bluuebunny/crossref_metadata_2025 huggingface dataset:
Proposed Search for Fast Variables
Authors: Duthie J. G. , Renaud B. , Savedoff M. P.
Published: June 2019

We propose the examination of trailed photographs as a medium of search for fast variable stars. Diurnal rotation and seeing permit access to the period range from 0.1s to 10s for a resolution of 1″, exposures of one minute and a plate field of 30′, while slower or faster periods can be studied by mechanically trailing at the appropriate rate. This permits examination of a wide period band over a field of perhaps 0.1 square degree in a minute's time, while photoelectric devices now available permit only star by star examination. Thus we can contemplate examination of an appreciable fraction of the sky with moderate telescope time required.
A κ-ϵ Model of the Lower Overshoot Layer
Authors: Petrovay K.
Published: June 2019

One region where discrepancies between the seismic and standard solar models continue to exist is the overshoot layer below the convective zone (Gough et al. 1996). A main reason for this discrepancy is clearly the lack of a realistic physical model for astrophysical overshoot. Beside numerical experiments, the most promising approach to the construction of such a model is based on the Reynolds-stress formalism of turbulence theory (Speziale 1991). As a first step toward the development of a more complete Reynolds stress model of the overshoot, here we present a simple κ-ϵ model, valid under the following conditions:

(a).

Incompressibility: ∂iVi = 0. Owing to the short length scale (cf. Fig. 1), this assumption is somewhat better founded here than in other models.

(b).

Closure: Let and . (w = vz vertical velocity; κ ≡ V2/2: kinetic energy; ϵ: dissipation rate). Now assume Cwk = const., Cwt =const. This is warranted if l/Hv ≃constant (Hv: scale height of V2), which will be seen indeed to be the case in our model, cf. eqs. (3)–(4).

(c).

No correlation with thermodynamic fluctuations: . The assumption implies that these correlations vanish in a very thin (≪ Hp) transition layer below △▽ = 0. No change in the geometrical flow properties is expected in such a thin layer, so lo, Cwk, and Cwϵ should be the same as in the lower part of the unstable layer. On the basis of numerical experiments here we use lo = HP, Cwk = 0.6, Cwϵ = 3, q = 2.4. (The index ‘0’ refers to values at z = 0 i.e. at △▽ = 0.) Note however that V may be significantly reduced in the transition layer, so Vo (and thus ) is undetermined in the present model.
Comments on the Influence of Solar Activity on P-Mode Oscillation Spectra
Authors: Gizon L.
Published: June 2019

The systematic p-mode frequency changes which are observed through the solar cycle are believed to be associated with near-surface perturbations confined to the magnetically active latitudes. In this paper, we study the perturbation arising from the presence of a large “active region”, corresponding to a localized structural change in a thin region close to the photosphere. We shall ignore the difficult question of the magnitude of the effect, and simply consider some geometric and observational implications for low-degree modes.
Seismology of the ZZ Ceti Stars
Authors: Clemens J. Christopher
Published: June 2019

The pulsations of white dwarf stars are potentially a rich source of information about white dwarf structural properties. Extracting and applying this information to improve our knowledge of white dwarf interiors requires measuring individual eigenperiods in a complex power spectrum, and identifying the character of the eigenmodes they represent. This review will summarize observational progress in these areas for the ZZ Ceti pulsators.
The Discovery of Non-Radial Gravity-Mode Pulsations in γ Doradus-Type Stars
Authors: Krisciunas K.
Published: June 2019

Over two dozen early F-type variable stars have been identified which constitute a new class of pulsating stars. These stars typically have periods between 0.5 and 3 days with V-band variability of several hundredths of a magnitude. Given the time scale of the variability, the pulsations would have to be non-radial gravity-mode pulsations. The pulsational nature of some of these stars has been proven by means of coordinated multi-longitude photometric campaigns, radial velocity (RV) variations and line profile (LP) variations, indicating low degree spherical harmonics (ℓ = 3 or less). Evidence is that these stars are younger than 300 Myr; one would surmise that a rapid onset of convection in their outer photospheric layers puts an end to the pulsations. Further observation and modeling of these stars is important for our understanding of stellar evolution, the search for g-modes in the Sun, and is even relevant to the interpretation of radial velocity variations of solar-type stars (e.g. 51 Peg) in the search for extrasolar planets.
Recovering the Pulsation Velocity Distribution on Stellar Surface
Authors: Hao J.
Published: June 2019

The analytical expression between the line profile and its corresponding pulsation velocity field is derived by the assumption of Doppler Imaging (DI). Based on this approach, numerical experiments of the recovery of the one dimensional nonradial pulsation velocity distribution from the residual line profiles are presented.
Asteroseismology of β Cephei
Authors: Shibahashi H. , Aerts C.
Published: June 2019

We discuss the oscillation features of β Cephei, which is a magnetic star in which the magnetic axis seems to be oblique to the rotation axis. We interpret the observed equi-distant fine structure of the frequency spectrum as a manifestation of a magnetic effect on an eigenmode, which would be a radial mode in the absence of the magnetic field. Besides these frequency components, we interpret another peak in the frequency spectrum as an independent quadrupole mode. By this mode identification, we deduce the mass, the evolutionary stage, the rotational frequency, the magnetic field strength, and the geometrical configuration of β Cephei.
The New Chromosphere
Authors: Carlsson Mats , Stein Robert F.
Published: June 2019

