bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal Line Blanketed Non-LTE Model Atmospheres for Central Stars of Planetary Nebulae
Authors: Werner K. , Dreizler S.
Published: June 2019

Absorption lines of highly ionized iron group elements dominate the UV spectra of many hot stars. They were identified in several central stars as well as in sdO stars, in PG 1159 stars and in the hottest DO and DA white dwarfs. Due to the high effective temperatures atmospheric modelling including metal line blanketing has to be done under NLTE conditions. Adequate models have become available only very recently (Dreizler & Werner 1992). We present new NLTE model atmospheres blanketed by some 120 000 lines from iron group elements (Sc through Ni). We adopted Anderson's (1991) statistical approach along with an opacity sampling technique using our Accelerated Lambda Iteration (ALI) code. We generally found:

— Many strong metal lines cause substantial blocking at the flux maximum.

— The temperature in the continuum forming layers is increased by backwarming due to iron group lines; outer layers, cooled by CNO lines, are unaffected.

— The line profiles of H and He become deeper and broader, indicating that the neglect of NLTE metal line blanketing could cause the discrepancies encountered when fitting He II and H I lines in hot subdwarfs.
Electron Density and Nitrogen Abundance from FIR Lines
Authors: Rubin R.H. , Colgan S.W.J. , Erickson E.F. , Haas M.R. , Lord S.D. , Simpson J.P.
Published: June 2019

In order to study the physical properties of nebulae and determine their elemental abundances, it is important to observe lines from many different ionic species. Such studies have been enhanced in recent years with the measurement of lines in the far-infrared (FIR). The [N III]57μm line provides a way to assess the N++ abundance – which is not readily done from any other spectral region. Recent detection of the [N II]122 and 205μm lines provides a new way to assess both the electron density in the N+ region and the total N abundance in an object. When there are few observations to warrant a detailed modeling approach, it may be necessary to use another approach which has been referred to as a semi-empirical method (hereafter SEM) (e.g. Aller 1984). We delineate a SEM scheme for doing this and apply it to observations for the H II region G333.6–0.2.
Radiation Charge Exchange and Radiation Ion-Atom Recombination as a Source of Continual E-M Radiation from Astrophysical Plasma
Authors: Mihajlov A.A. , Dimitrijevic M.S. , Ermolaev A.M.
Published: June 2019

We show that for the study of emission from weakly ionized low temperature hydrogen plasmas, the processes A+ + A → A+ + A + ħω and A+ + A → A+2 + ħω (where A denotes a neutral atom in ground state and, A+ and A+2 atomic and molecular ions) must be treaded as a source of continual electro–magnetic radiation from low temperature plasma. Both reaction channels are treated separately and the corresponding total and separate spectral intensities are determined for hydrogen plasma at T < 10000K. The obtained results have been also compared with the corresponding spectral intensities for electron–ion bremsstrahlung and electron–ion photorecombination.
Probable Type I Planetary Nebulae
Authors: Moreno H. , Gutierrez-Moreno A. , Cortes G.
Published: June 2019

During a program of observations of planetary nebulae (PN) made at CTIO in 1982 using the 1.5 m telescope equipped with a Cassegrain spectrograph and a Vidicon detector, and repeated in 1991 using the same configuration with a CCD detector, we found four PN for which Hα < [N II] λ6583: He2-109, He2-145, He2-152, and He2-163. The analysis of the data was made using the computing facilities of Cerro Tololo Computing Center at La Serena, and of the Centro de Procesamiento Digital de Imágenes of the Departamento de Astronomía de la Universidad de Chile.
Collimating Discs and Bipolar Flows in SH 2–71
Authors: Cuesta L. , Phillips J. P.
Published: June 2019

Sh 2–71 appears to represent a diffuse, ellipsoidal nebulosity extending over a range Δα × Δδ = 1.7 = 3 arcmin2. Early spectroscopy by Glushkov et al (1975), and Chopinet and Lortet-Zuckerman (1976) suggested the presence of a high excitation central star, and Kaler (1983) has more recently determined Zanstra temperatures Tz(HeII) > 7.7 · 104 K. The observed central star clearly constitutes a much cooler companion, and luminosity variations in this source have been attributed to binary eclipse.
Spindles, Spheres and a Few Jets: The Radiation Gasdynamics of Planetary Nebulae
Authors: Frank Adam
Published: June 2019

We present the results of accurate numerical radiation-gasdynamic models for spherical (1-d) and aspherical (2-d) planetary nebulae (PNe). The models confirm and surpass previous efforts by recovering the detailed morphologies, kinematics, and ionization structure of real PNe. Our 1-d simulations include the evolution of the central star and a superwind/AGB wind interaction. The importance of the forward wind-blown shock and time-dependant ionization in redistributing mass in the nebulae is demonstrated. Our 2-d simulations, the first of their kind, confirm that aspherical PNe can develop through the interaction of a spherical fast wind with an aspherical superwind. We demonstrate that the full range of nebular morphologies can be recovered by considering the combination of wind/wind interactions, the ionization state of the gas and the projection angle on the sky
High Resolution Optical Imaging of Proto-Planetary Nebulae
Authors: Langill P.P. , Kwok Sun , Hrivnak B.J.
Published: June 2019

