bluuebunny/crossref_metadata_2025 huggingface dataset:
New results on OGLE Cepheids and PL relations in the LMC and SMC
Authors: Udalski A.
Published: July 2016

We present results of the search for pulsating variable stars in the Magellanic Cloud fields covering central parts of these galaxies. The data were collected during the second phase of the Optical Gravitational Lensing Experiment survey (OGLE-II) from 1997 to 2000. In total, several thousand pulsating stars (Cepheids, RR Lyr) were found in both Magellanic Clouds. The photometric data of all objects are available to the astronomical community from the OGLE Internet archive. We present basic properties of pulsating stars in the Magellanic Clouds including Period–Luminosity relations for Cepheids. We also discuss observational prospects for the pulsating star field in the ongoing third phase of the OGLE project (OGLE-III) which started in 2001.
Dust enshrouded AGB stars in the LMC
Authors: Hinkle Kenneth H. , Joyce Richard R. , Do Tuan
Published: July 2016

A near-infrared (J and K) survey of the LMC Bar West region was undertaken with CIRIM on the CTIO 1.5-m telescope to search for obscured carbon stars. A number of very red stars were detected, and from this list five highly reddened, ‘Obscured’ stars were identified. Subsequent to our survey we identified these sources in the 2MASS survey data. Using our J, K photometry as well as J, H, K from 2MASS, 8.28 µm from the MSX satellite, and L photometry from Phoenix on Gemini, we have measured the color temperature and flux of the detected obscured stars. None of these objects is as cool as the bright galactic enshrouded carbon star CW Leo, although the MSX survey does appear to detect objects similar to CW Leo. Using the Phoenix high-resolution infrared spectrograph on Gemini we have observed the first overtone CO spectra of four of the LMC obscured stars. All the spectra are those expected for obscured carbon stars, but a surprising variety of line profiles was found.
AGB variables in globular clusters
Authors: Lebzelter T. , Wood P. , Hinkle K.H. , Joyce R. , Fekel F.
Published: July 2016

With a large number of newly detected red variables in globular clusters we construct a log P – K diagram of these stars and compare it with findings from the LMC. We show the existence of a relation between the location in log P – K diagram and the velocity amplitude in the near infrared.
A census of AGB stars in the Milky Way and M31 subgroups of dwarf-spheroidal galaxies
Authors: Kirschbaum F. , Heiling B. , Nowotny W. , Spindler Ch. , Olofsson H. , Schwarz H.E.
Published: July 2016

From photometric observations out to the tidal radii of the galaxies, we were able to identify hundreds of new carbon stars, to derive mean absolute magnitudes〈Mi〉, luminosity functions, and the spatial/radial distributions of the carbon stars in these galaxies. For each galaxy this new material will allow estimates of the tips of their RGBs to derive distance moduli, to derive C/M ratios of the AGB populations and bolometric magnitudes Mbol. At the end of our survey a comparison of all quantities of the late-type stars as a function of the properties of the host galaxies will be made possible.
The effect of stellar evolution on the light curves’ shapes of RR Lyrae stars in M3
Authors: Jurcsik Johanna
Published: July 2016

The light curve characteristics of a homogeneous sample of variables in M3 are studied in detail. Accurate light curves and mean magnitudes of about 100 RRab and 50 RRc stars which do not show any type of modulation are analyzed. According to their mean magnitudes and Fourier parameters the variables can be sorted into four groups, representing different stages of the horizontal branch stellar evolution.
Latitude distribution of nonradial pulsations in rapidly rotating B stars
Authors: Jankov S. , Mathias P. , Domiciano de Souza A. , Uytterhoeven K. , Aerts C.
Published: July 2016

We present a method for the analysis of latitude distribution associated with temperature and/or velocity perturbations of the stellar surface due to non-radial pulsation (NRP) modes in rapidly rotating B stars. The technique is applied together with Fourier Doppler Imaging (FDI) to high resolution and high signal-to-noise ratio spectroscopic observations of ϵ Per. The main advantage of this approach is that it decomposes complex multi-periodic line profile variations into single components, allowing the detailed analysis of each mode separately. We study the 10.6-d−1 frequency that is particularly important for modal analysis of non-radial pulsations in the star.
Pulsational velocity fields in the atmospheres of two roAp stars HR1217 and γ Equ
Authors: Sachkov M. , Ryabchikova T. , Kochukhov O. , Weiss W.W. , Reegen P. , Landstreet J.D.
Published: July 2016