The natural state of the Solar chromosphere is very dynamic. Any photospheric disturbance will grow and naturally form shocks over the twenty scale-heights in density between the photosphere and the corona. Observations in the resonance lines from singly ionized calcium and recently in the ultraviolet region of the spectrum observed with the Solar and Heliospheric Observatory satellite also show a very dynamic chromosphere. This dynamic picture is further supported by numerical simulations. Static and dynamic pictures of the chromosphere are fundamentally different. The simulations also show that time variations are crucial for our understanding of the chromosphere itself and for the spectral features formed there.
Infrared Line Emission by Broadly Distributed Gas
Authors: Harwit Martin
Published: June 2019

Diffuse infrared background radiation measurements have traditionally been carried out across broad wavelength bands, primarily because there seldom appeared to be sufficient energy available in individual spectral lines to make such observations possible. In the past few years, far-infrared searches for spectral line background radiation have become possible, and considerably greater use of these capabilities will become available in the next few years. The promise of this kind of observation is reviewed.
The Galactic Far Ultraviolet Background
Authors: Bowyer Stuart
Published: June 2019

Measurements of the far ultraviolet background are reviewed. A major turning point occurred in the study of this field in the early 1980s, when evidence was first presented that this flux was primarily galactic in origin rather than extragalactic, as had been generally believed. A number of experiments have confirmed this result, and it has been established that the flux is the result of scattering of starlight by dust. However, the detailed scattering properties of dust in the far ultraviolet are uncertain; a wide range of albedos and scattering phase functions have been reported. Very recent evidence indicates that ultraviolet scattering grains are different from grains that scatter in the visible in that they have a low albedo and scatter isotropically. There is evidence that this dust is present at some level in all view directions in the galaxy. Spectral emission features have been detected recently in the diffuse background. Lines of C IV and O III] have been observed and lines of O IV/Si IV and N III have probably been observed. It has been established that the 105 K gas producing these lines is 2–3 kpc above the galactic plane. Overall mass flux rates of 5 to 25 M⊙ yr−1 for this gas are indicated, which provides strong support for the galactic fountain model for this material. Emission from molecular hydrogen has been detected in directions of high and low neutral hydrogen column density. This emission emanates from low density molecular clouds and indicates clumping of the emitting material in the clouds. Our knowledge of the sources of the far ultraviolet background has increased dramatically in the past 10 years. The results obtained have yielded surprising new insights on a variety of astrophysical topics.
The Relationship Between Gas and Cirrus Dust Filaments at the Edge of the Expanding Shell in Eridanus
Authors: Verschuur G. L. , Verter F. , Rickard L. J. , Leisawitz D. T.
Published: June 2019

At the boundary of a large expanding shell in Eridanus around l = 187°, b = −50° the morphology observed in the HI emission is well mimicked by the 100 μm surface brightness but with associated structures offset by as much as 0.°5. A point-to-point comparison between I100μm and NHI in filaments of neutral hydrogen and dust (IR cirrus) produces only a weak dependence. However, when I100μm at a cirrus dust peak is compared with NHI at the associated H i peak, a relationship closer to that reported by other workers is found. Preliminary CO observations have set low limits on the molecular gas in these filaments. Since the H i and dust in our region are associated with a large expanding shell (or superbubble), shocks may be responsible for separation of gas and dust. The existence of small-scale structure in both the HI and IR is noted. We conclude that attempts to correlate HI and IR must invoke high-resolution area surveys.
Spectrum and Origin of the Extragalactic Optical Background Radiation
Authors: Tyson J. Anthony
Published: June 2019

Ultra-deep CCD surveys to 29 mag from .32 to .9 μ wavelength reveal an isotropic population of very blue galaxies. There are over 150,000 of these objects per square degree per magnitude. Saturation of their number density at 27 mag indicates that most of the optical light from this population has been detected. The resulting extragalactic background radiation from the UV to the near-IR due to this population of objects is shown. Gravitational lens and Lyman-break observations show that the redshift of galaxies fainter than 24 mag is in the range 1–3. Small-scale dark lane structures may be intergalactic dust clouds or tunnels through the luminous galaxy distribution.
The Extragalactic Background Included in IRAS Point Source Samples
Authors: Meurs E. J. A. , Harmon R. T. , Adorf H.-M
Published: June 2019

The sky survey performed by the IRAS satellite provides a very homogeneous and almost complete view of the sky at infrared wavelengths. Suitable methods from multivariate statistics and decision theory are employed to extract the extragalactic background included in the IRAS Point Source Catalog. The resulting map comprehensively represents the distribution of extragalactic objects on the sky. The various selections may be used to assess large-scale structure in the distribution of galaxies and the total infrared background due to galaxies, to follow such structures closer to the Galactic Plane than is possible with optical data and to address cosmological questions (e.g., Harmon, Lahav, and Mauers 1987). These investigations are to be extended to the more sensitive Co-Added Catalog.
Far Infrared Emission from an Intergalactic Dust Cloud?
Authors: Wszolek Bogdan , Rudnicki Konrad , Masi Sivia , de Bernardis Paolo
Published: June 2019

The possible presence of general extragalactic extinction has been studied by many authors. Extragalactic dust can be associated with a pregalactic star population and/or it can be ejected by galaxies during their evolution.
Intensity Fluctuations of the Cosmic Background Radiation Due to Polarization Effects
Authors: Rudak Bronislaw
Published: June 2019

