bluuebunny/crossref_metadata_2025 huggingface dataset:
How Common are Earths? How Common are Jupiters?
Authors: Lineweaver Charles H. , Grether Daniel , Hidas Marton
Published: June 2019

Among the billions of planetary systems that fill the Universe, we would like to know how ours fits in. Exoplanet data can already be used to address the question: How common are Jupiters? Here we discuss a simple analysis of recent exoplanet data indicating that Jupiter is a typical massive planet rather than an outlier. A more difficult question to address is: How common are Earths? However, much indirect evidence suggests that wet rocky planets are common.
How Unusual are Stars with Planets?
Authors: Reid I. Neill
Published: June 2019

Comparative analysis of the parent stars of extrasolar planetary systems and the local disk population shows a strong trend for increasing frequency with increasing abundance. Approximately 4.5% of solar-abundance (−0.15 < [m/H] ≤ +0.15) stars have detectable planetary-mass companions.
Refining the Search for 6Li in Stars with Planets
Authors: Mandell A. M. , Ge J. , Murray N.
Published: June 2019

The primary conflict between studies attempting to measure 6Li in stars harboring planets, a potential indicator of planet formation, is the incompleteness and inaccuracy of current line lists for the lithium region. We are attempting to resolve these issues using very high-resolution (R ∼ 120,000) and very high quality (S/N between 250 and 1000) spectra of stars with a range of abundances.
Extraterrestrial Chirality
Authors: Bailey Jeremy
Published: June 2019

The homochirality of biological molecules — the almost exclusive use of L-amino acids and D-sugars — is a fundamental property of life, but its origin poses a problem. Recent work has shown an excess of the L enantiomer in amino acids in the Murchison and Murray meteorites, supporting the model, first proposed by Rubenstein et al. (1983) of an extraterrestrial origin for homochirality. This paper discusses the evidence for extraterrestrial chiral asymmetry, the processes which could have led to such asymmetry, and the possible relevance for the origin of biological homochirality on Earth.
From Stardust to Meteorites: The Synthesis of Inorganic and Organic Grains in AGB and Post-AGB Stars
Authors: Kwok Sun
Published: June 2019

Infrared spectroscopic observations of the circumstellar envelopes of AGB and post-AGB stars have identified a variety of inorganic grains including amorphous silicates, crystalline silicates, silicon carbide, carbonates, corundum, spinels and possibly rutiles. Isotopic studies of meteorites have also identified similar species of presolar origin. The existence of aromatic and aliphatic features in the spectra of post-AGB stars suggests that organic compounds in solid-state form are made during the post-AGB phase of stellar evolution. These features show similarity with the IR spectra of kerogen, which is also found in meteorites. These grains therefore represent an important link between stars and the solar system.
Astrobiology: Towards an Understanding of the Emergence of Life in the Universe
Authors: Lazcano Antonio
Published: June 2019

Long before the idea of spontaneous generation was incorporated by JeanBaptiste de Lamarck into evolutionary biology to explain the first emergence of life, the possibility that other planets were inhabited had been discussed, sometimes in considerable detail, by scientists and philosophers alike (Lazcano 2001). More often than not, these were speculations that rested on the idea of a uniform universe but with little or no empirical basis. Today our approaches to the issue of life in the Universe have changed dramatically; neither the formation of planets nor the origin of life are seen as the result of inscrutable random events, but rather as natural outcomes of evolutionary events. The interconnection between these two processes is evident: understanding the formation of planets has major implications for our understanding of the early terrestrial environment, and therefore for the origin of living systems.
The Origin of Organic Matter in the Solar System: Evidence from the Interplanetary Dust Particles
Authors: Flynn G. J. , Keller L. P. , Jacobsen C. , Wirick S.
Published: June 2019

Interplanetary dust particles (IDPs), ∼ 10μm particles from comets and asteroids, have been collected by NASA from the Earth's stratosphere. We compared carbon X-ray Absorption Near-Edge Structure (XANES) and Fourier Transform Infra-Red (FTIR) spectra of anhydrous and hydrated interplanetary dust particles and found that anhydrous and hydrated IDPs have similar types and abundances of organic carbon. This is different from results on meteorites, which show that hydrated carbonaceous meteorites contain abundant organic matter, while anhydrous carbonaceous meteorites contain less carbon mostly in elemental form. But all anhydrous carbonaceous meteorites are depleted in moderately volatile and volatile elements in a pattern that suggested they experienced temperatures in excess of 1200°C, a temperature sufficient to destroy any organic matter they originally contained, while many anhydrous IDPs show no evidence of severe heating. These IDP results indicate that the bulk of the pre-biotic organic matter in extraterrestrial materials formed before aqueous processing, possibly by irradiation of C-bearing ices or by a Fisher-Tropsch type process operating in the gas phase of the nebula or in the interstellar medium.
Optical SETI at Lick Observatory: A Status Report
Authors: Wright Shelley A. , Stone Remington P. S. , Drake Frank , Muñoz Melesio , Treffers Richard , Werthimer Dan , Evans Robert A. , Isotalo Tero , Vance Steven
Published: June 2019

