bluuebunny/crossref_metadata_2025 huggingface dataset:
Cold Collapse as a Way of Making Elliptical Galaxies
Authors: Aguilar L.A. , Merritt D. , Duncan M.
Published: June 2019

We investigate whether dissipationless collapse starting from very cold, non-rotating initial conditions can produce objects resembling real elliptical galaxies. We also study the effect of various initial geometries on the shape of the final object. Collapses that are initially very cold (2T/W < 0.1) are different from warmer collapses, due to the presence of a dynamical instability associated with clumping of nearly-radial orbits (Polyachenko 1981). This instability can produce very elongated bars (1.6 to 2.1 axis ratio) from spherical initial conditions. the instability is also present in models evolved from oblate and triaxial initial conditions. Warm collapses tend to preserve their initial shapes. Cold initial conditions produce objects whose surface density profiles are well fit by a de-Vaucouleurs law; warm collapses, on the other hand, produce a core-halo profile. A large collapse factor seems necessary to produce objects resembling real galaxies; the same collapse factor guarantees the presence of the radial orbit instability. It thus appears that initial flattening is not crucial for producing prolate or nearly prolate galaxies. Oblate galaxies, on the contrary, seem very difficult to form, unless extremely flattened initial conditions are invoked. Preliminary experiments suggest that these results are not changed by realistic amounts of angular momentum.
The Dynamical Evolution of a Star Cluster
Authors: Som Sunder G. , Kochhar R.K.
Published: June 2019

Using the second order tensor virial equations and the equation for the rate of change of the kinetic energy tensor, we follow the dynamical evolution of a star cluster with anisotropic velocity distribution. We show that the cluster executes finite amplitude oscillations both in size and eccentricity. However, unlike in the isotropic case, the amplitude now depends on the initial eccentricity.
Abundances in the Galactic Center
Authors: Wannier Peter G.
Published: June 2019

Abundance measurements in the Galactic Center (GC) probe material with a nucleosynthetic history unique in our Galaxy. The measurements are of two types: probing interstellar and stellar material. Measurements of gas-phase abundances are mostly toward SgrB2 and SgrA. They reflect the current state of nuclear evolution in the GC and include several important isotope abundance ratios. The isotope ratios provide the most accurate information and allow for comparison with results elsewhere in the interstellar medium. The second type of measurement is of abundances in (and around) stars, yielding chemical abundances in the bulge and disc populations, and reflecting the state of nuclear evolution when the stars were born.

When combined with our knowledge of evolution in the solar neighborhood, several of the results are consistent with the the greater nuclear “maturity” of the inner Galaxy. However, there are several important exceptions, which point to the fact that we really do not understand nuclear processing in the GC region. Some of the open issues may be resolved observationally, and with new infrared and millimeterwave techniques a clear opportunity exists to improve the observational record. Results should increase our understanding of stellar nucleosynthesis and of the history of star formation in the GC.
OH in the Galactic Centre
Authors: Boyce P. J. , Cohen R. J.
Published: June 2019

Preliminary results are reported from an OH mainline absorption study of the galactic centre. The molecular clouds form a well-defined structure 2 kpc in projected diameter, which is warped in its outer regions. The distribution of molecular clouds is highly organised. There are places where the line-widths are anomalously high. The possible nature of these broad-line clouds is briefly discussed.
A Possible Molecular Counterpart to the G359.54+0.18 Non-Thermal Filaments
Authors: Bally John , Yusef-Zadeh Farhad , Hollis J. M.
Published: June 2019

We present new 30″ resolution J=2–1 12CO observations of the molecular gas located close to a group of non-thermal radio emitting filaments recently detected near the Galactic center (Bally and Yusef-Zadeh, 1989). The new data provide some support for the association of the non-thermal filaments G359.54+0.18 with the projected edge of a molecular cloud.
G359.3–0.82: An Unusual Radio Source
Authors: Yusef-Zadeh F. , Yusef-Zadeh F.
Published: June 2019

An unusual radio source exhibiting an axisymmetric, cometary morphology was recently reported by Yusef-Zadeh and Bally (1987) near the Galactic center. This source, G359.3–0.82, consists of a bright head containing a compact source followed by a tail exhibiting sinuous structure. Radio emission is highly polarized and has a nearly flat spectrum between λ6cm and λ20cm. Its location in the sky, spectrum, and lack of resemblance to any other extragalactic radio source suggested to us that this radio source is a Galactic object possibly lying near the Galactic center. New high-reslolution radio images obtained using the VLA confirm the remarkable morphology and strengthen the distinction between G359.3–0.82 and any known extragalactic radio source. The characteristics of G359.3–0.82 suggest that it may be a nonthermal radio wake produced by an object moving through the interstellar medium at a high relative velocity.
Large-Scale Ejection Structures in the Galactic Center
Authors: Sofue Yoshiaki
Published: June 2019

Radio continuum observations of the galactic center region have revealed a number of vertical structures running across the galactic plane, most of which are reasonably attributed either to vertical magnetic fields or to energy release out of the galactic plane. We review the observed radio structures and discuss their properties and origins with a particular attention to the unusual manifestation of energy release in the galactic center. The relation of the continuum structures to the expanding and/or contracting molecular gas rings is also discussed.
Unusually Wide, High-Velocity Radio Recombination Lines from G0.15–0.05 in the Radio Arc
Authors: Yusef-Zadeh F. , Morris Mark , van Gorkom J. H.
Published: June 2019

