bluuebunny/crossref_metadata_2025 huggingface dataset:
The Quest for Fine-Scale Anisotropy in the Relict Radiation
Authors: Boynton Paul E.
Published: June 2019

Up to Symposium Session IV, the observed properties of the large scale structure of the Universe have been discussed in terms of studies based on the spatial distribution of galaxies with redshift less than one; studies which indicate clustering on characteristic scales up to ~20 Mpc or equivalently ~1015M⊙. Such a survey is rather local in scope compared to what in principle could be inferred from the measurement of temperature fluctuations in the relict radiation surviving from Z ≃ 1000 as the fossil imprint of “primordial” density fluctuations on scales up to the horizon at the epoch of decoupling, M ≃ 1019M⊙. However, the investigation of structure over a still-larger sample volume and scales greater than 1015M⊙ is not a possibility which I wish to stress in this paper. Rather, given our present state of ignorance about the formation of structure, perhaps a more fruitful first approach would be to examine small angular scales in the relict radiation for insight into the evolution of density perturbations by a careful comparison between the observationally inferred “initial” spectrum of mass inhomogeneities present back at the epoch of decoupling, and the mass spectrum of clustering which characterizes the present Universe.
Fluctuations of the Microwave Background Radiation
Authors: Sunyaev R. A.
Published: June 2019

Investigations of small scale angular fluctuations and the spectrum of the microwave background radiation is one of the main methods of studying the large scale structure of the Universe. Figure 1 shows the principal stages of the evolution of the Universe. Today we can directly observe galaxies, clusters of galaxies and quasars in the redshift range z ≤ 3.5 by optical, radio and X-ray astronomy. These observations show that significant density perturbationsδρ/ρ > 1 are present on mass scales M < 1016M⊙. the Universe is essentially uniformδρ/ρ < 1 on large scales M ≫ 1016M⊙.
The Whirl Theory of the Origin of Structure in the Universe
Authors: Ozernoy L. M.
Published: June 2019

There are at least two reasons for examining different theories of galaxy formation:
Activity in the Envelope of the G-type Hypergiant HD 217476
Authors: Smoliński J. , Climenhaga J.L. , Fletcher J.M.
Published: June 2019

Yellow hypergiant, HD 217476, (HR 8752) is known to have extensive circumstellar envelope. Its unusual spectrum makes it enigmatic object. On the H-R diagram this hypergiant lies among the most luminous stars known in six Local Group galaxies (Humphreys et al., 1984). We have observed it with the same equipment during last fifteen years at the Dominion Astrophysical Observatory. Our present results arg based upon several hundreds of high dispersion spectra (6 and 10 Å/mm).
Star Formation of Star Clusters in the SMC and their Adjoining Fields
Authors: Kontizas M. , Kontizas E.
Published: June 2019

Photometric and recent spectroscopic studies of the SMC have shown that the differences observed in the SMC clusters and those of our Galaxy could be attibuted to differences in metallicity, star formation rate and/or the Initial Mass Function (IMF) (Humphries, 1983). The studied clusters NGC152 and KRON3 are located at the west side of the bar of the SMC and their adjoining fields represent the halo population of this galaxy.
Instability in Massive Stars: An Overview
Authors: Appenzeller I.
Published: June 2019

Dynamical, vibrational, and thermal instabilities of massive blue stars are discussed as possible mechanisms for the observed brightness variations of such objects. Relaxation oscillations (on local thermal time scales) due to dynamical instabilities of the stellar wind flows appear to be the most likely mechanism, at least for the S Dor variables. Very massive main-sequence stars with M > 103 M⊙ should be violently vibrationally unstable and therefore should differ significantly from stable main-sequence stars of lower mass.
MWC 300: A Runaway Hypergiant
Authors: Wolf B. , Stahl O.
Published: June 2019

We analysed highly resolved CASPEC spectra with a high S/N-ratio of the peculiar emission-line B-star MWC 300, which is surrounded by a circumstellar dust shell. These high quality spectra enabled us to study the photospheric spectrum of MWC 300. By comparing the absorption spectrum of MWC 300 with the ones of early B supergiants we found a close resemblance with the B1 hypergiant HD 169454. We also found luminosity sensitive fluorescence lines of Fe III 115 and 117 both in MWC 300 and in the most luminous stars of our sample, confirming the hypergiant nature of MWC 300. We estimated an absolute visual magnitude Mv = −8 for MWC 300. Assuming a bolometric correction of B.C. = −1.5 mag we derive Mbol = −9.5. This shows that MWC 300 is very similar to the B e supergiants of the Magellanic Clouds. From its absolute magnitude we derive a distance of z = 560 pc from the galactic plane. It is conjectured that MWC 300 is a runaway hypergiant, released via a supernova explosion in a very massive binary star system.
How to form a 200 M⊙ star
Authors: Zinnecker Hans
Published: June 2019

Stellar coalescence is suggested as a possible mechanism for doubling the upper stellar mass limit from ∼100M⊙ to ∼200M⊙ in a moderately dense cluster of a few hundred young massive stars (∼105 M⊙ pc−3). The merger will be between the two components of the dominant central tight binary formed in the core of the cluster by the N-body evolution. This process may occur in some giant extragalactic HII regions.
Massive Star Evolution: Mass Loss and Mixing
Authors: Maeder André
Published: June 2019