Optical SETI at Lick Observatory is characterized by its robust approach to initial detections. Our three-detector system has distinguished itself by successful rejection of nearly all false positive signals. We present observational progress, discuss use of data analysis procedures such as FFTs and analysis of double coincidences, and mention plans to upgrade our instrumentation.
Megachannel Extraterrestrial Assay Candidates: No Transmissions from Intrinsically Steady Sources
Authors: W. Lazio T. Joseph , Tarter Jill , Backus Peter R.
Published: June 2019

This paper reports new, more sensitive observations of nine of the eleven extrastatistical signals in the Megachannel Extraterrestrial Assay (META). These extrastatistical signals had all of the expected characteristics of extraterrestrial transmissions, except that they did not repeat. Cordes, Lazio, & Sagan (1997) showed that this lack of repeatability could be explained by interstellar scintillation of intrinsically steady sources. We use their methodology and our observations to exclude the scintillation hypothesis at a confidence level of at least 97.8% (for the case of an intrinsically weak source) to a level in excess of 99% (if the source strengths are comparable to that favored by Cordes, Lazio, & Sagan 1997). We also demonstrate that gravitational microlensing cannot account for the initial detection of these candidates nor is microlensing likely to play a role in future SETI programs. We conclude that the META candidates do not reflect a large population of powerful beacons.
Algorithmic Communication with Extraterrestrial Intelligence
Authors: McConnell B. S.
Published: June 2019

ACETI (algorithmic communication with extraterrestrial intelligence) builds upon mathematical languages to create a general purpose programming language. While the underlying framework may be quite simple, the programs derived from even a small instruction set, when run on a sufficiently fast computing substrate, may interact with their users in real-time and may exhibit complex behavior.
Creation of Educational Resources: A Research Scientist's Role
Authors: Christian Carol A.
Published: June 2019

Material and resources for use in science education must contain accurate, up-to-date data and research results. Clearly when curricula and other materials for use in informal science education and for public understanding of science are developed, the direct interaction and influence of research scientists is beneficial. What is the role of scientists in resource development? In colleges and universities, educational materials are scientist-centric since scientists are the principal science educators and therefore create the specific courseware they need. In a pre-college educational environment, and in science museums (for example), appropriate product creation is driven by experienced educators and other experts. The research scientist, drawn from a research environment, may not be the best instigator of those resources.
An Upper Level Astrobiology Course with Discussion Sections
Authors: Theison Dave
Published: June 2019

ASTR 380, Life in the Universe, has been offered here every semester since the mid-seventies. One of four upper level, special topic classes for junior and senior non-science students, the enrollment in ASTR 380 always reached the maximum of 80 students per section. A few years ago, as a result of a change in University requirements, the enrollment dropped to 20–30 students per section. Taking advantage of this situation and keenly aware of student interest in examining certain aspects of the course content more closely, I decided to teach the course with an additional hour per week devoted to a discussion section. While ASTR 380 is the only one of the four upper level classes to have a discussion section, students have enthusiastically seized the opportunity to discuss specific areas of astrobiology.
Line-profile variability of EZ CMa
Authors: Georgiev L. , Ivanov M. M.
Published: June 2019

CCD spectra for the unusual Wolf-Rayet star EZ CMa (WR6) are presented. The analysis of the profile changes of HeII lines shows a correlation between the gravity center of the line and the skewness (Robert et al. 1992). The fourth moment (kurtosis) changes with phase and looks epoch independent. These observable effects could be treated as manifestations of wind variability rather than consequence of orbital motion.
The absence of a short period in the WN5 star EZ Canis Majoris
Authors: Antokhin Igor I. , Bertrand Jean-François , Lamontagne Robert , Moffat Anthony F.J.
Published: June 2019

Several suggestion have been put forward to explain the 3.d766 periodicity of EZ CMa (WR6): (i) WR+c system; (ii) rotating single WR star; (iii) pulsations (non—radial (NRP) or radial) with frequency reduced by some kind of filtering in the wind. In this paper, we report on a photometric investigation based on a long continuous observing run, in an attempt to verify whether EZ CMa does in fact show a unique periodicity. In particular, this work was motivated by the claim by Gosset & Vreux (1987), based on the data from Lamontagne et al. (1986, hereafter LML), that EZ CMa may have a shorter period besides the one at 3.d766, a frequency close to but not equal to the third harmonic of the 3.d766 period.
Multiwavelength study of the WO star Sand 2
Authors: Norci L. , Polcaro V.F. , Rossi C. , Viotti R.
Published: June 2019

We present the results of a multifrequency observation of the WO star Sand 2 in the LMC. Two ROSAT PSPC observations, with exposure times of 8953 s and 4540 s, are used to investigate possible X-ray emission from Sand 2. The optical spectrum observed with the ESO 2.2m telescope close to the time of the ROSAT observations, shows strong emission lines of HeII, CIV, OV and OVI. All lines have a velocity broadening of 4 200±100 km s−1. The UV spectrum from the IUE archive shows a CIV resonance doublet at 155 nm with a P-Cygni absorption at ∼ −5 000 km s−1, with wings extending to about −8 000 km s−1. A combination of two different BB temperatures (80 000 K and 25 000 K) are required to fit the UV-optical continuum, dereddened by EB-V = 0.25.
The imprint of massive stellar evolution on circumstellar gas
Authors: García-Segura Guillermo , Mac Low Mordecai-Mark , Langer Norbert
Published: June 2019