Several Proto–Planetary Nebulae (PPN) candidates have been observed at the Canada France Hawaii Telescope with the High Resolution Camera (HRCam) (McClure et al. 1989, PASP, 101, 1156). Candidates were selected based on their IRAS [12]–[25] and [25]–[60] colors and their lack of variability. With HRCams' small angular pixel size (0.13″/pixel) and active optics we achieved an average angular resolution of 0.65″ in V and I waveband images.
High-Resolution Radial Velocity and Hα Study of Proto-Planetary Nebulae
Authors: Hrivnak B.J. , Woodsworth A.W.
Published: June 2019

We are engaged in a program to monitor radial velocity variability in proto-planetary nebulae (PPN). Observations are being made with the radial velocity spectrometer at the DAO, with a precision of ±0.5 km s−1. Radial velocity variability can arise from binary motion and/or pulsation in these post-AGB stars. The demonstration of a binary nature for some of these objects can have important implications for the understanding of their physical properties, and for the shaping of their circumstellar shells.
Shock Modelling and High Resolution Spectroscopy of NGC 6905
Authors: Cuesta L. , Phillips J. P.
Published: June 2019

NGC 6905 appears to be an unusual source in displaying conical outflow lobes superimposed upon a spheroidal inner shell.
Further Models of Planetary Nebula Spectral Evolution
Authors: Volk K.
Published: June 2019

Four new calculations of planetary nebulae spectral evolution are presented, as in Volk (1992). These models use the 0.64 M⊙ central star evolution track of Schönberner (1983) but with the rate of evolution accelerated by a factor of 2, as the original models evolve to the planetary nebula phase too slowly to match the observations. Models were calculated for mass-loss rates of 2.1 × 10−5 and 5.2 × 10−5 MM⊙ yr−1 using solar composition and silicate dust, and using the average observed planetary nebula composition and graphite dust. An interacting winds shell was assumed to form. The model results were combined with an assumed Galactic distribution of 25000 planetary nebula to simulate a variety of observables including V magnitudes, Hβ fluxes, the IRAS colours, the 5 GHz radio flux densities, and the nebular radii.
HST Observations of the Nuclei of EGB 6 (0950+139) and Abell 58 (V605 Aql)
Authors: Bond Howard E. , Meakes Michael G. , Liebert James W. , Renzini Alvio
Published: June 2019

This paper deals with the central stars of two large, low-surface-brightness planetary nebulae: V605 Aquilae, central star of Abell 58, and 0950+139, central star of EGB 6. Both of these nuclei are associated with compact emission-line nebulosities, which are unresolved from the ground. We obtained images with the Faint Object Camera (FOC) on the Hubble Space Telescope of both objects, in order to determine the nature of the compact nebulae.
The Helium-to-Metals Enrichment Ratio in Planetary Nebulae
Authors: Chiappini C.M.L. , Maciel W.J.
Published: June 2019

The helium-to-metals enrichment ratio (dY/dZ) and the pregalactic helium abundance (Yp) are important parameters for the understanding of the galactic chemical evolution, and also as a cosmological test to the Big Bang theory. In this work, we present a new determination of these parameters based on a sample of galactic HII regions, HII galaxies, and planetary nebulae.
Astrometry and Photometry of 400 Million Stars Brighter than 18 Mag
Authors: Høg E.
Published: June 2019

A satellite mission for accurate astrometry and multi-colour photometry is discussed, similar in principle to the ESA Hipparcos mission and here called theRoemer mission.The limiting magnitude will be aboutV= 18 mag while 13 mag is the limit of the present Hipparcos mission. Luminosities of stars up to 2 kpc away can be obtained, corresponding to a volume 10000 times larger than with Hipparcos. A mission of 5 years will provide an accuracy of 0.1 milli-arcsec at 12th magnitude for positions and parallaxes and 0.05 milli-arcsec for annual proper motions. This is achieved by a satellite using a mosaic of CCD detectors in the focal planes of two beam-combiner telescopes of 0.29 m aperture. The instrument is described and the expected performance with an input catalog of 400 million program stars is given.
Research of the Kinematic of the Gould Belt
Authors: Xu Tongqi , Lin Qing
Published: June 2019

Using the proper motions, radial velocities and distances of bright O, B stars taken from the FK5/FK5 suppl. stars, the velocity field of the Gould belt stars has been analysed. The results have been compared with that of the FK4 stars given by Fricke and Tsioumis.
A New Proper Motion Survey of the Pleiades Cluster
Authors: Schilbach E. , Guibert J. , Geffert M. , Hirte S.
Published: June 2019

A programme for the determination of proper motions and photographic B, V, R magnitudes for stars up to 18m within a 4° by 4° region centered near Alcyone is described. We use MAMA measurements of plates taken with Tautenburg and OCA Schmidt telescopes as well as with the double refractor of Bonn and Carte du Ciel plates. To check the stability of the solution three different methods of reduction are applied.

According to the results of the pilot programme a final proper motion accuracy of about 2 mas/a can be achieved for the majority of stars in the survey.
Comparing Parametric and Nonparametric Statistical Methods for Studying the Velocity Distributions of Population I Stars
Authors: Arenou F. , Bougeard M. L.
Published: June 2019

This Paper investigates population I star samples from the viewpoint of the velocity distributions, each being viewed as a mixture. To obtain information on the class centers, clustering techniques are first applied. Secondly, we use a parametric maximum likelihood formulation that we solve by Redner-Walker's E.M. algorithm. The obtained results are compared and discussed from an astrophysical viewpoint.
Derivation of the initial luminosity function and the past rate of star formation
Authors: Schmidt M.
Published: June 2019