The Nagoya-Berkeley experiment has revealed a substantial excess over the blackbody radiation in the submillimetre part of wavelengths. Its origin is unknown. The concept of high-redshift cosmological dust (e.g., Hayakawa et al., 1987), though not without problems, remains one of the simplest explanations. It is clear that other types of observations will be necessary to identify the source of the excess. Needless to say, searches for cosmic background radiation (CBR) intensity fluctuations on fine angular scales in the submillimetre region are especially desired.
Small-Scale Fluctuations and Anisotropies in the 1–3 keV X-Ray Background
Authors: Barcons X. , Fabian A. C.
Published: June 2019

The spatial distribution of the 1–3 keV X-ray background (XRB) in five Einstein Observatory Imaging Proportional Counter fields has been analyzed. The autocorrelation function does not exceed 9% on scales ~5′. The observed count probability distribution is then used to check the source number-flux distribution at faint levels. Agreement with the Einstein Observatory deep survey is obtained. A cutoff in the number-flux distribution for a Euclidean population of sources at a flux approximately one-half of the deep survey limit, previously suggested by Hamilton and Helfand (1987), is also inferred.
Kapteyn and statistical astronomy
Authors: Paul E. R.
Published: June 2019

If Jacobus Cornelius Kapteyn (1851–1922) were here today, he would undoubtedly be among those asking the new questions on the cutting edge of contemporary astronomy. It is likely that he would even find a survey of his own contributions to the study of the Milky Way irrelevant. Nevertheless, Kapteyn's life-long interest in the Milky Way shaped the work of many astronomers, including, of course, his students, Willem de Sitter, H.A. Weersman, Pieter van Rhijn, and through van Rhijn: Jan Oort, Bart Bok and many others. But Kapteyn's influence extended far beyond his native Holland. After Kapteyn became a close colleague of George Ellery Hale and a Research Associate at the Mount Wilson facilities in 1908, Hale began to employ a number of Dutch astronomers, including van Rhijn, Adriaan van Maanen, and Kapteyn's Danish future son-in-law, Ejnar Hertzsprung. Moreover, Kapteyn's astronomical colleagues world-wide found his enthusiasm and penetrating insights infectious.
Young galactic clusters and the rotation curve of our Galaxy
Authors: Hron J. , Maitzen H. M.
Published: June 2019

The most recent determination of Oort's galactic rotation constant ‘A’ from open clusters was made by Taff and Littleton (1972). They obtained A=15 km/s/kpc, but unfortunately they omitted a detailed description of their cluster sample. For the present work we compiled a catalogue of O-B3 clusters for which radial velocities and distances are available. The individual cluster references given by Janes and Adler (1982) have been used to find best distances for the clusters. Radial velocities were taken from the list of Dr. Wramdemark (private communication) and from Hron et al. (1984). The catalogue contains 105 clusters distributed over the four galactic quadrants as 16:27:35:27.
The old population
Authors: Freeman K. C.
Published: June 2019

We review the kinematical and chemical properties of the old population of our Galaxy. Comparison is made with the properties of the old population in other disk galaxies.
Near-infrared studies of the Milky Way
Authors: Okuda H.
Published: June 2019

The inner region of the Galaxy has been explored by means of near-infrared observations; the distribution and population of the stars are studied from the near-infrared brightness mapping and star counts in the Milky Way, while the magnetic-field configuration is probed by the near-infrared polarimetry.
Survey of Galactic HI emission at |b| ≤ 20°
Authors: Burton W. B. , Hekkert P. Te Lintel
Published: June 2019

We have used the NRAO 140-ft telescope to survey galactic HI near the galactic equator. The observations cover the part of the sky north of δ = −40° in the latitude range b = −20° to at least +20°; in some regions the survey extends to b = +33°. The longitude coverage in the equator ranges from ℓ = 340° to 270°. The data represent an improvement over existing large-scale HI surveys in terms of velocity coverage (±250 km s−3), velocity resolution (1 km s−1), sensitivity (3σ = 0.2 K), and extent of sky coverage, but not in density (δℓ × δb = 1° × 1°) of coverage.
Comments on the distribution of molecules in spiral galaxies
Authors: Rickard L. J , Palmer Patrick
Published: June 2019

Young and Scoville (1982) have argued that the CO distribution, and by inference the H2 distribution, follows the shape of the blue luminosity of the disk, and is thus exponential. However, full maps of bright-CO galaxies (Rickard and Palmer 1981) show considerable structure, with real peaks and depressions on scales as small as the telescope beam. This means that the noise in the determination of the underlying structure is dominated not by the instrumental contribution but by the intrinsic noise of the structure itself. A correct analysis of the axisymmetric structure requires the use of statistical tests comparing the observations with different hypothetical distributions. One finds that equally good fits can be obtained with exponential distributions, r-1 distributions, or even flat disks with central nuclei. However, profiles of the full map data averaged over azimuth, with “error” bars determined by the structural variation with azimuth, show a clear deviation from the optical luminosity profile in the outer disk of NGC 6946. Furthermore, if the profiles for NGC 6946 and IC 342 are fit with exponentials, the scale lengths are rather larger than previously suggested (8.9 and 6.6 kpc, respectively). By sampling only a few radii, one can miss much of the emission of the outer parts of the galaxies, and also underestimate the intrinsic noise of the structure.
Spiral structure of the Milky Way and external galaxies
Authors: Elmegreen Debra Meloy
Published: June 2019