The H92αrecombination line was observed at 8 GHz toward the “pistol-shaped” HII region G0.15–0.05 using the VLA2in its most compact configuration. The line profiles of individual components of this source peak at VLSR=123 km/s and have total line widths of ~90 km/s. The kinematical structure of the “pistol” is unusual in that much of the neutral and ionized gas in this region is seen predominantly at either +50 or +20 km/s. The line width and radial velocity are the largest found in the Galactic center region with the exception of Sgr A West. We also found gas at VLSR=140 km/s associated with G0.18–0.04: the sickle-shaped feature which surrounds G0.15–0.05. The kinematic properties of G0.18–0.04 and G0.15–0.05 suggest that these two features are components of a single, but complex thermal system interacting with the nonthermal filaments of the radio Arc. In this regard, the width of the broad recombination line from G0.15–0.05, and its large radial velocity, might be explained as the interaction of streaming relativistic particles in the nonthermal filaments of the Arc impacting upon ambient gas clouds lying in the Galactic plane.
MHD Aspects of Galactic Center Physics
Authors: Heyvaerts J.
Published: June 2019

This review addresses the question of MHD phenomena in the galactic center, which are expectedly important in view of the large value of the magnetic field. A physical similarity with other MHD environments where magnetic fields are dominated by a dense driver and dominate a more tenuous halo is recognized. Known physics rules this type of coupling. Most proposed MHD theories of the galactic center fit, at least partly, in this general frame. One of them views Sgr A and its environment up to 50pc as an active corona, similar to that of the sun. whose driver is some central accretion disk, which may (or may not) be the molecular ring. This unified picture is outlined and is shown to naturally explain a number of otherwise puzzling observed features, such as the radio arc and bridge, possibly the ionized minispiral and some aspects of the general energy balance of this region.
The Strong Magnetic Field Galactic Center-AGN-Quasar Model
Authors: Greyber Howard D.
Published: June 2019

The energy storage and dynamics at the center of galaxies is explained using a new construct, the gravitationally bound current loop (GBCL), produced when the galaxy formed under gravitational collapse. Thin toroidal plasma around the slender intense relativistic current loop is bound to it by the Maxwell “frozen-field” condition, and also binds gravitationally to the central object (presumably a black hole). The Strong Magnetic Field model (SMF) explains directly the Milky Way (MW) galactic center radio observations of a vertical magnetic field perpendicular to the galactic disk and the extended radio arcs, as well as the production of successive radio blobs ejected from the compact cores of active galactic nuclei (AGN) or quasars.
Shocked Molecular Gas Near the Galactic Center
Authors: Szczepanski J. C. , Ho P. T. P. , Haschick A. D. , Baan W. A.
Published: June 2019

A 3′ × 6′ field centered ~4′ south of the Galactic center and a ~2′ × 4′ field east of the Galactic center have been mapped using the 4–1 → 30 E line (36.169 GHz) of methanol (CH3OH). Line profiles typically consist of broad (~10–20 km s−1) components, as well as narrow (~1 km s−1), spike-like components. The narrow features are bright and unresolved with 60″ resolution, and are probably due to maser activity. We found maser activity immediately adjacent to the non-thermal “wisp” (SgrA-E) ~4′ south of SgrA-West, the secondary knot at SgrA-F, and the eastern edge of SgrA-East. Position-velocity diagrams suggest that the molecular material has been shocked to a higher velocity in the same vicinities. We propose that the maser activity, and the shift in velocity south of the Galactic center, heretofore interpreted as an increasingly steep velocity gradient toward the Galactic center, may be due to the impact of a SNR and the resulting shock of the ambient molecular material. The dynamical effects on the molecular gas of such a shock may have implications on gas feeding toward the nucleus.
H76α Emission from the Sgr A 15 km s−1 Cloud
Authors: Armstrong J. T. , Jackson J. M. , Ho P. T. P.
Published: June 2019

We report VLA observations of H76α emission from the H II region in M–0.13–0.08, the Sgr A “15 km s−1 cloud.” The line to continuum flux ratio implies an electron temperature Te ~ 7500 K, slightly lower than measurements of Te in Sgr B2. The deduced number of early stars and the infrared luminosity are consistent with a normal IMF in this cloud.
Magnetized Structures in Sgr A West
Authors: Aitken D. K.
Published: June 2019

Spectropolarimetric studies of Sgr A West at 10μm reveal intrinsically polarized emission from the northern arm. The polarization, of amount 7–8 %, is attributed to emission from dust grains which are aligned by a magnetic field directed along the line of the northern arm. Along the eastern arm the polarization is smaller and indicates either a weaker field or one directed closer to the line of sight.

Polarized emission has also been observed at 100μm from aligned grains in the ring of molecular gas which apparently encircles Sgr A. The aligning magnetic field lies in the plane of the ring and is probably toroidal. The correspondence between the polarization position angles at 10 and 100μm suggests a model in which the northern arm is a disrupted filament from the molecular ring.