The initial luminosity function ψ(Mv) was introduced by Salpeter. He assumed uniform formation of stars and derived the initial luminosity function from the observed main-sequence luminosity function and the life time of a star of magnitude Mvon the main sequence. Recently van den Bergh considered the depletion of the interstellar gas by star formation. He found that at a constant rate of star formation the gas in the solar vicinity will be exhausted about 7 × 108years from now.
Rate of mass loss by stars of different classes
Authors: Mustel E. R.
Published: June 2019

The present communication contains mainly the discussion of the problem of mass loss by stars of early classes. The investigations show that the loss of mass by the Sun may proceed in different ways. In the atmospheres of O stars different mechanisms of ejection of gases must also exist: thermal dissipation of gases, the ejection of prominences (electromagnetic mechanisms), the ejection of atoms by radiation pressure, the ejection of atoms from active regions which may exist in the atmospheres of O-Stars, a very rapid rotation of stars etc. However our present knowledge on the mechanisms of ejection of gases from the surface of stars of early types is extremely scanty. Therefore it seems that there exists only one way to estimate the rate of mass loss by O-stars. This is the investigation of those effects which can be produced by gases ejected from the star.
The Stellar Kinematics of Elliptical Galaxies
Authors: Davies Roger L.
Published: June 2019

The kinematic properties of elliptical galaxies are summarized. New developments are discussed in four areas: (i) the Faber-Jackson relation and the role of second parameters (ii) the luminosity-rotation relation (iii) the figures of elliptical galaxies and (iv) the mass-to-light ratio as a function of radius.
Dust and Gas: Overview
Authors: Schweizer François
Published: June 2019

Progress in the 50 years since the discovery of ionized gas in NGC 1052 is reviewed. As discovery has proceeded from H II to H I and recently to 107 K gas, the known amount of gas in ellipticals has increased dramatically: from 103–6M⊙ for H II, to 105–9M⊙ for H I in some 15% of E's, to 109–10M⊙ for the X-ray emitting gas. Although a few ellipticals with dust have long been known, recent CCD surveys have revealed dust lanes in nearly half of all E's. The cooler gas — as traced by H I, warm H II, and dust — is generally distributed in the form of a disk that often shows an outer warp. To deduce the true shapes of ellipticals from the geometry and kinematics of such disks has proven a challenging task. There is mounting evidence that many disks consist of gas accreted by mass transfers and mergers, and that some of them may not yet have reached dynamical equilibrium. Some of the major unsolved problems concern the atmospheric balance between sources and sinks of gas, and the importance of cooling flows and galactic winds.
Spherical Galaxies: Methods and Models
Authors: Richstone Douglas O.
Published: June 2019

Over the last 5 years, considerable progress has been made in our ability to construct self-gravitating stellar equilibria. One of these new methods is essentially a variant of Eddington's (1916) method. Two other key approaches are logical extensions of Schwarzschild's Linear Programming method, and can be applied to nonspherical models as well. These methods are reviewed below.

The application of these methods to galaxies has yielded a few very interesting results within the last year or two. The methods described below unambiguously establish M/L's for M87 and M32 within about 30 arc seconds. They strongly support Tonry's contention that the nucleus of M32 contains a large invisible mass, possibly a 107M⊙ black hole. They also suggest that observational recovery of the projected velociy distribution might permit the observer to distinguish between a massive halo and an increasingly tangential velocity distribution function.
Correlations between r1/4-Law Parameters for Bulges and Elliptical Galaxies
Authors: Hamabe Masaru , Kormendy John
Published: June 2019

The correlation between the effective radius re and surface brightness μe for elliptical galaxies is a fundamental scaling law that theories of galaxy formation must explain. When re and μe are derived by fitting two-parameter fitting functions such as the de Vaucouleurs r1/4 law to brightness profiles, the errors in the parameters are strongly coupled. The purpose of this paper is to rederive the μe(log re) relations for ellipticals and bulges, taking account of the coupling in the errors and using only high-accuracy CCD data. Our preliminary conclusions are: (1) The coupled errors are too small to affect significantly the correlation derived for elliptical galaxies. (2) The correlation for bulges is not very different from that for ellipticals, but the galaxy sample is small and the errors in the parameters are large due to the inherent uncertainty in bulge-disk decomposition.
Surface Photometry of Bright Ellipticals
Authors: Schombert James M.
Published: June 2019

Surface brightness profiles of bright ellipticals (MV < −17, Ho = 100) in rich clusters and the field are reduced to structural parameters. Most fitting functions are found to be inadequate in describing the overall shape of profiles with only the r1/4 law providing a good match over the range of surface brightness from 19 to 24 mag arcsec−2. The systematic deviations in structure of first-ranked ellipticals from normal ellipticals (i.e. enlarged characteristic radii and shallow profile slopes) are well explained by comparison to the N-body simulations of merging systems from Duncan, Farouki, and Shapiro (1982).
The Unusual Box-Shaped Elliptical(?) Galaxy IC 3370
Authors: Jarvis Brian
Published: June 2019

Photometic and kinematic observations are presented for the box-shaped “elliptical” galaxy IC 3370, that show that this galaxy has characteristics more akin to an S0 galaxy than an elliptical and should be classified Sopec.
Gas, Dust and Radio Emission in Elliptical Galaxies
Authors: Sparks W. B.
Published: June 2019