We discuss spectroscopic observations of pulsations in the roAp stars γ Equ and HR 1217. In both stars we observe strong variations of rare-earth lines and detect running magneto-acoustic waves, but do not find evidence for a standing pulsational wave. In γ Equ we find strong pulsational variations across line profiles, characteristic of l ≥ 2 modes.
Chemical abundances ofβCephei stars from low- and high-resolution UV spectra
Authors: Daszyńska-Daszkiewicz Jadwiga , Niemczura Ewa
Published: July 2016

We determined the stellar parameters (Teff, [m/H],θ) andE(B – V)for allβCephei stars observed during the IUE satellite mission. All parameters were derived using an algorithmic procedure of fitting theoretical flux distributions (Kurucz 1996) to the IUE observations.
Multiperiodicity in pulsating red giants
Authors: Percy J.R. , Bakos A.G. , Besla G. , Hou D. , Velocci V. , Henry G.W.
Published: July 2016

We describe several aspects of the variability of bright pulsating red giant (PRG) stars, with emphasis on the determination of pulsation modes and pulsation masses by using observed multiperiodicity and pulsation constants (Q- values). Our studies of bright PRGs provide a model for the analysis and interpretation of the thousands of PRGs being discovered in surveys of Local Group galaxies.
The Period-Radius Relation: Classical Cepheids and RR Lyrae stars
Authors: Marconi M. , Bono G. , Nordgren T.E.
Published: July 2016

We present the period-radius relations predicted by nonlinear convective models of Classical Cepheids and RR Lyrae stars. For the former variables we show that the metallicity effect is negligible for both fundamental and first overtone pulsators. This confirms the power of the period-radius relation to estimate Cepheid radii and in turn distances. For the latter class of variables we show that the dispersion of the period-radius relation of both fundamental and first overtone pulsators is significantly reduced once the metallicity dependence is taken into account. This provides a robust method to evaluate the radius of observed RR Lyrae with measured period and metal abundance.
VINCI/VLTI Interferometric Observations of Cepheids
Authors: Nardetto N. , Kervella P. , Mourard D. , Bersier D. , Coudé du Foresto V.
Published: July 2016

We report the angular diameter measurements of seven classical Cepheids, X Sgr, η Aql, W Sgr, ζ Gem, β Dor, Y Oph, and l Car, that we have obtained with the VLT Interferometer Commissioning Instrument, installed at ESO’s VLT Interferometer. For four of these stars, η Aql, W Sgr, β Dor, and l Car, we detect the pulsational variation of their angular diameter. This enables us to compute directly their distances using a modified version of the Baade-Wesselink method. For X Sgr, ς Gem, and Y Oph, we apply a hybrid method that makes use of published estimates of their linear diameters to derive their distances.
The Study of δ Scuti Stars in The Transition Era from Ground-Based to Space Photometry
Authors: Garrido Rafael , Poretti Ennio
Published: July 2016

The different research teams involved in the study of δ Sct stars have slightly changed their strategy in the past years. The observational effort to secure worldwide coverage of case studies has been continued, but the requirements have become more severe, especially about target characterization and frequency resolution.

After the successful launch of the Canadian satellite MOST, which will be the pioneer of asteroseismology from space, the future missions are programmed to properly take into account the need for adequate frequency resolution: COROT will spent 30 and 150 d (additional and core programs, respectively) on the target, while EDDINGTON will spend up to 3yr. Such a requirement is a direct consequence of the observational results on δ Sct, γ Dor, SPB, and other stars obtained from ground. It should be noted that without these results (see Poretti 2000 for a review about δ Sct stars) the scientific background of the space missions would be much less defined and the risks of incomplete results (owing to inaccurate selection of targets, insufficient resolution, underestimate of the influence of the rotation) much higher.
The Absolute Magnitudes of RR Lyrae Stars and the Age of the Galaxy
Authors: Sandage Allan
Published: July 2016

It is shown that the intrinsic spread in the absolute magnitudes of the RR Lyrae variables in a given globular cluster can reach 0.5 magnitudes at a given period or at a given color, due to luminosity evolution away from the zero age horizontal (ZAHB). The size of this intrinsic luminosity spread is largest in clusters of the highest metallicity.

