bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of water maser sources at Arcetri
Authors: Comoretto Giovanni , Valdettaro Riccardo , Palla Francesco , Brand Jan , Cesaroni Riccardo , Felli Marcello , Natale Enzo , Palagi Francesco , Panella Dario , Tofani Gianni
Published: June 2019

We present the current activity of the Arcetri group in the field of water masers. This is mainly represented by observations with the Medicina radiotelescope, whose main outcome has been the compilation of the Arcetri Catalog and the study of time variability of selected sources. The Arcetri Catalog update reports the results of the observations carried out from January 1993 to April 2000 on a sample of 300 sources. The global properties of the complete Arcetri Catalog (including Comoretto et al. 1990, and Brand et al. 1994) are discussed. Of the 1013 sources, 937 have an IRAS counterpart within 1 arcmin from the nominal position of the maser. We establish a classification scheme based on the IRAS flux densities which allows to distinguish between water masers associated with star forming regions and late-type stars. The time variability study shows a large variety of behaviors. Generally more luminous sources present less variable emission and spectral components over a wider velocity range.
CO J=2-1 observations toward the OH 1720 MHz maser in Kes 69
Authors: Reynoso Estela M. , Mangum Jeffrey G.
Published: June 2019

We present CO J=2-1 observations made with the 12 Meter Telescope of NRAO using the On-The-Fly technique, towards the OH 1720 MHz maser detected in direction to the supernova remnant (SNR) Kes 69. OH 1720 MHz masers associated to SNRs are strong evidence of shocked molecular gas, and are proposed to be tracers of SNRs kinematical distances. In our images, the most conspicuous feature positionally coincident with the maser is a cloud at ∼ +41 km s−1. The difference between the velocity of the OH 1720 MHz maser and this cloud is ∼ 30 km s−1. At the systemic velocity of the OH 1720 MHz maser, we detected a weak, small clump with the maser lying at its edge, in agreement with previous findings in other SNRs. We suggest that this small clump has been shocked by the expanding SNR, and the ∼ +41 km s−1 component probably corresponds to gas accelerated by the shock front. We do not discard, however, that the ∼ +41 km s−1 component be just a quiescent, foreground cloud unrelated to Kes 69.
Oxygen Abundances in Bulge-like Dwarf Stars
Authors: Pompéia Luciana , Barbuy Beatriz , Grenon Michel
Published: June 2019

High resolution échelle spectra were obtained with the FEROS spectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars. From Hipparcos data it appears that the turn-off of this population indicates an age of 10–11 Gyr (Grenon 2000).

Oxygen abundances are calculated using the [O I] line at 6300.3 Å. The derived results show an oxygen overabundance for most of our sample stars when compared to their disk counterparts.
NGC 3603 — a Local Template for Massive Young Clusters
Authors: R. Brandl Bernhard , Brandner Wolfgang , Eisenhauer Frank , F. J. Moffat Anthony , Palla Francesco , Zinnecker Hans
Published: June 2019

We present a study of the star cluster associated with the massive Galactic HII region NGC 3603 based on near-IR broad- and narrowband observations taken with ISAAC/VLT under excellent seeing conditions (≤ 0.4″). We discuss color-color diagrams and address the impact of the high UV flux on the disk evolution of the low-mass stars.
The NICMOS View of M31's Metal Rich Globular Clusters
Authors: W. Stephens Andrew , A. Frogel Jay , Freedman Wendy , Gallart Carme , Jablonka Pascale , Ortolani Sergio , Renzini Alvio , Rich R. Michael
Published: June 2019

We have obtained HST-NICMOS observations of five of M31's most metal-rich globular clusters: G1, G170, G174, G177 & G280. For the two clusters farthest from the nucleus, G1 and G280, we statistically subtract the field population and estimate metallicities using K-(J - K) color-magnitude diagrams (CMDs). Based on the slopes of their infrared giant branches we estimate [Fe/H] = −1.22 ± 0.43 dex for G1 and −0.15 ± 0.37 dex for G280. We combine our infrared observations of G1 with two epochs of optical HST-WFPC2 F-band data and identify at least one LPV based on color and variability. The location of G1's giant branch in the K, (V - K) CMD is very similar to that of M107, indicating a somewhat higher metallicity than our purely infrared CMD; [Fe/H]= −0.9 ± 0.2 dex.
Elemental Abundances of Three Giants in Terzan 7
Authors: Wallerstein George , Gonzalez Guillermo , Geisler Doug
Published: June 2019

Using VLT UVES spectra of resolving power near 23,000 we have analyzed three stars in Terzan 7, a globular cluster associated with the Sagittarius Galaxy. We find [Fe/H] = −0.61±0.1, [O/Fe] = +0.25, [α/Fe] = +0.23 dex, and an enhancement of r/s elements as compared with the Sun and Arcturus.
Clusters in Extragalactic HII Regions and their Modelling
Authors: González Delgado Rosa María
Published: June 2019

This review deals with properties of very young (≤ 10–20 Myr) stellar clusters which are in the nebular phase and are embedded in photoionized regions (classical extragalactic HII regions (RHIIs) or starburst galaxies). Based on the analysis of the integrated light of these clusters at the UV and optical wavelengths, different techniques are discussed that allow to estimate in consistent the stellar content and the evolutionary state of the ionizing clusters. Figures illustrating this contribution can be found in: http://www.iaa.csic.es/∼rosa/
Star Clusters in Galactic Resonance Rings
Authors: Buta R.
Published: June 2019

