bluuebunny/crossref_metadata_2025 huggingface dataset:
Past Star Formation History of the Magellanic Clouds
Authors: Rocca-Volmerange B.
Published: June 2019

From far-UV to visible integrated photometry of the Magellanic Clouds we give an estimate of the past star formation parameters. Most of our results can be applied to Irregular galaxies.
Chemical Evolution of the Magellanic Clouds
Authors: Matteucci Francesca
Published: June 2019

According to the stochastic self propagating star formation theory (SSPSF, Gerola and Seiden, 1978), the star formation process in galaxies changes from a fluctuating but continuous mode to a bursting one, when the size of the system becomes relatively small (R ≤ 3 Kpc). Then, due to its size, the LMC should be a system undergoing fluctuating but continuous star formation activity, whereas the SMC should be in the region between continuous and bursting modes (Gerola et al. 1980). In order to look better inside this problem a model of chemical evolution of the two Clouds, which takes into account the stochastic star formation rate, has been built. For the SMC both the continuous and the bursting modes of star formation have been considered. As a result we find that the different chemical histories of the two Clouds may be related to the fact that SMC has undergone several bursts of star formation (between 50 and 60), while a continuous star formation activity was present in LMC.
Distribution and Radial Velocities of Late Supergiant Stars in the LMC and the SMC
Authors: Martin N. , Maurice E. , Prévot L. , Rebeirot E. , Rousseau J.
Published: June 2019

In 1983, our group published two catalogues of KM supergiants, respectively members of the LMC (Rebeirot et al., 1983) and of the SMC (Prevot et al., 1983).
From What Radius Do the Winds of Magellanic Cloud Supergiants Produce Fe II Emission Lines?
Authors: Friedjung M. , Muratorio C.
Published: June 2019

Maximum values for the inner radii at which Fe II emission line formation can take place in the winds of three Magellanic Cloud supergiants have been determined. The lie between 3 × 1013 and 3 × 1014 for R50, R82, and R126.
An Unstable Ofpe Star in the LMC
Authors: Walborn Nolan R.
Published: June 2019

The extreme Ofpe star HDE 269858 = Radcliffe 127 in the Large Magellanic Cloud (Walborn 1977), which has ejected nitrogen-rich material (Walborn 1982), was observed to be in a state of outburst on December 20, 1982. Spectroscopic observations at 2.5Å resolution with the Cerro Tololo Inter-American Observatory 1.5 meter SIT vidicon system showed a blue magnitude of 10.2, more than 1 magnitude brighter than previously, and a qualitatively changed spectrum. The Of emission features and the strong He I P Cygni profiles (especially λλ3889 and 4471) had disappeared, while the hydrogen Balmer emission remained very intense. IUE observations by S. Shore and N. Sanduleak provide evidence that the star has been in this “high” state since at least March 1981. Hence, a phenomenon related to those of P Cygni and/or Eta Carinae may be indicated. A current preprint by 0. Stahl, B. Wolf, G. Klare, A. Cassatella, J. Krautter, P. Persi, and M. Ferrari-Toniolo announces the prior discovery of the outburst at the European Southern Observatory in January 1982 and discusses extensive observations of its development, making a convincing case for interpretation of HDE 269858 as the hottest known Hubble-Sandage variable and a prime candidate for an 0 star becoming a WR via episodic enhanced mass loss.
New Optical Observations of R136
Authors: Chu You-Hua
Published: June 2019

R136 is the luminous central object of the 30 Doradus nebula in the LMC. Its bluest and brightest component R136a has been interpreted as a supermassive star with a mass of approximately 2000 M⊙, based on its unusual UV spectral properties and the assumption that it is responsible for most of the ionization of the 30 Dor nebula (Feitzinger et al. 1980; Cassinelli et al. 1981; Savage et al. 1983). On the other hand, R136a has also been argued to be the core of a dense cluster, since the integrated light distribution from 0.2 to 22 pc radius centered on R136a is similar to that of a globular cluster (Moffat and Seggewiss 1983), and its optical spectrum can be synthesized by its nearby early-type stars (Melnick 1983).
Spectroscopy of Stellar X-ray Sources in the Magellanic Clouds
Authors: Hutchings J. B.
Published: June 2019

In the Magellanic Clouds, about 75 candidate stellar X-ray sources have been detected. Most of these positions have now been investigated and optical identifications made for ~ 50%. The majority of sources are foreground dwarf stars or background active galaxies. Detailed investigations exist for 3 SMC sources and 6 LMC sources. It is possible to make a preliminary comparison with the population of galactic X-ray sources. The Magellanic Cloud X-ray binaries have a number of unique or remarkable properties and the most important ones are presented and discussed. These include the most rapid pulsars (SMC X-1, 0538–66), the possible precessing disk in LMC X-4, and the black hole candidates LMC X-3, LMC X-1. The properties of these objects relate to the evolution of stars in the Magellanic Clouds and how it differs from the Galaxy.
Gas-to-Dust Ratios in the Magellanic Clouds
Authors: Koornneef Jan
Published: June 2019

From radio observations it has been known for some time that a relatively large fraction of the total mass of the Magellanic Clouds is in the form of atomic Hydrogen. In contrast, optical photometry shows that both galaxies suffer rather little obscuration by dust, except in regions where the stellar population indicates recent star formation. However, the possibilities of discussing gas-to-dust ratios have been limited by the poor spatial resolution of the 21 cm HI-observations and uncertainties with respect to the relative location of the various components (gas, dust and stars).
The Composition of H II Regions in the Magellanic Clouds
Authors: Dufour Reginald J.
Published: June 2019