The spiral structure of the Milky Way galaxy has always been somewhat elusive because of our internal vantage point. This review will present methods and data for determining the overall pattern, and will summarize various models that have been proposed. Observations of spirals in external galaxies will also be discussed, because they can provide insight into the spiral structure of the Milky Way.
Fine structure of molecular clouds within 1 minute of arc of the Galactic Center
Authors: Kaifu Norio , Inatani Junji , Hasegawa Tesuo , Morimoto Masaki
Published: June 2019

We have observed the HCN(J=1–0) line in the vicinity of the galactic center with the 18″ beam of the Nobeyama 45-m telescope. Profiles were taken at 53 points within 1 arcmin from the galactic nucleus [R.A. = 17h42m29.29s, Dec. = −28°59′17.6″ (1950)] with a 10″ grid (see figure 1). A SSB cooled-mixer receiver (TRX = 600 K) and a wideband AOS (acousto-optical radiospectrometer) with 250 kHz resolution were used.
Highlights of high-velocity clouds
Authors: Van Woerden Hugo , Schwarz Ulrich J. , Hulsbosch Aad N.M.
Published: June 2019

Twenty years after their first discovery at Dwingeloo (Muller, Oort and Raimond 1963), the nature and origin of high-velocity clouds (HVCs) remain enigmatic. Yet, much important progress has been made in the study of their properties, and prospects are brightening that the problem of their distances, which holds the key to their understanding, may soon be solved.
Distribution and motions of HI in M31
Authors: Brinks E. , Burton W. B.
Published: June 2019

It has become clear in the past few years that the distribution and kinematics of HI in M31 is far from simple. The new high-resolution survey made with the Westerbork SRT in the 21-cm line of atomic hydrogen by Brinks and Shane (1983) shows this dramatically. Along almost any line of sight through M31 two separate velocity systems are sampled. Based on a previous survey Shane (1978) and later Bajaja and Shane (1982) proposed that the extra component is due to warping of the plane of the galaxy into the direction of and crossing the line-of-sight. Roberts et al. (1978) and Whitehurst et al. (1978) emphasized that the observed profile structure ruled out confinement of the gas to a thin plane. Unwin (1983) reached a similar conclusion on the basis of his survey. The most complete model produced up until now which accounts for the two velocity systems is the one by Henderson (1979), based on the 100-m Effelsberg survey of M31 by Cram et al. (1980)
Stellar velocity distribution in the presence of scattering massive clouds
Authors: Renz W.
Published: June 2019

The purpose of this contribution is to show

1. a systematic perturbation-theoretical method of solving multivariate Fokker-Planck equations (FP eq.) as they appear in galactic dynamics.

2. that it is not only important to consider the cooling of the stellar disk by birth of new stars but also to include stellar death processes in the equation. This leads to different stellar velocity distributions.

3. that the input of new stars into circular orbits as it is done in recent numerical work (Sellwood and Carlberg, 1983) leads not only to the cooling effect wanted but also to an additional damping effect on spiral waves.
Star formation in molecular clouds
Authors: Shu Frank H.
Published: June 2019

We examine how star formation occurs in the Galaxy and come to the following conclusions. (1) The distribution of newly-born stars in the Galaxy depends on the origin of giant-molecular-cloud complexes. For individual complexes, we favor the mechanism of Parker's instability behind galactic shocks. The production of “supercomplexes” may require the mediation of Jeans instability in the interstellar gas. (2) Magnetic fields help to support the clumps of molecular gas making up a complex against gravitational collapse. On a timescale of 107years, these fields slip by ambipolar diffusion relative to the neutral gas, leading to the formation of dense cloud cores. This timescale is the expected spread in ages of stars born in any clump. (3) When the cores undergo gravitational collapse, they usually give rise to low-mass stars on a timescale of 105years. (4) What shuts off the accretion flow and determines the mass of a new star is the onset of a powerful stellar wind. The ultimate source of energy for driving this wind in low-mass stars is the release of the energy of differential rotation acquired during the protostellar phase of evolution. The release is triggered by the entire protostar being driven convectively unstable when deuterium burning turns on.
The chemical evolution of the Galaxy
Authors: Twarog Bruce A.
Published: June 2019

Over the last few years, our picture of the chemical evolution of the Galaxy has changed substantially. These changes are of interest because chemical evolution provides a common point of contact for most astrophysical processes of importance to galaxy evolution. By astrophysical processes we mean star formation, stellar nucleosynthesis, gas dynamics, etc. An understanding of galactic chemical evolution would allow us to place constraints on all of these topics simultaneously. This property, however, is a double-edge sword because, with so many variables involved, unique solutions to problems in chemical evolution are almost impossible.
II.—On the History and Antiquities of Paphos
Authors: James M. R.
Published: June 2019

In this section of the Report it will be my object to present as complete a statement as I can of what is known and what has been written on the subject of Paphos; and this should include a short specification of the chief points on which the late excavations either have thrown, or may be expected to throw, more light. On large and general questions, such as the origin and history of the Aphrodite worship in general, or even its history in the whole of Cyprus, I cannot enter here.