While the uncertain magnetic properties of grains prevent a reliable direct estimate of field strength, circumstantial evidence suggests it is larger than elsewhere in the Galaxy and possibly large enough to influence the dynamics of the region.
The Mass Distribution in the Galactic Center
Authors: McGinn M. T. , Sellgren K. , Becklin E. E. , Hall D. N. B.
Published: June 2019

We present the results of a project to map the profile of the 2.3 μm CO V = 2–0 band-head in the integrated starlight in the central 10 pc of the Galaxy. This is the first detailed determination of the kinematics of the faint stars that are the major constituent of the mass of the stellar cluster. The stars exhibit systematic rotation in the same sense as Galactic rotation, with VLSR increasing with Galactocentric radius. The stellar velocity dispersion generally dominates the rotation and shows clear evidence for a radial gradient, in the sense of σ decreasing with Galactocentric radius. The data are consistent with the dynamical center of the Galaxy being located at IRS 16 (to an accuracy of ± 10″). The mass distribution has been derived via the theory of stellar hydrodynamics and is shown in Fig. 1. For an assumed core radius of 10″ (~0.4 pc), the best fitting model is a combination of a central mass of 2.5 × 106 M⊙ and a stellar cluster with a density dependence of r-2.1 (Fig. 1). If the core radius is small (~1″) then the mass distribution could be just due to a stellar cluster; a central condensed mass is not required to model the data in that case.
The Stars that Power the Galactic Centre
Authors: Allen D. A. , Hyland A. R. , Hillier D. J. , Bailey J. A.
Published: June 2019

Using the infrared grating spectrometer FIGS on the Anglo-Australian Telescope we have mapped the inner parsec of the Galaxy. We used spectral resolutions of 1000 to observe He I λ2.058 and Brackett α, and 400 for complete K-band spectra.
Observations of HI Br α, [Ne II], and [Ar III] from the Central Parsec of the Galaxy
Authors: Lacy John H. , Achtermann J. M. , Bruce D. E.
Published: June 2019

H I Br α (4.05 μm), [Ne II] (12.8 μm), and [Ar III] (9.0 μm) emission lines from Sgr A West were mapped with ~100 km/s and 2″ resolution. The observations were made with the U. T. infrared echelle spectrometer (IRSHELL) on the IRTF in April 1988. The instrument simultaneously measures 10 64-point spectra along a 2 × 10″ slit. Data analysis is still in progress; preliminary results are presented here.
Long-Term Variations of the Compact Radio Source Sgr A∗ at the Galactic Center
Authors: Zhao Jun-Hui , Ekers R. D. , Goss W. M. , Lo K. Y. , Narayan Ramesh
Published: June 2019

We investigate the long-term flux density variations of the compact radio source Sgr A∗ at the galactic center by combining recent VLA observations with previous Green Bank interferometer data. We present radio flux density light-curves for Sgr A∗ at 20, 11, 6 and 3.7 cm from 1974 to 1987. Long-term variability with a timescale of at least 5 years is seen at 20 cm and there is evidence for more rapid variations at the shorter wavelengths. The variability timescales at 20, 11 and 6 cm fit the λ2 scaling predicted by the theory of refractive scintillation suggesting that the variability could be due to this cause. However, the timescales are relatively short, implying an unusually high velocity in the scattering screen. The modulation index of the variability is large and relatively independent of wavelength.
MeV Gamma Ray Observational Constraints on the Galactic Center Region
Authors: Diehl R. , v.Ballmoos P. , Schönfelder V. , Morfill G. E.
Published: June 2019

MPE Compton Telescope observations of MeV radiation from the direction of the Galactic Center result in constraints on the central gamma-ray source in the Galaxy: The extent of 1.8 MeV line emission from26Al suggests an26Al production process with pronounced concentration towards the Galactic Center. The absence of other gamma-ray lines constrains nucleosynthesis and cosmic ray excitation parameters in the Galaxy. Calculations demonstrate that time variable Galactic Center annihilation radiation may be related to a central26Al source.
Two-colour observations of spikes and flares by high time resolution
Authors: Zalinian V.P. , Karapetian A.A. , Tovmassian H.M.
Published: June 2019

Observations of flare stars with high time resolution permit to register spiky type flares and also to study in detail bright curves of flares. In Byurakan observatory observations of EV Lac have been made with 0.1 s time resolution simultaneouslyin two filters “U” and “B” [1-3]. These observations permited to detect flares of a burst type (Fig.1) and also to reveil multipeak structure of long duration flares. It is necessary to stress that simultaneous observations in two colours increas appresiably the thrustworthiness of the registered spiky flares.
New observations of flare stars in the pleiades by the method of stellar tracks
Authors: Chavushian H.S. , Broutian G.H.
Published: June 2019

In 1984-1986 new observations of flare stars in the Pleiades region were carried out by the method of stellar tracks with 40″ Schmidt telescope of the Byurakan observatory. The effective observational time is 100 hours in U-rays (ORWO ZU-21 plates combined with UG-1 filter were used). The stellar tracks have 1-1.5 cm length, the limiting stellar magnitude on the plates is 13m-14m, time resolution is 5S-20s. 17 flares of 13 stars were detected. Six of these stars were detected as flare stars for the first time. According to the Hertzsprung catalogue all these stars are the Pleiades cluster members. The flare amplitudes reach up to 1.5-3.0 magnitudes, the duration vary from 2.5 to 10.5 seconds.
Possible new, bright flare star in the Pleiades region
Authors: Kelemen Janos
Published: June 2019

With the aid of the star track method we discovered a possible new, relatively bright, flare star in the Pleiades region.
Spectral observations of flare stars
Authors: Mirzoyan L.V. , Hambarian V.V. , Garibjanian A.T.
Published: June 2019

Spectral observations of 6 flare stars in the Pleiades cluster are carried out which occupy different positions on the Hertzsprung-Russell diagram relative to the main sequence: above and below it. The spectral indices which are sensible to luminosity or temperature of the star photosphere are determined. Significant differences between indices of the stars belongings to these two groups are not detected.
A catalogue of flare stars in the Cygnus region
Authors: Tsvetkov Milcho K. , Tsvetkova Katya P.
Published: June 2019