The state of our knowledge concerning the chemical composition of H II regions in the Magellanic Clouds is reviewed. New abundances derived from all modern published spectroscopy are presented. Some of the implications of the results regarding the nucleosynthesis of the elements and galactic chemical evolution are noted.
The Effect of Mass-Loss On the Evolution of HII Regions in the L.M.C.
Authors: Wilson I.R.G. , Dopita M. A.
Published: June 2019

Empirical calibrations based on prior studies of Galactic OB Stars are used to determine the integrated stellar wind mechanical luminosity (Lw) and the integrated Lyman continuum photon luminosity (S*) for 10 OB clusters in the L.M.C. These values of Lw and S*, together with narrow band H-α surface photometry of an overlapping sample of 15 L.M.C. HII regions, are used to show that the large shell-like HII regions, in the L.M.C. are stellar wind bubbles 3 to 5 million years old. In order to reproduce the general properties of these HII shells, a thick cushion of shocked stellar wind gas must have been present on the inside of the shell for most of the life time of the nebula, and the shell itself must be ram pressure confined by the HI/molecular cloud out of which it formed.
Molecular Line Observations in the Large Magellanic Cloud
Authors: Gardner F. F.
Published: June 2019

This is a preliminary report on on-going observing programs in the LMC using CSIRO facilities. Molecular-line observations made with the 64-m Parkes telescope include OH at 18 cm (Whiteoak & Gardner 1976b; Caswell & Haynes 1981), H2CO at 6 cm (Whiteoak & Gardner 1976a) CH at 9 cm (Whiteoak et al. 1980) and H2O at 1.3 cm with beamwidths between 13′ and 1′.7 arc; observations of HCO+ at 3.4 mm (Batchelor et al. 1981) and CO at 2.6 mm have been made with the 4-m Epping telescope.
Thermal Bifurcation of the Outer Photosphere
Authors: Ayres T. R.
Published: June 2019

The degree of thermal heterogeneity at the base of the solar chromosphere is substantially beyond that simulated in the best-available multi-component models; casting serious doubts on inferences drawn from them.
Results from 2-D Numerical Simulations of Solar Granules
Authors: Steffen M. , Gigas D. , Holweger H. , Krüss A. , Ludwig H.-G.
Published: June 2019

We have carried out detailed numerical simulations of solar granular convection cells of different horizontal dimension. The calculations account for the basic physics of compressible convection, including the ionization of H I, He I and He II, and H2 molecule formation as well as non-local, multi-dimensional radiative transfer (grey approximation in LTE). A more detailed description of the simulations has been given by Steffen and Muchmore (1988) and by Steffen et al. (1989).
Classification of Magnetoatmospheric Modes in Sunspot Umbrae
Authors: Hasan S.S. , Sobouti Y.
Published: June 2019

We examine the wave modes in a sunspot umbra. Assuming a stratification, based on a model atmosphere in a sunspot, the normal mode spectrum is determined. The modes are classified using a scheme based on a Helmholtz decomposition of the displacements into l(longitudinal) and t(transverse) components. In certain cases these can be related to the usual fast and slow MHD waves. We compute the theoretical eigenfrequencies and note the existence of umbral oscillations with periods in the range 2-3 min, which are interpreted as slow and mixed modes. The frequencies of the Alfvén waves are also calculated. It is suggested that these modes might also have been observed.
Inverse Cascade in Hydrodynamic Turbulence and its Role in Solar Granulation
Authors: Krishan V.
Published: June 2019

Self-organization i.e. the formation of large ordered structures in a turbulent medium is a consequence of inverse cascade where energy preferentially transfers towards large spatial scales. It is envisaged that this may be one way of explaining solar granulation at various scales.
Large-Scale Internal Magnetic Field of the Sun
Authors: Dudorov A.E. , Krivodubskij V.N. , Ruzmaikin A.A. , Ruzmaikina T.V.
Published: June 2019

The behaviour of the magnetic field during the formation and evolution of the Sun is investigated. It is shown that an internal poloidal magnetic field of the order of 104 − 105 G near the core of the Sun may be compatible with differential rotation and with torsional waves, travelling along the magnetic field lines (Dudorov et al., 1989).
Does a Common Dynamo Mechanism Exist for Lower Main Sequence Stars?
Authors: Teplitskaya R.B. , Skochilov V.G.
Published: June 2019

Based on an extended list of lower main sequence stars from Rutten (1987), the relation between chromospheric activity and Rossby number has been revised. The increased statistics changes the shape of the curve as compared with that of Noyes et al. (1984). The saturation at small Rossby numbers has disappeared. The dependence on Rossby number in the range of very large Rossby numbers has weakened. The standard deviation of the activity indices from the mean curve is about 40%. This scatter of individual stars is not due to differences in the spectral type or age of the stars.
Outstanding Theoretical Problems
Authors: Durrant C.J.
Published: June 2019