At first it may be surprising that mass loss, overshooting and mixing, which are indeed very different physical processes, have similar consequences on stellar evolution. These various processes may increase the Main-Sequence (MS) lifetime, extend the width of the MS, bring CNO-processed materials to stellar surfaces and, in extreme cases, lead to quasi-homogeneous evolution. The physical reason of this similarity is that these processes increase the relative mass fraction of the stellar cores. Thus we understand that, on the basis of their evolutionary consequences, it may not be easy to disentangle the contributions of mass loss, overshooting and mixing processes. The present status of our knowledge on these effects, which appear to have major consequences on the evolution of massive stars, is now examined in detail.
The Initial Mass Function of Massive Stars in Galaxies: Empirical Evidence
Authors: Scalo John M.
Published: June 2019

Observational constraints on the form of the high-mass stellar IMF are reviewed. The evidence includes star counts in the solar neighborhood, individual and composite star clusters, and nearby galaxies, and arguments based on integrated light and chemical evolution modeling. There is no convincing evidence for any systematic variations of the shape of the high-mass IMF. However, the various determinations are very uncertain, and do not allow any firm estimate of the logarithmic slope of the upper IMF; the appropriate value is somewhere between −1.3 and −2.3, with region-to-region variations smaller than about ±0.5. A number of lines of evidence suggest that the lower mass limit or mode mass of the IMF increases with increasing star formation rate, reaching perhaps 10–15 m⊙ in some starburst galaxies. It is also possible that the upper mass limit depends on metallicity, based on variations in excitation conditions of HII regions.
Luminous Stellar Content of the Galaxy: Inferences from Radio and Infrared Data
Authors: Mezger P. G.
Published: June 2019

Lyman continuum (Lyc) photon production rates can be estimated from radio free-free emission and used to estimate the star formation rate (SFR) of 0 stars. If this SFR is linked to the total SFR through a constant IMF (m ≳0.1 m⊙) one derives for our Galaxy a present-day SFR of ∼10 m⊙ yr−1, which is close to the average SFR over the age of the galactic disk. This is difficult to reconcile with a formation law of the form SFR φ∝Mgask with k>0 which yields SFRs which decrease with time. Even more severe is the fact that the mass distribution of the galactic disk cannot be reproduced by the present-day SFR with a constant IMF. Bimodal star formation, however, reduces the rate at which matter is permanently locked up in low mass and dead stars by nearly a factor of three, and gets reasonable agreement between the present-day distribution of stellar mass and lock-up rate. Bimodal star formation means that stars with m >0.1 m⊙ form in the interarm region while in spiral arms induced star formation produces only stars with m >mc ∼2–3 m⊙.
Giant H II Regions in M81
Authors: Kaufman Michele , Kennicutt R. C. , Bash F. N.
Published: June 2019

Giant HII regions are important tracers of recent star formation in distant galaxies. For a selection of HII regions in our galaxy where the exciting stars can be identified, Rumstay (1985) finds that the measured Hα and radio continuum luminosities of an HII region correlate with the stellar ionizing flux derived from model atmospheres and the known exciting stars. Therefore, we use flux measurements of giant HII regions as an index of the distribution of O stars in M81.
Warmers: Massive Stars in the Nuclei of Galaxies
Authors: Melnick Jorge , Terlevich Roberto , Moles Mariano
Published: June 2019

A very small minority of all galaxies exhibit activity in their nuclear regions. The best known and most studied signature of nuclear activity is the presence of emission lines in the optical spectrum. In fact, active galaxies are classified as Seyferts, Liners or Starburst galaxies according to the strengths, widths and intensity ratios of their nuclear emission lines (figure 1).
Biases in Mass Estimates of Groups of Galaxies
Authors: Mamon Gary A.
Published: June 2019

The knowledge of the masses of small groups of galaxies is important, because the timescales for collapse and virialization of groups depend on their mass-density. While the large inefficiency of the virial mass statistic is well known (Bahcall and Tremaine 1981, hereafter BT, and references therein), biases in the virial mass may produce wrong evolution timescales for small groups. These biases originate from group contamination by interlopers, and from the different galaxy and dark matter distributions inside the groups (caused by mass segregation). This second bias was first studied by Smith (1980, 1984) although already implicit in the work of Limber (1959). It formally arises because the ratio 2T/C where C = ΣFα·Rα (the Clausius virial) is not the same for the luminous and global matter distributions. We illustrate here some quantitative aspects of this Limber bias from the output of N-body simulations of groups of 8 galaxies described elsewhere (Mamon 1986).
Measurement of Dark Matter in Spiral Galaxies
Authors: Kent Stephen M.
Published: June 2019

Luminosity profiles and rotation curves for 37 Sb and Sc galaxies have been combined to derive mass/light ratios for the stellar component and scale parameters for a dark halo component.
Dark Matter: Observational Aspects
Authors: Einasto Jaan , Joeveer Mihkel , Saar Enn
Published: June 2019