A catalogue of known flare stars in the region of the emission nebulae NGC 7000 - IC 5068-70 and IC 1318 a,b,c in Cygnus is presented. The UBV magnitudes and spectral types, as far as available, for 96 flare stars and their 144 flares were collected. Patrol observations from the Asiago, Byurakan, Konkoly, Rozhen and Tonantzintla observatories, covering a total of 1500 hours effective observing time were used.
Radio flare on η Gemini Star
Authors: Herouni P.M. , Oskanian V.S.
Published: June 2019

The first at the world Radio-Optical Telescope ROT-32/54/2, 6 was mounted on the southern slope of Mount Aragats in Armenia at 1700 m above sea level. The Large Antenna of ROT with the unmovable hemisperical main mirror of 54 m in diameter and movable small correcting mirror is the extremely accurate and shortwave (down to 1 mm). Using aperture is 32m. The diameter of the Optical Telescope is 2.6 m. General view of ROT is shown in Fig.1.
The variability of T Tauri stars
Authors: Herbst W.
Published: June 2019

For many years we have monitored the variability of some bright T Tauri stars with the 0.6 m “Perkin telescope” at Van Vleck Observatory. Collaborators in this endeavor have included several astronomers at the Crimea Astrophysical Observatory, at Capidomonte Observatory, at the U.S. Naval Observatory, and even some sophisticated amateurs.
The polarization discovery and investigation of T Tau stars in Byurakan
Authors: Vardanian R.A.
Published: June 2019

The results of the polarization observations of T Tau, RY Tau and of field stars are presented (Fig.1). The ratio p/Av for RY Tau is equal to 0.066 and is larger than the same ratio for surrounding field stars. The observed variations of the polarization parameters of T Tau and RY Tau as well as the maximum value of the ratio p/Av for RY Tau have permited already in 1964 to suggest that these stars have intrinsic polarization.
The UBVRI photometric and polarimetric observations of the T Tau star HDE 283572
Authors: Shakhovskaya N.I.
Published: June 2019

The preliminary analysis of UBVRI photometric and polarimetric observations of the naked T Tau star HDE 283572 indicates that:

(i)there is intrinsic and variable component of polarisation;

(ii) the distribution and the area of the active regions on stellar surface are variable on time scale of a year.
Circumstellar phenomena and the position of T Tauri stars in the colour magnitude diagram
Authors: Götz W.
Published: June 2019

On the basis of investigations concerning the character and the behaviour of circumstellar shells at T Tauri stars it is shown that the position of these objects in the colour magnitude diagram, below and above the main sequence, is caused by cosmogonic circumstellar effects originated by the mass loss of the stars.
The results of spectral observations of collimated outflows
Authors: Magakyan T.Yu. , Movsessian T.A.
Published: June 2019

The results of spectral investigations of collimatee outflows from young stellar objects, including HL/XZ Tau, L723, Bernes 48, RNO 43N, CoKu Tau/1, obtained on 6-m telescope BTA with two-dimensional photon counting system in 1986-1988 are presented.
Review of the theoretical models of flares of the UV Ceti-type stars
Authors: Grinin V.P.
Published: June 2019

The observations of stellar flares in optics, radio and X-ray show the general similarity of the flares on UV Ceti-type stars and on the Sun. At the same time there exist a lot of data showing that the analogy between these processes is not full. From this point of view the analysis of the theoretical models of stellar flares is given.
A model for the observed periodicity in the flaring rate on YY Gem
Authors: Doyle J. G. , van den Oord G.H.J. , Butler C. J. , Kiang T.
Published: June 2019

Four flares were observed on the late-type binary YY Gem in March 1988 during a total monitoring time of 408 min. The flares were unusual in that there is a periodicity in their occurrence, being separated by 48 ± 3 min. Considering the flares to be formed as a stochastic process, we find that the probability of these events occurring by chance is 0.5%. Modelling indicates that for quite reasonable input parameters (e.g. a spot field strength of 1000 G and a filament with mass per unit length of 106g cm-1), the flare periodicity can be explained in terms of filament oscillations. The only requirement is that there should be a filament at these heights where the magnetic field drops inversely proportional to the height.
Magnetic activity and evolution of low-mass young stars
Authors: Montmerle Thierry
Published: June 2019

X-rays turned out rather unexpectedly to be of fundamental importance in studying, and especially in discovering, pre-main sequence stars. The bulk of the data we now have comes from observations using the Einstein satellite, operating in the imaging mode between ~0.4 to ~4 keV (for reviews, see, e.g., Feigelson 1984, Feigelson, Giampapa, and Vrba 1990); because many of the detected sources turned out to suffer a relatively large absorption (Av up to several magnitudes, see below), EXOSAT, sensitive to softer X rays, unfortunately proved to be of little use.
Planet Detection using the Advanced Camera for Surveys on the Hubble Space Telescope
Authors: Sparks William B. , Krist John , Clampin Mark , Ford Holland
Published: June 2019

The Advanced Camera for Surveys was installed on the Hubble Space Telescope in March 2002. The instrument science team will search for planets using direct imaging with the ACS coronagraph and with precise astrometric and photometric measurement of suitable stars and disks. The camera is operational and performing to expectation.
The Galactic Ecosystem
Authors: Burton Michael
Published: June 2019