The absolute magnitude of the ZAHB itself also differs from cluster to cluster as a function of metallicity, being brightest in clusters of the lowest metallicity. Three independent methods of calibrating the ZAHB RR Lyrae luminosities each show a strong variation of MV(RR) with [Fe/H]. The pulsation equation of P<ρ>0.5 = Q(M,Te, L) used with the observed periods, temperatures, and masses of field and of cluster RR Lyraes gives the very steep luminosity-metallicity dependence of dMv(RR)/d[Fe/H] = 0.42. Main sequence fitting of the color-magnitude diagrams of clusters which have modern main-sequence photometry gives a confirming steep slope of 0.39. A summary of Baade-Wesselink MV(RR) values for field stars determined in four independent recent studies also shows a luminosity-metallicity dependence, but less steep with a slope of dMV(RR)/d[Fe/H] = 0.21.

Observations show that the magnitude difference between the main sequence turn-off point and the ZAHB in a number of well observed globular clusters is independent of [Fe/H], and has a stable value of dV = 3.54 with a disperion of only 0.1 magnitudes. Using this fact, the absolute magnitude of the main sequence turn-off is determined in any given globular cluster from the observed apparent magnitude of the ZAHB by adopting any particular MV(RR) = f([Fe/H]) calibration.

Ages of the clusters are shown to vary with [Fe/H] by amounts that depend upon the slopes of the MV(RR) = f([Fe/H]) calibrations. The calibrations show that there would be a steep dependence of the age on [Fe/H] if MV(RR) does not depend on [Fe/H]. No dependence of age on metallicity exists if the RR Lyrae luminosities depend on [Fe/H] as dMV(RR)/d[Fe/H] = 0.37. If Oxygen is not enhanced as [Fe/H] decreases, the absolute average age of the globular cluster system is 16 Gyr, independent of [Fe/H], using the steep MV(RR)/[Fe/H] calibration that is favored. If Oxygen is enhanced by [O/Fe] = – 0.14 [Fe/H] + 0.40 for [Fe/H] < –1.0, as suggested from the observations of field subdwarfs, then the age of the globular cluster system decreases to 13 Gyr, again independent of [Fe/H], if the RR Lyrae ZAHB luminosities have a metallicity dependence of dMV(RR)/d[Fe/H] = 0.37.
The Globular Cluster ω Centauri and its RR Lyrae Variables
Authors: Dickens R.J.
Published: July 2016

The significance of some of the unusual characteristics of the globular cluster ω Centauri in various fundamental problems is explored. Interest is centred on the properties of the cluster RR Lyraes, and what they can contribute to studies of early cluster chemical enrichment, stellar pulsation, the distance scale, stellar evolution, stellar ages and the Oosterhoff period-shift problem. This article, which is intended to highlight problems and progress rather than give a comprehensive review, includes new results based on photometry of the RR Lyraes, red giants, subgiants, horizontal-branch and main sequence stars in the cluster.
The Luminosity-Metallicity Relation for RR Lyrae Stars and its Implications for the Astronomical Distance Scale
Authors: Clementini G. , Cacciari C.
Published: July 2016

The 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

Two 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

Attention 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

The 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

We 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

High 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

X-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

In 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

We 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

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

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

The 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.
A pulse calibration system for the VLBA
Authors: Thompson A.R. , Bagri D.S.
Published: July 2016

In pulse calibration of an interferometer a series of short pulses is inserted into the receiver input to produce a spectrum of equi-spaced lines. The use of these for calibration, and the proposed system for the VLBA, are described.
Burst Mode VLBI and Pulsar Applications
Authors: Wietfeldt R.D. , Frail D.A.
Published: July 2016

The 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.
Simulations of space VLBI
Authors: Murphy David W.
Published: July 2016

The use of simulations to examine various trade-offs and estimating the scientific return from the space VLBI missions RADIOASTRON and VSOP is discussed. The impact of the on-board spacecraft constraints is determined.
The three dimensional structure of astronomical sources through optimal inversion
Authors: Keto Eric , Jeffrey William
Published: July 2016

We 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

We 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

A 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

The 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

The 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

We 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

Techniques 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.
Characterisation of the Dynamics of a Variable Star
Authors: Auvergne M. , Baglin A. , Goupil M. J.
Published: July 2016

Tentatives to detect chaos in variable stars are presented. Constraints on the accuracy on individual measurements and length of the records, necessary to obtain defenitive conclusions, are discussed. Some directions for future improvements are sketched.
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

Walraven, 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

With 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).
The Coupling Coefficients of Radial Pulsation in Third Order
Authors: Ishida T. , Takano R. , Yamakawa F. , Takeuti M.
Published: July 2016

