-locking states are observed in fractal patterns.
A Unified Model of Dwarf Nova Outbursts Based on the Disk Instability
Authors: Osaki Y. , Hirose M. , Ichikawa S.
Published: July 2016

A unified model for outbursts of dwarf novae is proposed based on the disk instability model in cataclysmic variable stars. In this model, two different intrinsic instabilities (i.e., the thermal instability and the tidal instability) within accretion disks are considered in non-magnetic cataclysmic variable stars. It is suggested that all of three sub-classes of dwarf novae (i.e., U Gem-type, Z Cam-type and SU UMa-type dwarf novae) may be explained in terms of two model parameters of the orbital period of the binary and of the mass transfer rate within the framework of the disk instability model.
Numerical Simulations of Pulsationally Unstable Accretion Disks around Supermassive Black Holes
Authors: Honma F. , Matsumoto R. , Kato S.
Published: July 2016

The innermost region of slim accretion disks with standard α viscosity is unstable against axisymmetric radial inertial acoustic perturbations under certain conditions. Numerical simulations are performed in order to demonstrate behaviors of such unstable disks. It is shown that oscillations with the period of ~ 10−3(MBH/M⊙) s can be excited near the inner edge of the disks, where MBH is the mass of the central object. This kind of unstable disks is a possible origin of the periodic X-ray time variabilities with period of ~ 104s observed in a Seyfert galaxy NGC 6814.
Interstellar Molecules of Prebiotic Interest
Authors: Winnewisser Gisbert
Published: July 2016

The field of interstellar molecules is reviewed with special consideration of molecules which are of potential biological interest. At present more than 110 interstellar molecules have been identified in interstellar clouds and circumstellar envelopes. The more complex molecules are found in the dense cores which are often the sites of active star formation. These locations represent prime targets for the search of larger molecules such as glycine and possibly other amino acids. However, in the list of detected interstellar molecules still many simple hydrides are missing, e.g. SH, PH, PH2, etc., which constitute the building blocks for larger molecules and biomolecules. With the technological opening of the terahertz region to both laboratory and interstellar spectroscopy, great scientific advances are to expected such as the direct detection of the low energy bending vibrations of larger (linear) molecules or the ring-puckering motion of larger ring molecules like the polycyclic (multiring) aromatic hydrocarbons, which might shed new light on the assignment of the «unidentified infrared» features or even on the diffuse visible interstellar bands (DIBs).