bluuebunny/crossref_metadata_2025 huggingface dataset:
Longpath Fourier Transform Spectra of Ammonia
Authors: D'Cunha R. , Urban S. , Narahari Rao K.
Published: June 2019

The ammonia molecule is known to be useful as a probe for studying conditions inside interstellar clouds and planetary atmospheres. Correct interpretation of interstellar and planetary spectra need to be supported by adequate laboratory measurements. in the present studies we report the high resolution Fourier transform spectra of ammonia recorded with a pathlength of 192m at the Kitt Peak National Observatory. Transitions with intensities that are two orders of magnitude weaker than those that have been reported earlier, have been observed and assigned. These include high J transitions, hot bands and forbidden transitions. These transitions are not saturated under long paths such as those available in planetary atmospheres and are therefore useful in the estimation of temperatures. The forbidden transitions have been processed with other relevant data to provide complete information on the energy levels. Such information is required for the calculation of equilibrium population of energy levels and partition functions, which go into the estimation of spectral intensities and abundances in terrestrial, interstellar and planetary atmospheres.
Theoretical Studies of Diffuse Cloud Chemistry
Authors: Black John H.
Published: June 2019

Some recent work on diffuse cloud chemistry is summarized. Distinctions between gas phase chemistry in steady state and alternative mechanisms are discussed.
Evolutionary Models of Interstellar Chemistry
Authors: Prasad Sheo S.
Published: June 2019

The goal of evolutionary models of interstellar chemistry is to understand how interstellar clouds came to be the way they are, how they will change with time, and to place them in an evolutionary sequence with other celestial objects such as stars. To this end, we present an improved Mark II version of our earlier model of chemistry in dynamically evolving clouds. The Mark II model suggests that the conventional elemental C/O ratio less than one can explain the observed abundances of CI and the non-detection of O2in dense clouds. Coupled chemical-dynamical models seem to have the potential to generate many observable discriminators of the evolutionary tracks. This is exciting, because, in general, purely dynamical models do not yield enough verifiable discriminators of the predicted tracks.
Inter Stellar Shocked Region Chemistry Certain Reactions between Interstellar Molecules and O and N Atoms
Authors: Ghosh K. K. , Saleem S. S. , Kutty K. N.
Published: June 2019

The reactions between O and N atoms and certain interstellar molecules (H2S, NH3, H2CO, CH3 OH, C2 H5 OH) are studied using the dynamicalflowing after glow method. It is found that NH and OH radicals are formed which can be used as a diagnostic probe to differentiate between interstellar shocked and heated regions.
Evidence for the Presence of Pre-Solar Grains in Iron Meteorites
Authors: Goel P. S.
Published: June 2019

Though it is now well accepted that some interstellar matter has been preserved in many stone meteorites, the suggestion that iron meteorites also contain pre-solar matter is a recent one. Experimental results will be presented that show that iron meteorites contain isotopically anomalous Xe, Os and Hg. In acid residues of iron meteorites Xe is often depleted in the lightest isotopes, 124Xe and 126Xe. Osmium in many residues is enriched in 184Os. the measured 196Hg/202Hg ratios in some residues of iron meteorites show values 30% of the normal ratio. This pattern is also noted in some portions of a stone meteorite (Ambapur Nagla). These results, while on one hand bring into focus the importance of iron meteorites as preservers of interstellar matter, on the other hand, suggest that the genesis of iron meteorites has been by a non-magmatic process.
New Observational Near-Infrared Spectroscopic Results on Several IRAS Sources with Emission Features
Authors: De Muizon M. , D'Hendecourt L.B. , Geballe T. R. , Baas F. , Perrier C.
Published: June 2019

We have obtained spectra in the three micron region of a sample of IRAS sources showing a strong 11.3 micron emission feature in their IRAS Low-Resolution Spectra (LRS). The observations have been carried out from ESO (La Silla, Chile) and from UKIRT (Mauna Kea, Hawaii), between March and September 1985. All sources but one turn out to have a more or less strong 3.3 micron emission feature, and additionally in most cases a feature at 3.4 micron, extending into a plateau from 3.45 to 3.60 micron. in one particular case we have resolved the plateau into 3 features at 3.45, 3.51 and 3.56 micron. These are detected for the first time.
A Survey and Related Observations of the Kiso Ultraviolet-Excess Galaxies
Authors: Takase B. , Maehara H. , Noguchi T. , Miyauchi-Isobe N.
Published: June 2019

We have detected 3, 141 ultraviolet-excess galaxies in the sky area of some 1,500 square degrees by means of the UGR three-image photographs taken with the 105-cm Kiso Schmidt. For each of these galaxies which we call KUGs the morphological type and the degree of ultraviolet-excess are given in the catalogues. The frequency distribution for these characteristics of KUGs is shown in a form of histogram. The results of a spectroscopic study for the 57 selected KUGs are that 85% of the sample have emission-lines and most of them are situated in the domain of HII regions on the emission-line ratio diagram.
Markarian Galaxies and Zwicky Clusters
Authors: Petrosian A.R. , Turatto M.
Published: June 2019