CCD data are used to compare the isophotes, colour and dust-content of radio (1021<P5GHz<1024WHz-1, HO = 75kms-1Mpc-1) and radio-quiet ellipticals. Radio ellipticals are round but not spheroidal, reddened and occasionally have disturbed dust lanes. X-ray emission correlates with both radio emission and shape. Detailed investigations of dust in NGC 1316 reveal a possible nuclear gas disc orthogonal to the radio jet.
Ultraviolet Energy Distributions of (32) Early–Type Galaxies
Authors: Bertola F. , Burstein D. , Buson L.M. , Faber S.M. , Lauer T.R.
Published: June 2019

New, self–consistent energy distribution have been generated from 52 short – wavelength and 40 long–wavelength IUE spectra of 31 early–type galaxies, plus the bulge of M31. All galaxies in this sample have measurements of the absorption–line index Mg2 and central velocity dispersion, and a (1550–V) color is determined by combing the IUE data with photoelectrically–measured V magnitudes.
Integrals of Motion in an Elliptical Galaxy Model
Authors: Wilkinson Althea , de Zeeuw Tim
Published: June 2019

The structure of a galaxy model is described completely by its phase–space distribution function f. By Jeans' Theorem f can be written as a function of the integrals of motion admitted by the potential of the model. Various independent combinations of the integrals may be used as arguments of f; in many cases the action integrals are to be preferred. For a general N–body model, these can be obtained by numerical integration and subsequent spectral decomposition of each orbit (Binney and Spergel 1984).
Violent Relaxation and Mixing in 1-D Gravitational Systems
Authors: Luwel Marc
Published: June 2019

The one dimensional gravitational model consists of N mass sheets with surface density mi, parallel to the (y, z)–plane and constrained to move along the x-axis under influence of their mutual gravitational force Fij = −2πGmimj sgn(xi – xj). in order to study the evolution of this one–dimensional system, the N Newtonian equations of motion are integrated numerically, using an “exact” double precision algorithm.
Quadratic Integrals of Motion and Stellar Orbits in the Absence of Axial Symmetry of the Potential
Authors: Kuzmin G.G.
Published: June 2019

As is well known, in the case of an axially symmetric and time-invariant gravitational potential, if the potential satisfies one particular additional constraint, there exist three isolating integrals of motion: the energy integral, the area integral, and the third integral which is quadratic in the velocities. This work discusses the case in which there exist quadratic integrals in the absence of axial symmetry of the potential. Such a case has already been examined by Eddington [1], but in their explicit form, the integrals were introduced by Clark [2].
Gas and Dust in the Inner Few Degrees of the Galaxy
Authors: Güsten Rolf
Published: June 2019

This review discusses the complex morphology and perturbed kinematics, as well as the outstanding physical characteristics of the interstellar medium within a few 100 pc of the galactic center. A total of ~107.9 Mo of dense molecular gas, representing ~10% of the Galaxy's neutral mass content, has settled in a thin layer [size: 450 × 40 pc], composed of giant molecular cloud complexes. The spatial distribution is highly asymmetric with respect to the center, and motions differ considerably from equilibrium conditions. The dynamical situation is still obscure (explosive event vs. response to distorted gravitational potential), but any disturbance must have occurred quite recently (τdy ~106 yr). Evidence for large–scale star–forming activity is reviewed, and for a standard IMF, a total star formation rate Φ ~0.5 M0 yr−1 is inferred.

The galactic center clouds differ considerably in their physical and chemical characteristics from GMC's in the outer Galaxy. Pervasive high bulk gas temperatures (Tkin ~70 K), mean H2 densities of n ~104 cm−3, and linewidths ≥10–20 kms−1 are probably a consequence of the clouds' location in the steep gravitational potential of the central bulge.
IRAS Observations of the Galactic Center
Authors: Cox P. , Laureijs R.
Published: June 2019

IRAS observations of the Galactic Center are presented. The maps at 12, 25, 60 and 100 μm have a typical resolution of a few arcmin and cover an area 6×2 deg2 centered on SgrA. All data have been corrected for the zodiacal light contamination and for the diffuse emission associated with the galactic disk. The infrared radiation originating in the Galactic Center arises from well-defined sources which can be identified with known radio sources and from an extended emission which accounts for most of the infrared luminosity. The total infrared luminosity associated with the Galactic Center (area 3°×2°) amounts to 109L⊙. The sources contribute 10% to this luminosity. A comparison with surveys in the radio continuum and in the near infrared is presented. Results are analyzed in terms of star formation history. In particular, it is suggested that the dominant heating source for the dust is the population of cool stars - K and M giants - comprising the galactic nucleus.
On Heating, Ionization, and Star Formation in the Galactic Center Region
Authors: Morris Mark
Published: June 2019

The ionization of interstellar gas and the heating of dust near the galactic center are usually assumed to be dominated overall by the radiation emanating from young, massive stars. This paper questions that assumption by pointing to the paucity of direct evidence for current star formation and by considering alternative sources of ionization and luminosity. It is suggested that star formation can be inhibited by the strong, poloidal magnetic fields observed in the galactic center. The presence of some red supergiants (e.g., IRS7) can be understood if massive star formation occurs episodically.
Distribution of the H2O Masers in the Sagittarius B2 Core
Authors: Kobayashi H. , Ishiguro M. , Chikada Y. , Ukita N. , Morita K-I , Okumura-kawabe S. , Kasuga T. , Kawabe R.
Published: June 2019

