bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale
Authors: Clementini G. , Cacciari C. 
Published: July 2016

AbstractThe surface brightness version of the Baade-Wesselink method, has been applied to 7 field RR Lyrae stars with metallicity ranging from [Fe/H]= −0.2 to −1.5. V magnitudes, V-R and V-I colors and CORAVEL radial velocities were used, and the analysis was performed over a restricted phase range in order to avoid the complications caused by the pulsating atmospheres. The combination with previous results of the B-W method, which used comparable criteria (Jones, Carney, & Latham, 1988, preprint; Jameson, Fernley, & Longmore 1987, in press M.N.R.A.S; Cohen & Gordon 1987, Ap.J., 318, 215) leads to the following relation between the absolute luminosity and metallicity:Mv = (1.0 ± 0.05) + (0.17 ± 0.05) [Fe/H]This relation is in very good agreement with the preliminary results found by Liu and Janes (this volume). The application of the above relation to the RR Lyraes in M31 and the Magellanic Clouds leads to distance moduli of (m–M)o= 24.21 ± 0.20 for M31, (m–M)o = 18.26 ± 0.20 for the LMC, and (m–M)o =18.85 ± 0.20 for the SMC, and the distance to the galactic center turns out to be approximately 7.2 kpc. From the absolute magnitude of the RR Lyraes and adopting a constant visual magnitude difference between the RR Lyraes and the turn-off ΔV = 3.55 (Buonanno 1986, Mem.S.A.It., 57, 333), we estimate ages of 18.8 and 15.7 Gyr for globular clusters of metallicity [Fe/H] = −2.2 (e.g. M92) and [Fe/H] = −0.8 (e.g. 47 Tuc) respectively, using the age-turnoff luminosity relation derived by Sandage (1982, Ap.J., 252, 553) or 20.9 and 16.9 Gyr using Buonanno’s relation.
Oscillation Frequencies of Solar Models
Authors: Cox Arthur N. , Guzik Joyce A. , Kidman Russell B. 
Published: July 2016

AbstractTwo precision solar models have been constructed with the Iben evolution program, one with no diffusion of the internal atomic nuclei, and another that includes the effects of gravitational settling, thermal diffusion, and concentration gradient diffusion on the element abundances. The opacity at the bottom of the convection zone was increased 15-20 percent (within its theoretical uncertainty) to allow a few microhertz agreement with the observed solar p-mode frequencies. The original helium mass fractions of the mixtures were 0.291 and 0.289 for the no-diffusion and diffusion models, respectively. The diffusion model evolved to a surface Y=0.256 at the solar age, and the original Z value of 0.0200 decreased to 0.0179. Agreement of asymptotic theory 1=0 and 2 p-mode frequency separations and those directly calculated with nonadiabatic theory is good, and there is good agreement with observations also. Calculation of g-mode solutions shows that they do not have equal period spacings until high radial order. Nonadiabatic solutions for these g-modes modes enable us to predict their relative surface visibility. For 1=1-5, the lowest order modes seem to be more detectable assuming that they all have the same kinetic energy. Our high helium results in high central temperatures that give over 9 SNUs from the B and 1.5 SNUs from the Be reactions, but a lower more conventional helium abundance would reduce this B neutrino flux by maybe two SNUs. Models with iron condensed-out deeper than the convection zone, and with the presumed WIMPs to cool the central regions and reduce the SNU flux, agree less well with the p-mode frequency separations.
The Unusual Period Distribution of the RR Lyrae Variables in NGC 5897
Authors: Wehlau Amelia 
Published: July 2016

AbstractAttention is called to the rather unusual distribution of the periods of the RR Lyrae variables in NGC 5897, a metal-poor halo globular cluster with a very low central concentration. Of the seven RR Lyrae stars known in the cluster, three have periods between 0.797 and 0.856 day and two have periods of 0.45 and 0.42 day. The other two have periods of 0.34 and 0.35 day with much lower amplitudes of variation. Due to the lack of crowding in this cluster photoelectric observations and Fourier decompositions of the resulting light curves should be possible for at least six of the RR Lyrae variables. In addition, the cluster appears to contain a non-variable horizontal branch star, SK 120, lying within the instability strip. As this is the only well documented case of such a star, photoelectric observations of this star would also be desirable.
Relativistic Free-free Gaunt Factor of the Dense High-Temperature Stellar Plasma
Authors: Itoh Naoki , Nakagawa Masayuki , Kohyama Yasuharu 
Published: July 2016