It is inevitable that the chapter must consist largely of quotations. The source of these is not far to seek. Meursius' ‘Cyprus’ in Creta, Cyprus, et Rhodos (Amsterdam, 1675, in 4to) contains a wonderfully comprehensive survey of the ancient literature of the subject. An essay by Frederick Münter, Bishop of Seeland, carries this survey a stage further, and makes some further additions to it. This essay is entitled, Der Tempel der Himmlischen Göttin zu Paphos (Copenhagen, 1824, 4to). It forms a supplement to his former tract, Religion der Karthager. It is illustrated with four plates, and supplemented by an architectural essay on the plan of the temple, from the pen of Gustav Friedrich Hetsch. These two books have assisted me to most of my quotations. I have added a few others from later books, and from my own reading.
Inscription on a Limestone Block
Authors: Hicks E. L.
Published: June 2019

Letters Slight apices. Date about 200 B.C.; not earlier. Line 1: iota adscriptum possibly omitted in Line 21: for see I.B.M. 925 (Branchidae). In line 12 there is a space after indicating a stop, but Mr. Paton cannot find any trace of after

Telmissos is described by Polemo (apud Suidam s.v.) as a town in Caria at a distance of sixty stadia from Halicarnassos [which answers very nearly to the distance between Budrum and the site above Ghiöl (J. L. M.)]. It has been frequently confused with its namesake, an important city in the west of Lycia. But we may take it for granted now that it was the little Carian town that was so famous in ancient times for its augury. Cicero is quite explicit on the point (De Divin. i. 41): Telmessus in Caria est, qua in urbe excellit haruspicum disciplina; and again in ch. 42: Turn Caria tota, praecipueque Telmesses, quos ante dixi, quod agros uberrimos maximeque fertiles incolunt, in quibus multa propter fecunditatem fingi gignique possunt, in ostentis animadvertendis diligentes fuerunt.
Inferences about Seeing
Authors: Alexander Peter
Published: June 2019

In his book Attention, Professor Alan White says ‘When you see X, it follows that if X is Y, you see Y whether you realise it or not.’ If, in passing through Paris, I saw a tall complex iron structure and that structure is the Eiffel Tower, then I saw the Eiffel Tower whether I realised it or not. I accept this, but because recent philosophical writings and discussions have cast doubt on the validity of the inference-pattern

I saw x; x is y; so I saw y

and certain related patterns, it is clear that we cannot be content with this unvarnished statement. Various entertaining examples are produced to show that some instances of this pattern are invalid and therefore that the pattern itself is invalid. If I saw Jones at noon and at noon Jones was bribing Smith then, it is alleged, I cannot conclude that I saw Jones bribing Smith. Similarly, it is said, from the facts that I saw a man in the far distance and that that man was my father, I cannot conclude that I saw my father in the far distance; from the facts that I saw a foot and that that foot was Lloyd George's I cannot conclude that I saw Lloyd George.
Internal Motions of Trapezium Systems
Authors: Allen Christine , Poveda Arcadio , Hernández-Alcántara Alejandro
Published: June 2019

The separations of the various components of 44 trapezia as a function of time are studied, taking advantage of many new, high precision observations for these objects. A previous study revealed that some systems have components moving with velocities larger than the escape velocity (Allen et al.1974). The present work updates our previous study, extending the observations by about 30 years, and thus allowing an improved determination of the relative transverse motions of the components. The analysis of the new data confirms the conclusions we reached in our previous work: most of the trapezia show the internal motions expected for bound, virialized small clusters, but a few have escaping components. The available observational material lends support to the concept that trapezia are unstable systems with lifetimes of the order of a few million years.
Modelling the Dust Emission of the L1551 IRS5 Binary System
Authors: Osorio M. , D’Alessio P. , Muzerolle J. , Calvet N. , Hartmann L.
Published: June 2019

We model the L1551 IRS5 source as a system containing two protostars, each surrounded by a circumstellar disk, both encircled by a circumbinary disk, and all disks surrounded by an extended infalling flattened envelope With this composite model, we can calculate self-consistently the spectral energy distribution of the source the shape of the ice and silicate features, and the spatial intensity distributions of the envelope and disks. We compare our model results with the observations, determining the physical parameters of the disks and the envelope. We find that flattened envelope collapse models are required in order to explain the observations and that the infall rate of the envelope is much larger than the accretion rates of the binary disks.
SN 1987A at Radio Wavelengths
Authors: Staveley-Smith L. , Manchester R.N. , Gaensler B.M. , Kesteven M.J. , Tzioumis A.K. , Bizunok N.S. , Wheaton V.C.
Published: June 2019

SN1987A has an intrinsic radio luminosity some four orders of magnitude less than SN1993J at maximum, largely a reflection of the tenuous wind . from the progenitor of SN1987A before explosion. Both remnants have an edge-brightened, ring-like morphology though, in the case of SN1987A, the expansion rate is currently only around 3500 km s−1. The flux density of the remnant of SN1987A continues to rise at all measured radio frequencies. Its spectral index is gradually flattening, indicating its transition into the supernova remnant phase. A campaign to increase the resolution of radio imaging by observing at higher frequencies is underway with the Australia Telescope Compact Array (ATCA).
X-ray Emission from Gamma-Ray Bursts
Authors: Frontera Filippo
Published: June 2019

In this paper I will present and discuss some of the relevant results obtained with the Italian satellite BeppoSAX on the prompt and afterglow emission of Gamma Ray Bursts (GRBs).
Dynamical Evolution of v-cooled Disks Following Compact Binary Mergers
Authors: Lee William H.
Published: June 2019