The distribution of H2O masers in the Sgr B2 core was observed with a 2.5′×2.5′ wide field and with 540 km s−1 total velocity coverage by the Nobeyama Millimeter Array. Thirty-nine resolved maser spots were detected with a relative positional accuracy of 0.3″, which are clustered into four separate regions. In Sgr B2 north, the cluster lies at the edge of the continuum ridge. One of the maser spots shows strong and wide velocity-spread emission, suggesting it may correspond to a center of star forming activity. In Sgr B2 main, the strong maser spots are projected just on the face of a compact HII region, and are red-shifted relative to the central velocity of the HII region. There are two possibilities to interpret our results in Sgr B2 (M). One is that the H2O maser spots are distributed around the HII region and are infailing to the HII region. The other is that the H2O maser sources are associated with the cloud in the foreground of the HII region.
OH in the Environment of Sgr A
Authors: Sandqvist Aa. , Karlsson R. , Whiteoak J. B.
Published: June 2019

The 18-cm distribution of OH in the Galactic Center region near Sgr A has been mapped in all four of the 1612, 1665, 1667 and 1720 MHz OH absorption lines using the VLA with 4 arcsec angular resolution and 9 kms-1 velocity resolution. The OH gas at +50 and +20 kms-l is seen clearly in absorption against the shell structure of Sgr A East but not against the spiral structure of Sgr A West, possibly implying that this molecular gas lies between the two continuum components - behind Sgr A West and in front of Sgr A East. Inside the Circumnuclear Disk, there is a new neutral streamer which sweeps from the disk in towards Sgr A∗ as the observed radial velocity decreases from +78 to +16 kms-1. The streamer may have a negative-velocity counterpart on the opposite side of Sgr A∗.
Mapping the Galactic Center Region with GRASP
Authors: Durouchoux Ph. , Bignami G. , Dean A. , Lund N. , McBreen B. , Schonfelder V. , Swanenburg B. , Vedrenne G. , Winkler C.
Published: June 2019

The GRASP mission (Gamma-ray Astronomy with Spectroscopy and Positioning) is currently under study as an ESA space astronomy mission to be launched in the mid 90's. GRASP is designed as a high quality spectral imager (E/ΔE ≈ 500 at 1 Mev) with positioning to the arc minute level within a large field of view (≈7°) which operates over a wide spectral range (30 Kev-100 Mev) with a 3σ sensitivity of typically 10 mcrab or better over the entire operational range within an observational period of ≈105 seconds. In this paper, we will mainly discuss the capability of the instrument with respect to the study of both point source and diffuse source measurements of the galactic center region.
A short-lived flare of EV Lacertae
Authors: Zhilyaev B. E. , Romanjuk Ya. O. , Svyatogorov O. A.
Published: June 2019

Flare events on a time scale of the order of one second were observed on EV Lac by Gershberg and Petrov [1], Zalinian and Tovmassian [2], Tsvetkov, Antov and Tsvetkova [3]. The nature of such phenomena is very mysterious. We hope that monitoring of EV Lac with high time resolution will yield the information about growing and decay times as well as fine structure of the light curve and color one. A short-lived flare of EV Lac was recorded in U and V bands in 1989, September 3 2h 14m 30s UT. The duration of the event was about 150 milliseconds.
Statistics of flares observed for UV Ceti type stars YZ CMi, AD Leo, and EV Lac at the Okayama Observatory
Authors: Ishida K.
Published: June 2019

Photoelectric monitoring of flare stars YZ CMi, AD Leo, and EV Lac has been done at the Okayama Observatory since early 1970s. This is a simultaneous UBV observations with a high time resolution. Some statistics of the flares of the UV Ceti type stars are presented.
Distribution of red dwarfs in general galactic field on the basis of stellar star statistics
Authors: Garibjanian A.T. , Hambarian V.V. , Mirzoyan L.V. , Mirzoyan A.L.
Published: June 2019

The mathematical expectation for detection of stellar flare on UV Ceti type stars in the solar vicinity during photographic patrol observations with 40″ Shcmidt camera of the Byurakan Astrophysical Observatory is estimated. We use the luminosity function of the flaring red dwarfs the assume a uniform distribution in the general galactic field. Comparison with the results of photographic patrol supports this assumption. The numbers and total mass of the flare and non-flare red dwarf stars in the Galaxy for the uniform distribution are determined. They are not in contradiction with Oort's estimate of total mass of red dwarfs.
On two possible groups of flare stars in Pleiades
Authors: Mirzoyan A.L. , Mnatsakanian M.A.
Published: June 2019

The correlation between the magnitude of the proper motion and the mean frequency of flares for flare stars in the Pleiades cluster region is discussed. The magority of them are physical members of this star cluster. It is shown that there exist probably two groups of flare stars which differ each other by their parameters, in particular by the magnitude of proper motions. A possible explanation of this phenomenon is suggested.
The relative number of flare stars in systems of different ages
Authors: Hambarian V.V. , Garibjanian A.T. , Mirzoyan L.V. , Mirzoyan A.L.
Published: June 2019

The problem of flare activity frequency among red dwarf stars is discussed. The observational data on stars in Orion, Pleiades and solar vicinity are used. It is shown, that relative number of flare stars among all red dwarf stars in the considered samples is increasing towards the lower luminosity stars. The flare stars are found in the considered samples begining with a definite luminosity, this limiting luminosity being decreased with the aging of the system which includes flare stars. A possible explanation of the observed phenomenon is given.
T Tauri stars and flare stars: common properties and differences
Authors: Appenzeller I.
Published: June 2019

T Tauri stars and flare stars are both magnetically active late-type stars of low mass and low to moderate luminosities. The flares observed in these two classes of variables show similar properties and, thus, probably have the same physical origin. On the other hand, at least the majority of the classical T Tauri stars seem to be surrounded by cool, dusty (accretion) disks, which are absent or undetectable in most classical flare stars.
The statistical analysis of the optical and infrared luminosities of young stars
Authors: Movsessian T.A.
Published: June 2019