From 1344 Markarian galaxies lying in the same area covered by Markarian survey and CGCG, 592 are positioned within the contours of Zwicky clusters. On the basis of these data statistical investigation of the relation of Markarian galaxies with Zwicky clusters is carried out. Markarian galaxies take part in the tendency of clustering of galaxies and they lie in any type of Zwicky clusters. Markarian galaxies coincide with greater probability with medium compact clusters than with open ones where they follow the distribution of normal galaxies. In medium compact and compact clusters they appear near the centres of concentration of galaxies but probably not in their dense cores.
Star formation and the circumstellar matter of young stellar objects
Authors: Shu Frank H. , Adams Fred C.
Published: June 2019

We propose that the formation of low mass stars in molecular clouds takes place in four stages. The first stage is the formation of slowly rotating cloud cores through the slow leakage of magnetic (and turbulent) support by ambipolar diffusion. These cores asymptotically approach quasistatic states resembling singular isothermal spheres, but such end states cannot actually be reached because they are unstable. The second phase begins when a condensing cloud core passes the brink of instability and collapses dynamically from “inside-out,” building up a central protostar and nebular disk. The emergent spectral energy distributions of theoretical models in the infall stage are in close agreement with those of recently found infrared sources with steep spectra. As the rotating protostar gains mass, deuterium will eventually ignite in the central regions and drive the star nearly completely convective if its mass is less than about 2 M⊙. This initiates the next step of evolution - the bipolar outflow phase - in which a stellar wind pushes outward and breaks through the infalling envelope. The initial breakout is likely to occur along the rotational poles, leading to collimated jets and bipolar outflows. The intense stellar wind eventually widens to sweep out gas in nearly all 4π steradian, revealing the fourth stage - a T Tauri star with a surrounding remnant nebular disk. Radiation from a disk adds an infrared excess to the expected spectral energy distribution of the revealed source. The detailed shape of this infrared excess depends on whether the disk is largely passive and merely reprocesses stellar photons, or is relatively massive and actively accreting. Both extremes of spectral shapes are observed in T Tauri stars; the amount of circumstellar material in the form of disks around nearly formed stars may be related to the dual issues of the origins of binary-star and planetary systems.
Multiple dust shells around Herbig Ae/Be stars
Authors: Thé P.S. , Dawanas D. N.
Published: June 2019

Intermediate mass (2 < M/M⊙ < 9) pre-main sequence objects, also named Herbig Ae/Be stars, are known to have excess radiation in the near-infrared. From IRAS o bservations it turns out without doubt (quality 3, high S/N radio), that these objects are very strong far-infrared emitters at 12, 25, 60 and often also at 100 μm. The spectral energy distribution, depicted in Fig. 1 for intermediate mass pre-main sequence stars, show clearly this large excess. From the difference curves it is apparent that this excess radiation is most probably caused by several dust shells. Using very simplified methods it is possible to derive the average temperature of the dust shells (see Thé, Wesselius, Tjin A Djie and Steenman, 1986). If the chemical composition of the mixture of the dust grains and their average size are assumed it is also possible to estimate other characteristics like the distance from the central star and the mass of the dust shells (see Thé, Hageman, Westerlund, Tjin A Djie, 1985).
Filtered CCD images of southern Herbig-Haro objects
Authors: Whitmore B. , Cameron D.H.M. , Warren-Smith R.F.
Published: June 2019

It is currently believed that Herbig-Haro (HH) objects are a consequence of a high-velocity (up to at least 200 km s−1) outflow of material from a young embedded star. These flows can often be detected by deep observations of optical emission lines using CCD cameras.
Circumstellar matter as detected by IRAS - Some systematics
Authors: Bidelman W. P.
Published: June 2019

Most of the sources noted by the Infrared Astronomical Satellite are, as expected, more or less normal cool giant stars, but a very large number of objects of earlier spectral type were also picked up. These cases must involve, in a variety of ways, circumstellar gas and dust. From a large-scale program of identification of the IRAS objects, some systematics emerge.
Images of the envelope of Alpha Orionis
Authors: Hebden Jeremy C. , Hege E. Keith , Eckart Andreas
Published: June 2019

Two images have been obtained, from observations made almost two years apart, of the H-alpha chromospheric envelope of Alpha Orionis at the diffraction limited resolution of the co-phased Multiple Mirror Telescope. Significant emission out to a distance of several stellar radii above the photosphere is observed.
Jets from symbiotic stars
Authors: Kafatos M. , Cassatella A. , Michalitsianos A.G. , Piro L. , Viotti R.
Published: June 2019

R Aquarii is the closest symbiotic variable that shows extended emission with multiple jet components. A number of other symbiotics also show jet activity and this phenomenon may be common, particularly among D-type symbiotics.
Millimeter wave observations of circumstellar envelopes with the IRAM telescope
Authors: Omont A. , Forveille T. , Guilloteau S. , Lucas R. , Rieu Nguyen-Q , Likkel L. , Morris M.
Published: June 2019

We report various recent observations of molecules in circumstellar envelopes of late type stars, mainly possible proto-planetary nebulae at various stages of evolution, and supergiants, including.