Understanding the dynamical evolution of post-merger accretion disks over a long timescale (comparable to their lifetimes) is essential to determine if these can power short GRBs. Here we present preliminary results of such a study, spanning 0.2 seconds, by using a realistic equation of state and taking into consideration the effects of neutrino cooling (the main agent, given the physical conditions in the disks).
Expected Changes of SNe with Redshift due to Evolution of Their Progenitors
Authors: Domínguez Inma , Höflich Peter , Straniero Oscar , Limongi Marco , Chieffi Alessandro
Published: June 2019

We have analyzed the influence of the stellar populations, from which SN progenitors come, on the observational outcome, including the metal free Pop. III. We use our models to study the evolution of the progenitor, the subsequent explosion and the light curves. For Type Ia, the variation of the main sequence mass of the progenitor of the exploding WD produces an offset in the maximum-decline relation of 0.2 mag. This effect is critical for the use of high redshift Type Ia SNe as cosmological standard candles. In contrast, the metallicity does not change the above relation (at maximum, ΔMV ≤0.06 mag). For Type II, we find a dependence of the light curve properties with both main sequence mass and metallicity of the progenitor, and we identify a rather homogeneous subclass, “Extreme II-P,” that may be used as a quasi-standard candle. Note that, although not as good as Type Ia for distance determinations, Type II are expected to have occurred since the first stars were formed.
Ultraprecise Photometry from Space: The MOST Microsat Mission
Authors: Matthews J. M. , Kuschnig R. , Walker G. A. H. , Pazder J. , Johnson R. , Skaret K. , Shkolnik E. , Lanting T. , Morgan J. P. , Sidhu S.
Published: June 2019

MOST (Microvariability & Oscillations of STars / Microvariabilite et Oscillations STellaire) is a Canadian microsatellite mission intended to detect rapid photometric oscillations at theμmag level in stars brighter thanV∼ 6. This limit is set primarily by the 15-cm aperture of the MOST telescope. The small size and mass of the MOST bus (similar to a suitcase) sets a limit on the pointing accuracy of about ±10 arcsec. To achieve the required photometric precision under these conditions, the MOST focal plane features a set of Fabry microlenses which can spread the target starlight into a pupil image of the telescope onto a CCD. The large size (∼1600 pixels) and positional stability (±0.1 pixel) of these images makes MOST insensitive to CCD flat-fielding errors. MOST is currently on schedule to be launched in early 2002.
Short Period M Giant Stars in the Hipparcos Catalogue
Authors: Koen Chris , Laney Dave
Published: June 2019

A number of M giant stars with periods of the order of a few days were discovered by the Hipparcos mission. Similar stars may also have been found by other large-scale surveys. Parallaxes and colour indices of a sample of these stars were used to estimate their radii, temperatures and luminosities. It is shown that it is very unlikely that they are ellipsoidal or spotted variables, and that they are most likely pulsating in high overtone modes.
Link between Mass-Loss and Variability Type for AGB Stars?
Authors: Ivezić Željko , Knapp Gillian R.
Published: June 2019

We discuss difficulties in explaining the distribution of AGB stars in the 25–12 vs. 12–K color–color diagram by steady-state radiatively driven models, and propose that the discrepancy may be due to changes of mass-loss rate with the time scales of ∼ 100 yr.
The Distance to the Large Magellanic Cloud
Authors: Popowski Piotr
Published: June 2019

I demonstrate that the two unexpected results in the local Universe: anomalous intrinsic (V – I)0 colors of RR Lyrae stars and clump giants in the Galactic center, and very short distances to Magellanic Clouds inferred from clump giants, can be at least partially resolved with a modified coefficient of selective extinction AV/E(V – I). With this modification, I find a new clump-giant distance modulus to the Large Magellanic Cloud, μLMC = 18.27 ± 0.07, which is 0.09 larger than the Udalski (1998b) result. When distance estimates from the red clump, RR Lyrae stars and the eclipsing binary HV2274 are combined, one obtains μLMC = 18.31 ± 0.04 (internal).
The Distance to the Galactic Center
Authors: McNamara D. H. , Madsen J. B. , Barnes J. , Ericksen B. F.
Published: June 2019

The Optical Gravitational Lensing Experiment (OGLE) data on high-amplitude δ Scuti Stars (HADS) and RR Lyrae stars have been analyzed to determine the distance to the galactic bulge. We find a mean value of 14.47 ± 0.08 mag for the bulge distance modulus. A small additive correction leads to 7.9 ± 0.3 kpc as the best distance to the galactic center.
Cepheid Distance to the Virgo Cluster
Authors: Mazumdar Anwesh , Narasimha D.
Published: June 2019

A reanalysis of the HST data on Cepheids in the Virgo cluster spiral M100 is presented, based on our study of the Galactic Cepheids. A distance modulus of 31.49 mag is derived, which is higher than the HST Key Project value of 31.04 mag obtained from the same data earlier (Ferrarese et al. 1996). The increase in the distance is caused by nearly equal contributions from a different calibration of the slope and the zero point of the period–luminosity relation and a correction for the flux-limited incompleteness bias.
Pulsational Amplitudes of Cepheids – Their Application to Reveal Companions
Authors: Szabados László
Published: June 2019

Two parameters are defined involving the observed (peak-to-peak) amplitudes in U, B, V, and R photometric bands as well as that of the radial velocity variation. They are used to detect companions to Cepheids for a sample about 300 Galactic Cepheids.
The Instability Strip of M3
Authors: Bakos G. Á. , Jurcsik J.
Published: June 2019