A review of observational work on dark matter in USSR is given. Dynamically the dark matter can be located (i) in the galactic disk and/or in dwarf galaxies, (ii) in coronas of galaxies and in clusters of galaxies, and (iii) distributed smoothly in voids. The possible amount of matter in all three forms is discussed. Physically dark matter can be baryonic or non-baryonic, in the latter case either hot, warm or cold. Available information on the nature of dark matter is indirect, coming from theories of the formation of structure in the Universe. Two constraints to the formation scenarios are discussed, the galaxian correlation function and their morphology.
Non-Linear Evolution of Inhomogeneities in Universes Dominated by Dark Matter
Authors: Shandarin S. F.
Published: June 2019

The astronomical data show that most of the mass in the Universe is dark. At present there are a few models of the dark matter: (i) the standard neutrino model, (ii) the model with unstable neutrinos, (iii) axion model. All models can be modified with Λ - term which plays role of the homogeneous component of the dark matter. In this paper the non-linear processes of gravitational instability are briefly discussed.
Constraints on Dark Matter from Primordial Nucleosynthesis
Authors: Audouze Jean
Published: June 2019

Primordial nucleosynthesis which is responsible for the formation of the lightest elements (D, 3He, 4He and 7Li) provides a unique way to determine the present baryon density pB in the Universe and therefore the corresponding cosmological parameter ΩB. After a brief summary of the relevant abundance determinations and of the consequences of the Standard Big Bang nucleosynthesis, it is argued that one needs to call for specific models of chemical evolution of the Galaxy in order to reconcile the observations with the predictions of this model. In this context the predicted values for ΩB should range from 4 10−3 to 6 10−2. These values are significantly lower than those deduced from current M/L determinations.
Variable star observations with automatic telescopes
Authors: Genet Russell M. , Boyd Louis J. , Hall Douglas S.
Published: June 2019

Small automatic telescopes have been used for several years to make wide band, differential photometric observations of brighter variable stars. For example, a single automatic telescope located in Arizona has been used to study essentially the entire class of RS Canum Venaticorum binaries. These stars have changing spot structures that require once-a-night photometric observations - an ideal job for an automatic telescope located in the clear skies of Arizona. The operation of such automatic systems has become so routine that an “Automatic Photoelectric Telescope Service” now makes photometric observations for any institution so requesting. A list of stars is sent to the Arizona site of this service, and every three months the observational results are returned, with the cost typically being similar to the publication page charges. Currently the use of automatic telescopes is being extended to fainter stars and narrower bandwidths. For instance, a highly specialized one-meter telescope has been designed for automatic observations of Ca II K-line emissions from brighter active chromosphere stars. Further extensions of such automation seem likely.
The use of wide angle cameras and high speed measuring machines for generating programmes for small telescopes
Authors: Dodd R J , MacGillivray H T
Published: June 2019

The classical method of discovering objects that vary in position and/or time is to examine well-matched pairs of plates using a blink comparator. This method, being manual, is slow, subjective and, unless several matched plate pairs are used, suffers from incompleteness. The combination of wide angle Schmidt cameras, high speed measuring machines and sophisticated computer software has enabled objective methods for searching for variable objects to be devised. Using such methods it is possible to intercompare stacks of plates digitally. The deepest plate may be used as a master in position and magnitude, eliminating the need for the rest to be well matched. Following measurement and analysis it is a relatively simple matter to prepare lists of variable objects such as RR Lyrae stars, Mira long period variables, cataclysmic variables, active galaxies, comets and asteroids which may then be used as a basis for more intensive study by smaller dedicated instruments.

This, however, is only one aspect of the cooperation possible between Schmidt telescopes, measuring machines and small telescopes. In projects involving the study of large numbers of mainly non-variable objects (stars or galaxies) the small telescope has a most important role to play in providing photoelectric magnitude calibrations to convert machine measured magnitudes to a standard system. To date this has been the principal use to which the small telescope has been put, even in the study of the distribution of faint galaxies from Schmidt plates it was a small telescope which provided the necessary measurement of the background sky brightness.

A further dimension is provided by the addition of an objective prism to the Schmidt camera. In this case objects readily detected include emission line stars and galaxies. The calibrating power of the smaller instrument is now of value in providing standard galaxy radial velocities to calibrate red shifts measured from the very low dispersion prism.
An optical fiber feed for small telescopes
Authors: Weller W. G. , Ingerson T. E.
Published: June 2019

We have constructed an optical fiber link between the CTIO 1.5 meter telescope and the instrument development laboratory located in the 4 meter telescope building. We have successfully observed a variety of objects using the 4 meter échelle spectrograph fed with light from the 1.5 meter telescope. These first observations indicate that the system is extremely stable, both in its spectral response and in wavelength calibration. The principal aim of the project was to provide the capability of recording high resolution spectra at the 1.5 meter, using linear detectors. Even with the loss of light associated with the use of the fiber, a conservative estimate of the speed of the system indicates a factor of 20 increase in speed over the existing coudé spectrograph.
Esiderata for nearby - star quantities observable with small telescope
Authors: Gliese W.
Published: June 2019

At the General Assembly of the IAU at New Delhi van Altena reported on the new General Catalogue of Trigonometric Stellar Parallaxes (GCTSP) which was completed recently at the Yale Observatory. Time seems to be ripe now for the compilation of a Third Catalogue of Nearby Stars which will include all objects known to be nearer than 25 parsecs. This catalogue will contain positions, proper motions, radial velocities, spectral types, broad-band photometry, and parallaxes - quantities won by observations.
Times of minima and period changes of eclipsing binaries as a programme for small telescopes
Authors: Kreiner J. M.
Published: June 2019