First observation of SO2 (Lucas et al. 1986) in five stars and SO in one. S O 2 is particularly strong in OH 231.8+4.2 (OH 0739-14) and OH 26.5+0.6, where one of its lines is the strongest non-maser line observed in these envelopes (Guilloteau et al. 1986).
Molecular catastrophes and the formation of circumstellar dust
Authors: Stencel Robert E.
Published: June 2019

Radiative instabilities due to simple molecules may convert chromospheric material into masering molecules and dust capable of being removed from the star by radiation pressure.
Triplicity of Pulsar Profiles and Orthogonal Polarization Modes
Authors: Gil J. A.
Published: June 2019

A mechanism for generation of two concentric pulsar beams corresponding to the core and conal pulsar emission is proposed. The inner beam originates close to the star, where the radius of curvature of the dipolar magnetic field lines is suitable for coherent curvature emission at pulsar radio frequencies. Further from the star where the outer beam originates, the radius of curvature of dipolar lines is probably too large, but the actual curvature can be dominated by the toroidal component of field lines twisted back due to the pulsar rotation. One can show that for even moderate twisting the actual radius of curvature leads again to pulsar radio frequencies. Thus, the pulsar emission is a superposition of two beams originating at widely radially separated locations. When the observer's line-of-sight cuts both beams, a three-component profile should be observed. Because of the retardational time delay, the inner (core) component should appear late with respect to the profile midpoint, that is, closer to the traling component. Such an asymmetry is indeed observed in complex profile pulsars. In pulsar magnetosphere, the radius of curvature of dipolar field lines depends on the radius of the emission region in the opposite way than that of the toroidal lines. This explains why core and conal components dominate the mean profile at low and high frequencies, respectively.
Neutron Stars in Twelve Supernova Remnants
Authors: Seward Frederick D.
Published: June 2019

X-ray observations of selected SNR are summarized. Five contain internal spinning neutron stars–four isolated and one in a binary system. Another seven contain central unresolved sources or bright nebulae. Observations of these nebulae, probably due to synchrotron emission, are used to estimate characteristics of the unseen pulsars.
Search for Plerions in the Direction of Two Young Pulsars
Authors: Krishnamohan S. , Mohanty D.K. , Patnaik A.R. , Velusamy T.
Published: June 2019

Two of the recently discovered pulsars PSR 1800-21 and 1823-13 have characteristics ages of 17,000 and 22,000 yr respectively and all the three known pulsars that are younger than these two lie within the known supernova remnants (Clifton and Lyne, 1986). These two pulsars are expected to have, by scaling from the Crab nebula, plerions of ∼1 Jy each associated with them at 327 MHz. We mapped a field of 1.˚95 × 1.˚5 around both the pulsars with the Ooty Synthesis Radio Telescope (Swarup, 1984). As the fields are on the galactic plane having complex large scale emission and as the plerions are expected to be compact, we have made maps by excluding baselines less than 500 λ. This would make our maps insensitive to emission regions larger than ∼7 arc min. The synthesised beam is 96 × 36 arc sec in PA 0°. No source with a surface brightness greater than 60 mJy/beam was detected in the direction of PSR 1823-13. An unresolved source of ∼150 mJy was detected, in the positional error box of PSR 1800-21, as is shown in the figure. No pulsed emission with an average flux density greater than 10 mJy was detected from this continuum source. It is possible that the pulse is so highly scatter broadened that it becomes undetectable at 327 MHz and the detected source is the scatter broadened pulsar. But, such a possibility seems unlikely as the pulsar's dispersion measure is only 230 cm−3 pc, leaving the interesting possibility that the detected source is a plerion associated with the pulsar.
Accreting Neutron Stars
Authors: White N.E.
Published: June 2019

This paper reviews accreting neutron stars in X-ray binaries, with particular emphasis on how variations in magnetic field strength may be responsible for explaining the spectral and temporal properties observed from the various systems. This includes a review of X-ray pulsars in both low and high mass systems, and a discussion of the spectral properties of the low mass X-ray binaries.
Accretion onto Magnetized Neutron Stars: Polar Cap Flow and Centrifugally Driven Winds
Authors: Arons Jonathan
Published: June 2019

Some basic concepts of accretion onto the polar caps of magnetized neutron stars are reviewed. Preliminary results of new, multidimensional, time–dependent calculations of polar cap flow are outlined, and are used to suggest the possible observability of fluctuations in the X–ray intensity of accretion powered pulsars on time scales of 10–100 msec. The possible relevance of such fluctuations to Quasi–Periodic oscillations is suggested. Basic concepts of the interaction between a disk and the magnetosphere of a neutron star are also discussed. Some recent work on the disk–magnetosphere interaction is outlined, leading to the suggestion that a neutron star can lose angular momentum by driving some or all of the mass in the disk off as a centrifugally driven wind. The relevance of such mass loss to the orbital evolution of the binary is pointed out.
Hubble Space Telescope Images of Four Magellanic Cloud Planetary Nebulae
Authors: Barlow M. J. , Blades J. C. , Osmer S. ,   The Faint Object Camera I.D.T.
Published: June 2019

Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through narrow-band filters isolating [O III] λ5007 and Hβ, for a nominal exposure time of 1000 seconds in each filter. The f/96 optical chain of the FOC was used, yielding 512×512 0.022 arcsec square pixels. Considerable detail is evident on the raw images and after deconvolution using the Richardson-Lucy algorithm, structures as small as 0.06 arcsec are easily discernible. Figure 1 shows NS and EW intensity cross-cuts through the deconvolved [O III] λ5007 images of SMC N2 and SMC N5. SMC N2 is a slightly ellleptical ringlike nebula, with its greatest elongation in the EW direction. The peak-to-peak dimensions of the ring are 0.21×0.26 arcsec2. SMC N5 has a circular ring shape, with the [O III] λ5007 image showing a clearly defined, nearly uniform structure, apart from a bright patch at the northern edge. The peak-to-peak diameter of the ring is 0.26 arcsec and the ring itself is significantly narrower than that of SMC N2, with a width as small as 0.06 arcsec (FWHM) in some places. LMC N201 is very compact, with a FWHM of 0.21 arcsec in the Hβ image. The Type I PN LMC N66 is a multi-polar nebula, with the brightest part having an extent of about 2 arcsec. Its structure is extremely complex, with several bright knots and faint loops visible outside the two bright lobes. A full description of our results can be found in Blades et al., ApJ,398, L41–44.
Post-AGB Candidates
Authors: Waters L.B.F.M. , Sahu K.C.
Published: June 2019