We present new multicolour CCD photometry of the central part of the globular cluster M3, mapping the precise position of ~ 120 RR Lyrae stars (RRab, RRd, RRc) on the horizontal branch (HB). The location of the double-mode variables (RRd) is in perfect agreement with recent theoretical results. We find a significant internal spread of metallicity amongst the RRab variables.
Theory of Amplitude Modulation II. The Resonant Mode Interaction Model
Authors: Van Hoolst Tim
Published: June 2019

With about one fourth of the RRab stars showing the Blazhko effect, amplitude modulation on long time scales is a common phenomenon in stellar pulsation. The role of nonradial oscillation modes is studied here, and it is proposed that the amplitude modulation is a result of a dynamical, nonlinear resonance between the observed radial mode and a low-degree nonradial mode. In this scenario, a nonradial mode is resonantly excited in Blazhko-type RR Lyrae stars. Degree one modes are found to have the highest probability of being excited and a crucial test of the model would be the observational determination of the degree of the proposed nonradial mode.
Mixing in the SMC Stars: Implication for Cepheids
Authors: Cordier D. , Lejeune T. , Lebreton Y. , Goupil M.-J.
Published: June 2019

We compare the recent OGLE 2 data of stars in the Small Magellanic Cloud (SMC) with stellar evolutionary models of low metallicity computed with the updated and numerically accurate code CESAM. The conversion between theoretical and observational data has been carefully done using the BaSel Library. This enables us to derive new observational constraints at SMC chemical composition: on the overshooting parameter αover during the main sequence, and on the mixing-length parameter αMLT for the red giant branch. The occurrence of an instability strip-crossing episode is strongly related to these mixing parameters.
Understanding Pulsations in OB Stars
Authors: Balona L. A.
Published: June 2019

Our understanding of pulsations in β Cep, SPB and ζ Oph stars is discussed. We do not understand why there are no β Cep stars earlier than O9, though the models show that the instability strip extends to hotter stars. The main problem among the SPB stars is why rotation has a strong inhibiting effect on pulsation. The ζ Oph stars are an extension of the β Cep and SPB stars to higher spherical harmonic degrees. The pulsational stability of models of B stars to modes of high degree is discussed. Results are compared with two well observed ζ Oph stars. Although there is good agreement with ζ Oph itself, the periods of the high-degree modes in α Vir are incompatible with model predictions.
CCD Studies of δ Scuti Stars in Open Clusters
Authors: Kjeldsen Hans
Published: June 2019

Asteroseismology on δ Scuti stars has until now produced very few convincing results – if we aim at doing strong tests of details of stellar modelling. The main reason for the lack of success is probably that these stars often rotate, which split nonradial oscillation frequencies into many more frequencies. These many frequencies and the fact that the more evolved δ Scuti stars contain a strong chemical composition gradient at the edge of the convective core, produce a very complicated eigenfrequency spectrum. In contrast to this, we expect, in principle, seismological studies of δ Scuti stars to be a very simple task: One has to compare theoretical oscillations in model stars with the observed oscillations. However, in order to produce convincing asteroseismological results, we need to do three things: (1) Detect as many eigenfrequencies as possible at high precision, (2) identify the eigenmodes and (3) improve the theoretical models. By observing δ Scuti stars in open clusters using CCDs, we have a possibility to improve on (1) and (2) as well as providing an opening for an improvement in the theoretical models by doing accurate calibrations of the basic cluster properties. In this paper I shall describe some of the results from CCD studies of δ Scuti stars in open clusters and identify some future prospects for this technique.
Optical Variability of the λ Eri Star HD 105382: Pulsation or Rotation?
Authors: Briquet M. , Aerts C. , De Cat P.
Published: June 2019

HD 105382 is clearly a monoperiodic, very active λ Eri star with the frequency 0.7721 d−1. Its photometric behaviour and the moment variations are not typical for a standard pulsational model.
Time-Series CCD Photometry of Northern Open Clusters Using the BOAO 1.8-m Telescope: III. NGC 2301
Authors: Kim S.-L. , Park B.-G. , Chun M.-Y. , Sung H. , Jeon Y.-B. , Yuk I.-S. , Ann H. B. , Lee S. H. , Lee M. G.
Published: June 2019

A time-series CCD photometric survey of variable stars in open clusters has been in progress using 1.8-m telescope at the Bohyunsan Optical Astronomy Observatory (BOAO) in Korea. We present preliminary results of time series photometry for the intermediate-age open cluster NGC 2301.
Pulsation Investigation of V647 Tau – Preliminary Results of STEPHI Campaign in 1997
Authors: Liu Y. Y. , Michel E. , Barban C. , Garrido R. , Alvarez M. , Hernández M. M. , Belmonte J. A.
Published: June 2019

V647 Tau was observed during a 1997 STEPHI campaign; 228 hr of observations in v were obtained, together with another 50 hr of simultaneous data in y. The data were analyzed and main results are discussed in the text.
Time Scales for Period Change in Pulsating White Dwarf Stars
Authors: Kepler S. O. , Costa J. E. S. , Winget D. E. , Reed M. D. , Kawaler S. D.
Published: June 2019