AbstractThe free-free Gaunt factor of the dense high-temperature stellar plasma is calculated by using the accurate relativistic cross section, and is compared with the Gaunt factor derived by using Sommerfeld’s exact nonrelativistic cross section. A wide range of electron degeneracy is accurately taken into account. Significant deviations from the nonrelativistic relsults are found for high-temperature cases.
Non-equilibrium Ionisation in Tycho’s Supemova Remnant
Authors: Brinkmann W. 
Published: July 2016

AbstractWe present a detailed numerical study of the X-ray emission of Tycho’s supernova remnant. Using Nomoto’s W7 model of an exploding white dwarf as intial condition we follow the hydrodynamical and ionisation evolution for different densities of the interstellar medium and compare the emitted spectra with EXOSAT GSPC observations. The results indicate that the density of the ambient medium is 0.5 ≤ no ≤ 1.0 cm-3, the distance to Tycho is about 3 kpc.
A Comparison of Three Regions of Puppis A
Authors: Fischbach K.F. , Bateman L.M. , Canizares C.R. , Markert T.H. , Saez P.J. 
Published: July 2016

AbstractHigh resolution X-ray spectral observations of Puppis A were performed with the FPCS on the Einstein Observatory at three regions of the remnant: the shock front, the bright eastern knot, and the interior. Plasma diagnostics of lines from OVII and OVIII constrain the values of electron temperature, ionization timescale, and hydrogen column density. We compare results of the diagnostics for these three regions. A non-equilibrium analysis of previously published fluxes of oxygen lines shows that the interior has not yet reached ionization equilibrium.
X-ray Spectra of Clusters of Galaxies
Authors: Sarazin Craig L. 
Published: July 2016

AbstractX-ray line observations of clusters of galaxies have shown that the X-ray emission in clusters is mainly thermal emission from hot diffuse gas, and that much of this gas has come out of stars, probably having been ejected from galaxies in the cluster. Future high resolution observations should allow us to determine the physical state of the gas. X-ray line measurements and abundance determinations can lead to strong constraints on the origin of the intracluster gas, and on the chemical evolution and history of galaxies. Some of the stronger resonant X-ray lines may be observable as absorption lines against a background quasar. Such X-ray absorption line measurement can be used to directly derive distances to clusters, using a technique similar to (and possibly complementary to) that the well-known method using the Zel’dovich-Syunyaev effect.
A Cooling Flow Cluster at Redshift Z=0.2
Authors: Wolter Anna , Gioia I.M. , Maccacaro T. , Morris S.L. , Nesci R. , Perola G.C. , Schild R. 
Published: July 2016

AbstractIn this paper we discuss the cluster of galaxies 1E0839.9+2938, serendipitously discovered at x-ray wavelengths. The collected data imply that this is an example of cooling flow cluster.
Observing Soft X-ray Line Emission from the Interstellar Medium with X-ray Calorimeter on a Sounding Rocket
Authors: Zhang J. , Edwards B. , Juda M. , Kelley R. , Madejski G. , McCammon D. , Moseley H. , Skinner M. , Schoelkopf R. , Szymkowiak A. 
Published: July 2016

AbstractWe have been developing X-ray calorimeters that have high spectral resolution and high quantum efficiency. For an X-ray calorimeter working at 0.1 K, the energy resolution ideally can be as good as one eV for a practical detector. A detector with a resolution of 17 eV FWHM at 6 keV has been constructed. We expect to be able to improve this by a factor of two or more. With X-ray calorimeters flown on a sounding rocket, we should be able to observe soft X-ray line emission from the interstellar medium over the energy range 0.07 to 1 keV. Here we present a preliminary design for an X-ray calorimeter rocket experiment and the spectrum which might be observed from an equilibrium plasma. For later X-ray calorimeter sounding rocket experiments, we plan to add an aluminum foil mirror with collecting area of about 400 cm2 to observe line features from bright supernova remnants.
The Composition of Comets
Authors: Krankowsky Dieter 
Published: July 2016