We follow the interaction of massive stars with their circumstellar media over their entire lifetimes by combining several numerical models. We use a stellar evolution model for 35 and 60 M⊙ stars (Langer et al. in preparation) as inner boundary conditions for one- and two-dimensional gas dynamical models of the circumstellar medium using ZEUS (Stone & Norman 1992). In this poster, we focus on circumstellar evolution during the Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stages.
The inner ML-67 nebula: coronagraphic imaging and echelle observations
Authors: Nota A. , Clampin M. , Sirianni M. , Greenfield P. , Golimowski D. A.
Published: June 2019

Coronagraphic and spectroscopic observations of the nebula M1-67 surrounding WR124 reveal an axisymmetric outflow.
A search for Wolf-Rayet stars in NGC 300
Authors: Azzopardi M. , Muratorio G. , Breysacher J. , Testor G.
Published: June 2019

Preliminary results of our NGC 300 Wolf-Rayet star survey are presented.
Status of Wolf-Rayet models
Authors: Hillier D. J.
Published: June 2019

In the last decade there has been a tremendous advance in our understanding of the atmospheres and stellar winds of Wolf-Rayet (WR) stars. This has arisen through improved observations, and through the application of extensive radiative transfer codes which has allowed us to model some of the complex processes occurring in WR envelopes. Present models are able to simultaneously treat detailed atomic models for H, He, C, N, O and Si. In the near future we will be able to treat Fe, and to more accurately treat the formidable problem of non-LTE line-blanketing. In this review we address current limitations in modeling the extended atmospheres of WR atmospheres. These limitations fall into two classes — those reflecting our inability to accurately compute the “Standard Model”, and those referring to assumptions in the “Standard Model” that need to be relaxed. Under the first category we include inaccuracies in the atomic data, the neglect of line-blanketing in the model calculations, and the inability of the present generation of models to compute the velocity law. Under the second category we include the assumption of spherical geometry, the assumption of homogeneity, the neglect of rotation, and the influence of X-rays arising from shocks in the stellar wind.
Hydrodynamic line blanketed atmospheres of Wolf-Rayet stars
Authors: Schmutz Werner
Published: June 2019

In this paper I examine the acceleration of Wolf-Rayet winds in the optically thin part of the atmosphere. First, I investigate the radiative force using atmosphere models with specified velocity structures. It is found that “standard” model atmospheres that reproduce the observed spectra of Wolf-Rayet stars do not provide by a large factor (≈10) the force needed to accelerate the adopted velocity structure. Second, using clumping in order to have a favorable luminosity to mass loss ratio, it was attempted to find a hydrodynamic solution of a WR wind. If large clumping factors of the order of 30 are assumed then solutions are possible. However, such models are very unlikely to be correct since they predict much stronger emission lines than observed in any WR star. Third, a modification of the non-LTE rate equations is investigated. It is assumed that a Bowen resonance-fluorescence mechanism removes a small fraction of photons from the radiation field of the helium Lyα resonance line. It turns out that the ionization equilibrium of winds where helium is recombining from He++ to He+ is extremely sensitive to a modification of the radiation field of this line. A removal of 1% of the photons is sufficient to initiate an abruptly changing ionization equilibrium. It is proposed that the key to understand the acceleration of WR winds is the correct calculation of the ionization structure. If this hypothesis is true then today's non-LTE atmospheres yield systematically wrong results. This would not only affect the radiative acceleration but also the observable helium lines that are used for the diagnostic of the stellar temperature. It would imply that the luminosities of WR stars are underestimated by the present atmosphere models.
The evolutionary status of WNL stars
Authors: Crowther Paul A. , Smith Linda J. , Hillier D. John
Published: June 2019

We discuss the evolutionary and mass loss implications of recent non-LTE analyses of late WN (WNL) stars in the Galaxy, LMC and M33 using the Wolf-Rayet standard model and address the observed dichotomy of WNL stars discussed by Moffat (1989). Individual subtypes belong to two distinct groups. We find that the single WNL+abs and WN7 stars evolve directly from very massive O stars (60–100 M⊙) with the former intimately related to extreme Of stars and found exclusively in the youngest clusters in our Galaxy. Conversely, the observational properties and chemistries of WN8-10 stars suggest that they are descended from lower initial mass progenitors (∼25–60 M⊙). These stars are either dormant LBVs (= WN9–10) or at a phase immediately after this stage (= WN8) although a previous RSG phase cannot be excluded. Included in this subgroup are the LMC and M33 Ofpe/WN9 stars, re-classified as WN9–10 since they appear to be genuine WN stars.
An empirical study of Wolf-Rayet stellar wind ionization stratification
Authors: Dalton Matthew J. , Crowther Paul A. , Willis Allan J.
Published: June 2019

We present an analysis of high resolution UV (IUE) and optical (INT, AAT and ESO) spectroscopy of eight galactic WN and WC stars. We examine the correlation between ionization potential (IP) and the velocity structure of the stellar winds and find important correlations between line-width, IP and excitation potential (EP). These results provide potential constraints on the velocity law used in models of WR atmospheres.
New analysis of Wolf-Rayet infrared lines
Authors: Eenens P.R.J. , Williams P. M.
Published: June 2019

New infrared spectra of Wolf-Rayet stars are analysed to derive C/He abundance ratios and ionization ratios. These ratios are discussed in relation with subtype, terminal velocity and local metallicity. They are compared with the predictions of evolutionary models.
Thick winds from Wolf-Rayet stars
Authors: Eichler D. , Shalom A. Bar , Oreg Y.
Published: June 2019