Investigations of times of minima in eclipsing binaries give us important clues concerning a number of quite different and frequently unrelated phenomena such as the apsidal motion, mass-loss, mass-transfer or gravitational radiation. It is hard to over-estimate the importance of these relatively easy observations. However, simple statistics show that much remains to be done to assure proper data for even a moderate-size sample of eclipsing binaries. Here we present essential results of such statistics made for stars brighter than 12 magnitude in minima (this limit assumed arbitrarily as accessible to small-telescope observers).
Multiple stellar systems
Authors: Duquennoy A. , Mayor M.
Published: June 2019

A spectroscopic survey of visual binaries with known orbital elements has been carried out with the radial velocity scanner CORAVEL at the Haute-Provence Observatory, since 1977, (Baranne, Mayor, Poncet, 1979). This survey of more than 100 visual systems, selected from Dommanget's catalogue (1967) (see also a new edition 1982) was first devoted to the determination of stellar masses. Several multiple systems were detected and have permitted also a study of the structure of triple systems. We have detected and measured in particular a class of triple systems with radial velocity variations of small amplitude. Taking advantage of the high resolution and high signal-to-noise ratio accessible with the cross-correlation technique, such small amplitude radial velocity curves are sometimes derived only through the change of width and shape of the cross-correlation function. Let us recall that the cc-function of a SB2 (or SB3) system is only the weighted sum of the individual cc-functions (Mayor, 1985). This property of the cross-correlation combined with the linearity of the detector allow a very simple analysis of blended dips. The full width at half depth of the cross-correlation dip is about FWHD = 16 km/s (in absence of noticeable rotation). Analysis of blended systems allows a good determination of the two individual velocities if the difference |vr1 -Vr2| is equal or larger than about 0.15 *FWHD (about 2 km/s).
A long-term radial velocity program of high accuracy with a small telescope
Authors: McMillan R. S. , Smith P. H. , Frecker J. E. , Merline W. J. , Perry M. L.
Published: June 2019

We are making accurate observations of the change in Doppler shift of stellar absorption lines. The purpose is to detect the oscillatory reflex motion due to planets orbiting stars. The scrambling of incident light by an optical fiber and the stability of wavelength calibration by a Fabry-Perot etalon provide immunity to systematic errors. Selecting several echelle diffraction orders in the vicinity of 4250–4600 A, which are imaged on a CCD, about 350 points on the profile of the stellar spectrum are sampled by successive orders of interferometric transmission through the etalon. At 4300 A each interference order is 47 milliangstroms wide and the sample points are 0.64 A apart, causing distinct, widely-spaced monochromatic images of the entrance aperture to be formed in the focal plane of the camera. Changes in Doppler shift modify the relative intensities of these images, according to the slope of the spectral profile at each point sampled. To simplify operation and enhance sensitivity, the instrument is being operated as a null-measurement accelerometer, responding only to changes in radial velocity. With an argon emission line lamp the interferometer is calibrated to two parts in 100 million; this corresponds to ± 6 meters/sec in Doppler shift. These calibrations show instrumental variations of ± 27 meters/sec on a time scale of months; observations of stars are corrected for such changes. The internal repeatability of observations of the differential Doppler shift of Arcturus (K1 IIIb; B=1.19) is ± 6 meters/sec for each exposure of 600 square meter-seconds. These exposures are obtained in 15–20 minutes with a 0.9-meter telescope. The external repeatability (day-to-day differential accuracy) of nightly averages of stellar observations is ± 20 meters/second.
Recent Advances in the studies of Reaction Rates relevant to Interstellar Chemistry
Authors: Adams Nigel G. , Smith David
Published: June 2019

The current status of laboratory measurements of the rate coefficients for ionic reactions involved in interstellar molecular synthesis is discussed and the experimental techniques used to acquire such data are briefly described. Examples are given of laboratory data which are being obtained at temperatures close to those of interstellar clouds. Particular attention is given to the results of recent theoretical and experimental work which show that the rate coefficients for the binary reactions of ions with polar molecules at low temperatures are much larger than previously assumed. It is shown how these new developments in experiment and theory are reconciling the differences between predicted and observed abundances for some interstellar molecules. Also briefly discussed are: - the phenomenon of isotope exchange in ion/neutral reactions which explains the apparent enrichment of heavy isotopes in some interstellar molecules, the role of atoms in molecular synthesis, some studies of ion/neutral reactions pertaining to shocked regions of interstellar clouds, ternary association reactions and the analogous radiative association reactions, and recent new laboratory measurements of dissociative recombination coefficients. Finally, some guidance is offered in the proper choice of critical kinetic data for use in interstellar chemical modelling and some further requirements and likely future developments are mentioned.
Collision Induced Transitions of Molecular Systems of Interstellar Interest through Microwave Pulse Techniques
Authors: Mehrotra S. C.
Published: June 2019