Abstract.The chemical composition of gases in the coma of Comet Halley obtained from in situ and remote observations is reviewed. Water vapor with an abundance of approximately 80% by number is the dominant parent gas. Carbon monoxide is the second most abundant molecule, with about one-seventh of the water abundance. The other expected parent gases—carbon dioxide, methane, and ammonia—contributed with at most a few percent to the coma gas. Molecular nitrogen is found to be a minor species, with an abundance of less than one percent. Formaldehyde is relatively abundant, with a few percent relative to water. Gas-phase isotope ratios of nitrogen, oxygen, and sulfur are found to agree with solar system values within experimental errors. Halley’s hydrogen isotope ratio is comparable to the values found in other solar system objects poor in hydrogen, but distinctly different from the protosolar nebula and objects that accreted hydrogen in gaseous form. Carbon in the cyanide radical is enriched by 35% in13C compared to the bulk solar system value that indicates the presence of non-homogenized interstellar carbon in Halley. Volatiles released from grains contribute noticeably to the coma gas. Complex organic molecules, inferred from various observations as constituents of the dust grains, are believed to be the origin of the distributed CO source, CN, and other jet structures in the coma.
Hydrodynamic Models of the Collisional Coma
Authors: Crifo J.F. 
Published: July 2016

Abstract.The hydrodynamic approach to the modeling of the collisional regions of the cometary atmospheres is reviewed. A concise account of the existing Monte Carlo simulations is also incorporated. Emphasis is placed on works stimulated by the Halley flyby missions. The basic physical processes are described, based on the analogy with the physics of underexpanded jets. The general structure of the governing equations is presented and their legacy discussed. A detailed intercomparison is made of the application of these methods to the modeling of the comas. The reliability of the conclusions brought forward by existing models is discussed.
Plasma Processes in the Inner Coma
Authors: Cravens T. E. 
Published: July 2016

AbstractThe solar wind interaction with comets is characterized by the mass-loading of the solar wind with heavy cometary ions that are produced by the ionization of neutrals in the extensive cometary coma. This mass-loading slows down the solar wind and ultimately leads to the formation of a magnetic barrier and a magnetotail. Solar wind protons disappear in the vicinity of the cometopause due to charge-exchange collisions with neutrals. The plasma and fields inside the cometopause of comets Halley and Giacobini-Zinner were observed by instruments on board several spacecraft. Several plasma populations were detected in the inner coma, including cold (less than 1 eV) and energetic (several keV or more) ions, and cold and hot electrons. The Giotto magnetometer observed a diamagnetic cavity surrounding the nucleus, which is a consequence of an outward ion-neutral drag associated with the flow of cometary neutrals past plasma frozen onto field lines in the magnetic barrier. In addition to large-scale structures, many small-scale structures in the plasma and fields have been observed in comets, including tail rays and kinks, and plasma pile-ups and depletions in the barrier. Theoretically, the existence of a very narrow layer of enhanced plasma density just inside the diamagnetic cavity boundary has been predicted. The behavior of plasma in the inner coma (within the cometopause) of an active comet is determined both by plasma processes, such as magnetohydrodynamics, and by collisional processes such as ion-neutral friction, resistivity, electron and ion thermal cooling, ion-neutral chemical reactions, and electron-ion recombination.
Burst Mode VLBI and Pulsar Applications
Authors: Wietfeldt R.D. , Frail D.A. 
Published: July 2016

AbstractThe technique of Burst Mode (BM) VLBI is described and its particular application to the observations of pulsars is explored. The wideband pulsed radiation from these objects is exploited to acquire data at two ends of an interferometer baseline in high-speed bursts and only during the pulsar on-times. The result at the VLBI correlator is an improvement in sensitivity by as much as the inverse pulsar duty cycle, and is a consequence of the bandwidth expansion offered by BM and the intrinsic use of gating. As a result, precision astrometrical studies of pulsars will benefit through the greatly increased instantaneous bandwidths achieved by pulsar BM. The problems, implications, and limitations of acquiring and processing pulsar BM data are discussed.
The three dimensional structure of astronomical sources through optimal inversion
Authors: Keto Eric , Jeffrey William 
Published: July 2016