When the effective opacity becomes sufficiently great, a qualitatively different type of radiatively driven wind solution appears, in which a high wind thickness and trapping of radiation cause each other in a bootstrap fashion. It is proposed that the thick winds from Wolf-Rayet stars can be understood in this manner. Opacity computations using the method of super transition arrays (STA) are presented that show that outflows from WR stars can attain the needed opacities.
Spectropolarimetry and wind asymmetries of Wolf-Rayet stars
Authors: Schulte-Ladbeck Regina E.
Published: June 2019

Motivated by the question of what drives the winds of Wolf-Rayet (WR) stars, I have been investigating the structure of WR winds. Observational evidence has been accumulated which demonstrates that the winds of some (but not all) WR stars are not spherically symmetric or homogeneous. I review results of work in the literature pertaining to the detection of such wind asymmetries in single WR stars and WR binary components. Particular emphasis is placed on the technique of spectropolarimetry, and how it has contributed to our knowledge of the wind-geometry of WR stars.
Winds from rotating Wolf-Rayet stars: the wind-compressed zone model
Authors: Cassinelli J. P. , Ignace R. , Bjorkman J. E.
Published: June 2019

Theoretical models for Wolf-Rayet winds that include the effects of rotation and magnetic fields are discussed. These are of two types: magnetic rotator models and wind compression models. The magnetic rotator models are examples of equatorial expulsion models, typically requiring large rotation rates to produce significant equatorial density enhancements. Wind- compression models are introduced here as an application of the two-dimensional Wind-Compressed Disk (WCD) model that has recently been developed for Be stars. An equatorial disk forms because of the supersonic confluence of the flow from the upper and lower hemispheres of the star. In the application to WR stars, we suggest that disk formation is not required, and instead a less extreme example that we call a wind-compressed zone (WCZ) may suffice. Because the winds of WR stars have a geometrically extended acceleration region, or a “slow” velocity law, there can be compressions by an order of magnitude, even with moderate stellar rotation rates of about 16% critical. Magnetic flux conservation is then used to estimate the enhancement of the field strength that occurs because of the equatorial wind-compression. We consider an application of the model to explain the occurrence of polarization and dust formation among only some WR stars. Finally, we consider the WR + compact companion system WR 147, and suggest that the enhanced accretion in a WCZ could help explain the large X-ray emission.
Wind absorption effects in the NIV 1718Å line in the WN4+O5 binary HD 90657
Authors: Lloyd C. , Stickland D. J.
Published: June 2019

Using a simple absorption line model the phase dependent effects of ‘wind eclipses’ have been studied for the N IV 1718Â line in the WN4+05 binary, HD 90657. The varying strength of the absorption, as measured by the equivalent width, has been compared with the model for a range of wind parameters and assumptions. It is found that the fraction of absorbing atoms drops quickly, to the first or second power of the radius, and that a significant fraction persists beyond 60 R⊙.
A radial-velocity curve for WR 46 (WN3p)
Authors: Veen P. M. , van Genderen A.M. , Verheijen M.A.W. , van der Hucht K.A.
Published: June 2019

As the first result of spectroscopic monitoring of WR46 (HD 104994, WN3p) in 1991, a preliminary radial-velocity curve is presented with P = 6.8 hr, confirming the binary nature suggested from photometry.
The multiple system Sk-67°18 in the LMC
Authors: Niemela V. S. , Seggewiss W. , Moffat A. F. J.
Published: June 2019

The bright star Sk—67°18 (Brey 5) in the Large Magellanic Cloud (LMC) contains an eclipsing binary system. Our radial velocity study reveals that the orbital period is almost exactly two days. The spectra also show that the star's primary component is not of spectral type WN, but that the star is rather an Of+O type binary where the primary is probably of type O3f*. Furthermore, Sk—67°18 appears to be a high-mass multiple system.
The changing spectrum and orbital motion of the SMC Wolf-Rayet binary HD 5980
Authors: Barbá R.H. , Niemela V.S.
Published: June 2019

Optical spectroscopic observations of the eclipsing binary WR star HD 5980 in the SMC, obtained during different epochs, show a remarkable change of the WR type spectrum from spectral type WN3-4 to WN7-8. Radial velocities of the WR emission lines from spectra obtained in August 1992, indicate an orbital motion corresponding to the secondary component which is in front of the system during the primary eclipse. We compare the RV curves and phase-dependent line-width variations observed in 1992 with previously published data.
New massive close binary models and the26Al yield of the WR component of γ VEL
Authors: Braun H. , Langer N.
Published: June 2019

We present new models of massive close binary evolution, using an up-to-date hydrodynamic binary code which includes time dependent mixing of chemical species in the stellar interior, and nuclear reaction networks for the CNO cycles as well as for the NeNa and MgAl cycles. Some of our models, tailored to fit γ Vel, provide for the first time detailed results for the production and ejection of26A1 into the interstellar medium by WR binaries. From our results one can estimate the contribution of WR stars to the amount of26Al presently seen in the Milky Way by γ-ray satellites.
Wolf-Rayet stars in starbursts: Effects of a change of mass loss rate
Authors: Meynet G.
Published: June 2019