A review is given of the properties of post-AGB stars. Methods to find candidate post-AGB stars are briefly discussed, along with some results and selection effects involved. Their photospheric parameters (Teff, log g, abundances), energy distributions and binarity are also discussed. Evidence for mass loss, both past and present, is reviewed.
Planetary Nebulae by Binary Nuclei
Authors: Livio Mario
Published: June 2019

Planetary nebulae with close binary nuclei are reviewed. It is shown that these systems can be used as a source of information for the physics of the common envelope phase in the evolution of binary systems. Mechanisms for the production of bipolar planetary nebulae are examined and it is concluded that presently the action of binary companions to the central stars appears to provide the most promising mechanism. Other systems (e.g. novae, supernovae) in which similar processes may be operating are discussed.
Thermal Pulses and Planetary Nebula Ejection
Authors: Wood P.R. , Vassiliadis E.
Published: June 2019

Thermal pulses in AGB stars cause large luminosity variations at the stellar surface. The role of these luminosity variations in the production of planetary nebulae is discussed. Results of theoretical evolution calculations which include mass loss modulated by thermal pulses are presented.
Evolution of a Dust Shell Along a Stellar Post-AGB Track
Authors: Marten H. , Szczerba R. , Blöcker T.
Published: June 2019

We study the spectral appearance of an evolving post-AGB object by means of two-fluid radiation hydrodynamics (gas and dust) in spherical symmetry. The stellar parameters as well as mass-loss rates are assumed to vary consistently with the stellar model calculations of Blöcker (1989, Diplom Thesis, University of Kiel) for a 3 M⊙ sequence, resulting in a 0.605 M⊙ remnant. The expelled mass is assumed to consist of spherical astronomical silicates with grain radii of 0.1 μm and an initial dust-to-gas mass ratio of 7.5·10−3. For further details on the computational method we refer to Szczerba & Marten (1992, in: Proc. of the ESO/CTIO Workshop, Mass Loss on the AGB and Beyond, La Serena 1992, in press).
New Eclipsing Phenomena of the Central Star in NGC 2346
Authors: Costero R. , Peña M. , Schuster W.J. , Tapia M. , Echevarria J. , Fierro J.
Published: June 2019

The central star of NGC 2346 is a well known binary with an A-type primary and a hot companion (Méndez and Niemela 1981). The star went through a series of periodic light variations which ceased in 1986 and were interpreted as an eclipse of a dust cloud passing in front of the binary system (e.g. Méndez et al. 1982, Costero et al. 1986). Recently, light variations reappeared with shallower minima compared to the previous eclipse (e.g. Kohoutek et al. 1992).
ROSAT Observations of Symbiotic Stars
Authors: Bickert K.F. , Stencel R.E. , Luthardt R.
Published: June 2019

The German X-ray astronomy satellite ROSAT (launched 1990 June 1) performed an all-sky survey (from 1990 Jul 30 till 1991 Jan 26) with the Position Sensitive Proportional Counter (2 deg FoV, .1–2.4 keV) covering 96% of the sky. Analysis of bright X-ray sources suggests PSPC positions can be accurately determined to within 30 arcsec, and 1‥2 arcmin for soft weak ones. We have examined the survey data for detections from among a list of 189 symbiotic and symbiotic-like objects compiled by Vaidis (1988) with own extensions, chosen for completeness. For 178 objects, all-sky data was available. Standard Analysis Software System (SASS) and EXtended Standard Analysis Software packages (EXSAS) both use a three-step approach to detect sources. After quality screening, a sliding-window algorithm (LD) locates bright sources. These are excluded in the 2D-spline interpolated smoothed background map. A second sliding window MD runs on the background subtracted event files. All possible sources were then tested by maximum likelihood in the background-subtracted, exposure-corrected image. If LD, MD, or ML did not detected a source at the optical position, an upper limit ML program tried to find enhanced emission. For EXSAS, photon event files contain all photons within 20 arcmin radius around a source. Cut radii, background determination, and other parameters can be iteratively improved.
A Spectacular Mass-Loss Event of the Central Star of Longmore 4
Authors: Werner K. , Hamann W.-R. , Heber U. , Napiwotzki R. , Rauch T. , Wessolowski U.
Published: June 2019