Resonance rings are intriguing sites of organized star formation in some galaxies. The Hubble Space Telescope Wide Field and Planetary Camera 2 has been used to image several resonance rings at high resolution in order to study the star clusters in the rings. Here I summarize results on inner Lindblad resonance rings in ESO 565–11 and NGC 1326, and on an inner 4:1 resonance ring in the Seyfert 2 galaxy NGC 3081. The latter ring provides one of the strongest cases illustrating the connection between star formation and dynamics in disk galaxies.
Super Star Clusters in NGC 7673 and Mrk 8
Authors: Homeier N. , Gallagher J.S.
Published: June 2019

We present an analysis of super star cluster populations using WFPC 2 on theHubble Space Telescopefor two starburst galaxies: NGC 7673 and Markarian 8. Both galaxies are luminious and have signatures of massive star formation, such as emission-line dominated optical spectra. Their optical appearances are highly disturbed, featuring prominent knots of intense star formation. Using HST F255W, F555W, and F814W images, we perform aperture photometry for a select sample of star clusters in different regions of each galaxy, and compare the results with evolutionary population synthesis models.
Broad-band Photometric Evolution of Star Clusters
Authors: Girardi Léo
Published: June 2019

I briefly introduce a database of models that describe the evolution of star clusters in several broad-band photometric systems. Models are based on the latest Padova stellar evolutionary tracks - now including the α-enhanced case and improved AGB models - and a revised library of synthetic spectra from model atmospheres. As of today, we have revised isochrones in Johnson-Cousins-Glass, HST/WFPC2, HST/NICMOS, Thuan-Gunn, and Washington systems. Several other filter sets are included in a preliminary way, like those used by the EIS and SDSS projects. The database contains also integrated magnitudes of single-burst stellar populations and Monte-Carlo simulations that show the stochastic dispersion of the colours as a function of cluster mass, age, and metallicity. The models are useful for several kinds of studies, including estimates of masses and ages of extragalactic star clusters observed by means of broad-band photometry.
Large Fundamental and Global Transit Circle Catalogs
Authors: Corbin T. E.
Published: June 2019

The fundamental system is currently based on the Dynamical Reference Frame as defined by the motions of the Earth and other Solar System objects. The link to this frame has traditionally been made by the observation of these objects and of stars in absolute transit circle programs. The zero points of the link are applied to quasi-absolute catalogs, and these are combined with the absolute catalogs to define the fundamental system. The individual positions and motions of the fundamental stars are then strengthened by incorporating differential catalogs reduced to the fundamental system. The system can be extended to higher densities and fainter magnitudes by further systematic reduction and combination of differential catalogs. The fundamental system itself, however, can only be extended through a planned series of observations resulting in absolute stellar positions over a range of epochs. A new fundamental catalog being compiled at the U.S. Naval Observatory is discussed and compared with the existing standard, the FK5.
Improvement and Maintenance of the Extragalactic Reference Frame
Authors: Arias E.F. , Gontier A.M.
Published: June 2019

Very Long Baseline Interferometry (VLBI) is at present the most powerful technique to construct the best approximation to an inertial reference frame. After more than a decade of VLBI observations several hundreds of extragalactic objects have positions known within ±0.0003″. Since 1988 the International Earth Rotation Service (IERS) elaborates a global extragalactic celestial reference frame (IERS Celestial Reference Frame, ICRF) that is tied to the international terrestrial reference frame through the high precision monitoring of the Earth's rotation. The direction of the ICRF axes relative to the IAU definitions are known within better than ±0.001″ for the polar axis and ±0.003″ for the origin of right ascensions. The FK5 axes are consistent with the ICRF ones within their uncertainties (0.050″-0.100″). The maintenance of this high accuracy extragalactic frame will be necessary for the long term programs, such as the future monitoring of the tie of the Hipparcos galactic frame as well as of the dynamical planetary frame (millisecond pulsars, lunar laser ranging).
European Space Interferometry
Authors: Noordam J.E.
Published: June 2019

Optical interferometry is ensconced as an ‘area of future interest’ (a socalled Green Dream) in Horizon 2000, the long-term scientific plan of ESA. Over the years, there have been three large ESA workshops on Space interferometry, where many different concepts and designs were proposed, and several ESA committees have studied the possibilities. These committees were also involved, in an advisory role, in a modest technological research program (TRP) by ESTEC. In 1990, the Space Interferometry Study Team (SIST) recommended building an optical interferometer, consisting of 10-15 small telescopes attached to an 100m inflatable structure, as a scientifically interesting first step. The SIST even produced a workable design. It quickly became clear, however, that such an undertaking would cost much more than an ESA cornerstone mission, and was thus far too ambitious. Simultaneously, another ESA study team (LIST) came to the conclusion that the Moon, contrary to earlier beliefs, does not offer a particularly suitable environment for interferometry. At the Beaulieu workshop in 1992, it was decided to try to achieve cornerstone status for one or two smaller interferometry missions in Space: a 10m UV imaging interferometer, or an interferometric successor to the astrometry satellite Hipparchos. The latter seems to have a good chance at the moment, in the form of the GAIA proposal which has been selected for further study for the new ‘post-Horizon 2000’ program. GAIA may have some limited imaging capability, but a true imaging interferometer in Space will have to wait for a few decades yet.
A Program of Infrared Astrometry
Authors: Kharin A.S.
Published: June 2019