We present here starburst models based on the most recent grids of stellar evolutionary tracks obtained by the Geneva group. These new models, computed with enhanced mass loss rates during the main sequence and the Wolf-Rayet WNL phases, very well reproduce the luminosities, surface abundances and statistics of WR stars (Maeder & Meynet 1994). This change of the mass loss rates considerably affects the way the WR stars, born in a starburst's episode, are distributed among the different WR subtypes. We compare the theoretical predictions with recent observations and conclude that: (1) to reproduce the high observed ratios of WNL to O-type stars, a flat IMF seems to be required; and (2) the models which reproduce the best the observed characteristics of WR stars, i.e., those computed with an enhanced mass loss rate, can also account for the observed properties of the WR populations observed in starbursts. Moreover, the possible presence of numerous WC stars found in the low metallicity He2-10 A starburst by Vacca and Conti (1992), can only be accounted for when the high mass loss rate stellar models are used.
New models for Wolf-Rayet stars: global diffusion
Authors: Deng L. , Bressan A. , Chiosi C.
Published: June 2019

We present a scenario for the evolution of massive stars in which a new mixing mechanism (named global diffusion) is taken into account. This type of mixing stands on the critical Reynolds number and radiative viscosity (Schatzman 1977) and allows mixing of material to take place between the core and the surface during the whole evolution on a very slow time scale. The physical processes triggering global diffusion deserve further study. We find that stellar models of massive stars calculated with global diffusion offer interesting clues to understanding the properties of Wolf-Rayet stars and their location in the HRD.
Semiconvection mixing and its influence on case B mass exchange in massive binaries
Authors: Staritsin E. I.
Published: June 2019

In case of moderate matter mixing in the semi-convective zone the primary loses part of its mass on a nuclear time-scale. It looks like a CNO-supergiant during the first part of the helium burning stage. Another part of the mass is lost on the thermal time-scale. The primary looks like a WR star during the second part of the helium burning stage.
IR excesses of late-type WC stars: no dust needed in most cases
Authors: Nugis T.
Published: June 2019

Many late-type WC stars exhibit strong IR excesses which have usually been explained by hot dust radiation. Alternatively, we found that free-free and free-bound radiation of a small number of high density clumps beyond the effective radio-emission zone may give rise to “dust-like” IR excesses.
A colliding wind model for WR 79
Authors: Lührs S.
Published: June 2019

The variable peaks on the flat–topped CIII-569.6nm line of the WC-star in the WR 79–system are interpreted as additional emissions, produced in the colliding wind region of the two stars. The minimum and maximum distances of the appertaining radial velocity curves yield the important parameter i and so the system-masses. Synthetic profiles strongly support the present model.
The X-ray view of the Wolf-Rayet stars
Authors: Pollock A.M.T.
Published: June 2019

Ever since the earliest work, X-ray observations have been central in the chequered development of the study of interacting high-velocity winds in binaries. This review assesses how confidently the observations of Wolf-Rayet stars may be interpreted as the result of colliding winds, drawing attention to the wide range of X-ray luminosities even among the relatively bright binaries. Although the data do not generally conform to the simplest binary models, some suggestions are made to reconcile theory and observation.
The ROSAT PSPC survey of the Wolf-Rayet stars
Authors: Pollock A.M.T. , Haberl F. , Corcoran M.F.
Published: June 2019

We report X-ray measurements of nearly all known galactic Wolf-Rayet stars from the ROSAT all-sky survey and derive 0.2–2.4 keV luminosties.
Stagnation-point flow in colliding-wind binary systems
Authors: Stevens Ian R. , Pollock Andrew M.T.
Published: June 2019

The low X-ray temperatures and luminosities of colliding wind binaries compared to theoretical expectations has been a long standing problem. As a potential solution to this problem we present quantitative calculations of the radiation hydrodynamics in colliding wind binary systems, accounting for the effect of two radiation fields on the dynamics of both winds, using a formulation similar to that of Castor et al. (1975, ApJ 195, 157). A more detailed description of this work can be found in Stevens & Pollock (1994, MNRAS in press). Consider only the WR wind being driven under the influence of the WR and O-star radiation fields and motion only on the line-of-centers. Near the WR-star, its own radiation field dominates, and the mass-loss rate will be largely unaffected by the presence of the companion. However, moving towards the O-star, the O-star radiation field becomes a significant fraction of the total flux. As the O-star radiation field is opposed to the WR radiation field the radiative line-force will be diminished and the wind acceleration diminished. This will lead to the WR star wind colliding with the O-star wind at a lower velocity than would be expected from single star models. This mechanism will only be at work in close binary systems. In wide binaries both winds will be at terminal velocity before the other radiation field makes a difference. Results for a sample calculation are shown in Fig 1, using parameters for V444 Cyg from Schmutz et al. (1989, A&A 210, 236). In the absence of any deceleration effects the WR wind velocity at the shock would be ∼ 1300 km s−1, corresponding to kT ∼ 2 keV. The reduction in the WR star velocity at the shock interface caused by the O-star radiation field is predicted to be ∼ x2 leading to kTx ∼ 0.5 keV, in line with X-ray observations.
Radio images of Wolf-Rayet 147
Authors: Davis R.J. , Bode M. F. , van der Hucht K.A. , Williams P. M.
Published: June 2019