AbstractWe explore the application of optimal inversion techniques to astronomical data with a goal of developing a set of procedures for the determination of the three dimensional structure of astronomical sources. Astronomical data present a particularly difficult problem in inversion because: In any observation, 3 of 6 spatial and velocity dimensions are lost in projection onto the plane of the sky and the line of sight velocity. In any inversion, we would like to solve for a number of physical parameters. Generally, these parameters are closely related in their effect on the single observable, the sky brightness.The dimensional deficiency leaves us with an unavoidably large degree of ambiguity (non-uniqueness) in any solution, while the inter-related parameters lead to a high probability of correlated errors and hence instability in the presence of to noise.We show how constraints of symmetry and smoothness source allow us to handle an inversion with an insufficiently sampled data base and mutually dependent solution parameters (mathematically ill-posed and ill-conditioned). The constraints represent a priori information incorporated into the solution; thus very highly constrained inversions are similar to model fitting. In any case the inversion procedure provides us with quantitative statistics on the goodness of fit which may be used to assess the degree of ambiguity in a particular model, and the expected errors and cross-correlated errors on the parameters defining the source structure.We briefly discuss the background and motivation, and outline the procedure in general terms. We refer to papers published in the Ap. J. where different aspects of the inversion are applied to observational data bases collected at the VLA.
Visibility based continuum subtraction
Authors: van Langevelde Huib Jan , Cotton Bill 
Published: July 2016

AbstractWe have been looking into the possibility to subtract out the continuum contribution in spectral line databases from the ungridded visibilities. It turns out that our simple method offers quite interesting possibilities in a lot of practical cases. In this contribution we show how and why this method works. Details of this work can be found in van Langevelde and Cotton (1990). We have tried to compare the results of this method with the mote conventional ways of subtracting the continuum. This comparison has to be done with simulations of which we show some results.
EVN as a phase stable interferometer
Authors: Bååth Lars B. , Mantovani Franco 
Published: July 2016

AbstractA technique has been developed by which the data from the Mk3 correlator are read directly into the AIPS package. The data are Fourier transformed from delay lags into frequency channels and kept separately for each IF channel. The data are then corrected for multiand single band delays. We have used this technique to solve for fringe solutions on a reference source and then apply the solution to correct the data on the target source. In a recently analysed experiment we managed in this way to phase reference, using the European VLBI Network (EVN) at 18cm, the quasar OQ208 and the radio quasar 1422+202. These sources are separated by more than 9° on the sky.
The Proposed Radio Schmidt Telescope: The technical challenges
Authors: Dewdney P.E. , Landecker T.L. 
Published: July 2016

AbstractThe concept of the Radio Schmidt Telescope is designed to fill a scientific requirement for a radio telescope which is very sensitive to diffuse, extended emission, but has much higher resolution than singleantenna telescopes. This telescope undertakes to utilize a new region of “parameter space” in the aperture synthesis technique. The emphasis of this article is on a process leading to the best implementation of the concept at reasonable cost while satisfying all the scientific objectives.
The Hydrogen Array
Authors: Wilkinson P.N. 
Published: July 2016

AbstractThe time is ripe for planning an array with a collecting area of 1 km2 (14 times larger than Arecibo and 75 times larger than the VLA). In view of its major astronomical target I have dubbed this concept ‘The Hydrogen Array’, although 1μJy continuum sources will also be reliably detected. I present some initial thoughts about the issues involved.
A test of Radio Interferometry by Lunar reflection
Authors: Belkora L. , Hagfors Tor , Phillips J.A. 
Published: July 2016

AbstractWe discuss the use of the moon as a passive reflector for radio interferometry experiments with baselines on the order of the radius of the orbit of the moon. Because of the extreme loss in the lunar interferometer path, only exceptionally strong point sources are candidates for this kind of interferometry. As the moon is far from an ideal reflector due to the irregular surface, the data processing necessary to optimize the fringe detectability is rather complicated. What we present here is a very brief summary of a paper describing the lunar interferometer in the Astrophysical Journal (Hagfors, Phillips and Belkora, 1990) and an experiment currently underway at Arecibo to test the lunar interferometer using Jupiter’s strong bursts at 25 MHz as a source. All references pertaining to the lunar interferometer are to be found in the Astrophysical Journal paper; this summary includes references concerning the test of the interferometer at Arecibo.
Patterns of Aperiodic Pulsation
Authors: Spiegel E. A. 
Published: July 2016