We discuss how the process of star formation across the spiral arms of galaxies functions as an ecosystem. The carbon abundance plays a crucial role in both its self-regulation and evolution.
Circular Polarisation in Star Forming Regions: The Origin of Homochirality?
Authors: Lucas P. W. , Hough J. H. , Chrysostomou A. C. , Bailey J. A.
Published: June 2019

The origin of homochirality is one of the longest-standing puzzles in understanding the origins of life. In the laboratory, illumination by circularly polarised UV radiation (asymmetric photolysis) is an effective means of producing an enantiomeric excess in an otherwise racemic mix of chiral molecules. In the natural world, however, it has proven difficult to identify a suitable source of Circularly Polarised Light (CPL). Recent observations of L-excesses of 2–9% for a number of α-methyl amino acids in the Murchison meteorite and our discovery of large degrees of CPL in some star forming regions has added weight to the suggestion that the origin of homochirality is extra-terrestrial. Here we report initial modelling of the production of that CPL.
The Dual Life of RNA
Authors: Meli M. , Maurel M-C.
Published: June 2019

Molecular biology techniques have enabled us to prepare and select RNA aptamers that can bind specifically to small targets. RNA oligonucleotides can also be used as fluorescent probes. We have combined the two approaches to obtain Aptamer Beacons, in which molecular recognition is linked to the emission of an optical signal. These RNA biosensors could be used to detect directly the signatures of life in samples of mineral and extra-terrestrial material.
Terrestrial Permafrost as a Model Environment for Bioastronomy
Authors: Tsapin A. , McDonald G. D.
Published: June 2019

The extent to which organisms can survive extended periods of metabolic inactivity in cold environments such as permafrost is one of the key questions in the study of life in extreme environments and for astrobiology. Viable bacteria have been cultured from million year-old Siberian permafrost samples, but the relationship between the age of the bacteria and the age of the sediments remains controversial. In this study we analyze the level of racemization of amino acids in permafrost samples collected from several sites in Northern Siberia. We have shown that even during long exposures to low temperatures (−10°C to −15°C), the bacterial cells in permafrost are not completely dormant, but continue to metabolize and at least partially control the extent of amino acid racemization.
A Microscopic Approach to Investigate Bacteria under In-Situ Conditions in Arctic Lake Ice: Initial Comparisons to Sea Ice
Authors: Junge Karen , Deming Jody W. , Eicken Hajo
Published: June 2019

To better understand constraints on bacteria at extremely low temperatures in ice, we describe here the adaptation of methods previously developed for sea ice to high magnification imaging of bacteria within fluid inclusions of Arctic lake ice under insitu conditions. Bacterial staining procedures, using the DNA-specific fluorescent stain DAPI, epifluorescence microscopy and image analysis were applied to lake-ice sections at in situ temperature (-5°C). Abundances of total, attached, free-living and metabolically active lake-ice bacteria were also determined from samples melted at 0°C using the fluorescent stains DAPI and CTC. Initial results indicate that, compared to sea ice at the same in situ temperature, lake ice contains fewer and more isolated liquid inclusions, limiting transport of fluids and motion of bacteria. Metabolically active cells were found in all ice samples (0.1 to 2.0% of the total counts), but on average less than in sea ice. Up to 50% of the total bacterial community were found to be associated with particles > 3 μm in size; of the metabolically active cells, a smaller fraction may be attached than in sea ice. Our results expand the spectrum of information available on bacteria in ice on a scale relevant to the organism and provide insight into characteristics of frozen microbial habitats on Earth and perhaps elsewhere in the Universe.
Scaling For SETI: All The Sky, All The Time
Authors: Cullers Kent.
Published: June 2019

The Search for Extraterrestrial Intelligence (SETI) has been, in its modern sense, a search for signs of technology beyond the Solar System. Such a search is a natural companion to visual and radio astronomy, which searches the electromagnetic spectrum to glean information about natural cosmic events. To succeed, SETI must demonstrate the existence of signals that cannot be explained by natural events and that are not of terrestrial origin.
Teaching Astrobiology Online
Authors: Maddison S. T.
Published: June 2019

As part of Swinburne Astronomy Online (SAO), we run an online short course entitled Searching for Extrasolar Planets and Extraterrestrial Life. The main aim of the short course is to act as a “feeder” into our graduate programs and allow students to trial online education while exploring one of the new hot topics of astronomy – astrobiology.

I will present a brief overview of how SAO works, followed by an outline of our short course which has been running for four semesters. In particular, I will focus on why astrobiology is a good choice of topics for an online short course, and look at the successes (and failures) of the course in attracting students to both online education and astronomy –and astrobiology in particular.
Bringing Breakthroughs in Science to the Public Through Webcasting
Authors: Christian Carol A.
Published: June 2019

In the rapidly changing milieu of space science, keeping the public informed and engaged in the progress of science is challenging. Beautiful images, scientific artifacts, and exciting space launches can be a compelling hook but the challenge for scientists and educators is to provide context and basic information that is equally exciting. For the past 5 years, the use of Internet video streaming (webcast) technology has grown in popularity. We have used this technology to bring together scientists, educators and the public to provide virtual access to the research environment for the audience. The growth of new technologies will provide new opportunities for the public to “get behind the scenes” of observatories and laboratories to better appreciate the texture of scientific research as well as the scientists and technical personnel engaged in investigative endeavors.
Science, Fiction and Curriculum Innovation
Authors: Brake Mark , Griffiths Martin
Published: June 2019