We present preliminary MERLIN radio maps at 1.7 and 5GHz of the Wolf-Rayet star WR147 (AS431). These provide the highest spatial resolution images of this object at these frequencies to date. Our results confirm that WR147 comprises two primary radio sources lying on a N-S axis. Combining results at 1.7 and 5 GHz gives a spectrum for the southerly source consistent with optically thick thermal emission. The northerly source appears to be non-thermal. In addition, extended emission is observed at both frequencies which links the two sources. The northerly source is elongated in a direction roughly perpendicular to the axis of this extended emission, and the southerly source appears double on the 5 GHz map.
Radio monitoring of the non-thermal Wolf-Rayet objects WR125, WR146 and WR147
Authors: Van Der Hucht K.A. , Williams P.M. , Spoelstra T.A.Th. , Swaanenvelt J.P.
Published: June 2019

The radio emission from WR125 (WC7+O9) has faded to a new low, apparently below its stellar wind level, while continuous, variable non-thermal emission has been observed from WR146 (WC6) and WR147 (WN8).
Radio Source Counts at 15 GHz: Implications for CMB Experiments
Authors: Taylor Angela C.
Published: June 2019

In preparation for Very Small Array (VSA) observations we have surveyed the first three VSA fields at 15 GHz using the Ryle Telescope in Cambridge, finding 217 sources with flux density greater than ˜ 20 mJy over 178 deg2. This is the highest radio frequency at which a survey has been done that is relevant to the issue of radio source contamination in CMB experiments. Our results show that source fluxes, and indeed the existence of many sources, cannot be predicted at 15 GHz by extrapolation from lower frequency. The spectra and variability of the sources and their implications for CMB experiments at cm-wavelengths are discussed.
The Matter Power Spectrum
Authors: Peacock J. A.
Published: June 2019

The main tools describing the formation of large-scale structure are reviewed. Detailed emphasis is given to the Cold Dark Matter model, since this appears to be a close match to observation. A consistent normalization that satisfies both CMB constraints and the cluster abundance requires Ωm ⋍ 0.35 for a flat universe and scale-invariant fluctuations. Discrepancies between observed galaxy power spectra and CDM predictions are discussed; a heuristic model for galaxy bias is proposed that potentially allows such scale-dependent bias to be understood.
H0 from Gravitational Lenses: Recent Results
Authors: Schechter Paul L.
Published: June 2019

The 0th, 1st and 2nd derivatives of a “Fermat potential” give the three D's of gravitational lensing: delay, deflection and distortion. Observations of these delays, deflections and distortions for doubly and quadruply imaged quasars give estimates of Hubble's constant, H0. The single largest contribution to the uncertainty in H0 arises from the difficulty in constraining the degree of central concentration of the lensing potential. Fortunately, astronomers have spent a good deal of effort over the past quarter century addressing just this question. If galaxies at z = 0.5 are like nearby galaxies, the associated systematic uncertainty in H0 is less than 10%. The expected lens-to-lens scatter is 20%. Results from three particularly well constrained systems are reported.
Dynamical Evolution of the Universe in the Quark-Hadron Phase Transition and Nugget Formation
Authors: Goyal Ashok. , Chandra Deepak.
Published: June 2019

We study the dynamics of first-order phase transition in the early Universe when it was 10 −50μs old with quarks and gluons condensing into hadrons. We look at the evolution of the Universe in small as well as large super cooling scenario.
Radio Microlensing: Past, Present & Near Future
Authors: Koopmans L. V. E. , de Bruyn A. G. , Fassnacht C. D. , Wambsganss J. , Blandford R. D.
Published: June 2019

Strongly correlated non-intrinsic variability between 5 and 8.5 GHz has been observed in one of the lensed images of the gravitational lens B1600+434. These non-intrinsic (i.e. ‘external’) variations are interpreted as radio-micro-lensing of relativistic μas-scale jet components in the source at a redshift of z=1.59 by massive compact objects in the halo of the edge-on disk lens galaxy at z=0.41. We shortly summarize these observations and discuss several new observational and theoretical programs to investigate this new phenomenon in more detail.
The Initial Condition of Cosmological High-Resolution Simulations
Authors: Ogawa Tomoya. , Ebi Shuuichi. , Yamashita Kazuyuki. , Den Mitsue.
Published: June 2019

Recently, High-resolution algorithms such as the adaptive mesh refinement (AMR) method have been applied to cosmological simulations by several authors. However, the resolution of their INITIAL conditions is not high. We argue the need for cosmological high-resolution simulations to use a high-resolution initial condition or an initial condition including high-frequency components. Then we present the method of creating such initial condition, and estimate its computational cost.
How flat is the Universe?
Authors: Roos M. , Harun-or-Rashid S. M.
Published: June 2019

We consider independent astrophysical constraints in the space of the density parameters Ωm of gravitating matter and ΩΛ of vacuum energy.
Constraining Galaxy Formation Epoch
Authors: Yi Sukyoung. , Brown T. , Heap S. , Hubeny I. , Landsman W. , Lanz T. , Sweigart A.
Published: June 2019

Pinning down the ages of high redshift galaxies is the most direct way of constraining the galaxy formation epoch. There has been a debate on the age of LBDS 53W091, a red galaxy at z=1.5. The discrepancy in the age estimates of various groups is due to the difference in the population synthesis model. However, there is generally a good agreement among popular models. Polishing the models and assessing their internal uncertainties are crucial in the analysis of high redshift galaxies.
Long-term variability of H2O masers in YSOs
Authors: Valdettaro Riccardo , Palla Francesco , Brand Jan , Cesaroni Riccardo , Comoretto Giovanni , Felli Marcello , Palagi Francesco
Published: June 2019