The development of model atmospheres from the ‘classical’ static but deductive models to present-day dynamic but inductive models is sketched. The main problems facing theory are defined in terms of the need to produce a post-classical inductive model. Attention is focused on the most promising tool available today, the computers able to realize simulations of astrophysical systems. The direction of progress in the areas of radiative transfer, convective transport, waves and oscillations, and MHD is reviewed. It is concluded that the major outstanding radiative and hydrodynamic problems are likely to be elucidated in the foreseeable future, especially if there is a suitable commitment by the international community. However, the understanding of the behaviour of magnetic fields and their associated activity will require a longer, but no less urgent, programme.
Theory of Wolf-Rayet Atmospheres
Authors: Hillier D. John
Published: June 2019

Theoretical modeling of line and continuum formation in Wolf-Rayet (W-R) atmospheres is reviewed. We examine the basic premises on which the models are built, and critically compare theoretical models with observation. Discrepancies between theory and observation are analyzed to determine their implication for our understanding of W-R atmospheres. Line formation, continuum formation, and the ionization structure of W-R envelopes are examined in detail. Abundance determinations are briefly reviewed.
Chemical Composition in the Envelopes of Different WR Subtypes
Authors: Nugis T.
Published: June 2019

Valuable model-independent information about the chemical composition of WR stars can be obtained by using lines of different ions arising at transitions between highly excited energy levels. We determine the abundances of He, H, C, N, O using theoretical line intensities obtained by solving statistical equilibrium equations for level populations for different subtype WR envelope conditions.

The chemical composition of WR stars strongly differs from the mean cosmic composition. In the case of WN stars nuclear processed CNO products of H-burning are revealed in the envelopes and He-burning products in the WC envelopes.

The abundance of oxygen in WC stars differs from the predictions of recent evolutionary calculations which account for the new 12C(α,γ) 16O reaction rate.
Identification and Analysis of Infrared Lines of WC Stars
Authors: Eenens P.R.J. , Williams P.M. , Wade R.
Published: June 2019

We present 1 – 3.4 μm spectra of six Wolf-Rayet stars: WR 146 (WC4), WR 111 (WC5), WR 86 (WC7), WR 140 (WC7+O4), WR 135 (WC8) and WR 88 (WC9). Examination of the relative strengths of the emission lines has enabled us to make over 20 new line identifications. Recombination analyses of the carbon and helium lines yield C/He abundance ratios much in excess of the solar value and correlated with spectral subtype.
The Nitrogen Spectra of WN Stars: The WN6 “Standard” Star HD 192163 (WR136)
Authors: Wessolowski U. , Hamann W.-R. , Schmutz W.
Published: June 2019

Hitherto our quantitative analyses of WR spectra [2][5] have been based on pure-helium models [1][6]. Now we further improved our non-LTE calculations by including a complex model atom of nitrogen (90 energy levels, 351 line transitions; with low-temperature dielectronic recombination) into our model atmospheres in order to synthesize adequately the spectra of WN subtypes (Wessolowski et al., in preparation). Together with the nitrogen (the most important “metal” in WN atmospheres), we introduced an improved temperature structure into our model calculations [3], now accounting for non-grey radiative equilibrium instead of the grey approximation applied so far. Moreover we took into account the line overlap of the considered elements (here: helium, nitrogen) and also their blanketing effects on the continuous radiation field.
Long Period WR Binaries
Authors: Annuk K.
Published: June 2019

Now it is clear that there exist some long period (periods exceed a year) Wolf-Rayet binaries. This paper presents the results of our radial velocity study for three WR binaries: HD193077 (WN6 + O9), HD193793 (WC7 + O5-6) and HD192641 (WC7 + O9). Our spectroscopic observations confirm that HD193077 and HD193793 are long period systems with the periods of 1538 and 2886 days. Most likely, HD192641 is also a long period WR binary (P ≥4400 days).
Observations of Wolf-Rayet Mass Loss
Authors: J Willis Allan
Published: June 2019

Current knowledge of the stellar winds and mass loss rates for WR stars is reviewed. Recent IR spectroscopy and reassessments of UV resonance line P Cygni profiles have led to revisions of terminal velocities, with v∞ ≃ 0.75 × previous estimates. Radio and IR (10μm) free-free emission for well-established thermal sources, coupled with recent considerations of the wind ionisation balance and chemistry, leads to WR mass loss rates lying in the range 10-5 − 10-4 M⊙ yr–1. This scale is confirmed by independent analyses of optical polarisation modulation in WR+O binaries. No significant differences are apparent between the mean mass loss rates of: (a) single and binary WR stars; (b) WN and WC stars, and (c) the WN and WC subclasses. The overall mean WR mass loss rate is ~ 5 × 10-5 M⊙ yr–1. Although WR radiative luminosities are uncertain, there may be a rough scaling of MWR with L∗, with a spread of up to an order of magnitude at a given L∗. WR winds have the highest momenta of the hot luminous stars, with values of M v∞ c/L∗ in the range 1-30 (WN7,8 and WC9 stars may lie near the lower bound). An additional mechanism to radiation pressure may be required to initiate the high WR mass loss, although thereafter the winds may be radiatively accelerated. Intrinsic variability in optical light, polarisation and emission lines, and in UV P Cygni profiles, indicate significant instability in the WR winds. For extragalactic WR stars in the Local Group, optical line strengths and widths do not suggest substantial differences in wind velocities and mass loss rates of subtypes compared to galactic counterparts.
Infrared Observations of Mass Loss from Massive Stars
Authors: Barlow M.J.
Published: June 2019