There exist no special astrometric telescopes or devices suited to determine precise positions, proper motions and parallaxes in the infrared. Only astrophysical IR observations are carried out now in the range of 1-350 μm. But many astronomical problems concerning galactic structure and kinematics and others may be solved if astrometric instruments and methods are developed and implemented for IR observations. Development of new technology and infrared array receivers gives the hope that many astrometric problems in the infrared would be solved successfully.
Joint Program for Automatic Analysis of Astrographic Plates
Authors: Garcia A. Lopez , Valdes Navarro J.L. , Gil A. Ortiz , Gonzalez J.M. Martinez , Yershov V.N. , Poliakov E.V. , Potter H.I. , Yagudin L.
Published: June 2019

Pulkovo and Valencia observatories are developing measuring machines based on the “Ascorecord” microscope that allow to undertake automatic measuring programs of different kind of plates (Ortiz et al., 1993). All aspects of astrometry work are covered now by our software: field maps and plate files creation from the PPM and the GSC; precise ephemeris calculation of minor planets and comets, including planetary perturbations; image identification and automatic plate measurement and reduction (Lopez et al., 1994a). For these tasks, correction tables for GSC catalogue vs. PPM, systematic errors (Lopez et al., 1994b) have been obtained. Observing programs using plates and CCD devices at telescope focus are planned (the search of new asteroids and comets, big planets satellites observation, new high density photographic catalogues and some other projects).
First Results of the Bordeaux Meridian Circle Equipped with a CCD Detector
Authors: Réquième Y. , Montignac G. , Le Campion J.F. , Bosq F. , Chauvet F. , Benevides-Soares P. , Teixeira R.
Published: June 2019

The Bordeaux automatic meridian circle has been working for 10 years with a tracking photoelectric micrometer. This micrometer was recently replaced by a focal CCD camera in order to extend the differential position measurements to much fainter stars with improved accuracy.
Dynamic Events in the X-Ray Corona (A Progress Report from the AS&E X-ray Telescope on Skylab)
Authors: Vaiana G. S. , Krieger A. S. , Silk J. K. , Timothy A. F. , Chase R. C. , Davis J. , Gerassimenko M. , Golub L. , Kahler S. , Petrasso R.
Published: June 2019

Data obtained by the AS&E X-ray Telescope Experiment during the first Skylab mission have revealed a variety of temporal changes in both the form and brightness of coronal structures. Dynamical changes have been noted in active regions, in large scale coronal structures, and in coronal bright points. The coronal activity accompanying a series of Hα flares and prominence activity between 0800 and 1600 UT on 10 June 1973 in active region 137 (NOAA) at the east limb is shown in Figure 1. It is characterized by increases in the brightness and temperature of active region loops and a dramatic change in the shape and brightness of a loop structure. Figure 2 shows the reconfiguration of an apparent polar crown filament cavity between 1923 UT on 12 June 1973 and 1537 UT on 13 June 1973. A ridge of emitting material which attains a peak brightness at least four times that of the surrounding coronal structures appears within the cavity during the course of the event. Typical X-ray photographs with filters passing relatively soft X-ray wavelengths (3–32, 44–54 Å) show 90 to 100 X-ray bright points (Vaiana et al., 1973). On twelve occasions in the data from the first mission, such bright points were seen to increase in intensity by two orders of magnitude in less than 4 min. Such an event is shown in Figure 3.
The Formation of Galaxies in Friedmannian Universes
Authors: Doroshkevich A. G. , Sunyaev R. A. , Zel'Dovich Ya. B.
Published: June 2019

A short review of the theory of the formation of galaxies and clusters of galaxies is given within the framework of the non-linear theory of gravitational instability. Probable initial conditions are discussed as well as processes which bring about the origin of galaxies and clusters of galaxies. Possible observational tests are discussed.
The Low Density Symmetric Cosmology
Authors: Elvius Aina , Karlson Erik T. , Laurent Bertel E.
Published: June 2019

Most cosmological models are based on the ‘cosmological principle’ according to which the Universe is homogeneous and isotropic on a certain level, chosen such that the present mean density is of the order of 10-30±1 g cm-3.
Optimization of Gravitational Burst Detectors Using Piezoelectric Transducers
Authors: Maeder D.
Published: June 2019

A general approach to overall system optimization is developed using the concepts of mechanical and electrical signal-to-noise ratios (MSNR and ESNR). These are proportional to and to respectively, where Qsys=mechanical Q of the complete detector, μ = (transducer mass/metal mass), and n = resolving time in units of one-half of the detector fundamental period. The overall SNR becomes a maximum for n = n∗ = optimum resolving time; this procedure yields whereas

Application to ‘strong-coupling’ type antennae (such as divided-cylinder systems) gives a high SNR∗ which depends very little on μ if μ > 0.01. Q-factor and coupling efficiency relations were checked for 22 kg-prototypes using μ = 0.26%, 0.9%, and 1.8%. Two new detector configurations are suggested: the ‘bridged-tube’ allows strong-coupling for very long detectors; the ‘folded-tube’ operates at lower frequencies for a given length.
Amplification of Waves Reflected from Kerr Black Holes
Authors: Starobinsky A. A.
Published: June 2019