The nucleus of the PN Lo4 is very hot and H-deficient and may be classified as a PG 1159 star (Werner 1992). Besides K 1–16, it is the second known pulsating central star. New spectra were taken between May 1991 and Febr. 1992. Within 18 days we witnessed a rapid decline of an emission line phase, which has begun less than 7 months ago. During this time Lo4 has changed its spectral type from PG 1159 to early WC (WC2 or WC3) and back to PG 1159. This phenomenon has never been observed before in hot post-AGB stars. The event is interpreted as an intrinsic phenomenon. Because of the short time scales, the variations are probably confined to the outermost stellar layers. It is known that the pulsation driving zones are close to the stellar surface and we speculate about a causal relation between enhanced mass-loss and possible variations in the pulsation behaviour. Spectral analysis was performed using NLTE model codes for spherically expanding atmospheres (Hamann et al. 1991) to analyze the WC-type spectrum and for plane-parallel static atmospheres (Werner 1992) to analyze the PG 1159 type spectrum. We find Teff=120kK and log g=5.5 during the PG 1159 phase. For the WC phase we obtain the same Teff and the mass-loss rate log (·/(M⊙/yr))=−7.3. The element abundances are typical for PG 1159 stars (He:C:O=46:43:ll, by mass) and v∞=:4000 km/s. More details can be found in Werner et al. (1992).
Luminosity Functions of Planetary Nebulae
Authors: Jacoby George , Ciardullo Robin
Published: June 2019

Luminosity functions of planetary nebulae contain information about the central star mass distributions, nebular, central star, and progenitor evolution, stellar death rates, and a galaxy's star formation and chemical evolution histories. Appropriate observing strategies can be used in combination with various models to extract some of the parameters of these functions. The principal results from these studies are that the central star mass distribution is narrow (σ ∼ 0.02–0.04M⊙), the number of PN in a galaxy depends on galaxy color, and the number of PN in the Galaxy is ∼ 104.

The most extensive application of luminosity function studies has been exploiting the bright end cutoff as a distance indicator. Distances for 25 galaxies have been measured using the methodology outlined by Jacoby, Ciardullo, and collaborators. The PNLF method compares extremely well with other techniques, and is accurate to ∼ 5%. In fact, there is no evidence for systematic effects of any kind, although a small (5–10%) metallicity correction needs to be applied for metal-poor systems.
PN Abundances in Different Galactic Systems
Authors: Clegg R.E.S.
Published: June 2019

Developments in the measurement of abundances in planetary nebulae since IAU Symposium 131 are reviewed. Present uncertainties and outstanding problems in the interpretation of emission-line measurements are discussed. Results for different samples of PN are reviewed, in terms of the galactic site. Results for the Galactic disk, Galactic Bulge, Galactic Halo, LMC & SMC, Fornax Dwarf galaxy and M31 are discussed. Attention is drawn to the importance of Magellanic Cloud samples for testing dredge-up theory, and to the strong variation of PN C/O ratios with the local site's metallicity and age. New results for carbon in Cloud PNs are presented. Important problems in the interpretation of the metallicity of Bulge PNs are highlighted. Attention is drawn to the idea that metal-rich stellar populations do not produce PNs, such stars leaving the lower AGB early.
Dependance of the Metallicity of Planetary Nebulae by the Galactic Height Above the Disk
Authors: Cuisinier F. , Acker A. , Köppen J.
Published: June 2019

Abundances of O, N, He, S, Ar have been derived from the observations of PN at various heights above the plane with the plasma diagnosis code HOPPLA (Köppen et al. 1991). A gradient in O and N appears in the first 1000 pc. No correlation is found above.
An Observational Method for the Lower Latitude Meridian Circle (LLMC) with a CCD Camera
Authors: Wei Mao , Yu Fan , Qinyu Peng , Zhiming Li , Kaifan Ji , Xiaochun Hu
Published: June 2019

A principle for absolute determination of an object' position by means of LLMC with a CCD camera and the method for finding the error from the instrument and the CCD chip are described in this paper. The observational power and application of the LLMC with a CCD are also discussed.
Recent Advances with the USNO (Flagstaff) Transit Telescope
Authors: Stone Ronald C.
Published: June 2019

The Flagstaff Astrometric Scanning Transit Telescope (FASTT) has been equipped with a new CCD detector, and further improvements in instrumentation have been made. An evaluation of its performance indicates that the telescope can determine accurate star positions, tied into the VLBI/VLA extragalactic reference frame, for stars as faint as V ∼ 17.5 mag. With further improvements, it is hoped this accuracy can be improved. A special scanning technique for stars at high declinations has been developed that allows scanning up to the pole. Positions tied into the extragalactic reference frame for FK5 and radio stars have been determined with the FASTT, and a comparison of these positions with their catalog values is given.
Monitoring Earth Rotation and Polar Motion Using Space VLBI: A Feasibility Study
Authors: Kulkarni Madhav N.
Published: June 2019

Space Very Long Baseline Interferometry is an extension of the ground based VLBI to the space. With the launching of two Space VLBI satellites in the future, Space VLBI observations will be available for astrometric, geodetic and geodynamic applications. This new technique holds potential for various important applications including monitoring Earth rotation. The aim of this feasibility study has been to investigate the possibility of precise estimation of Earth rotation parameters from the Space VLBI observations. A simplified mathematical model is derived in terms of estimable parameters. Sensitivity analysis has been carried out to study the sensitivity of this system to the geodetic parameters of interest. Some of the dominant systematic effects have been investigated. Simulation studies have been carried out to study the influence of these systematic effects and a priori information on the estimation of the Earth rotation parameters. The results indicate that the Space VLBI technique may be used to complement other existing techniques for monitoring Earth rotation, only if the orbital systematic effects can be modeled to a high degree of accuracy (or the satellites can be tracked, with high accuracy, independently), and precise a priori information on station coordinates from other sources is used.
Transformations Among CISs Defined by Various ERP Series
Authors: Xiao N.Y. , Zhang H.W.
Published: June 2019