A sample of 14 water maser sources associated with young stellar objects (YSOs) has been monitored over 13 years with the Medicina 32-m antenna. The YSOs have been selected with bolometric luminosities from 20 L⊙ to 2 × 106 L⊙ with the aim of investigating the relationship between H2O maser variability and stellar mass. The results are presented in various graphical forms which allow to follow the variation of the different spectral components. In particular, four quantities have been considered in our analysis: the intensity of the maser lines as a function of time and velocity; the flux integrated over the observed velocity range as a function of time; the maximum flux ever observed at each velocity; and the frequency of occurrence of the maser emission at any given velocity.
VLBA multi-epoch water maser observations towards Cepheus A
Authors: Torrelles José M. , Patel Nimesh A. , Gómez José F. , Ho Paul T. P. , Rodríguez Luiz F. , Anglada Guillem , Garay Guido , Greenhill Lincoln , Curiel Salvador , Cantó Jorge
Published: June 2019

We have carried out and recently reported VLBA multi-epoch water maser observations toward Cepheus A with an angular and velocity resolution of 0.5 mas and 0.2 km s−1, respectively. Some of the masers detected previously with the VLA (observations made with angular and velocity resolutions of 80 mas and 1.3 km s−1, respectively) are resolved now into linear/arcuate coherent “microstructures”. These structures, while smaller than the VLA beam, are 6-200 times the size of the VLBA synthesized beam. The morphology and the observed proper motions found in these structures imply three different centers of star formation activity in a region of ⋍ 0.3 radius (⋍ 200 AU). The most remarkable result from these observations is the discovery of an arc of water masers which is perfectly fitted by a circle to one part in a thousand. This arc is expanding and suggests a spherical “puff” of ejected material ejected 33 years ago from a protostar located 600 mas south of the radio jet HW2. This spherical ejection represents a very strong challenge for theoretical studies of star formation.
Dynamics of the superfine structure in the Orion KL jet
Authors: Matveyenko Leonid I. , Diamond Phil J. , Graham David A.
Published: June 2019

We have studied the superfine structure of the active H2O maser region in Orion KL with an angular resolution of ≤ 0.3 × 0.7 mas. The high level of H2O maser emission from 1979-1988 was due to an accretion disk, which is divided into five groups of protoplanetary rings. The peak brightness temperatures of the structures was Tpeak = 1013-14 K. The region is located in the OMC-1 molecular cloud, VLSR ⋍ 7.74 km/s. The cloud amplifies by more than two orders of magnitude the emission from the structures, whose radial velocities are within the maser window ±0.3 km/s. Due to this, the velocity of the H2O super maser emission is constant. In the quiescent period of 1995 a 6 AU jet was discovered, PA = −32°, Tb ⋍ 1011K. In 1998 the jet's brightness temperature increased by more than 3 orders of magnitude. Initially the jet's position angle was PA = −45°, and then changed to PA = −38°. During the period of decreasing emission in 1999 the jet had changed its form and became a helix, that suggests the precession of the rotation axes. In the central part of the jet there is a compact bright source - “the ejector” - with Tejc = 1017 K.
Space-VLBI observations of OH masers
Authors: Slysh Vyacheslav I. , Voronkov Maxim A. , Val'tts Irina E. , Migenes Victor , Shibata K.M. , Umemoto Tomofumi , Inoue Makoto
Published: June 2019

We report on the first space-VLBI observations of the OH masers in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The maps of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature 6 × 1012 K was obtained. The masers seem to be located in the direction of low interstellar scattering.
Variability studies of 6.7 GHz methanol masers at HartRAO
Authors: Goedhart Sharmila , Gaylard Michael J , van der Walt D. Johan
Published: June 2019

A program monitoring the variability of a sample of 56 6.7 GHz methanol masers was started in December 1998. The sources are observed on a weekly basis. We present preliminary results of the monitoring program.
The Onsala blind 6.7 GHz survey of the galactic plane: new methanol masers in the northern hemisphere
Authors: Pestalozzi Michele R. , Minier Vincent , Booth Roy , Conway John
Published: June 2019

We review the state of the Onsala blind survey of the galactic plane, searching for new 6.7 GHz methanol masers. We also describe preliminary results of millimeter follow-up observations of the new detections and high resolution observations using the EVN. We conclude that blind surveys are important to complement targeted searches done until now and give the possibility to detect new classes of objects.
H2 and methanol masers - outflow from the earliest stages of high-mass star formation?
Authors: Lee J.-K. , Walsh A.J. , Burton M.G.
Published: June 2019

We report the discovery of shocked H2 emission at 2.12 μm associated with methanol masers, and discuss its implication for massive star formation.
Supernova OH (1720 MHz) masers in Sgr A East, W28 and G359.1-0.5
Authors: Yusef-Zadeh F. , Roberts D.A. , Bower Geoff , Wardle M. , Goss W.M.
Published: June 2019