The academic world is now becoming so specialized that the advantages of a cross disciplinary education are being lost in the tidal wave of scholarship concentrating upon narrow subject fields whilst displacing the values of connected disciplines from the sciences and humanities. The almost rigorous segregation of science and the arts at degree level is being felt not only within academia, but within society. The more a subject is concentrated, the less profound and applicable it appears to the public who should ultimately be the beneficiaries of such knowledge. In order to achieve a form of parity through which our modern world can be examined, the University of Glamorgan has introduced an innovative degree course aimed at developing a multidisciplinary knowledge of science and the arts via an exploration of the science, history, philosophy, religious, artistic, literary, cultural and social endeavours of the fields of astronomy and fantastic literature.
Properties of hot massive stars from studies of their ring nebulae
Authors: Smith Linda J.
Published: June 2019

Wolf-Rayet (WR) stars and their possible precursors, the Luminous Blue Variables (LBVs), are often surrounded by ring nebulae. It is believed that these nebulae are formed by the action of the stellar wind, matter being ejected from the star in the past, or a combination of these two processes. The various research applications of LBV and WR nebulae are reviewed with regard to the information they provide on the properties of the central stars. They are very useful probes of stellar evolution since the details of the previous evolutionary phases of the central stars are contained in the nebulae. In particular, abundance studies can provide insights into the chemical processes operating during the precursor phases. The nebulae can also be used as probes of the far-UV ionizing flux distribution of the central WR stars by comparing the observed levels of nebular ionization with those produced with non-LTE WR model flux distributions. Comparisons of stellar effective temperatures and luminosities derived using this technique with those determined by modelling stellar emission lines can identify deficiencies such as the lack of line-blanketing in WR model atmospheres. Very hot WR stars can also be identified by searching for nebular HeII emission. Studies of bipolar structures in LBV and WR nebulae provide valuable clues on wind asymmetries in the central stars.
Wolf-Rayet and OF stars in the OB associations LH 101 and LH 104 in the LMC
Authors: Testor G.
Published: June 2019

We observed in the Large Magellanic Cloud the associations LH 101 and LH 104, containing six Wolf-Rayet stars: one WN and five WCE subtypes. These regions are located south of the 30 Dor nebula. The new observations include UBV photometry for a thousand stars and spectroscopy in the range from 3600 to 5300 Å for about 90 stars. In LH 101 an 06.5f, an 06.5 + WN8 and a hydrogen emission star are identified. Cluster HR diagrams of these OB associations reveal their age structure.
Observational aspects of Wolf-Rayet atmospheres
Authors: Antokhin I. I.
Published: June 2019

Observational data suggest that WR atmospheres must be considered as highly inhomogeneous objects incorporating strong shocks induced by radiative instability and full-scale supersonic turbulence, with relatively small mean mass-loss rates.
Alfvén waves and radiation pressure in the winds of Wolf-Rayet stars
Authors: Dos Santos L. C. , Jatenco-Pereira V. , Opher R.
Published: June 2019

We recently showed that Alfvén waves acting jointly with radiation pressure in Wolf-Rayet winds can possibly solve the momentum problem (dos Santos, Jatenco-Pereira and Opher 1993a, 1993b). In these analyses, however, constant radiation luminosity as a function of the distance to the star was assumed. We impose here conservation of the energy flux and examine the effect on the radiation luminosity.
Multi-line transfer and line blanketing in a clumpy Wolf-Rayet wind
Authors: Schaerer D.
Published: June 2019

We present a Wolf-Rayet wind model including clumping, which is assumed to be due to full-scale supersonic compressible turbulence as suggested by Moffat & Robert (1994). It is shown that clumping leads to a larger transfer of radiative to mechanical luminosity, which corresponds to a momentum ratio of (Ṁv∞)/(L/c) = 12 for a typical WN5 star. We also show how clumping reduces the effects of line blanketing in spectral analyses.
The ‘momentum problem’ of Wolf-Rayet stars: can it be explained by the multiple scattering mechanism?
Authors: Springmann U. , Puls J.
Published: June 2019

The possibility of driving the dense winds of Wolf-Rayet stars via multiple scattering of photons in resonance lines is examined. For the case of many overlapping lines it is found that the diffuse radiation arising from the multiple scattering process leads to a radiative acceleration grad even larger than the commonly used unattenuated flux models where each line is assumed to interact separately with the unattenuated photospheric flux. The radial dependence of grad in the outer parts of the wind is now weaker than r−2, which in turn leads to a steeper rise in the velocity field.
UBVRI polarimetry of WR stars
Authors: Georgiev L. , Kaltcheva N.
Published: June 2019

Five-colour polarimetry of a sample of twelve southern WR stars is presented. We suggest a method for separation the interstellar and intrinsic polarization components. Based on the observed data, a dependence of λmax on the terminal velocity v∞ is suggested. Its possible origin could be related to circumstellar envelopes.
Optical and X-ray observations of stellar winds in Wolf-Rayet binaries
Authors: Cherepashchuk A. M.
Published: June 2019

New spectrophotometric, photometric and polarimetric observations of V444 Cygni confirm the basic conclusion that the WN5 star has a small core radius (rc < 4 R⊙) and a high core temperature (Tc > 60 000 K), which are characteristic of massive helium stars. Values of rc < 3 — 6 R⊙ and Tc > 70 000 — 90 000 K for the core of the WN7 star in the Cygnus X-3 system agree well with this conclusion. A clumping structure of WR winds is suggested. X-ray observations of colliding winds in WR+O binaries suggest radial expansion and anomalous chemical composition of WR winds.
Wolf Rayet stars in galaxies and the role of binaries and hydrodynamics
Authors: Maeder André
Published: June 2019