The effect of amplification of electromagnetic and gravitational waves reflected from a rotating black hole (‘superradiance scattering’) is investigated. This effect was proposed by Zel'dovich (1971). It leads, as well as the Penrose process, to the energy extraction from a Kerr black hole at the expense of its rotational energy and momentum decrease. The coefficient of wave reflection R>1 if ω<nω, where ω is the wave frequency, n - its angular momentum and ω is the black hole angular velocity. The value of this effect is not small in the case of gravitational waves, for example, if l=n = 2, ω →nω and a = M, then R≈2.38.

There also exists a quantum version of the effect, namely, the one of spontaneous pair creation in the Kerr metric, but this quantum effect is exceedingly small in real astrophysical conditions, because its characteristic time is of the order G2M3/hc4, where M is the black hole mass.
On the Description of High-Frequency Gravitational Waves
Authors: MacCALLUM M. A. H.
Published: June 2019

Taub and I have used the ‘Average Lagrangian’ method (Whitham, 1971; Dougherty, 1970) for the case of gravitational waves (MacCallum and Taub, 1973; Taub, 1973). A difficulty arises in going beyond first-order effects as gauge waves and physical waves appear to interact (MacCallum, 1973). The source of this difficulty is not yet known, but doubt is cast on the usual conceptual framework.
Tidal Tensor and the Emission and Absorption of Gravitational Radiation
Authors: Sejnowski Terrence J.
Published: June 2019

The absorption and emission of gravitational radiation can be calculated in the long wavelength limit by use of the tidal tensor, defined as the gradient of the gravitational pseudoforce,
thus
where ηb is orthogonal to the 4-velocity ua, and normal coordinates are understood.

The exchange of energy and momentum between an extended body and the gravitational field is governed by appropriate integrals of the tidal tensor over space and time.

The tidal tensor is the trace Tabdb of the Bel-Robinson tensor Tabcd. In emty space this trace is zero and the tidal tensor vanishes; there is no local exchange of energy.
Optical Observations of Galactic and Extragalactic Light: Implications for Galactic Structure
Authors: Toller Gary N.
Published: June 2019

A historical review of integrated starlight, diffuse galactic light, and extragalactic light studies is presented. Together, these components compose the “background light.” Methods ranging from star counts to space-based photometric surveys have succeeded in quantifying the contribution of each component of the background. Integrated starlight is the dominant component. The contribution of diffuse galactic light in the general interstellar medium peaks slightly off the galactic plane and declines toward higher latitudes. The extragalactic light has been determined from both galaxy counts and photometric methods. The blue and red intensity and B–R color distribution of background light have been mapped. The relation between galactic structure and background light measurements is established. The distribution of interstellar extinction is the primary regulator of the brightness. However, spiral arm and stellar distribution effects are discerned in Carina and Sagittarius. The sun lies 13 pc north of the galactic plane as defined by brightness and dust distributions.
Continuum Wavelength Emission from Embedded, Young, and Massive Stellar Objects Beyond 1 μm
Authors: Henning Thomas , Pfau Werner
Published: June 2019

One of the components of the galactic infrared background (GIRB) radiation is emission by warm dust grains heated by OB stars embedded in molecular clouds. The main contributors are compact HII regions and comparatively radioquiet infrared (IR) point sources such as the Becklin-Neugebauer object. We present the average energy distribution between 1 and 1300 μm for a sample of BN-type objects. The average color temperature between 60 and 100 μm is ~40 K, which is very similar to the color temperature of the observed warm galactic dust emission (WGDE).
Detection of Hα Emission on High Velocity 21 cm Clouds
Authors: Münch Guido , Pitz Eckhart
Published: June 2019

The measurement of Hα emission on two high galactic latitude clouds known to emit 21 cm lines with local standard of rest (LSR) velocities of −50 and −85 km s−1 is reported. The Hα lines have been found nearly at the velocities of the 21 CM features and have emission rates of 0.2 Rayleigh. The diffuse Lyman continuum intensity required to produce HI ionization at the measured rate is in agreement with the direct measurements made with the ultraviolet (UV) spectrometer of the Voyager 2 spacecraft.
Multispectral Analysis of IRAS Sky Flux Maps
Authors: Balázs L. G. , Kun M. , Tóth V.
Published: June 2019

We have tested the performance of principal components analysis and a single-pass clustering algorithm to identify different components of the cosmic dust. Applying these techniques on a training set of 2500 points extracted from the PL51 IRAS maps we recognized two main components with temperatures of 180 K and 28 K.
Measurements of the Diffuse Ultraviolet Radiation
Authors: Fix John D. , Craven John D. , Frank Louis A.
Published: June 2019

We have used the imaging instrumentation on the Dynamics Explorer 1 (DE) satellite to measure the intensity of the diffuse ultraviolet (UV) radiation on two great circles about the sky. We find that the isotropic component of the diffuse UV radiation (possibly of extragalactic origin) has an intensity of 530 ±80 units (a unit is one photon cm−2 s−1 sr−1 A−1) at a wavelength of 150 nm. The galactic component of the diffuse UV radiation has a dependence on galactic latitude, which requires strongly forward-scattering particles if it is produced by dust above the galactic plane.
Infrared Extragalactic Background Light
Authors: Matsumoto Toshio
Published: June 2019