The infrared IRAS data for supposed sources of optical outflows and young stars in Taurus-Auriga complex are studied. It is shown that there exists a group of stars with extremely low optical and infrared luminosities. It's suggested, that they are the stars with anisotropic sourface activity.
Timing Detection of Eclipsing Binary Planets and Transiting Extrasolar Moons
Authors: Doyle Laurance R. , Deeg Hans-Jörg
Published: June 2019

We investigate the improved detection of extrasolar planets around eclipsing binaries using eclipse minima timing and extrasolar moons around transiting planets using transit timing offered by the upcoming COROT (ESA, 2005), Kepler (NASA, 2007), and Eddington (ESA 2008) spacecraft missions. Hundreds of circum-binary planets should be discovered and a thorough survey of moons around transiting planets will be accomplished by these missions.
Interstellar Dust and the Organic Inventories of Early Solar Systems
Authors: Whittet D. C. B.
Published: June 2019

Interstellar dust grains are vectors for cosmic carbon and other biogenic chemical elements. They deliver carbon to protoplanetary disks in various refractory phases (amorphous, graphitic, etc.), and they are coated with icy mantles that contain organic molecules and water. The nature of the organics present in and on the dust appears to be closely related to physical conditions. Complex molecules may be synthesized when simple ices are irradiated. Astronomical observations show that this occurs in the vicinity of certain massive protostars, but it is not known whether our Solar System formed in such a region. Organic matter does not survive cycling though diffuse regions of interstellar space; any organics delivered to the early Earth must have originated in the parent molecular cloud, or in the solar nebula itself. A key question is thus identified: What was the star-formation environment of the Solar System? Possible constraints are briefly discussed.
Meteor Storms as a Window on the Delivery of Extraterrestrial Organic Matter to the Early Earth
Authors: Jenniskens P.
Published: June 2019

The unique rarefied flow and flash heating in meteors creates physical conditions that can change exogenous organic matter into unique prebiotic molecules. with the exception of rare giant comet impacts, most infalling matter at the time of the origin of life was deposited in the atmosphere during the meteor phase. Much new data has been obtained from observations in the Leonid Multi-Instrument Aircraft Campaign; a series of NASA and USAF sponsored Astrobiology missions that explored the 1998–2002 Leonid meteor storms. Here, we provide an overview of some of this recent insight, which provides a framework in which the prebiotic chemistry can be studied.
A High Resolution Survey of OH Masers in the Southern Hemisphere with a Parasitic SETI Program
Authors: Lemarchand Guillermo A.
Published: June 2019

We describe the ongoing high and ultrahigh-resolution survey of OH masers in the southern hemisphere. The study is made using one of the 30-m antennas of the Argentine Institute for Radioastronomy (IAR) connected simultaneously to two different spectrometers: (a) one 1008 channel correlator with a spectral resolution of 33 to 312 Hz, and (b) an eight million channel analyzer with a spectral resolution of 0.05 Hz (META II). The observations are performed with a high-gain feed with 35K system temperature. The preliminary survey is concentrated within a list of 24 strong OH masers at 1665 and 1667 MHz. The purpose of our research is to test theoretical considerations about the mechanisms of temporal variation in OH masers as well as the possible use of OH masers as natural amplifiers of extraterrestrial artificial signals.
The Technological Adolescent Age Transition: A Boundary to Estimate the Last Factor of the Drake Equation
Authors: Lemarchand Guillermo A.
Published: June 2019

Based on the study of several long-term societal indicators we estimate the phase transition between the “Technological Adolescent Age” (TAA) and the “Technological Mature Age” (TMA). Assuming the “Principle of Mediocrity” and using the Drake Equation we estimate a lower threshold for the number of technological civilizations in the galaxy.
SETI and the Media
Authors: Shostak Seth
Published: June 2019

Of all the research areas of modern discovery science, few attract more attention than the search for extraterrestrial intelligence. This is partially due to the fact that SETI is accessible, since the public can readily understand the goals of the research. The man in the street also finds SETI particularly exciting, a fact reflected by the ubiquitous presence of extraterrestrials in popular culture. The media interact with SETI in three areas: (1) reporting on research efforts, (2) being the principal conduit of information in case of a SETI detection, and (3) linking the subject deliberately or otherwise to the many stories of alien visitation. In this paper we will discuss the way science meets the media, and how and whether this often dicey relationship might serve to raise the general level of science literacy.
Resolution and evolution of the core of the giant HII region NGC 3603
Authors: Hofmann K.-H. , Weigelt G. , Seggewiss W.
Published: June 2019

We present diffraction-limited speckle-masking observations of the central object HD 97950 in the giant HII region and star cluster NGC 3603. Twenty-eight stellar components have been detected in the 6.″3 x 6.″3 field from our reconstructed images. Four different filter combinations were used for the selection of distinct spectral regions comprising Hα emission, the main Wolf-Rayet and Of-type emission lines, and two continuum bands. Stellar components having WN-type characteristics have been found. A color-magnitude diagram has been constructed. Isochrone fits yield a cluster age of about 3.2 Myr, which is in accordance with the time-scale of Wolf-Rayet star evolution.
Ring nebulae around moving Wolf-Rayet stars
Authors: Brighenti F. , D'Ercole A.
Published: June 2019