WR stars obey M-L-·-Teff-R-chemistry relations, which are in general model independent (with the exception of chemistry). The processes of WR formation (stellar winds, hydrodynamical mixing, binary mass transfer etc.) influence, however, the domain of parameters occupied by WR stars. We specifically examine the distribution of luminosities and H-contents of WN stars, which both support heavy mass loss rates, or possibly mixing, in the main sequence and WNL phases. Detailed studies of the number ratios WR/O, WC/WN, WC/WR, etc. are made for galaxies at various metallicities Z which exhibit extremely different WR populations. Good agreement of models and observations is found. It is also shown that the data are better explained if a certain fraction Φ (less than 10%) of the O-stars become WR stars, preferentially of type WNE as a result of Roche lobe overflow (RLOF) in binaries. This result necessarily implies that the fraction of WR stars, owing their existence to RLOF, is variable with Z, being nearly 100% at low Z and much smaller at high Z. We also identify several hydrodynamical developments physically required in stellar models. Among them, we collect the available observational and theoretical arguments supporting an important role of mixing in massive star evolution.
Similarities and differences between Wolf-Rayet winds and symbiotic novae
Authors: Nussbaumer Harry
Published: June 2019

It has frequently been suggested that Wolf-Rayet stars are present in symbiotic systems, in particular in symbiotic novae. We dismiss that suggestion as far as it concerns Wolf-Rayet of Population I. There may, however, be similarities to WR stars found as central stars of planetary nebulae. — When treating wind phenomena in our binary configurations, there are common properties which justify that for certain investigations Wolf-Rayet and symbiotic systems are considered together.
Chemical evolution and mixing processes in massive stars
Authors: Røed Ødegaard Knut Jørgen
Published: June 2019

The first results of new evolutionary calculations of massive stars are presented. The calculations cover ZAMS masses from 20—200 M⊙. Yields and abundances throughout the stars are presented.
Dust formation in hot stellar winds
Authors: Cherchneff I. , Tielens A.G.G.M.
Published: June 2019

WC-type Wolf-Rayet stars show episodic or persistent infrared emission attributed to amorphous carbon grains forming in their winds. The process of dust formation in the hydrogen-poor environments characteristic of WC winds is reviewed and compared to the chemical pathway to soot particle production in AGB stars. Emphasis is put on the formation of the dust precursors, and the physical conditions necessary to nucleate them in WC winds. In particular, it is concluded that dust formation around WC stars occurs in a dense, largely neutral, circumstellar disk.
The physics of carbon dust around WC stars
Authors: Zubko V. G.
Published: June 2019

The physical properties of dust in WR shells are investigated in detail. It has been found that carbon grains may grow in the severe conditions of WR shells due to collisions with impinging positive carbon ions. Detailed physical models of carbon dust and dust production rates for selected WC stars have been calculated. It is concluded that graphite rather than amorphous carbon is the most suitable grain material.
An IRAS-based search for new dusty WCL Wolf-Rayet stars
Authors: Cohen Martin
Published: June 2019

I have examined all InfraRed Astronomy Satellite (IRAS) data relevant to the 173 galactic Wolf-Rayet (WR) stars in an updated catalogue provided by van der Hucht (priv. comm.), including the 13 stars newly discovered by Shara et al. (1991). Using the exact coordinates given in these lists, I have examined the IRAS Point Source Catalog (PSC), the Faint Source Catalog, Faint Source Reject Catalog, and generated 1-dimensional spatial profiles (“ADDSCAN”s), and 2-dimensional full-resolution images (“FRESCO”s). The goal was to assemble the best set of observed IRAS colour indices for different WR types, in particular for known dusty WCL objects. These colour indices define zones in the IRAS colour-colour plane. By searching the PSC for otherwise unassociated sources that satisfy these colours, I have identified potential new WR candidates, too faint to have been recognized in previous optical searches. I have extracted these candidates' IRAS Low Resolution Spectrometer (LRS) data and compared the spectra with the highly characteristic LRS shape for known dusty WCL stars. Any surviving candidates must now be examined by optical spectroscopy. This work represents a much more rigorous and exhaustive version of the LRS study that identified IRAS 17380-3031 (WR98a) as the first new WR (WC9) star discovered by IRAS (Cohen et al. 1991).
Colliding winds in O-type binaries
Authors: Gies Douglas R.
Published: June 2019

In close binary systems of O-type stars, the individual stellar winds will collide between the stars to form shock fronts. The existence of the shock region can be established through observations of excess X-ray emission and orbital phase-related variations in UV wind features and optical emission lines. Here I report on work in progress on the orbital variations of the UV wind lines in a large sample of O-binaries that have been observed with the International Ultraviolet Explorer satellite. In most of these binaries, the blue absorption trough of the P-Cygni lines weakens when the strong wind component is behind its companion, in accordance with expectations for colliding winds. I describe how the radial velocity variations of the wind features differ from the orbital motions. Finally I discuss observations of Hα emission in these systems, with emphasis on HD 47129 (Plaskett's star). Such optical emission lines act as a probe of high density regions in the winds.
UV and optical spectroscopic observations of colliding winds in WR+O binaries
Authors: St-Louis Nicole
Published: June 2019