AbstractTechniques for deriving amplitude equations for stellar pulsation are outlined. For the simplest such equations with multiple instabilities, the derivation of a map for the patterns of pulsation phases is described. This map gives the time between two successive maxima of pulsation in terms of the time between the previous pair, under suitable conditions. The phase differences can be regular, chaotic or hyperchaotic.
On the Application of Fourier Decomposition Parameters
Authors: Petersen J. O. 
Published: July 2016

The application of Fourier decomposition parameters has revolutionized important areas of investigations of Cepheid type variables since the introduction of Fourier analysis in its modern form by Simon and Lee (1981).In the literature several different representations of the results of Fourier analysis have been utilized. In view of the growing interest for applications of Fourier decomposition it is important to use and publish Fourier data in an optimal way. Most studies until now have used amplitude ratios and phase differences derived from traditional light curves giving the light variation in magnitudes, following the original recipe of Simon and Lee (1981). However, Stellingwerf and Donohoe (1986) advocated the use of phases rather than phase differences. Recently, Buchler et al. (1990) argued that the standard Simon & Lee form contains all relevant physics, and suggested analysis of flux-values rather than of magnitudes, because this removes the distorting effects of constant, false light. Thus there are many choices to be made in practical applications of Fourier analysis, and there is at present no convincing argument for preferring one specific representation.
Period Variations and Evolution of Delta Scuti Variables
Authors: Shi-Yang Jiang 
Published: July 2016

The Short periods of Delta Scuti Stars allow the observational detection of the period changes expected from the stellar evolution within several tens years. For about 30 years we are keeping this topic as a small systematic observational program with our 60 cm telescope. Here we publish the period variation of 18 stars in table I. The data of 28 And are taken from R. Garrido et al. in AAp 144 (1983), 211; the period variation rate of 4 CVn is given by M. Breger. Both of them are low amplitude variables.From these data we find out that both the population I and II variables can have period increasing and decreasing. The rate is between 2 × 10−6 to 8 × 10−8 days/year. Due to the period range of about 0.2 days, the time scale of period variation in one direction is limited within about 2 million to 200 million years. Usually we take the mass of this A to F type variables as 1.5 to 2.0 solar mass, so the main sequence life time is about several billion years. If all these A to F type main sequence stars will be variable in some period of its life time the possibility for a star to show Delta Scuti type variation is about hundredth, especially for the high amplitude type. Up to now we have found some 50 high amplitude variables with V < 10.5, and the total number of A3 to F5 with V < 10.5 is about 1.2 × 105, so the incidence of high amplitude variables is about 0.04%.
Radial and Nonradial Periods and Growth Rates of an AI Velorum Model
Authors: Guzik J. A. 
Published: July 2016

AbstractWalraven, Walraven and Balona recently discovered several new periodicities in addition to the well-known fundamental and first overtone periods of the high-amplitude δ Scuti star AI Velorum. Linear nonadiabatic pulsation calculations were performed for an AI Velorum model of mass 1.96M⊙, 24.05L⊙, and Teff 7566 K for the radial and low-degree nonradial modes to help verify the tentative identifications made by Walraven, et al. Comparison of the calculated periods with the observations suggests some alternatives to the identifications proposed by Walraven, et al.
The Importance of Radiative Transfer in Stellar Pulsation Models
Authors: Davis C. G. 
Published: July 2016

AbstractWith the advent of new astrophysical opacities it seems appropriate to discuss the need for a full radiative transfer (RT) theory instead of the usual equilibrium diffusion theory used in most nonlinear pulsation codes. Early studies on the importance of RT in the calculation of light curves for Cepheid models showed little effect over diffusion theory. The new opacities though may help to explain the “bump” mass discrepancy problem. For RR Lyrae models the use of RT theory causes some effects both in the color differences (U-B) as well as in the light curves. New opacities help to explain the period ratios for double mode RR Lyrae and beat Cepheids. A new area of research is in the modeling of stars with high luminosity to mass ratios that show tendencies for doubling and transitions to chaos, such as W Virginis and RV Tauri stars. For these stars it has been shown that RT is necessary in calculating their light curves and that the understanding of the shock dynamics depends on the transfer of lines in the pulsating RT dependent atmospheres (Fokin 1991).