The rotational angles α1 and α2 for transformation between two CISs are derived from the differences of each two polar coordinate series. Then, their periodicity is analysed and they are fitted by trigonometric expansions. In terms of the fitting parameters each of them is developed into a sum of several terms with two nearly-diurnal ones involved.
The Hertzsprung-Russell diagram from photoelectric observations of nearby stars
Authors: Parenago P. P.
Published: June 2019

The progress in the investigation of the spectrum-luminosity diagram. The spectrum-luminosity diagram, or the Hertzsprung-Russell diagram, is of extreme importance in stellar astronomy, astrophysics and stellar cosmogony. A number of stellar characteristics can be read from the diagram, as well as the theoretical paths of stellar evolution. A very significant problem is the improvement of the diagram, i.e. the accumulation of more precise data concerning the subdivision into sequences, the contours of the latter (mean lines, dispersions, gaps) and other characteristics (masses, axial rotations, chemical composition, space-kinematical properties).
Machine calculations of evolution at constant mass
Authors: Hoyle F.
Published: June 2019

This communication is concerned with recent computations made with the aid of the IBM 704. The problem was set up in collaboration with C. B. Haselgrove, using a method already described in detail. Facilities for making the computations were generously provided by the IBM Corporation.
Properties of Elliptical Galaxies with Dust Lanes
Authors: Bertola Francesco
Published: June 2019

NGC 5128 (Cen A) has been known for many years as a peculiar elliptical, but only recently has it been recognized as the prototype of a new class of object (Bertola and Galletta 1978). This class of galaxy is characterized by an elliptical–like stellar body crossed along the minor axis by a dust lane, and was comprised initially of five objects. The class was extended in a remarkable way by Hawarden et al. (1981), who drew attention also to the existence of ellipticals with the dust lane along the major, and along intermediate axes. Ninety objects are now listed as dust lane ellipticals in the compilation by Ebneter and Balick (1985) and its updated version (Ebneter 1986).
Line-Strength Gradients in Early-Type Galaxies
Authors: Gorgas J. , Efstathiou G.
Published: June 2019

We have measured line-strength gradients in a sample of 15 early-type galaxies. The line-strength measures include the Mg2 index and the equivalent widths of Hβ and two iron blends at 5270Å and 5335Å. In most of the galaxies we find gradients in the metallic line-strengths. However, the gradients vary markedly from object to object and do not correlate strongly with other parameters such as total luminosity, rotation, etc. A comparison of the line-strengths in the outer parts of these galaxies with galactic globular clusters suggests relatively modest abundance gradients in early-type galaxies.
Dust in Early Type Galaxies observed at the CFHT
Authors: Kormendy J. , Stauffer J.
Published: June 2019

A program of CCD imaging of early-type galactic nuclei carried out at the Canada-France-Hawaii Telescope (Kormendy, these proceedings) reveals dust in an unusually large fraction of the galaxies. Often the dust is in a ring or disk whose radius is comparable to the core radius rc; since rc is small, our detection rate benefits from the excellent CFHT seeing (median FWHM = O.“7; scale = O.“22 pixel−1 for an RCA CCD used at the Cassegrain focus). We plan to prepare a photographic atlas of unsharp-masked images, and to study correlations between dust properties and nuclear emission lines, HI and X-ray gas content, radio continuum jets and the overall light distributions of the program galaxies.
The Discovery of Blazar-Type Nuclei in Two Nearby Radio Ellipticals
Authors: Sparks W B , Bailey J. , Hough J C , Brindle C. , Axon D J
Published: June 2019

Near infrared polarimetry of Centaurus A and IC5063 has revealed the existence of a steep spectrum highly polarized source in the nuclei of both galaxies. The position angle of polarization is perpendicular to the radio position angle. We interpret this polarized emission as synchrotron radiation. This, together with a luminosity of 5 × 1041erg s-1, suggests the galaxies are low luminosity blazars and that such nuclei may be common in elliptical galaxies.
Stellar Dynamics of Radio Elliptical Galaxies
Authors: Sansom A. , Wall J.V. , Sparks W.B.
Published: June 2019

Stellar kinematical and dynamical results are presented for 34 radio ellipticals. The radio galaxies we observed were brighter than m(B)=16. The results show that these radio ellipticals are not generally more rapidly rotating than their non-radio counterparts. Evidence for some rotation about the major axis is seen in two cases. These radio ellipticals do not appear to obey the luminosity, velocity dispersion trend seen for normal ellipticals.
OH-IR Sources and the Galactic Centre Distance
Authors: Cohen R. J. , Shepherd M. , Gaylard M. J. , West M. E.
Published: June 2019

The phase-lag technique of estimating distance to OH-IR sources is briefly described. Preliminary results are presented from a study of nine OH-IR sources in the galactic centre direction.
Fabry-Perot Images of Ionised and Molecular Hydrogen in Sgr A
Authors: Depoy D. L , Gatley Ian , Mclean I. S.
Published: June 2019