We present 2D numerical simulations of evolving ring nebulae around moving Wolf-Rayet stars. We have considered the interaction of the fast WR wind with the circumstellar matter modified by the previous action of the slow RSG wind. The resulting shell morphology is far from spherical and shows scallops due to several kinds of instabilities. The exact appearance of the ring nebula depends on the value of several parameters such as the unperturbed medium density and the velocity of the star.
Model atmospheres and spectral analyses of Wolf-Rayet stars
Authors: Hamann W.-R.
Published: June 2019

Stratified non-LTE models for expanding atmospheres have become available in the recent years. They are based on the idealized assumptions of spherical symmetry, stationarity and radiative equilibrium. The satisfactory agreement between calculated and observed Wolf-Rayet spectra suggests that this “standard model” is basically adequate for describing real WR atmospheres and hence can be applied for their quantitative spectral analyses. By the application of these models, the fundamental parameters have been determined meanwhile for the majority of the known Galactic WR stars. Most WN stars populate a vertical strip in the Hertzspung-Russell diagram at effective temperatures of ≈35 kK, the luminosities ranging from 104.5 to 105.9L⊙. Only three WN stars of earliest subtype, other early-type WN stars if they have strong lines, and the WC stars are hotter. The chemical compositions of the WR atmospheres correspond to nuclear-processed material (WN: hydrogen burning in the CNO cycle; WC: helium burning). Hydrogen is depleted but still detectable in the cooler members of the WN subclass. Quantitatively, the hydrogen abundances show an interesting correlation with the luminosity which can be compared with the predictions from evolutionary calculations.
The radial velocity variations of WR46 (WN3p)
Authors: Niemela V.S. , Barbá R.H. , Shara M.M.
Published: June 2019

Spectral observations of the WN3p star WR46 (HD 104994) obtained during June 1993 and January/February 1994 display large amplitude radial velocity variations of the strong emission lines Nv 4603-19Å and HeII 4686A, on a time scale of a fraction of a day. The most probable period found is 0.311 d, similar to the photometric period found by previous authors. The amplitude of the radial velocity variations of Nv emission is almost twice that of HeII. Noting the similarity of WR46 with low mass X-ray binaries, we suggest that the emission line spectrum corresponds to that of a luminous accretion disk in an evolved binary system.
Polarization in Wolf-Rayet binaries: Monte Carlo simulations
Authors: Rodrigues Cláudia V. , Magalhães Antonio Mário
Published: June 2019

We present some results on circumstellar envelopes using a Monte Carlo code we are developing. In contrast to analytical approaches, the effects of multiple scattering and the finite sizes of sources and envelope have been incorporated in the models. As an illustration, we fit the light-curve of V444 Cyg as well as the modulation of the linear polarization throughout its orbit.
The evolution of close binary stars: conditions in the winds
Authors: de Greve J.P.
Published: June 2019

The influence of mass transfer in an OB-type binary on the colliding wind characteristics of the following phase of WR binary is examined. We look to the changes in composition and orbital characteristics. Special attention is given to the formation of WR+OB systems and the colliding wind characteristics. The mass-luminosity behaviour after mass transfer is examined. We discuss the influence of the internal state, the composition of the wind, and rotational effects on the mass gainer. Recent models of both single stars and close binaries allow us to derive the dependence of these characteristics on the initial masses of the components. From this, constraints for the wind regimes at the WR+OB stage result.
Models of rotating Wolf-Rayet stars
Authors: Fliegner J. , Langer N.
Published: June 2019

We explore the influence of rotation on the evolution of massive stars (40 M⊙). We find the evolution in the HRD, the initial-final mass relation, and the duration of the various WR phases to depend sensitively on the initial rotation rate. We predict that, independent of the initial rotation rate, the majority of WR stars should be slow rotators.
Dynamics of the wind of LBV stars
Authors: Israelian G. L. , Nikoghossian A. G. , Tambovtseva L. V.
Published: June 2019

Luminous Blue Variables are among the brightest objects and lie at the Humphreys-Davidson empirical limit of maximum luminosity (Lamers 1986b). A distinct feature of these stars is the higher rate of mass loss and the relatively lower terminal velocity than for other stars of the same spectral type. LBV stars show moderate photometric variations with ΔV ⋍ 1 — 2m. They have higher Ṁ and lower v∞ when they are brighter (i.e., have a low Teff). These stars probable represent a short phase in the evolution along the chain O → Of → LBV → WR. After investigating the dynamics of the wind of P Cygni, Lamers (1986a) concluded that the wind was best explained by radiation pressure arising from a large number of optically thin lines in the Balmer continuum. Recently Chen & Marlborough (1993) applied this driving mechanism to Be stars. Application of this mechanism to P Cygni has been criticized by Pauldrach & Puls (1990) who found that P Cygni's wind is driven by radiation pressure due to both optically thick (60 %) and optically thin lines and that it gives rise to the typical β velocity law. In our calculations we used a method developed by Vilkoviskij and Tambovtseva (1992). We assume that Teff, M*, R*, Ṁ and initial velocity v0 at the stellar surface are given. The input parameters have been taken from Lamers (1986b). All four LBV's (except P Cygni) are considered in their maximum phase, i.e., when their winds are expected to be driven by radiation pressure in optically thin lines. A constant value of vo = 20 km/s has been adopted. Force-multiplier parameters k and δ have been taken from Abbott (1982). If we assume that the acceleration of the wind is due to optically thin lines of metals in the Balmer continuum, than we must have α ≪ 1 (Abbott 1982). We stress that there are no calculations available to determine that quantity in the optically thin limit. We will estimate α later for P Cygni but for other stars we will use a as a free parameter. Note that α depends on the ratio of optically thick to optically thin lines in the wind. Basically k depends on the number of lines that produce radiation pressure and in our case a value of k can be even larger than given by Abbott (1982). The results of our calculations are presented in Table I. We give the values of v∞ calculated for the indicated values of input parameters. The terminal velocities are in good agreement with the observational data (Lamers 1986b).
A CCD spectroscopic orbit and line-variability near periastron for HD 193793
Authors: Hervieux Yannick
Published: June 2019