Infrared extragalactic background light plays an important role in the study of the early history of the universe, especially as a probe to search for the primeval galaxies. In the near-infrared region, UV and visible light emitted from high redshift galaxies could be observable. Measurement of the sky fluctuation at 2.2 μm gives a very low upper limit. The rocket observation of the near-infrared diffuse emission reveals isotropic emission which is possibly ascribed to an extragalactic origin. The observed brightness and fluctuation are not consistent with the standard scenario of the primeval galaxies. In the far-infrared region, integrated light of dust emission of the distant galaxies forms another cosmic background radiation. IRAS and the Nagoya-Berkeley rocket experiment found a clear correlation between HI column density and far-infrared sky brightness; however, there remains an uncorrelated isotropic emission component. If we ascribe this emission to extragalactic origin, a fairly big evolution effect is required. In the submillimeter region, excess emission over the 2.74K blackbody spectrum was found, which requires the vast energy generation in the early universe.
Innate Ideas
Authors: Edgley R.
Published: June 2019

Empiricism, the philosophical theory that all our ideas and knowledge are derived from experience, has in recent years been the target of radical and persuasive objections. In the seventeenth century, and for long after, rationalism seemed the only alternative to empiricism, but, like Kant, many contemporary philosophers have been convinced that empiricism and rationalism are equally unacceptable, and that both positions, and the conflict between them, are the result of trying to answer confused, misleading, and perhaps senseless questions. Of all the traditional theories in particular, none, I suppose, has looked to modern philosophers less capable of being revived than the rationalist doctrine of innate ideas: the doctrine that some at least of our ideas and knowledge of things are not derived from outside the mind, through experience, but are present from birth in the mind itself and thus represent the mind's own contribution to our understanding of reality. What Strawson has called ‘those old and picturesque debates regarding the origin of our ideas’ seemed to have become museum pieces, charming, as antiques can be, but with little relevance to current issues. These complacent attitudes, if that is what they are, have been rudely disturbed by Chomsky and his colleagues. Chomsky has suggested ‘that contemporary research supports a theory of psychological a priori principles that bears a striking resemblance to the classical doctrine of innate ideas’. In the prevailing situation, the novelty of this suggestion is twofold. It is not only that the theory of innate ideas may be true after all, but also that the support alleged for the ancient doctrine has a distinctively modern look. The research that Chomsky claims supports the doctrine is research in the empirical science of linguistics. The implication is that empiricism is refutable empirically, and more generally that a philosophical dispute such as the dispute between empiricism and rationalism, once it is made clear, can be settled by science.
Is a Religious Epistemology Possible?
Authors: Penelhum Terence
Published: June 2019

Those who despair of the possibility of proving the existence of God tend, naturally, to hold that knowledge of God's existence and of those religious claims that depend upon it can only be had, if it can be had at all, through some direct religious awareness or insight. On this view appeals to authority or to revelation rest on appeals to such insight, if it is agreed that the credentials of the revealing authority cannot be established by the methods of natural theology. It is common for debate between believers and sceptics who share this despair about the possibility of proof to take on an air of hopelessness and unreality because of a fundamental epistemological cleavage: on the one hand the believer has an allegedly cognitive experience and on the other the sceptic lacks and suspects it. I want in this paper to scrutinise some aspects of this division. I shall not do much to mitigate the pessimism of my earlier statements, since I think the division really is, in certain critical ways, an unbridgeable one. But it is worth while to come to a clearer understanding of its nature than I think some philosophers have. What follows has been influenced by reflection on recent controversies about the meaningfulness of religious discourse, but is not intended to be a contribution to them. Some of the best-known contributions, however, seem to me to have made the epistemological cleavage I have referred to seem even worse than it is.
On the SN 1993J Radio Shell Structure
Authors: Marcaide J.M. , Martí-Vidal I. , Ros E. , Alberdi A. , Guirado J.C. , Lara L. , Pérez-Torres M.A. , Weiler K.W.
Published: June 2019

An accurate measurement of the expansion deceleration of SN 1993J depends on how well the shell size and its emission structure are known. With the goal of determining the emission structure of the shell, we have developed a new approach, which we call “Green Function Deconvolution” (GFD), based on iterative use of Green functions on the sky plane to reconstruct the radial emission profiles of spherically symmetric sources. This approach works reasonably well in the case of optically thin emitting sources, which is not the case for SN 1993J since, as we find, the emission from the central part of SN 1993J further away from us is strongly or totally absorbed. We describe the GFD method and present our findings about the emission structure of the shell. We also present the expansion of SN 1993J based on a method complementary to GFD, which will be described elsewhere.
SN 1994W: Evidence of Explosive Mass Ejection a Few Years Before Explosion
Authors: Chugai Nikolai N. , Cumming Robert J. , Blinnikov Sergei I. , Lundqvist Peter , Filippenko Alexei V. , Barth Aaron J. , Bragaglia Angela , Leonard Douglas C. , Matheson Thomas , Sollerman Jesper
Published: June 2019