The future use of space-borne IR spectroscopy to determine the ionization structure and abundances in the outer winds of WR stars is described. A mass loss rate of 1.7×10-5 M⊙ yr–1 has been derived from 10 μm photometry of the WO2 star Sanduleak 5 (WR 142). The He/H number ratios in the winds of P Cyg and AG Car have been derived from a recombination line analysis of their 1-4 μm spectra and mass loss rates of 2.2×10-5 M⊙ yr–1 and 3.7×10-5 M⊙ yr–1 have been respectively derived for them.
Radio Observations of Massive OB Stars
Authors: Howarth Ian D. , Brown Alexander
Published: June 2019

The mass-loss rates of O stars and B supergiants are of interest because of their influence on the evolution of these massive stars (among other matters). In principle, the ‘safest’ (i.e. most model-independent) method of determining M is to measure the free-free emission from stellar winds at radio wavelengths. This method is complicated, however, by the existence of poorly understood non-thermal emission in some stars, and by the possibility of hydrogen recombination in the winds of B supergiants.

We are in the process of carrying out a VLA survey of OB stars, initially at 3.5cm, to a flux limit of ~0.1mJy. Because all our targets should have thermal emission at detectable levels (based on mass-loss rates from Howarth & Prinja 1989 and terminal velocities from Prinja, Barlow & Howarth 1990), the survey is yielding an unbiassed estimate of the frequency of non-thermal emission. The improved sensitivity of our survey over earlier work defines the log M – log L relationship much more precisely than was previously possible, over a large range in luminosities; and allows us to make definitive statements on recombination in B supergiant winds. Our sample includes the first radio detections of an OC star, of a massive X-ray binary, and of thermal emission from a main-sequence star.
Photometric Determination of Mass Loss Rates and Orbital Inclinations for WR Binaries
Authors: Lamontagne R. , Robert C. , Grandchamps A. , Lapierre N. , Moffat A. , Drissen L. , Shara M.M.
Published: June 2019

Most Wolf-Rayet binaries show phase-dependent light variations with a broad dip occurring at phase zero, when the WR star passes closest to the observer. When the orbital period is long, or the inclination is low, this dip is buried in the noise. When eclipses of the stars occur, another dip is seen when the companion passes closest to the observer; in this case, both dips are relatively deep and sharp (e.g. V444 Cygni, HD5980).

In the cases when only one dip at phase zero is seen, a simple model is derived. This involves electron scattering of companion starlight as the orbit makes it systematically traverse different amounts of the WR wind, assumed to be spherically symmetric and to follow a monotonic velocity-radius law. The shape and amplitude of the dip yield estimates of M and i (hence M when combined with M sin3i from spectroscopic orbits).
Stellar Winds from Massive Stars: The Influence of X-Rays on the Dynamics
Authors: Stevens I. , Cooper G. , Owocki S.
Published: June 2019

We report on a theoretical investigation of the X-rays observed from early type stars on the global wind dynamics.
Cool Supergiants in the Solar Neighborhood
Authors: Jura M.
Published: June 2019

We have identified 21 mass-losing red supergiants (20 M-type, 1 G-type, L > 105 L⊙) within 2.5 kpc of the Sun. These supergiants are highly evolved descendants of main sequence stars with initial masses larger than about 20 M⊙. The surface density projected onto the plane of the Milky Way is between about 1 and 2 kpc–2. Although with considerable uncertainty, we estimate that the mass return by the M supergiants is somewhere between 1 and 3 10-5 M⊙ kpc–2 yr–1. In the hemisphere facing the galactic center there is much less mass loss from M supergiants than from W-R stars, but in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 2 and 4 105 years. During this phase a star of initially at least 20 M⊙ returns perhaps 3 to 10 M⊙ into the interstellar medium.
A Two-Component Dust Model for the Wolf-Rayet Ring Nebula RCW 58
Authors: Cassinelli J.P. , Mathis J.S. , Van Der Hucht K.A. , Prusti T. , Wesselius P.R.
Published: June 2019

The spectacular ring nebula RCW58 around the Wolf-Rayet star WR40 (HD 96548, WN8) has been observed by the IRAS-Survey instrument and by the IRAS Chopped Photometric Channel (CPC) to study its IR flux and morphology. The survey data were examined with the Groningen Exportable Infra-red High-resolution Analysis system (GEISHA) software, and analysed in terms of line and dust contributions.
Statistics of Wolf-Rayet Binaries
Authors: Yungelson L. R. , Tutukov A. V.
Published: June 2019

A theoretical model of the ensemble of galactic Wolf-Rayet stars is constructed, assuming that all of them are members of either close or wide binaries. The model provides a reasonable explanation of the observed number of WR stars, their distribution over masses, mass ratios of components in binary systems, and spatial velocities. It predicts that up to 10 % of the apparently single WR stars have relativistic companions hidden inside thick stellar winds.
AG Carinae and the WR Phenomenon in Luminous Blue Variables
Authors: Viotti R. , Baratta G. B. , Rossi C. , di Fazio A.
Published: June 2019

AG Car is a Luminous Blue Variable which recently evolved from AIe to Ofpe/WN9 in four years at about constant bolometric luminosity, while in the visual the star faded by two magnitudes. This change is probably associated with variable opacity of an unstable massive expanding envelope of a hot star. We discuss the main spectral features of the star and of its ring nebula, and the spectral variations.
Is Stellar Wind Mass Loss During Core Hydrogen Burning Important for Evolution
Authors: Blomme R. , Vanbeveren D. , Van Rensbergen W.
Published: June 2019