Images of the central 36 arcseconds of the Galaxy in the Brackett gamma line of atomic hydrogen (2.17μm) at a spatial resolution of 0.6 arcsec and a velocity resolution of 110 km/sec were obtained using UKIRT. The velocity separation between adjacent frames is 55 km/sec; 17 different velocities channels were imaged. Several distinct kinematic components are evident within the clumpy distribution of the ionised gas. An image in the v=1-0 S(1) line of molecular hydrogen (2.12μm) clearly resolves the structure of the “molecular ring.”
CO Along the Line of Sight to Galactic Center Infrared Sources
Authors: Geballe T. R.
Published: June 2019

High resolution spectra of the 4.64 micron 1–0 R2 line of CO toward infrared sources in the galactic center reveal absorption components identified with features in radio and millimeter wave spectra of molecular lines. They demonstrate that the +20 km/s cloud is situated in front of the Sgr A West and the +50 km/s cloud is behind it. The spectra of IRS 3 and IRS 7 have strong absorptions near +50 km/s, which may originate in the 2 pc radius circumnuclear ring; if so then the western side of the ring lies in front of the galactic center. A less likely interpretation is that these objects, which are only a few arc-seconds from IRS 16, are behind the +50 km/s cloud and, thus, well behind the galactic center.
A Search for Radio Recombination Lines of Positronium Near the Galactic Center
Authors: Anantharamaiah K. R. , Radhakrishnan V. , Morris D. , Vivekanand M. , Downes D. , Shukre C. S.
Published: June 2019

Several attempts were made to detect the possible radio recombination lines of positronium near the galactic center. An absorption feature seen at λ6cm, in the D-configuration of the VLA was not confirmed by subsequent observations at λ6cm and λ20cm using the B and C configurations of the VLA. An observation at λ3mm using the IRAM 30m telescope also did not detect any line. On the basis of one recombination line photon for every positron (McClintock 1984), our non-detections imply an upper limit to the positron production rate of < 3.1 × 1043 s−1, within about 2″ of the galactic center.
Flare stars in star clusters, associations and solar vicinity
Authors: Mirzoyan L.V.
Published: June 2019

The observational data on flare stars observed in star clusters and associations as well as in the solar vicinity (the UV Ceti type stars) are discussed. The analysis of these data show that they constitute one common class of objects possessing flare activity and the differences between them are conditioned by the age differences. The stage of flare activity is an evolutionary stage, one of the earliest stages of evolution passed by all red dwarf stars. It comes before the end of their T Tau stage of evolution. The UV Ceti type flare stars in the solar vicinity seem to be the population of the general galactic field, which were formed in the systems, already desintegrated. Most probably the stellar flares are the result of the release of the the surplus energy having intra-stellar origin.
An automatic search for flare stars in southern stellar aggregates of different ages
Authors: Aniol R. , Duerbeck H. W. , Seitter W.C. , Tsvetkov M.K.
Published: June 2019

Statistically relevant samples of flare stars in stellar aggregates can be used to specify the stellar mass-age-activity-relation when the ages of the aggregates are known from independent investigations. Associations and clusters of the southern sky are currently surveyed with the GPO astrograph of the European Southern Observatory. The plates are digitized with the PDS 2020 GMplusmicrodensitometer and the data are reduced automatically at the Astronomical Institute of Muenster University. The programme package “FLARE” is described. First results from the Orion association are presented.
Broadband spectral radio observations of flare stars
Authors: Benz A.O. , Güdel M. , Bastian T.S. , Fürst E. , Simnett G.M. , Pointon L.
Published: June 2019

Several nearby flare stars have been observed with spectrometers on various large telescopes. The experience of several attempts to record stellar radio flares is summarized including an event on AD Leo that was detected by three widely separated large telescopes. The event is analogue to solar decimetric pulsations. An interpretation in terms of coherent cyclotron emission (maser) is given and the source size, exciter drift velocity and source magnetic field are estimated.
Fu Orionis eruptions and early stellar evolution
Authors: Reipurth Bo
Published: June 2019

The FU Orionis phenomenon has attracted increasing attention in recent years, and is now accepted as a crucial element in the early evolution of low mass stars. The general characteristics of FUors are outlined and individual members of the class are discussed. The discovery of a new FUor, BBW 76, is presented, together with a discussion of photometric and spectroscopic observations of the star. The evidence for circumstellar disks around T Tauri stars is briefly outlined, and the FUor phenomenon is discussed in the context of a disk accretion model. A large increase in the accretion rate through a circumstellar disk makes the disk self-luminous with a luminosity two or more orders larger than that of the star. Massive cool winds rise from FUors, and it is conceivable that they are related to the initiation of Herbig-Haro flows. The FUor phenomenon appears to be repetitive, and newborn low-mass stars may be cycling between the FUor state and the T Tauri state.
On a differential equation for electromagnetic wave transmission in flare stars and the possible existance of cohesive wave solutions
Authors: Papas Charles Herach
Published: June 2019

Ambartsumian's celebrated hypothesis that stellar flares and other phenomena of stellar instability are due to a novel source of energy and a novel means of transporting this energy to the outer layers of the star has drawn the attention of electrodynamicists to a number of fundamental problems. One of these problems, namely the energy transport problem, is the subject of this communication. Herein, by assuming that the matter of the star is an isotropic collisionless plasma, from Maxwell's field equations and Newton's equation of motion with nonlinear Lorentz driving force, we have derived a vector differential equation for electromagnetic wave propagation. This equation contains the Debye radius and the plasma frequency as parameters, and reduces to the well-known wave equation when its nonlinear terms are neglected. We have indicated that the nonlinear equation has cohesive (solitary) wave solutions for both the longitudinal and transverse components of the electromagnetic field. Such cohesive waves are appropriate for transporting energy from the prestellar core of the star to its outer layers since they hold their shape, are free from dispersive distortion, and can carry energy in discrete amounts.
Chances for Earth-Like Planets and Life Around Metal-Poor Stars
Authors: Zinnecker Hans
Published: June 2019