We present and analyze spectra of the Type IIn supernova 1994W obtained between 18 and 202 days after explosion. During the first 100 days the line profiles are composed of three major components: (i) narrow P Cygni lines with absorption minima at −700 km s−1; (ii) broad emission lines with blue velocity at zero intensity ~ 4000 km s−1; (iii) broad, smooth, extended wings most apparent in Hα. These components are identified with the expanding circumstellar (CS) envelope [5], shocked cool gas in the forward postshock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P Cygni lines from the supernova (SN) is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the Thomson optical depth of the CS envelope, τT ≥ 2.5 during first month, its density (n ~ 109 cm-3) and radial extent, ~ (4 — 5) × 1015 cm. The plateau-like SN light curve, which we reproduce by a hydrodynamical model, is powered by a combination of internal energy leakage after the explosion of an extended presupernova (~ 1015 cm) and subsequent luminosity from circumstellar interaction. We recover the pre-explosion kinematics of the CS envelope and find it to be close to homologous expansion with outmost velocity ≈ 1100 km s-1 and a kinematic age of ~ 1.5 yr. The high mass (≈ 0.4 M⊙) and kinetic energy (≈ 2 × 1048 erg) of the CS envelope combined with small age strongly suggest that the CS envelope was explosively ejected only a few years before the SN explosion.
Radio Monitoring of Supernova 2001ig: The First Year
Authors: Ryder Stuart D. , Sadler Elaine , Subrahmanyan Ravi , Weiler Kurt W. , Panagia Nino , Stockdale Christopher
Published: June 2019

Supernova 2001ig in NGC 7424 has been observed with the Australia Telescope Compact Array at ~2 week intervals since its discovery, making this the best-studied Type IIb radio supernova since SN 1993J. We present radio light curves for frequencies from 1.4 to 20 GHz, and preliminary attempts to model the observed behavior. Since peaking in radio luminosity at 8.6 and 4.8 GHz some 1-2 months after the explosion, SN 2001ig has on at least two occasions deviated significantly from a smooth decline, indicative of interaction with a dense circumstellar medium and possibly of periodic progenitor mass-loss.
Models of Supernova Explosions: Where Do We Stand?
Authors: Hillebrandt Wolfgang
Published: June 2019

The present status of our understanding of core-collapse and of thermonuclear supernovae is reviewed. It will be argued that the failure of numerical simulations of the collapse of massive stars to produce explosions is probably caused by our incomplete knowledge of the (micro-) physics involved. In contrast, for thermonuclear (type Ia) supernovae the basic physics seems to be well under control and, therefore, it is not surprising that model predictions and observations are in good agreement.
Neutrino Gas in Equilibrium with Self-Interaction
Authors: Sirera M. , Perez A.
Published: June 2019

We study a neutrino gas in equilibrium both at T = 0 and at finite temperature. The neutrinos are assumed to be massive Dirac particles with two generations interacting with each other via neutral currents and with a background of matter. We analyze the main properties of the neutrino eigenmodes in the medium, such as effective masses and mixing angle.
The MicroObservatory Net
Authors: Brecher Kenneth , Philip Sadler
Published: June 2019

Beginning in 1990, a group of scientists, engineers and educators based at the Harvard-Smithsonian Center for Astrophysics (CfA) developed a prototype of a small, inexpensive and fully integrated automated astronomical telescope and image processing system. The MicroObservatory combines the imaging power of a cooled CCD, with a self contained and weatherized reflecting optical telescope and mount. A microcomputer points the telescope and processes the captured images. Software for computer control, pointing, focusing, filter selection as well as pattern recognition have also been developed. The telescope was designed to be used by teachers for classroom instruction, as well as by students for original scientific research projects. Probably in no other area of frontier science is it possible for a broad spectrum of students (not just the gifted) to have access to state-of-the-art technologies that allow for original research projects. The MicroObservatory has also been designed to be used as a valuable new capture and display device for real-time astronomical imaging in planetariums and science museums.
Computer as a tool in astronomy teaching
Authors: Berthomieu Francis
Published: June 2019

As yet, astronomy, the most ancient of all sciences, surprisingly is not included in French secondary science classes. Recent trends in favour of a more attractive and motivating scientific education have taken it up.

Astronomy has, at all times, been arising curiosity, and now provides a privileged field to scientific approach :

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Observation of the vault of heaven and its peculiarities

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Description of its general appearance and of the specific movement of stars and planets

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Measurement of distances, coordinates and angles.

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This will make it possible to define successive models, which will be ever closer to the observed reality.
The presence of multimedia in astronomy teaching
Authors: Fogh Olsen H. J.
Published: June 2019

Sometimes I find my self in a society in the middle of The Global Village and sometimes in a society in a little state with a large number of computers not speaking the language I usually talk. When a prevailing part of the population are working in one area the society is named after that area, allthough a lot of other things can characterize the society. The latest societies are:

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Agricultural society

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Industrial society

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Information society

The agricultural and industrial societies have come to an end. When a society comes to an end, it is usually because the efficiency of production reaches a level higher than necessary, to keep all the workers busy. Many of the workers are attracted to other kinds of work, which gives rise to the next culture.
The Current Role of Planetariums in Astronomy Education
Authors: Gutsch William A. , Manning James. G.
Published: June 2019

For decades, planetariums have been created to serve the cause of astronomical enlightenment - to offer people knowledge and understanding and a sense of place in a universe far bigger than themselves. It is an important role and one that we in planetariums continue to play - changing, we hope, as times, technology, educational philosophies, and our view of the universe change.