The third order theory of coupling is discussed regarding the radial pulsation of stellar models.
Influence of Cell Wall Composition on the Fossilisation of Bacteria and the Implications for the Search for Early Life Forms
Authors: Westall Frances
Published: July 2016

The oldest cell-like structures on Earth are preserved in silicified lagoonal, shallow sea or hydrothermal sediments, such as some Archean formations in Western Australia and South Africa. Previous studies concentrated on the search for organic fossils in Archean rocks. Observations of silicified bacteria (as silica minerals) are scarce for both the Precambrian and the Phanerozoic, but reports of mineral bacteria finds, in general, are increasing. The problems associated with the identification of authentic fossil bacteria and, if possible, closer identification of bacteria type can, in part, be overcome by experimental fossilisation studies. These have shown that not all bacteria fossilise in the same way and, indeed, some seem to be very resistent to fossilisation. This paper deals with a transmission electron microscope investigation of the silicification of four species of bacteria commonly found in the environment. The Gram positiveBacillus laterosporusand its spore produced a robust, durable crust upon silicification, whereas the Gram negativePseudomonas fluorescens, Ps. vesicularis, andPs. acidovoranspresented delicately preserved walls. The greater amount of peptidoglycan, containing abundant metal cation binding sites, in the cell wall of the Gram positive bacterium, probably accounts for the difference in the mode of fossilisation. The Gram positive bacteria are, therefore, probably most likely to be preserved in the terrestrial and extraterrestrial rock record.
Pattern in the rise of High Technology
Authors: Morrison Philip
Published: July 2016

First of all, evolutionary convergence works. Both earlier primates and non-primates have long made tools to a pattern. But one presumed master tool, a protolanguage, is not tangible. It is likely to have been present for two million years during which brain volume steadily grew among our predecessors. Then small societies of foragers very rapidly managed worldwide exploration and settlement, created art, and left a tide of novel techniques and artifactswithout any further increase in cranial size. This suggests a new software power, not visible in bony relics. A linguist has identified that second empowering step with a major feature universally found in human language. A precondition for interstellar signaling is ahardwaretechnology far beyond any open to clever foragers. Here the additional requirement may be a population large enough to support such elaborate technology. A new formal model suggests that large population growth is as intrinsic to our kind as language. Should such proposals hold, distant counterparts to human development may be frequent.
The Search for Extraterrestrial Civilizations in Optical Range – Methods, Objects, Results
Authors: Beskin Gregory , Borisov Nikolai , Komarova Victoria , Mitronova Sofia , Neizvestny Sergei , Plokhotnichenko Vladimir , Popova Marina
Published: July 2016

Perspectives and possibilities of search for signals of extraterrestrial civilizations in optical range are discussed. Two criteria of an artificial origin of an optical emission – the variations of its intensity which have a time structure of semiotic character and the presence of narrow laser lines are analyzed. For detection and study of these signals we propose to investigate the astronomical objects under suspection with extremely high time resolution – 10−7s. To solve this problem we use a special hard/software photometrical complex MANIA (Multichannel Analysis of Nanosecond Intensity Alterations) which consists of a photometer, a registration system which is a «time-code» converter, a PC/AT 486 computer and a tape recorder. Special statistical methods and programs for the search for and the analysis of any type of brightness variability of astronomical objects on a time scale of 10−7-102s are described. Criteria of choice of objects to search for extraterrestrial civilizations signals in their emission are discussed. To search for civilizations of I type (with energy consumption equal to one for our civilization) it is proposed to investigate 161 stars of F9V-G5V spectral classes in neighbourhood of the Sun with radius of 25 pc. As possible beacons (transmitters) of extraterrestrial civilizations of II type (with energy consumption equal to star luminosity) we propose to consider the objects that have unusual characteristics, particularly, lineless optical spectra. The results of observations of 60 objects of mentioned types and the limits for possible signals power are reported.
A Search for Dyson Spheres around Late-Type Stars in the Solar Neighborhood II
Authors: Jugaku Jun , Nishimura Shiro
Published: July 2016

We continued our search for partial (incomplete) Dyson spheres associated with 50 solar-type stars (spectral classes F, G, and K) within 25 pc of the Sun. No candidate objects were found.
Seti Figure of Merit
Authors: Dreher John W. , Cullers D. Kent
Published: July 2016