The influence of wind mass loss during core hydrogen burning on the evolution of massive stars can be investigated using a relation between Ṁ-L-M-Teff based on
The Mass of WR Progenitors
Authors: Vanbeveren D.
Published: June 2019

A search through literature reveals four methods in order to derive the mass of WR progenitors, i.e.

a. WR stars must be descendant from the most massive stars which share their galactic distribution,

b. the computation of detailed evolutionary models of massive close binaries up to the WR phase, able to explain the observational constraints of these WR binaries,

c. comparing the very narrow mass-luminosity relation of massive core helium burning stars predicted by evolution and estimated bolometric luminosities of WR members of stellar aggregates,

d. the minimum mass of the progenitor of a WR member of a cluster equals the mass of the most luminous star (or the star with the earliest spectral type) in the cluster.
The Distance to the S Dor Type Star HR Carinae
Authors: van Genderen A.M. , Robijn F.H.A. , van Esch B.P.M. , Lamers H.J.G.L.M.
Published: June 2019

The distance of HR Carinae is determined with the reddening distance method, resulting into r ~ 5 kpc.
Supernovae from Wolf-Rayet Stars
Authors: Langer Norbert , Woosley Stanford E.
Published: June 2019

The complete evolution of a star with an initial mass of 60 M⊙ and Z = Z⊙ (i.e. a typical W R progenitor) from the ZAMS through the supernova phase has been investigated. Mass loss in the different evolutionary stages, especially mass dependent W R mass loss, leads to a WO star (surface mass fractions {He,C,O} = {0.14, 0.38, 0.48}; cf. Fig. 1) of 4 . 2 M⊙ as pre-SN configuration. The low final mass may be typical for a wide range of initial masses (cf. Langer, 1989, Astr. Ap. 220, 135).
Wolf-Rayet Stars in Nearby Galaxies: Facts and Fancies
Authors: Massey Philip , Armandroff Taft E.
Published: June 2019

Surveys for Wolf-Rayet stars in nearby galaxies are briefly reviewed. The completeness and yield of these surveys are discussed in light of recent follow-up spectroscopy. A critical evaluation is made of our current knowledge of the Wolf-Rayet population in nearby galaxies, particularly the WC/WN ratio, the WR/O ratio, the WR surface density, and how these quantities vary within a galaxy and between galaxies, particularly as a function of metallicity. We compare the spectroscopic properties of Galactic and Magellanic Cloud WR stars with those in the more distant systems.
Galactic Wolf-Rayet Distribution and IMF
Authors: Hidayat Bambang
Published: June 2019

Wolf-Rayet star to OB star number ratios in some selected regions in the Galaxy are presented. The variations of the number ratio as a function of location is found to be marginal.
Multiplicity of Very Massive Stars
Authors: Heydari-Malayeri M.
Published: June 2019

Are there very massive stars (VMSs) of mass greater than 100 M⊙? This question constitutes one of the fundamental problems of astrophysics. We present observational evidence against the existence of such stars in the Magellanic Clouds. The multiplicity of VMSs has several important consequences for astrophysics. If VMSs do not exist we need to revise our ideas about the formation and evolution of stars.
A WC9 Star in the LMC
Authors: Heydari-Malayeri M. , Melnick J.
Published: June 2019

We have discovered the only WC9 star in the Large Magellanic Cloud on the basis of observations made at several ESO telescopes, especially NTT. The latest Wolf-Rayet stars of the carbon sequence so far observed in the LMC are WC5-6. The lack of late type WC stars is understood in terms of an abundance effect, according to the models of Maeder. Our observations therefore pose a new observational challenge to the theory of the evolution of massive stars.
Summary of Symposium
Authors: Conti Peter S.
Published: June 2019

“It is a significant fact that the emission and absorption lines of Wolf-Rayet spectra cannot be regarded as being formed in one body of gas at one representative temperature and pressure” (Underhill 1968)

“I think it fair to say that the demonstration of… diversity has brought the Wolf-Rayet stars from being a curiosity to being an important part of the ‘main stream’ evolution of all massive stars” (Smith 1982)
The (log g, log Teff)-Diagram, a Fundamental HR-Diagram
Authors: Newell E. B.
Published: June 2019

Spectroscopic and photometric parallaxes are based on the assumption that to each point in the relevant region of (g, Teff, a)-space there corresponds a unique mass. The implications of a breakdown in this assumption are discussed briefly and an alternative approach to problems that traditionally have required spectroscopic or photometric parallaxes is presented. This alternative approach involves the use of the (log g, log Teff)-diagram as an HR-diagram.
Line Blanketing in Real Stellar Atmospheres
Authors: Bernacca P. L.
Published: June 2019

Ultraviolet observations of line blanketing in the spectrum variables α Scl and α2 CVn show that the usual procedure of allowing line blocking in model atmospheres has to be revised. It is also suggested that the region around 2900 Å could be safely used for determining effective temperatures.
New Developments in CCD Technology for the UV-EUV Spectral Range
Authors: Bonanno Giovanni
Published: June 2019