The first projection planetarium was demonstrated by the Zeiss Optical Company at the Deutsches Museum in Munich, Germany in 1923. By 1970, the height of the Apollo moon program, there were an estimated 700 to 800 planetariums in the world, half of them less than six years old. Today, 26 years later, that number has more than doubled to a little over 2,000.
Teaching Astronomy at Secondary School Level in Europe
Authors: Ros R. M.
Published: June 2019

The status of teaching Astronomy in European countries is variable. Sometimes Astronomy appears as a compulsory subject or as an optional subject, but on many occasions Astronomy appears within another subject, depending on the country. It is even possible for Astronomy not to appear anywhere in the curriculum. But of course the position here is better than in other less developed places. In Europe there are various topics which can be organized into two main groups: aspects related to relative motions and aspects related to properties of light. Some examples of teaching activities and materials in various countries will be described.

It is also necessary to emphasize several initiatives such as the review of Astronomy curricula, the publication of general books on Astronomy for secondary schools and the organisation of new journals to promote Astronomy in schools.
The Role of Astronomy in Education and ‘Public Understanding'
Authors: Rees Martin J
Published: June 2019

A few comments first on education in schools - this is a special worry here in the UK, where our international rankings are disappointing. An appreciation of science is vital not just for tomorrow's scientist and engineers, but for everyone who will live and work in a world even more underpinned by technology - and even more vulnerable to its failures and misapplications - than the present one. Even more important, the option of higher education in science and technology should not be foreclosed to them. There is widespread concern particularly about the 16-18 age group. Many of us put strong emphasis on broadening the curriculum for this group, which currently enforces unduly early specialisation here in England. Young people opting for humanities should not drop all science when they are 16.
Observations of Rapid Variability in Be Stars (Review Paper)
Authors: Percy John R.
Published: June 2019

Photometric and/or spectroscopic variability on time scales of approximately 0.2 to 2 days has been observed in over 40 Be stars, and is suspected in many more. This paper reviews the observational aspects of this phenomenon: both surveys and studies of individual objects. This phenomenon is not easy to study and interpret: (i) the time scale is inconvenient (ii) there have been very few simultaneous photometric and spectroscopic studies of individual objects (iii) the photometric variability is small, often irregular and superimposed on longer-term variability and (iv) the spectroscopic variability is usually observed as absorption line profile variability, which requires special instrumentation. For these and other reasons, there is not yet a universal agreement about the nature of this phenomenon. Nevertheless, it deserves further intensive study, not only because it is common, but also because in one or two stars, there is evidence that the rapid variability may be related (causally perhaps?) to the longer-term variability in these stars - variability whose ultimate cause is still not known.
The Magnetic Be Star Sigma Orionis E
Authors: Bolton C. T. , Fullerton A. W. , Bohlender D. , Landstreet J. D. , Gies D. R.
Published: June 2019

Over the past two years, we have obtained high resolution high signal/noise (S/N) spectra of the magnetic Be star σ Ori E at the Canada-France-Hawaii Telescope and McDonald Observatory. These spectra, which cover the spectral regions 399-417.5 and 440-458.5 nm and the Hα line and have typical S/N>200 and spectral resolution ≃0.02 nm, were obtained at a variety of rotational phases in order to study the magnetic field structure, the distribution of elements in the photosphere, and the effects of the magnetic field on the emission envelope. Our analysis of these spectra confirms, refines and extends the results obtained by Landstreet & Borra (1978), Groote & Hunger (1982 and references therein), and Nakajima (1985).

The Hα emission is usually double-peaked, but it undergoes remarkable variations with the 1.19081 d rotational period of the star, which show that the emitting gas is localized into two regions which co-rotate with the star.
Short-Term Spectroscopic Variations of the Be Star 11 Cam
Authors: Chauville J. , Alvarez M. , Sareyan J.P. , Ballereau L. , Michel R.
Published: June 2019

11 Cam (HD 32343 = HR 1622) is a so-called “pole-on” Be star known for its long term variations, already noted by Merrill and Burwell (1943). Recent determinations of visual magnitude and spectral type are V = 5.222 and B2.5Ve (Rufener, 1981). The Balmer line profiles, especially Hα, have been frequently studied; Briot (1971), for instance, measured 40 and 4.9 Å equivalent widths for Hα and Hβ respectively; the Hα/Hβ peak to continuum ratio is 6.43/2.02 according to Gray and Marlborough (1974) who give v sin i = 131 km s-1, close to the value of 140 km s-1 adopted by Kogure (1968).
IUE Spectra of the Be Star HD 174237
Authors: Tarafdar S. P.
Published: June 2019

High-resolution spectra of the Be star HD 174237 taken on September 9, 1980 will be presented. They show stellar absorption lines and superionized NV lines shifted redward equivalent to a velocity of 20 km s-1. This velocity when compared to the earlier measured velocity of - 20 km s-1 (cf. Hoffleit) suggests that the Be star HD 174237 is really a binary and the IUE and previous observations are in different phases of binary motion. The spectra also show strong A1III and SilV absorption lines together with strong NV lines but surprisingly the CIV lines are very weak. It appears that the A1III doublet is associated with a narrow blue-shifted component suggesting an outflow of cool gas from the star.
Be Stars as Nonradial Pulsators (Review Paper)
Authors: Baade Dietrich
Published: June 2019