Microwave pulse techniques have proved to be very useful to obtain informations about coherence decay rates and population transfer rates in gas phase. the coherence decay rates have been measured by a technique which involves the detection of the transient emission signal of the molecular sample following an intense microwave pulse. the (π-τ-π/2) pulse sequence technique has been used to extract informations about population transfer rates. the experimental results on 1-doublet transitions of HCN and HCCCN perturbed by H2,D2and He are given. the theoretical results obtained from the perturbative approach to collision dynamics have also been computed, and compared with the experimental results. for the 1-doublet transitions of HCN, the population decay rates have found to be considerably less than the corresponding coherence decay rates.
Studies of Organic Molecules Containing Methyl Groups in Dark Clouds
Authors: Friberg P. , Irvine W.M. , Madden S.C. , Hjalmarson A.
Published: June 2019

We have observed transitions of methanol, methyl acetylene(1),(2) and acetaldehyde(3) in dark clouds. in methanol the 20−10 A+, 10−00 A+, 2-1−1−1 E lines and tentatively the 20−10 E line have been observed. The 10−00 E, 21−11 E and the 00−1−1 E lines were searched for but not detected. Maps of TMC1, L134N, and B335 in the 20−10 A+ and 2−1−1−1 E lines show that the methanol emission is very extended and follows the extent of the C180 J=1−0 emission well.
The Chemistry of Cold, Dark Interstellar Clouds
Authors: Irvine W. M.
Published: June 2019

In recent years the nearby cold, dark clouds have been shown to possess a rich chemistry, with interesting differences with respect to warmer massive-star-forming regions and also among the cold clouds themselves. 39 molecular species are now known in these regions. Recent molecular detections and upper limits in dark clouds are discussed, with particular emphasis on the tri-carbon species C3O, C3H, and C3H2.
X-Ray Emission as Evidence of Activity in Otherwise “Normal” Galaxies
Authors: Maccacaro T. , Gioia I.M. , Schild R. , Maccagni D. , Stocke J.
Published: June 2019

The very large majority of the galaxies selected in X-ray surveys are active galaxies (e.g. narrow emission line galaxies, Seyfert galaxies etc.). There are however a few examples of normal galaxies, which are sometimes characterized by an X-ray luminosity in excess of what is expected on the basis of their optical appearance. A closer look at these galaxies may reveal the presence of a mini active nucleus or of other processes responsible for the powerful X-ray emission. Here we consider the normal galaxies selected in the Medium Sensitivity Survey and we discuss the properties of the most X-ray luminous one. We show that this object, which has an optical spectrum lacking any evidence of nuclear activity and which has a radio luminosity typical of early type galaxies, is indeed a peculiar galaxy surrounded by a hot (>2 keV) halo extending out to a radius of 300 kpc, implying a total mass of ∼3 × 1013 M⊙.
Circumstellar dust around FU Orionis stars
Authors: Welin Gunnar
Published: June 2019

It is immediately apparent from IRAS and other far infrared data (figure 1) that all known FU Orionis stars, or fuors, are associated with substantial amounts of cool circumstellar dust.

The pre-outburst magnitudes for V1057 Cyg indicate that this star was immersed in circumstellar dust already before its flare-up in 1969–1970, and hence that this dust did not - as has been claimed - appear only after the outburst; regrettably there exist no far infrared data from that time. The colours also exclude the possibility that the star then was of the alleged spectral type KO, but point to it being of a rather early type and obscured by both interstellar, local, and circumstellar matter. For details, see Welin 1985.
Recent observations of Herbig-Haro objects, optical jets, and their sources
Authors: Mundt Reinhard
Published: June 2019

Recent observations of Herbig-Haro objects and optical jets are reviewed, including observations of the stellar objects responsible for these and related outflow phenomena. The review discusses observations obtained in the following wavelength bands: radio, far-infrared, infrared, optical, and ultraviolet.
Shock excited emission knots in cometary reflection nebula
Authors: Neckel Th. , Staude H. J.
Published: June 2019

Near infrared and Ha CCD images of the newly found cometary reflection nebula GN 20.18.3. led to the discovery of its illuminating star and of a bright Ha knot located on its axis of symmetry. The knot has a Herbig-Haro spectrum indicating the presence of a collimated outflow from the central star. Also in the Bok globule L 810 a red CCD image reveals a cometary reflection nebula surrounding the central star, from which a shock excited filament is emanating. These observations emphasize the common origin of cometary nebulae and collimated high velocity flows.
1612 MHz observations of southern IRAS sources
Authors: Dollery M. E. , Gaylard M. J. , Cohen R. J.
Published: June 2019

Eight of thirty-four previously unobserved IRAS sources were found to be relatively strong 1612 MHz OH emitters. Five of these emit at 1667 MHz. Of the eight half are high velocity range, population I type stars, the other half are low velocity range, population II type stars. The pump efficiencies are in the range 0.018 ≤ e ≤ 0.163.
Detection of the first extra-galactic OH/IR star
Authors: Wood P. R. , Bessell M. S. , Whiteoak J. B.
Published: June 2019