Lately, Charge Coupled Device (CCD) detectors have had great advances both in the visible and in the X-ray spectral range. However, the technology applied to these devices in the ultraviolet (UV) spectral region has not developed as well, because of some problems connected with the interaction between UV radiation and the materials typically used in semiconductor technology. In our laboratory the ultraviolet response of some UV-enhanced CCDs has been investigated. In particular, the quantum efficiency of coronene and lumigen coated and of back-illuminated ion implanted CCDs have been measured in the 304–11000 å spectral range. Very interesting results have been found, mainly for a one ion implanted CCD with quantum efficiency values of more than 60% at 304 å. Some measurements of the response uniformity of this spectral region have also been made. The results obtained encourage the possible use of these detectors in ultraviolet astronomy with very good performance.
Infrared Array Detectors: Performance and Prospects
Authors: McLean Ian S.
Published: June 2019

Infrared array detectors, like silicon CCDs a decade before, have revolutionized infrared astronomy. The quality and performance of the current generation of devices has already allowed astronomers to obtain infrared images at wavelengths out to 2.2 microns which are as deep as the best CCD images. High resolution infrared spectroscopy is now a reality and ground-based imaging to 35 microns has been achieved. Several classes of low-noise infrared array detectors with formats of 256 × 256 pixels are now in routine use, and developments are under way which will produce detectors of 1024 × 1024 pixels (for the near IR) within the next year. This paper will briefly review the state-of-the-art and compare and contrast the properties of available arrays. Progress in the field is illustrated with recent near infrared photometry obtained with a new two-channel imaging system developed at UCLA.
CCD Time-Series Photometry of Astronomical Sources
Authors: Howell Steve B.
Published: June 2019

CCDs are essentially the only instrument available today for photometry at most observatories; they are also becoming more readily available to amateurs as well. Thus, obtaining good photometric data with these two-dimensional devices is something we all need to understand. The history of and recent developments in CCD time-series photometry will be reviewed with some comments on future directions.
Array Polarimetry and Optical-Differencing Photometry
Authors: Tinbergen J.
Published: June 2019

Array detectors have improved the efficiency of optical polarimetry sufficiently for this technique to become part of the standard arsenal of observational facilities. However, we could gain even more: spatially-differentiating photometry can be implemented as an option of array Polarimeters and low-noise, high-frame-rate array detectors will allow extremely high precision both in polarimetry and in such differentiating photometry. The latter would be valuable for analyzing many kinds of optical or infrared images of very low contrast; the essence of the technique is to use optical (and extremely stable) means to produce the spatial derivative of the flux image, in the form of a polarization image which is then presented to a “standard” array polarimeter. The polarimeter should incorporate a polarization modulator of sufficient quality for the photometric application in mind. If developed properly, using a state-of-the-art array detector and the most sensitive type of polarization modulator (stress-birefringence), optical differencing will allow levels of relative photometric precision not otherwise obtainable. With the optical differencing option taken out of the beam, the same instrument can be used for high-quality polarimetry.
MOCAM: A 4k × 4k CCD Mosaic for the Canada-France-Hawaii Telescope Prime Focus
Authors: Cuillandre J. C. , Melliers Y. , Murowinski R. , Crampton D. , Luppino G. , Arsenault R.
Published: June 2019

MOCAM is a wide field CCD camera, currently nearing completion, which will be offered to the Canada-France-Hawaii Telescope (CFHT) user community in 1995. The project is a collaboration between the CFHT, the Dominion Astronomical Observatory (DAO, Canada), the Institut des Sciences de l'Univers (INSU, France), Laboratoire d'Astrophysique de Toulouse (LAT, France) and the University of Hawaii (UH). In the interests of producing a reliable and effective camera in the shortest time, it was decided to use existing technologies rather than innovative ones. Two-edge buttable 2048 × 2048 15 μm pixel CCDs were obtained from the LORAL aerospace foundry, based on a mask designed by J. Geary at Smithsonian Astrophysical Observatory (SAO). They are mounted in a dewar designed by G. Luppino (UH); the focal plane mounting keeps the mosaic flat to within two pixels and the CCDs are aligned to within two pixels. A mechanical interface designed and fabricated by the DAO holds a 150 mm shutter and a filter wheel which has a positioning repeatability better than five μm.

The four CCDs are operated in parallel by a San Diego GenIII controller adapted by LAT. The mosaic is read out in seven minutes and a single 33 Mb FITS file is generated to enable convenient on-line preprocessing. The user will control the system through a single CFHT Pegasus environment session. The camera field is 14′ × 14′ with a 0.″2 pixel sampling and the readout noise is less than seven electrons. The scientific goals of the initiators of the project are studies of distant clusters, deep galaxy counts and quasars surveys.
Spectroscopic Observations of Solar System Objects: Pushing the Limits
Authors: Cochran Anita L.
Published: June 2019

Targets within the solar system generally fall into one of two types: a) major planets (except Pluto) and our Moon; b) minor planets, comets, Pluto and planetary satellites. The first group is noteworthy for being reasonably bright. Most are also spatially extended. The inner planets never achieve large solar elongation. The second group comprises bodies which are generally faint. Comets are spatially extended. The minor planets and comets may be in orbits which are highly inclined or viewed at small solar elongations. Comets may even be in retrograde orbits. Planetary satellites may be bright or faint but suffer from being in the glare of the parent planet.
“Va-et-Vient” (“Back-and-Forth”) CCD Spectroscopy: A New Way to Increase the Limiting Magnitude of Very Large Telescopes
Authors: Soucail G. , Cuillandre J. C. , Picat J. P. , Fort B.
Published: June 2019