The observational status of the ubiquitous rapid variability of Be stars is summarized. The most comprehensive interpretation is obtained with a traveling velocity field and associated temperature variations. But neither the available observations nor theoretical predictions presently allow an unambiguous mode determination of these nonradial pulsations. In addition to rapid rotation, an NRP mode of low azimuthal order, m ≈ 2, seems another prerequisite for a B star becoming a Be star. The amplitudes of these modes are variable and have been observed to decrease with some delay after an outburst. For low-order sectorial modes, NRP's therefore have the potential of explaining the three oldest unsolved problems of Be stars: the difference between Be and Bn stars (the latter do not usually have a low-order mode), the episodic component of the mass loss from Be stars, and the equatorial density maximum of their winds. Mechanisms for the transfer of energy to the atmosphere and its transformation into the kinetic energy of an outburst are discussed.
Ultraviolet Observations of CX Draconis
Authors: Koubský P. , Horn J. , Harmanec P. , Peters G. J. , Polidan R. S. , Barker P. K.
Published: June 2019

CX Draconis /HD 174237, B2.5Ve, v.sin i = 160 km.s-1/ is a typical Be star displaying most of the well known spectroscopic and photometric characteristics of these stars.

Koubský /1978/ disclosed that CX Dra is a SB1 /P=6.69603d, K = 35 km.s-1, e = 0/. Penrod /1985/ confirmed that the secondary is a F star. Peters and Polidan /1984/ reported strong, variable lines of NV, CIV and SilV from high-resolution spectra secured with IUE satellite. These features were interpreted to arise from gas stream and accretion close to the photosphere of the B-component of the system.
Observations and Evolutionary Scenario For Be/X-Ray Binaries
Authors: Habets G.M.H.J.
Published: June 2019

Rappaport & Van den Heuvel (1982) suggested the following formation scenario for B emission (Be)/X-ray binaries: the progenitor of the neutron star is the initial primary star with mass M1 = 10-20 M⊙, which during hydrogen-shell burning transfers mass to the companion (with M2 < M1). The secondary is spun up due to disk-accretion (e.g. Packet 1981) and has become a rapidly rotating Be star (M ≃ 10-20 M⊙).

With this scenario the observed orbital periods (Porb > 15 d) of the Be/X-ray binaries can be explained. This was shown by van den Heuvel (1983) by adopting an idealized period distribution for unevolved O- and B-type close binaries with Porb, < 30 d (see Fig. 1) and assuming conservative evolution, i.e. that mass and angular momentum are conserved during mass transfer.
Period-Luminosity-Metal Abundance Relations for Population II Variable Stars
Authors: Nemec James M. , Lutz Thomas E.
Published: June 2019

New period-luminosity-metallicity (P-L-[Fe/H]) relationships for Pop. II Cepheids, RR Lyrae stars, anomalous Cepheids and SX Phe (variable-blue straggler) stars are presented. These were computed by fitting regression lines to observed pulsation periods and mean B, V, K magnitudes for over 1200 stars in ∼40 stellar systems. The stars were assumed to be pulsating in either the fundamental (F) or first-overtone (H) modes (excluding double-mode and other multi-periodic variables). Eight P-L-[Fe/H] relationships (one for each of the two pulsation modes for the four kinds of stars) were simultaneously fitted for each filter. After accounting for the metal abundance differences, the slopes of the P-L relations were tested for departures from equality. The results are consistent with the assumption that, for each kind of star, the relations for the F and H stars are vertically offset, with a family of lines corresponding to the different metallicities. In the case of the globular cluster Cepheids, the available B, V data support Arp's 1955 contention that the Cepheids are oscillating in the F and H modes; moreover, the majority of the short-period Cepheids (BL Her stars) appear to be first-overtone pulsators, while most of the Cepheids with periods between 10 and 30 days (W Vir stars) appear to be fundamental-mode pulsators. For the RR Lyrae stars, the slopes of the P-L-[Fe/H] relations in B, V and K show a clear trend with filter type, namely, the absolute values of the slopes increase from B to K. Finally, for the SX Phe stars the differences between the P-L-[Fe/H] relations in B and V for the F and H stars are found to be consistent with the known period-ratio for the double-mode star SX Phe.
Calibration of the Cepheid Distance Scale
Authors: Gieren Wolfgang P. , Fouqué Pascal
Published: June 2019

The absolute calibration of the Cepheid period-luminosity (PL) relation with galactic Cepheids is discussed. Various methods, most importantly the cluster ZAMS-fitting scale and the Baade-Wesselink scale are found to yield PL zero points which agree within ∼ ± 0.1 mag. The present Cepheid calibration sets the Large Magellanic Cloud at μ0 (LMC) = 18.6 ± 0.1 mag, in good agreement with the distance derived from SN 1987A and other methods except RR Lyrae stars which seem to give a shorter distance scale.
Magnetic fields of rapidly oscillating Ap stars
Authors: Mathys G.
Published: June 2019

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.

Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.