A search has been made for 1612 MHz OH maser emission from OH/IR stars in the Magellanic Clouds. Candidate objects were selected mainly on the basis of their 25μm flux densities and the 25 to 12μm flux ratio as given in the IRAS point source catalog; two known long-period variables and two HII regions (30 Doradus and N159) were also examined. One OH source (IRAS 04553-6825) was detected, this being the first OH/IR star found in the Magellanic Clouds. Upper limits were placed on the flux for 17 other sources. The expansion velocity of the circumstellar material surrounding IRAS 04553-6825, as indicated by the OH peak separation of 11 km s−1, is surprisingly small compared to Galactic sources of similar bolometric and OH luminosity. The OH intensity of IRAS 04553-6825, and the upper flux limits placed on many of the other objects examined, indicate that Magellanic Cloud OH/IR stars do not emit OH as strongly as their Galactic counterparts of similar 25μm/12μm flux ratio. Both the low expansion velocity of IRAS 04553-6825 and the low OH intensity of the Magellanic Cloud infrared sources may be explained by the low metal abundance in the Clouds.
Infrared speckle interferometry of OH-stars
Authors: Chapman Jessica M. , Wolstencroft R.D.
Published: June 2019

We have begun a co-ordinated programme of high angular-resolution radio and infrared measurements to study the physical structure of the circumstellar envelopes surrounding high mass-loss OH-stars. Here we give near-infrared (NIR) angular diameters for 5 stars. For each of these stars the spatial distribution of the OH maser emission at 1612 MHz or 1665 MHz has been previously mapped.
Modelling the outer atmospheres and winds of K giant stars
Authors: Judge P. G.
Published: June 2019

It is shown how empirically derived constraints affect models of the outer atmospheres and winds of K giants, taking α Boo (K 2III) as an example. The importance of empirical approaches prior to making semi-empirical models is stressed. The reliability of recent wind models is assessed.
Theory of stellar coronae
Authors: Serio S.
Published: June 2019

X-ray observations have shown in recent years that the existence of high temperature plasmas in stellar atmospheres is far more widespread than extrapolated from preexisting theories of the solar and stellar coronae, forcing a radical change in our understanding of the mechanisms of coronal physics. This paper reviews our current ideas on stellar coronae, in particular on the role of magnetic confinement in the atmospheres of late type stars.
Emission measures and heating mechanisms for stellar transition regions and coronae
Authors: Böhm-Vitense E.
Published: June 2019

In order to determine the heating mechanisms for stellar transition regions and coronae we try to determine the damping lengths for the mechanical flux(es) responsible for the heating. For the lower part of the transition regions (30,000 < T≤100,000 K) the damping lengths are consistent with Shockwave damping. This appears to be also true for the upper part of the transition region in Procyon, while for the upper part of the solar transition region the damping length is much larger.
What can be learnt from full disk X-ray observations of stellar flares?
Authors: Schmitt J.H.M.M. , Fink H. , Harnden F.R.
Published: June 2019

The Einstein Observatory demonstrated the existence of hot envelopes, i.e., stellar coronae, around most classes of normal stars (Vaiana et al. 1981). The coronae of late type stars of spectral type F through M are generally thought to be solar-like, i.e., structured and organised by the magnetic field topology and heated by some process(es) involving magnetic energy. Here the property “solar-like” does not refer to the optical appearance of a star, but rather to the role played by magnetic fields in the outer stellar envelope (Linsky 1985). Since it is difficult to measure magnetic fields on other stars directly, a number of indirect indicators is used in order to infer whether a corona should be considered “solar-like” or not.
Infrared and radio excesses of late-type stars
Authors: Skinner C. J.
Published: June 2019

The IRAS catalogues have been searched for cool (G,K,M) giant and supergiant stars to investigate the occurrence of circumstellar (C/S)silicate dust, revealed by its emission features at 9.7 and 18μm. Low Resolution Spectrograph (LRS) spectra covering the 7-23μm range were used, plus the 60 and 100μm photometric points. M Supergiants were found in White Wing (1978), other stars by correlating the Bright Star Catalogue with the LRS catalogue: this discriminated against very cool stars reddened by dust; however i t can be seen in Table I that there is a clear trend for cooler and more luminous stars to have a dust shell. M Supergiants almost all have dust shells, whilst only the cooler M bright-giants and giants do. Of the G and K stars, only a very few of the Supergiants have dust shells. The sili cate features fell into two categories:
Chemical composition and circumstellar shells of carbon stars - Any obvious relations?
Authors: Eriksson Kjell , Gustafsson Bengt , Olofsson Hans
Published: June 2019

Evidence for circumstellar absorption around the warm N-type carbon star TX Piscium was found in a high-resolution IUE spectrum by Eriksson et al. (1986). This investigation also included the search, with a positive result, for CO J=1−0 emission from the circumstellar shell. From the Mn I absorption and CO emission a column density of about 1020–1022 H atoms per cm2 was estimated, as well as a mass loss rate around 10−7–10−6 M per year.
Luminous blue variables - An evolutionary picture
Authors: Sreenivasan S. R. , Wilson W.J.F.
Published: June 2019

A considerable amount of observational information has been gathered on the so-called Hubble-Sandage Variables or S Doradus variable stars, largely due to the efforts of the Heidelberg group (see Wolf, this volume for a review). It is believed that the star P Cygni also belongs to this category. This group of objects is now being referred to as Luminous Blue Variables because they are massive (>10 M⊙), evolved (spectral type B or later) objects showing variability of more than one kind, and evidence of nuclear processed material at the surface.
A method for calculation of line profiles in expanding atmospheres: Application to winds from central stars of planetary nebulae
Authors: Cerruti-Sola M. , Lamers H.J.G.L.M. , Perinotto M.
Published: June 2019