In this paper, a review of spectroscopic evidence for colliding wind effects in WR+O binaries is presented with a particular emphasis on variability at ultraviolet wavelengths. In the optical, evidence for colliding winds comes from extra emission formed in the region of shocked gas and superimposed on the strong emission lines formed in the WR wind. At ultraviolet wavelengths, we observe the consequences of the fact that between the two stars the winds are prevented from reaching their terminal velocity because of the wind-wind interaction.
A spectroscopic search for colliding winds in a complete sample of WC/WO stars in the Magellanic Clouds
Authors: Bartzakos P. , Moffat A.F.J. , Niemela V. S.
Published: June 2019

The Magellanic Clouds provide an ideal laboratory to study the properties of Wolf-Rayet stars. In particular, the 25 WC/WO stars that they contain are nearly all of the same sub-class (21 WC4, one WC5, one WC6 and one WO in the Large Magellanic Cloud; one WO in the Small Magellanic Cloud). This, along with their formation in the same isolated environment, suggests that the wind structure is similar in each star. Thus, a study of other characteristics, such as the effects of binary separation and period on binary wind collisions, can be undertaken with little concern for differing winds. Some 30 high-quality CCD spectra for each of the 25 stars were obtained during three observing missions in the past decade. Although the analysis is not yet complete, the sample clearly contains four large-amplitude WR+O binaries with periods ranging from two to seventeen days and possibly other long-period systems. This paper deals with the wind interaction of the star B22.
IUE monitoring of WR140 (WC7+O4-5)
Authors: Setia Gunawan D.Y.A. , van der Hucht K.A. , Williams P.M. , Kaper L. , Henrichs H. , Wamsteker W.
Published: June 2019

We present the first results of the IUE monitoring campaign of the WC7+O4-5 binary system WR140. Thirty-four high-resolution short-wavelength spectra were obtained in 1979—93, i.e., over more than one orbital period of 7.9 yr. The spectra show variations in the strong resonance lines of CIV and SiIV: large variations occur at the blue edges of the absorption parts of their P-Cygni profiles just after periastron passage. The observed profile changes are discussed in terms of a velocity variation at periastron passage and/or turbulence in the sightline to the O4—5 star at this time.
Colliding wind X-rays in γ Velorum (WC8+O9I)
Authors: Willis Allan J. , Schild Hans , Stevens Ian R.
Published: June 2019

Our ROSAT observations of γ Velorum obtained over several binary cycles reveal substantial, and repeatable phase-dependent X-ray (0.1—2.5 keV) variations. The derived X-ray light-curve shows a 4 x increase in flux at phase ∼ 0.5, which is shown to arise in shocked gas formed in the collison of the two stellar winds, viewed through a cavity in the WC8 wind with an observed opening angle of ∼ 50°. This colliding-wind X-ray emission has Lx ≥ 1032 ergs−1 and kT ≥ 2 keV. Our 2-D hydrodynamical models of the system predict copious X-ray emission from the wind-collision region, at a level and spectrum similar to that observed. Harder (1—10 kev) X-ray observations with the ASCA satellite are being sought to provide improved constraints on the luminosity, spectrum and absorption of the wind-collision emission, and the complex theoretical models involved.
Radio light-curves and circumstellar mapping of the colliding wind binary WR140
Authors: Williams P.M. , van der Hucht K.A. , Spoelstra T.A.Th. , Swaanenvelt J.P.
Published: June 2019

New observations of the colliding wind Wolf-Rayet WC7+O4-5 binary WR140 (HD 193793) at 6 cm and 21 cm with the Westerbork Synthesis Radio Telescope are presented. They show that the 21 cm flux, in particular, rose to a sharp maximum in 1992, lagging about a year behind the 6 cm flux. After maximum, both fell simultaneously. The data are interpreted in terms of the varying circumstellar extinction to a non-thermal source in the wind interaction region due to the winds of both WC and O stars.
An ultraviolet radial velocity orbit for WR140 (WC7+O4-5)
Authors: Setia Gunawan D.Y.A. , van der Hucht K.A. , Stickland D.J. , Lloyd C. , Williams P. M. , Wamsteker W.
Published: June 2019

Ultraviolet high-resolution SWP images of the binary system WR140 (HD 193793, WC7+O4-5) were taken with IUE over the period 1979 — 1993. This poster presents a radial-velocity study of the absorption lines, attributed to the O-type component, applying the infrared period of P = 2900 days.
ASCA X-ray spectroscopy of WR140 near periastron
Authors: Pollock A.M.T. , Corcoran M.F. , Stevens I.R. , Williams P.M. , van der Hucht K.A.
Published: June 2019

Analysis of the X-ray spectrum of WR140 seven months after the 1993 periastron passage shows chemical abundances inconsistent with those used to model the earlier, more heavily absorbed, PV phase spectrum.
Search for TeV γ-rays from Wolf-Rayet stars
Authors: Rovero Adrian C.
Published: June 2019

A search for TeV γ-rays from the non-thermal radio stars WR125, WR140, WR144 and WR147 has yielded only upper limits. The implications are discussed.
Intensive narrow-band continuum photometric monitoring of the WN5+O6 binary V444 Cygni: evidence for wind collision?
Authors: Antokhin I.I. , Marchenko S.V. , Moffat A.F.J.
Published: June 2019

Narrow-band photometry of V444 Cyg shows evidence for a broad bump in the light curve near phase 0.5 for which different possible causes are considered.