A new class of OH (1720 MHz) masers unaccompanied by main-line transitions have recently been discovered (Frail, Goss and Slysh 1994). These masers lie at the interface between supernova remnants (SNRs) interacting with molecular clouds. We discuss three new aspects of SN masers found in the direction toward the Galactic center: (i) the detection of a new −130 kms−1 OH (1720 MHz) maser in the southern lobe of the molecular ring at the Galactic center: (ii) the detection of extended OH (1720 MHz) maser emission from W28 accompanying the compact maser sources and (iii) the detection of linear polarization of the brightest OH (1720 MHz) maser in SNR G359.1-0.5.
Recombination line masers in YSOs
Authors: Martín-Pintado Jesús
Published: June 2019

Maser emission from recombination lines has been detected towards the Young Stellar Object (YSO) MWC349 and the massive evolved star η Carinae. In spite of extensive searches of recombination line maser emission at millimeter wavelengths towards massive star forming regions, MWC349 remains unique. MWC349 is also a strong recombination line laser in the Far-IR with the largest amplification observed for transitions at wavelengths around 400 μm. The observational properties of the recombination line maser and laser emission from MWC349 are reviewed. Modeling of the maser and laser emission in MWC349 will be used to illustrate the potential of this kind of masers to understand the early phases of the evolution of massive stars. The impact that future instruments like the Herschel, the SMA and specially ALMA, will have in the investigation of recombination line maser emission from YSOs is briefly discussed.
Maser effects in the recombination lines of Eta Carinae
Authors: Abraham Zulema , Damineli Augusto , Durouchoux Philippe , Nyman Lars-Åke , McAuliffe Felipe
Published: June 2019

Eta Car is a variable star surrounded by a cloud of gas and dust that absorbs a large part of its optical emission and that showed, in the past two hundred years, several events of mass ejection. It presents a 5.52 year period in the high excitation Heλ 10830 line intensity, indicating periodic changes in the ionizing radiation. Changes in the central velocity of optical lines, with the same periodicity, suggests the presence of a companion star, in a binary orbit. At radio frequencies, the region shows an optically thick bremsstrahlung spectrum, extending to millimeter and submillimeter wavelengths, and strong recombination lines at low quantum numbers showing maser effects. The flux densities, both from the continuum and recombination lines show a periodic behavior similar to that observed at optical wavelengths. We present observations of radio continuum and recombination lines at different millimeter wavelengths for several epochs. Based on these observations we modeled the emitting region as a thin disk and determined its temperature, electron density and velocity distributions using the radiation transfer equations in NLTE.
OH masers in oxygen-rich late-type stars
Authors: Etoka Sandra , Le Squeren A.M.
Published: June 2019

We present here some noteworthy results of two related studies on oxygen-rich late type stars. The aim of this work was to study the OH circumstellar shell properties in terms of evolution. These studies are based on an OH monitoring programme carried out with the Nançay Radio Telescope. The first study concerns seven Miras distributed along the colour-colour diagram. They were observed at two or three different epochs covering one to seven cycles over a period from 1980 to 1995 at 1612, 1667 and 1665 MHz in both circular polarizations. The second study concerns thirty objects covering a wide range of mass loss rate from Miras to OH/IR stars. They were observed in 1994 at 1665 & 1667 MHz in both circular polarizations.
VLA observations of H2O and OH (1612 MHz) maser emission towards OH 231.8+4.2
Authors: Gómez Yolanda , Rodríguez Luis F.
Published: June 2019

We present Very Large Array (VLA) observations of H2O and OH (1612 MHz) maser emission toward the protoplanetary nebula OH 231.8+4.2. The H2O observations show two features at VLSR of 23.1 and 44.5 km s−1, coinciding in position within error with the SiO (v=1; J=2−1) maser position from Sánchez Contreras et al. (2000). The H2O and SiO masers are most likely tracing the position of QX Pup, the Mira near the center of OH 231.8+4.2. This position is, however, clearly offset by ∼1 from the axis of the bipolar outflow traced by the OH maser emission. These results suggest the presence of a binary system: one invisible star powering the bipolar outflow and the other, the Mira star QX Pup, associated with the H2O and SiO masers. This scenario requires that the two stars have evolved at very similar rates.
H2O maser emission from the Seyfert 2 galaxy IC 2560: evidence for a super-massive black hole and a probe for mass-accretion rate
Authors: Ishihara Yuko , Nakai Naomasa , Iyomoto Naoko , Makishima Kazuo , Diamond Phil , Hall Peter
Published: June 2019

Our observations of H2O masers have detected some high-velocity features and a secular velocity drift of the systemic features in the Seyfert 2 Galaxy IC 2560. The high-velocity features were blue- and red-shifted from the systemic velocity of 220-420 km s−1 and 210-350 km s−1, respectively. The velocity of the systemic features drifted at a secular rate of 2.62 km s−1 yr−1. Assuming the existence of a compact rotating disk as in NGC 4258, IC 2560 possesses a nuclear disk with inner and outer radii of 0.07 pc and 0.26 pc, respectively, and a confined mass of 2.8 × 106M⊙ at the center, making the central density > 2.1 × 109M⊙ pc−3. Such a dense object cannot be a cluster of stars, and this strongly suggests that the central mass is a super-massive black hole. Since the 2-10 keV luminosity of IC 2560 is 1 × 1041 erg s−1, the mass accretion rate of the suggested black hole must be 2 × 10−5M⊙ yr−1.