Over the last decade, the quantity of scientific results brought by the observations of very faint objects has been quite spectacular. In particular, they concern the photometry of faint galaxies up to B = 27 (Tyson 1988) or K = 22 (Cowie et al. 1994). The consequences of these observations are the detection of a large population of faint galaxies more numerous than any prediction given by standard galaxy evolution and probably a new vision of the distant universe. For faint object spectroscopy, the most recent surveys of field galaxies reach a magnitude range of 23–24 (Colless et al. 1990, 1993, Lilly and Cowie 1993, Tresse et al. 1993) with a reasonable S/N ratio that allows a redshift measurement from absorption-line identification. But in this magnitude range, the sky background flux is dominant with respect to the source, being at least 10 times brighter.
Some Problems of Wide-Field Astrometry by a Short-Focus CCD-Astrograph
Authors: Guseva I. S.
Published: June 2019

The worldwide application of CCDs in astronomy is concerned mainly with the problems of photometry and spectrophotometry. Astrometry with CCDs is limited by the small fields of view and now is used to solve some special tasks such as parallax determination of faint stars, observations of QSOs, etc. Very interesting results were obtained using a CCD with a meridian circle in a drift scanning mode to solve the problem of the extension of the reference system to stars of 16th–17th mag and the linkage between radio and optical reference frames (Stone 1994).

Based on the preliminary results of our observations, some proposals on astrometry with CCDs are discussed in the paper. The aim is to show the use of short-focus telescopes with CCDs in the mode of traditional astrographs. Numerous tasks may be solved with such instruments more simply and correctly than with meridian instruments in a drift scanning mode.

The problems of the application of CCDs with short-focus optics are also discussed. Some effects of CCD properties on the accuracy of astrometric and photometric measurements are also considered.
Performance of a 2048 × 2048 Pixel Three-Side-Buttable CCD Designed for Large Focal Planes in Astronomy
Authors: Cortiula J. A.
Published: June 2019

TH78997M is a 2048 × 2048 pixel full-frame CCD sensor featuring 15 × 15 micron pixels, MPP operating mode, four parallel outputs and buttability on three sides. This new device makes it possible to build very large focal plane detectors for telescopes (two × n butted CCDs) with less than a 25 dead pixel zone between adjacent sensors. Other features are high full-well capacity (typically 180 Ke−) and very low dark current thanks to four phase MPP clocking which allows a very long exposure time together with a high S/N ratio.

The readout of a complete frame is achieved through four parallel outputs running at frequencies ranging from ten KHz up to five MHz per output. The four on-chip amplifiers have been designed to be completely user controlled and to meet most of terrestrial and spaceborne astronomy requirements: very low noise (less than 4e− at 50 KHz, −40 degrees C), very low power consumption (150 micro-W/amplifier at 10 KHz/output), linearity better than 0.5% together with high conversion factor (4.2 micro-V/e−) over 2.5 V output range. The packaging of the device is compatible with the good flatness of the chip and with the low parasitic “cosmic event” rate thanks to specific care in selecting the packaging material.
Detector Controllers for the Galileo Telescope: A Progress Report
Authors: Bonanno G. , Bruno P. , Cosentino R. , Bortoletto F. , D'Alessandro M. , Fantinel D. , Balestra A. , Marcucci P.
Published: June 2019

The GALILEO telescope requires a flexible detector controller that allows one to drive single and mosaic CCDs in different modes of operation. The CCD controller can be divided into two main parts: the preamplifier, located close to the cryostat and the other modules, the Sequencer, the Bias generator, the Clock driver, the Preamplifier and the Correlated double sampler, located into a rack and connected together via a CCDC-BUS.
Astronomical Applications of CCDs in Hungary — the First Steps and Future Plans
Authors: Szécsényi-Nagy G.
Published: June 2019

The first century of non-visual astronomical image detection in Hungary was devoted exclusively to photography. The most famous Hungarian astronomers and astrophysicists of the last century were the pioneers of astrophotography too. The very first exhaustive description of photography as a scientific method was the one by Konkoly-Thege about astronomical photography in 1887. In his book one can find some interesting images printed of the plates taken by his friend and colleague, the enthusiastic astrophotographer J. Gothard, who was the first to demonstrate that the well-known bright planetary in Lyra (M 57 or the Ring Nebula) contains an extremely faint central star. His discovery, which opened new fields for astrophysics, was contested for a long time because his foreign contemporaries were unable to repeat this feat of arms.
A Simple CCD-System for Secondary Alignment of the Spectrum-UV Space Telescope
Authors: Didkovsky L. V. , Steshenko N. V. , Borzyak P. I. , Dolgushin A. I.
Published: June 2019

A CCD-system is proposed to maintain the alignment of an optical system of a large space telescope during ground tests and after launch. The system is able to detect alignment errors resulting from displacements of the main and secondary mirrors of the telescope and also from the tilts of these mirrors. Computer simulations have been performed to determine the sensitivity of the system to the displacements and/or the tilts. Different sources of errors have been also explored on a working stand; and the main requirements to the elements of the system have been determined. The system is to be installed on the space telescope “Spectrum-UV”. It can be also used in ground-based telescopes in a quasi-real time mode.
The NOAO CCD Controller — Arcon
Authors: Walker Alistair R.
Published: June 2019

The Array Controller (Arcon) developed at CTIO is a flexible and extendable system for acquiring astronomical data from a wide variety of optical and IR detectors. It has been designed from the outset to support expansion to more demanding applications such as large CCD mosaics. In its minimum configuration it can read a quad-readout CCD through all four amplifiers simultaneously.
On the Problem of Standard Fields for CCD Astrometry
Authors: Guseva I. S.
Published: June 2019