The structure of a stellar wind and its associated mass loss can be derived from the analysis of ñ Cygni-like line profiles. These do better occur in the UV range and have been extensively observed with the Copernicus (900–1450 A) and IUE Satellites (1150–3200 A).
The unstable 06.5f?p star HD 148937 and its interstellar environment
Authors: Leitherer Claus , Chavarría-k. Carlos
Published: June 2019

The massive, early-type star HD 148937 (spectral type O6.5f?p) is surrounded by a unique set of nebulosities. A spherically symmetric Strömgren sphere (Radius ≃ 25 pc), an ellipsoidal filamentary nebulosity (semimajor axis ≃ 5 pc) interpreted as a stellar-wind-blown shell, and a bipolar nebular complex (semimajor axis ≃ 1 pc) with HD 148937 located in the apparent center of symmetry. Here we report on observations of these nebulosities (narrow-band CCD imaging, IDS spectrophotometry, high resolution (ΔV ≃ 7 km sec−1) spectroscopy) in an attempt to establish a consistent model of HD 148937 and its nebulosities.
Ionisation fractions and mass-loss in O stars
Authors: Prinja Raman K. , Howarth Ian D.
Published: June 2019

The most sensitive indicators of mass-loss for stars in the upper left part of the HR diagram are the UV P Cygni profiles observed in the resonance lines of common ions such as N V, Si IV, and C IV. We present here some results from a study of these lines in the high resolution IUE spectra of 197 Ï stars. Profile fits were carried out in the manner described by Prinja & Howarth (1986) for all unsaturated P Cygni resonance doublets. The parameterisations adopted enable the product of mass-loss rate (Ṁ) and ion fraction (qi) to be determined at a given velocity, such that Ṁ qi°C Ni R* v∞, where Ni is the column density of the observed ion i, v∞ is the terminal velocity, and R⋆ is the stellar radius. The accompanying figures illustrate the behaviour of Ṁ qi (evaluated at 0.5 v∞) for N V and C IV.
The effects of boundary conditions on stellar evolution
Authors: Harpaz Amos , Kovetz Attay , Shaviv Giora
Published: June 2019

The effects of using different treatments of the surface boundary conditions are investigated in the context of the mass of He White Dwarfs. We find that since the White Dwarf progenitor is a star with a very extended atmosphere, the results are sensitive to the degree of accuracy implemented in the handling of the boundary conditions.
Optical/infrared observations of RV Tauri stars
Authors: Goldsmith M. J. , Evans A. , Albinson J. S. , Bode M. F.
Published: June 2019

Optical/infrared observations of RV Tauri stars obtained at SAAO have allowed the natures of the dust shells around stars with infrared excess to be investigated. The data suggest that dust formation occurs sporadically and that some stars have multiple shells. There is no photometrically discernible difference between carbon- and oxygen-rich stars or their dust shells. There is some evidence that stars with higher metallicity have more dust.
Nucleation in novae
Authors: Callus C. M. , Albinson J. S. , Evans A.
Published: June 2019

The observation of a deep minimum in the light curves of some novae, accompanied by a simultaneous rise in the infrared some weeks after outburst, is attributed to the rapid formation and growth of dust grains in the ejecta (Clayton & Wickramasinghe 1976). The observed nucleation rate J(obs) ~ 10−10cm−3s−1for typical dusty novae, whereas the expected homogeneous nucleation rate J(hom) ~ 6 × 10−26cm−3s−1. We suggest that heterogeneous nucleation on ions could be a possible grain forming mechanism. In this case J(het) ~ 3.3 × 10−12cm−3s−1, which is within an order of magnitude of the observed nucleation rate.
A Large Timing Discontinuity in the Vela Pulsar, July 1985
Authors: Flanagan C S
Published: June 2019

A pulsar-monitoring programme has been running at Hartebeesthoek Radio Astronomy Observatory over the last three years, at 2.32 and (during the last year) at 1.67 GHz. Twenty pulsars are observed once or twice a fortnight, and PSRs 1641-45 and 0833-45 (the Vela pulsar) daily.
The Galactic Pulsar Population and Neutron Star Birth
Authors: Narayan Ramesh
Published: June 2019

The radio pulsars in the Galaxy are found predominantly in the disk, with a scale height of several hundred parsecs. After allowing for pulsar velocities, the data are consistent with the hypothesis that single pulsars form from massive stellar progenitors. The number of active single pulsars in the Galaxy is ∼ 1.5 × 105, and their birthrate is 1 per ∼ 60 yrs. There is some evidence that many single pulsars, particularly those with high magnetic fields, are born spinning slowly, with initial periods ∼ 0.5–1s. This could imply an origin through binary “recycling” followed by orbit disruption, or might suggest that the pre-supernova stellar core efficiently loses angular momentum to the envelope through magnetic coupling. The birthrate of binary radio pulsars, particularly of the millisecond variety, seems to be much larger than previous estimates, and might suggest that these systems do not originate in low mass X-ray binary systems.
The Galactic Sources G5.4-1.2 and G5.27-0.90
Authors: Caswell J.L. , Kesteven M.J. , Haynes R.F. , Milne D.K. , Komesaroff M.M. , Stewart R.T. , Wilson S.G.
Published: June 2019

Long after a supernova event, the stellar core (neutron star) may continue to excite an extended remnant of ejecta surrounding it, as in the case of the Crab nebula. In contrast, the more common shell supernova remnants (SNRs) appear unaffected by any embedded neutron star.
The Globular Cluster Population of X-ray Binaries
Authors: Verbunt Frank , Hut Piet
Published: June 2019

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.

EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.
Observations of Quasi-Periodic Oscillations in Cyg X-2
Authors: Hasinger Günther
Published: June 2019

EXOSAT observations of Cyg X-2 reveal two types of QPO's (quasi-periodic oscillations) which are associated with different spectral behaviour. QPO's in the range 18–55 Hz with a hard spectrum are found in all observations where the source is on the ‘horizontal branch’ in an hardness-versus-intensity diagram. On the ‘vertical branch’, however, QPO's with a soft spectrum are found at a stable frequency of 5.6 Hz. A multitude of QPO frequency-intensity relations, found in different ‘horizontal branch’ observations, coalesce to an almost unique relation when the QPO frequency is correlated with spectral hardness. A cross-correlation analysis of the rapid variability reveals a time-lag of hard photons by 1.5–3.8 ms; the lag being smaller when the QPO frequency is larger. All results are consistent with a model where QPO's represent the Kepler frequency at the edge of the neutron star magnetosphere. In particular the data do not require the assumption of a beat frequency. The derived surface magnetic field strength is of the order of 1010G.
Secondary Components of Binary Pulsars & Magnetic Field Decay in Neutron Stars
Authors: Kulkarni Shrinivas R.
Published: June 2019

We report the discovery of white dwarf secondaries in 0655+64 and 0820+02 systems. In the 2303+46 system, we do not find any optical counterpart suggesting that the companion is another neutron star. The existence of a cool and therefore old white dwarf in the 0655+64 system implies that the surface magnetic field of neutron stars stops decaying beyond some value(s) of field strength.
Two Types of Pulsars
Authors: Huang J.H.
Published: June 2019

To sort out the whole sample of pulsars with measured P and P into two types has much something to do with the origin and evolution of neutron stars. Under the configuration of two types of pulsars with different spindown mechanism, we have discussed a variety of their properties, including their radio emission mechanism, space velocities, interior structures and evolutionary modes. The fact that different type of pulsars does have quite different properties indicates that the processes to create neutron stars may have two distinct types, say, Type II supernova explosion and the collapse of accreting white dwarfs. The evolutionary mode for our Type I pulsars provides such a key link between binary pulsars and X-ray binary pulsars that we may propose a self-consistent scenario for binary pulsars, X-ray binary pulsars, fast pulsars as well as Type I pulsars.
Cygnus X-3 and Other Ultra-High-Energy γ-Ray Sources
Authors: Barnard John J.
Published: June 2019

Recently, several binary X-ray sources have been found to be sources of ultra high energy γ-ray emission. Air shower observations indicate photon energies >∼ 1015 eV. We review the current status of observations from the source Cygnus X-3, and compare this data with that from the sources Hercules X-1, Vela X-1, and LMC X-4. Current theoretical models for the production of γ-rays and the acceleration of high energy particles are discussed and the consequences for the evolution of such systems are examined.
EXOSAT News on Geminga
Authors: Caraveo Patrizia A. , Bignami Giovanni F.
Published: June 2019

1E0630+178 was the target of a 64,000 sec EXOSAT observation on March 17–18, 1985. The 1200 photons recorded were folded around the value predicted by previous Einstein '79, '81 and EXOSAT '83 data. The region between 60.20 and 60.35 sec. was searched with independent steps of 0.005 sec, computed according to the relation: step = (period)2/observations length/number of bins in the light curve. A reduced χ2 of 3.85 (9 d.o.f.) was found for 60.285 sec. The data were then divided into five segments and the same search was performed yielding for the third segment a red. χ2 of 4.33. Moreover, the a posteriori periodogram shows also the presence of harmonics at 30.14 and 15.07 (see figure) wich appear to be even more significant (red. χ2 of 5.06 and 4.37, respectively) than the effect at 60.28.
New Distance Limit for the 3-5-79 Source
Authors: Liang E. P.
Published: June 2019

We provide new distance limits for the March 5, 1979 gamma ray transient source based on the synchrotron interpretation and the lack of low frequency self-absorption cutoff. This leads to upper limits of 0.6–11 kpc for emission areas ranging from 1 squared km polar caps to a 10 km radius stellar surface.
On the Phases of Period Variation of SS 433
Authors: Luo W.Q.
Published: June 2019

In a previous paper (Luo, 1986), we have improved the method by Katz (1982) and Fan et al (1983). We have also found some important features in a ring model with precession and nodding motion, i.e., all the higher periodical components contain the ones with n = 1,2,3. So we can call T1,T2, and T3 fundamental periods.
Strasbourg-ESO Catalogue of Galactic Planetary Nebulae
Authors: Agnès Acker , François Ochsenbein
Published: June 2019

A list of 1820 objects, each of them called at least once a planetary nebula, has been inspected; 1143 of them have been classified as true or probable planetary nebulae by the authors of the catalogue (Tables 1); 347 objects, the status of which is still unclear, were classified among the “possible” planetary nebulae (Table 2).; 330 objects have been rejected, on various grounds, from the community of planetary nebulae (Table 3).