We have used the rate of change of pulsation period for the hot (DOV) pre-white dwarf PG1159–035 and the cool (DAV) white dwarf G117–B15A to measure their evolutionary time scales. We show that, for any multiperiodic star, we must take into account the effect of all pulsations simultaneously on the times of maximum of the pulsations to get reliable measurements of periods and phases.
A Virtual Telescope for the Open University Science Foundation Course
Authors: Norton Andrew J. , Jones Mark H.
Published: June 2019

The Open University is the UK's foremost distance teaching university. For over twenty five years we have been presenting courses to students spanning a wide range of degree level and vocational subjects. Since we have no pre-requisites for entry, a major component of our course profile is a selection of foundation courses comprising one each in the Arts, Social Science, Mathematics, Technology and Science faculties. The Science Faculty's foundation course is currently undergoing a substantial revision. The new course, entitled “S103: Discovering Science”, will be presented to students for the first time in 1998.
Earth-based observations of impact phenomena
Authors: Nicholson Philip D.
Published: June 2019

Earth-based observations at near- and mid-infrared wavelengths were obtained for at least 15 of the SL9 impacts, ranging from the spectacular G, K and L events to the barely-detected N and V impacts. Although there were a few exceptions, most of the IR lightcurves fit a common pattern of one or two relatively faint precursor flashes, followed several minutes later by the main infrared event as the explosively-ejected plume crashed down onto the jovian atmosphere. Correlations with the impact times recorded by the Galileo spacecraft and plumes imaged by the Hubble Space Telescope lead to an interpretation of the twin precursors in terms of (i) the entry of the bolide into the upper atmosphere, and (ii) the re-appearance of the rising fireball above Jupiter's limb. Positive correlations are observed between the peak IR flux observed during the splashback phase and both pre-impact size estimates for the individual SL9 fragments and the scale of the resulting ejecta deposits. None of the fragments observed to have moved off the main train of the comet by May 1994 produced a significant impact signature. Earth-based fireball temperature estimates are on the order of 750 K, 30-60 sec after impact. For the larger impacts, the unexpectedly protracted fireball emission at 2.3 μm remains unexplained. A wide range of temperatures has been inferred for the splashback phase, where shocks are expected to have heated the re-entering plume material at least briefly to several thousand K, and further modelling is required to reconcile these data.
Growth and dispersion of the Shoemaker-Levy 9 impact features from HST imaging
Authors: Beebe Reta F.
Published: June 2019

The Hubble Space Telescope Wide Field Planetary Camera 2 imaging data provide the highest spatial resolution of individual Shoemaker-Levy 9 impact sites. Analysis of images obtained with the F410M filter yielded horizontal translation rates of tropospheric cloud structures and the east-west components have been interpreted as zonal winds which vary with latitude. When the tropospheric zonal winds between —60° and —30°, which were derived from the SL9 images, are compared with Voyager data there are no discernible changes in the magnitude or latitudinal positions of wind minima and maxima. This result provides additional evidence of the long-term stability of the zonal winds. Changes in individual sites during a two week period in July 1994 have been mapped. Their evolution is consistent with zonal winds decreasing with height and it provides evidence that local circulation associated with isolated weather systems perturbs the lower stratosphere.
Waves from the Shoemaker-Levy 9 impacts
Authors: Ingersoll Andrew P. , Kanamori Hiroo
Published: June 2019

Images of Jupiter taken by the Hubble Space Telescope (HST) reveal two concentric circular rings surrounding five of the impact sites from comet Shoemaker-Levy 9 (SL9). The rings are visible 1.0 to 2.5 hours after the impacts. The outer ring expands at a constant rate of 450 ms-1. The inner ring expands at about half that speed. The rings appear to be waves. Other features (diffuse rings and crescent) further out appear to be debris thrown out by the impact. Sound waves (p-modes), internal gravity waves (g-modes), surface gravity waves (f-modes), and rotational waves (r-modes) all are excited by the impacts. Most of these waves do not match the slow speed, relatively large amplitude, and narrow width of the observed rings. Ingersoll and Kanamori have argued that internal gravity waves trapped in a stable layer within the putative water cloud are the only waves that can match the observations. If they are correct, and if moist convection in the water cloud is producing the stable layer, then the O/H ratio on Jupiter is roughly ten times that on the Sun.
First Measurements of γ Cassiopeae's Hydrogen Envelope
Authors: Granes P. , Thom C. , Vakili F.
Published: June 2019

In the framework of an interferometric program on Be stars, first announced during the IAU general assemblies at Patras, 1982, recently at New Delhi, 1985 and reported in the “Be Star Newsletter” n°6 and l3, we try to measure the angular diameter of the central star, hydrogen envelope and, if possible, its movement, of the brightest Be stars in the context of pulsating atmosphere or binary star hypothesis.
Rapid Variation of Shell Line Parameters in ζ Tau
Authors: Bossi M. , Guerrero G. , Scardia M.
Published: June 2019

ζTau is a Be star which probably showed already in 1973 rapid variations in Hα emission strength with time scales of a few minutes (Bahng, 1976). It represents, moreover, the primary of a well-known binary system with a period of 132.91 days (e.g., Hynek and Struve, 1942), and its shell displays long term instabilities with time scales of some years (Delplace and Chambon, 1976). The basis of the present work is a compact set of 82 grating photographic spectrograms obtained at Merate by means of the 137 cm reflector with an inverse dispersion of about 35 Å/mm between Jan 17 and Jan 24, 1983. Forty four of these spectra cover the range between ˜ 4000 and ˜ 5000 Å, the other ones being centered on Hα.