At the start of CCD observations one must investigate the metrological properties of the complex instrument: optics + CCD. One needs a densely spaced set of stars with precise coordinates and magnitudes. We first used the Pleiades catalogue by Eichhorn et al. (1970). Experimental observations were started at Pulkovo in 1993 using a very small refractor (D = 100 mm, F = 712 mm) equipped with a CCD ISD015A (520 × 580 pixels, 18 × 24 microns). The focal length of our astrograph provides an angular field of view of 45 × 67 arcmin (angular scale is 5.2 × 7 arcsec/pixel). With different exposures we can observe all stars with magnitudes from 2 to 16. The first observations were made to evaluate the accuracy of our positional and photometric measurements. Unfortunately, it appears that the catalogue of the Pleiades by Eichhorn is not good enough for this purpose because its epoch is very far from that of our observations and proper motions were not provided for the majority of the stars. The internal precision of our measurements (0.1–0.3 arcsec) allows us to determine the corrections to the stellar positions by Eichhorn et al. (1970)
Technical CCD Systems for the ESO Very Large Telescope
Authors: Ehrich J.
Published: June 2019

The Technical CCD Systems (TCCDS) consist of thermo-electrically cooled CCD detector heads together with the electronic hardware and software for the control of the CCD and readout of the data. Two different types of CCD heads equipped with a small and a large format CCD chip are used. The small format CCD systems will be used primarily for auto-guiding and field acquisition at the main foci of the VLT. The large format CCD systems are intended mainly for wavefront sensing applications. An overview of the primary modes of operation of the TCCDS and the corresponding fields and exposure conditions for these modes is given in Table 1. The term “Technical CCD Systems” is derived from the intended application in the VLT because due to the excellent CCD head parameters and the system performance a scientific application will be offered too.
Reconnection in Sheared Magnetic Fields in Space and Astrophysics
Authors: Drake James F.
Published: June 2019

The current theoretical understanding of the linear and nonlinear evolution of resistive tearing instabilities in sheared magnetic fields is reviewed. The physical mechanisms underlying this instability are emphasized. Some of the problems which are encountered in developing a model of magnetic energy dissipation in coronal loops are discussed and possible solutions are suggested.
Particle Energization in Stochastic Double Layers
Authors: Lotko William
Published: June 2019

Electrostatic turbulence develops in current carrying plasmas when the relative electron-ion drift exceeds the critical value for laminar current flow. Recent 2D computer experiments (Barnes, 1982) indicate that many weak ion acoustic double layers form in such turbulence when the plasma is strongly magnetized (ωce ≳ ωpe), the electron/ion temperature ratio is large (≳10), and the relative electron-ion drift is comparable to or less than the electron thermal speed. The double layers emerge from the incoherent spectrum of electrostatic ion cyclotron and ion acoustic waves as intense localized electric field structures propagating subsonically relative to the ion bulk flow. The occurrence of weak ion acoustic double layers, excited by field-aligned currents in the Earth's auroral regions, has also been reported from in situ spacecraft measurements (Temerin et al., 1982). An important question concerns the effect of these coherent electric fields on plasma transport properties such as bulk heating and acceleration. For example, one might expect nonlinear diffusion processes, manifested as distinct nonthermal features in the particle spectra, to accompany the quasilinear diffusion of ions as they traverse turbulent regions in space. This idea motivates the work presented here.
A Unified Theory of Coronal Heating
Authors: Ionson James A.
Published: June 2019

This presentation focuses upon the coronal heating problem and reports the results of Ionson's (1984) unified theory of electrodynamic heating. This generalized theory, which is based upon Ionson's (1982) LRC approach, unveils a variety of new heating mechanisms and links together previously proposed processes. Specifically, Ionson (1984) has derived a standing wave equation for the global current, I, driven by emfs that are generated by the β≳1 convection. This global electrodynamics equation has the same form as a driven LRC equation where the equivalent inductance, L=4ℓ/πc2, scales with the coronal loop length and where the equivalent capacitance, C=c2 ℓ/4πv2A, is essentially the product of the free space capacitance, ℓ/4π, and the low frequency dielectric constant, c2/v2A. The driving emf, ∊=vBa/c, is a formal integration constant associated with the convective stressing of β≳1 magnetic fields. Since the transition from the β≳1 driver to the β<1 coronal loop is typically small compared to the “wavelength” of the associated magnetic fluctuation, this integration constant is not sensitive to details of the transition zone. The total resistance, Rtot = L(1/tdiss+1/tphase+1/tleak), represents electrodynamic energy “loss” from dissipation, magnetic stress leakage out of the loop and phase-mixing. These three processes have been parameterized by appropriate timescales. Note that Rleak=L/tleak and Rphase=L/tphase do not result in resistive heating but do participate in limiting the amplitude of the global current, I. This is fairly obvious with regard to magnetic stress leakage but not for phase-mixing. The phase-mixing resistance, Rphase, represents coupling between the global current and the local current density. Since the global current is essentially an integration of the local currents, the degree of coherency between the local currents can play an important role in determining the ultimate amplitude of I. The rate at which coherency between the local currents is lost is given by the phase-mixing time, tphase. A loss of coherency implies a corresponding reduction in the amplitude of I. In this sense, Rphase measures the phase-mixing contribution to the global current limitation process.