We develop a figure of merit for SETI observations which is anexplicitfunction of the EIRP of the transmitters, which allows us to treat sky surveys and targeted searches on the same footing. For each EIRP, we calculate the product of terms measuring the number of stars within detection range, the range of frequencies searched, and the number of independent observations for each star. For a given set of SETI observations, the result is a graph of merit versus transmitter EIRP. We apply this technique to several completed and ongoing SETI programs. The results provide a quantitative confirmation of the expected qualitative difference between sky surveys and targeted searches: the Project Phoenix targeted search is good for finding transmitters in the 109to 1014W range, while the sky surveys do their best at higher powers. Current generation optical SETI is not yet competitive with microwave SETI.
The Effect of a Close Binary upon Stellar Pulsation
Authors: Shibahashi H.
Published: July 2016

Through tidal deformation of the equilibrium state, the p-mode oscillations may show apparently complicated features. I discuss the fundamental characteristics of the tidally forced oscillation, and show the possibility that it leads to a triplet fine structure in the frequency spectrum of p-modes.
Pulsating Components of Eclipsing Binaries: New Asteroseismic Methods of Studies and Prospects
Authors: Mkrtichian D.E. , Kusakin A.V. , Gamarova A.Yu. , Nazarenko V.
Published: July 2016

We give a brief review on the present status of our research of A-F pulsating components of semi-detached Algol-type systems. We suggest a new asteroseismic approach for estimating the evolutionary stage of the mass-accreting components of Algols during rapid and slow mass-transfer phases, asynchronization and differential rotation.
Dwarf Cepheid Radii and the Distance Scale
Authors: Laney C.D. , Joner M. , Schwendiman L.
Published: July 2016

Baade-Wesselink radii for dwarf Cepheids (High Amplitude Delta Scuti stars) can give luminosities and distances independent of the classical Cepheid distance scale. Using optical and IR photometry together with precision radial velocities, the authors have obtained radii and luminosities for 7 stars, and combined these with two from the literature, obtaining results consistent with the luminosities of the 3 dwarf Cepheids with good Hipparcos parallaxes. Classical Cepheids and dwarf Cepheids appear to fit the same PL and PR relations. The results imply ‘bright’ RR Lyrae absolute magnitudes giving an LMC distance modulus of 18.51-18.54, in agreement with the distance derived from classical Cepheids.
New Distance Estimates to RR Lyrae Stars: Towards a Definitive Luminosity Calibration
Authors: Layden Andrew
Published: July 2016

We describe two projects currently underway to provide an improved calibration of RR Lyrae luminosities.
Application of the Image Subtraction Method to the OGLE-I Observations
Authors: Kopacki Grzegorz , Kołaczkowski Zbigniew , Pigulski Andrzej
Published: July 2016

The analysis of the OGLE-I data using the standard profile-fitting software yielded a large set of new variable stars. However, due to the severe crowding of the images many variables may have been missed. Therefore, we decided to reanalyze these data by means of the image subtraction method. Our main goal was the detection of new variables. In addition, we intend to extend the time-base of the observations for the variables found in the course of the OGLE-II project (Udalski et al. 1997). We present the preliminary results of our study.
Spectroscopic Nonadiabatic Observables as a New Tool for Mode Identification in β Cep Stars
Authors: Daszyńska J. , Cugier H.
Published: July 2016

We present a new method of mode identification based on the line profile variations. We calculate time series of Si III 455.26 nm for models of β Cep stars with a mass of 10 M⊙. The Spectroscopic observables are amplitude ratio and phase difference for various oscillation parameters derived from the line profile changes. Based on the computed values we plot diagrams to search for the best discriminators of modes.

In most Spectroscopic diagrams the unstable modes are grouped in well-defined regions with different m-values, and a few of them give also separation with respect to l-values. Moreover, on the basis of almost all of the diagrams we can distinguish the prograde modes from the retrograde ones, and the zonal modes from those with m ≠ 0.

In this paper we discuss also the influence of the inclination angle, the amplitude of the radius variation and the equatorial velocity on the diagnostic values of the Spectroscopic diagrams.
The Main Parameters of SPB Stars on the Basis of IUE Spectra
Authors: Niemczura E.
Published: July 2016

We derive mean stellar parameters for 14 SPB stars observed during the IUE satellite mission, using an algorithmic procedure fitting theoretical flux distributions (Kurucz, 1996) to the IUE low-resolution spectra. We focus our attention on the metallicity parameter [m/H]. We found the mean value of [m/H] = -0.27 ± 0.22.
53 Piscium, an SPB Star with Activity
Authors: Le Contel J.-M. , Mathias P. , Chapellier E. , Valtier J.-C.
Published: July 2016

The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.

New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.

No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1.