We discuss the difficulties of forming earth-like planets in metal-poor environments, such as those prevailing in the Galactic halo (Pop II), the Magellanic Clouds, and the early universe. We suggest that, with fewer heavy elements available, terrestrial planets will be smaller size and lower mass than in our solar system (solar metallicity). Such planets may not be able to sustain life as we know it. Therefore, the chances of very old lifeforms in the universe are slim, and a threshold metallicty (90% solar?) may exist for life to originate on large enough earth-like planets.
First Steps Towards Defining Galactic Niches
Authors: Morris Simon Conway
Published: June 2019

Terrestrial evolution encompasses many levels, from proteins to societies. Potentially any level can be encompassed by a multidimensional “habitation box”, of which only a minute fraction is occupied. on the basis of evidence from evolutionary convergence it is argued that life elsewhere will not only be similarly constrained, but also strangely similar.
The Microbial Community of a Radon Hot Spring
Authors: Anitori Roberto P. , Trott Cherida , Saul David J. , Bergquist Peter L. , Walter Malcolm R.
Published: June 2019

Paralana is an active, radon-containing hot spring situated in a region of South Australia's Flinders Ranges with a long history of hydrothermal activity. Gas bubbling into the pool is composed of radon (from the radioactive decay of radium), nitrogen, carbon dioxide, and trace helium and hydrogen. The microbial composition of mat and biofilm samples from Paralana was determined using culture-independent 16S rRNA techniques. We have previously demonstrated that the hot spring contains a diverse bacterial community. Here we summarise these findings and report on theArchaeaidentified in Paralana. Archaeal inhabitants include members of the Crenarchaeota and Euryarchaeota kingdoms.
Recurrent Neural Networks for Narrowband Signal Detection in the Time-Frequency Domain
Authors: Brodrick David , Taylor Douglas , Diederich Joachim
Published: June 2019

A recurrent neural network was trained to detect the time-frequency domain signature of narrowband radio signals against a background of astronomical noise. The objective was to investigate the use of recurrent networks for signal detection in the Search for Extra-Terrestrial Intelligence, though the problem is closely analogous to the detection of some classes of Radio Frequency Interference in radio astronomy.
Structure and evolution of massive single stars and their relevance for close binary systems
Authors: Langer Norbert
Published: June 2019

Differences in the evolution of massive single stars and components of massive close binary systems are investigated. While for stars above the red supergiant luminosity limit, single star and case B primary evolution merge into a single scenario, large differences for less massive stars are demonstrated to occur at the example ofMZAMS= 40M⊙, concerning the various WR subtypes, the nucleosynthesis yields, and the supernova stage.
The physical nature of WR8 (WN6/WC4)
Authors: Crowther Paul A. , Smith Linda J. , Willis Allan J.
Published: June 2019

An analysis of the UV, optical and IR spectra of the composite WN/WC star WR8 is presented using the WR standard model. All spectral features are consistent with formation in the same stellar wind. The stellar parameters are T*=49kK, log L/L⊙=5.1, log Ṁ = −4.2, v∞=1590 km s−1. The derived chemistry (C/He=0.025, C/N=3, C/O=4) is intermediate between normal WN and WC stars.
Synthetic line profiles from unified model atmospheres
Authors: Rey E. Santolaya , Herrero A. , Puls J.
Published: June 2019

Synthetic line-profiles from unified model atmospheres are presented. The main characteristics of the code are also shown concerning both the calculation of NLTE populations (in a consistent way with the radiation field), and the formal solution to obtain emergent profiles. Stark-broadening is considered in this last step. Emergent Hα profiles for a grid of models are shown for Teff = 50 000 K, covering a wide range of stellar radii and mass-loss.
X-ray emission from Wolf-Rayet stars: Pointed ROSAT PSPC observations of nine single WN stars
Authors: Wessolowski U. , Hamann W.-R. , Koesterke L. , Hillier D. J. , Puls J.
Published: June 2019

Results from pointed ROSAT PSPC observations of nine single WN-type Wolf-Rayet stars are presented. Spectra of sufficient quality were obtained for two of them (WR1, WR110). The long exposure (35.5 ksec) X-ray spectrum of WR1 is more closely investigated with a semi-empirical model developed by Baum et al. (1992).
Episodic dust formation in astrophysical sources
Authors: Bode Michael F.
Published: June 2019

At first sight, it is surprising that dust nucleation and growth can occur in the harsh environment of a Wolf-Rayet star wind. However, we know that episodic formation occurs in several different types of astrophysical source. Of particular relevance to our efforts to gain a fuller understanding of the process in WC stars is the extensive work that has been performed on classical novae. Thus, although episodic dust formation in other types of object is briefly described, this review concentrates on a comparison with this process as observed in novae in particular. It is argued that for efficient grain growth, clumping of ejecta (perhaps following shock-interactions) is essential.