Since 1987 we have been observing long-period WR binaries about once every two months with the 1.6m telescope at Observatoire du mont Mégantic. The spectra cover the range λλ ∼ 4000—6000Â with 2-pixel resolution (∼2.5Â) and S/N ∼ 500 in the strongest line-peaks. We present a new orbit obtained from several lines in the WC7 and the O4—5 components of the binary system HD 193793 (WR140) and discuss emission-line variability especially in the 2—3 month interval around periastron.
Some results of high-speed two-channel photometry of Wolf-Rayet stars with suspected compact companions
Authors: Zhilyaev B. E. , Khalack V. R. , Verlyuk I. A.
Published: June 2019

Strong transient chaotic high-frequency activity has been detected in WR148 on a time scale of a few minutes. The main property is the variability of the fluctuation power, not the light-curve. The same is true for WR136 but with a more permanent pattern. The power of fluctuations is of order of thousandth relative to the steady intensity. The maximum fluctuation power lies in the frequency band of 25–50 Hz.
DASI: The Degree Angular Scale Interferometer
Authors: Leitch E. M. , Carlstrom J. E. , Davidson G. , Dragovan M. , Halverson N. W. , Holzapfel W. L. , Laroque S. , Kovac J. , Pryke C. , Schartman E. , Yamasaki M. J.
Published: June 2019

We describe the design and current status of the Degree Angular Scale Interferometer (DASI), a compact cm-wave interferometer operating at the Amundsen-Scott South Pole research station. With 20-cm diameter primary antenna elements operating over the frequency range 26 − 36 GHz, DASI is optimized to measure the power spectrum of the cosmic microwave background radiation (CMBR) over the multipole range 140 − 920, (corresponding to scales of 25′ − 2°.6), as well as make high-sensitivity maps of the microwave sky. The telescope was built at the University of Chicago and deployed at the South Pole during the 1999-2000 austral summer.
Cosmological Parameters from the 2dF Galaxy Redshift Survey
Authors: Colless Matthew
Published: June 2019

This paper describes the goals, current status and some preliminary results from the 2dF Galaxy Redshift Survey. In particular we present the most precise measurement to date of the redshift-space distortion parameter, β ≡ Ω0.6/b = 0.39 ± 0.05. Combined with recent CMB anisotropy measurements, our results strongly favour a low-density universe.
Cosmological Parameters and Hyper-Parameters: The Hubble Constant from Boomerang and Maxima
Authors: Lahav Ofer.
Published: June 2019

We generalise the procedure for joint estimation of cosmological parameters to allow freedom in the relative weights of various probes. This is done by including in the joint Likelihood function a set of ‘Hyper-Parameters’, which are dealt with using Bayesian considerations. The resulting algorithm is simple to implement. We illustrate the method by estimating the Hubble constantH0from the recent Cosmic Microwave Background experiments Boomerang and Maxima. For an assumed flat Λ-CDM model with fixed parameters (n= 1, Ωm= 1 - Δ = 0.3, Ωbh2= 0.03,Qrms= 18μK) we solve for a single parameter,H0= 79 ± 4 km/sec/Mpc (95 % CL, random errors only), slightly higher but still consistent with recent results from Cepheids. We discuss how the ‘Hyper-Parameters’ approach can be generalised for a combination of cosmic probes, and for other priors on the Hyper-Parameters.
Gravitational Lensing Studies of High Resolution Cluster Simulations
Authors: King Lindsay , Clowe Douglas , Schneider Peter , Springel Volker
Published: June 2019

In our ongoing work, we use high resolution cluster simulations to study gravitational lensing. These simulations have a softening length of 0.7h-1kpc and a particle mass of 4.68 × 107M⊙(Springel 1999). Questions that can be addressed include the accuracy with which substructure on various scales can be recovered using the information from lensing. This is very important in determining the power of lensing in studying the evolution of cluster substructure as a function of redshift. We briefly consider how a weak lensing non-parametric reconstruction technique and theMap-statistic can be applied to the simulations.
Imaging of 2-mm dust continuum emission towards S106 FIR and its spectral energy distribution
Authors: Furuya Ray S. , Kitamura Yoshimi , Wootten Alwyn , Claussen Mark J. , Kawabe Ryohei
Published: June 2019

The class 0 source S106 FIR is a good candidate to investigate a very early phase of star formation because of the presence of an AU-scale Microjet, discovered by our VLBA H2O maser observations and the absence of an extensive CO outflow. In order to reveal the properties of S106 FIR, we conducted observations of 2-mm continuum emission with the Nobeyama Millmeter Array. We detected a weak compact continuum emission around S106 FIR. We analysed the spectral energy distribution of S106 FIR. It is found that the dust temperature and the β index of the dust opacity range from 31 to 55 K and from 1.4 to 1.6, respectively. Using these results, we computed the mass of the core aound S106 FIR and the bolometric luminosity of 3.1 to 5.8 M⊙ and 230 to 1070 L⊙, respectively.