bluuebunny/crossref_metadata_2025 huggingface dataset:
Metallicity Distribution and Kinematics of the Disk and Halo F-G Stars
Authors: Bikmaev Ilfan F.
Published: June 2019

The iron abundance of 160 disk and halo F-G-dwarfs is determined from 6-m spectra of 60 stars and published equivalent width data. Kurucz's (1979) model atmospheres and WIDTH6 programme are used for iron abundance determination. We have shown that FeI lines are formed under non-LTE conditions (Bikmaev et al.,1990), and so used Fell lines for iron abundance determination, following Bikmaev (1991). The use of the FeII lines and high quality homogeneous spectroscopic data decreases systematic and accidental errors and allows us to obtain qualitatively new results (Bikmaev, 1994). The distribution of the sample of stars is a non-monotonous function of metallicity: at least 3 groups of stars are seen, corresponding to the three Galaxy populations - disk ([Fe/H]=+0.1 to −0.3), thick disk ([Fe/H]=−0.7 to −0.8) and halo ([Fe/H]=−1.3 to −2.0). In contrast with previous studies, a sharp boundary in the kinematic characteristics (the eccentricity of space orbits and angular velocity) was found at [Fe/H]=−0.9, the boundary between disk and halo stars. These kinematic properties demand a relatively long time between halo and disk formation. The average metallicity of the thick disk stars is very close to the metallicity of the Large Magellanic Cloud. Perhaps an explanation is merging during the approach of the LMC to the Galaxy several billion years ago.
Density of Matter in the Galactic Disk
Authors: Flynn C. , Fuchs B.
Published: June 2019

A long standing issue in Astronomy is the amount of unseen matter in the Galactic disk. This has been addressed many times since Oort (1960) showed that about half the local disk mass is in unseen material. Oort's method infers the disk mass via the vertical change in density and velocity dispersion of appropriate tracer stars. Recently, Kuijken and Gilmore (1989) analysed a sample of K dwarfs at the South Galactic Pole and found in fact no compelling evidence for dark matter in the disk — a conclusion also reached by Bienaymé, Robin and Crézé (1987) based on faint star count data. However, Bahcall, Flynn and Gould (BFG, 1992), analysed K giants at the South Galactic Pole, and while they corroborated the Oort result, they could state at only the 85% confidence level that at least some disk matter is ‘missing’. Here we describe the Flynn and Fuchs (1994) analysis of a sample of nearby K-giants, which they combine with the BFG sample. The combined sample can be well fit without dark matter in the disk. The fit can be improved using a small amount of disk dark matter: our best fit has a disk surface density of Σ⊙ = 53 ± 13 M⊙ pc−2, compared to Σ⊙ = 49 ± 9 M⊙ pc−2 for the known disk matter. We conclude the disk is relatively light and the dark halo makes a significant contribution to the rotation curve at the sun.
A New Sample of Faint Halo B Stars
Authors: Mitchell Kenneth J. , Saffer Rex A. , Howell Steve B.
Published: June 2019

This poster reports the isolation of a new, complete sample of 24 faint halo B stars. These B stars were selected as blue- and ultraviolet-excess objects in the US survey at high Galactic latitudes (Usher and Mitchell 1990), and were given preliminary classifications using low-resolution spectrophotometry. The new sample is complete over 206 square degrees of sky to faint magnitude completeness limits in the range B = 16.5 and B = 18.3.

Stromgren color indices for the US B stars have been derived from the spectrophotometry through numerically convolved filters (Howell 1986). The colors have been used to help define the red completeness limit of the sample at (b – y) = −0.01, at the B9.5/A0 classification boundary. In addition, surface gravity and temperature estimates useful for separating the hotter B stars from sdB stars have been provided by atmospheric model fitting to the existing spectra (cf. Saffer et al. 1994).
Peripheral Members of M67
Authors: Platais I. , Kozhurina-Platais V. , Geffert M. , Frolov V. N.
Published: June 2019

Despite enormous effort put into the membership determination of M67, we do not know very well its peripheral members. Since the Bonn double astrograph as well as Pulkovo normal astrograph plates cover nearly 1°.5 × 1°.5 on the sky we have combined newly derived astrometric data from both instruments. Nearly 2,000 stars were measured down to the plate limit B ≈ 16.5. The proper–motion standard error for well-measured stars is ±0.3 mas/yr. For the membership probability solution we selected only 1363 stars, all brighter than V ≈ 15.0, with good proper motions. The membership solution yielded 446 cluster members showing convincing discrimination between the cluster and field stars. The spatial distribution of peripheral cluster members seems to be asymmetric, although, it does not indicate that the tidal radius of the cluster has been reached.
Low Mass Stars and White Dwarfs in NGC 6397
Authors: Marchi Guido De , Paresce Francesco , Romaniello Martino
Published: June 2019

Deep WFPC2 images in wide bands centered at 606 and 802 nm were taken with the HST 5.6 arcminutes from the center of the galactic globular cluster NGC 6397. The images were used to accurately position ~ 2120 stars detected in the field on a color magnitude diagram down to a limiting magnitude m814 ≃ mI ≃ 26 determined reliably and solely by counting statistics. A white dwarf sequence and a rich, narrow cluster main sequence are detected for the first time, the latter stretching from m814 = 18.5 to m814 = 24.0 where it becomes indistinguishable from the field population. Two changes of slope of the main sequence at m814 ≃ 20 and m814 ≃ 22.5 are evident. The corresponding luminosity function increases slowly from M814 ≃ 6.5 to 8.5 as expected from ground based observations but then drops sharply from there down to the measurement limit. The corresponding mass function obtained by using the only presently available mass-luminosity function for the cluster's metallicity rises to a plateau between ~ 0.25 and~ 0.15 M⊙, but drops towards the expected mass limit of the normal hydrogen burning main sequence at about 0.1 M⊙. This result is in clear contrast to that obtained from the ground and implies either a substantial modification of the cluster's initial mass function due to dynamical evolution in its lifetime, or that very low mass stars are not produced in any dynamically significant amount by clusters of this type. The white dwarf sequence is in reasonable agreement with a cooling sequence of models of mass 0.5 M⊙ at the canonical distance of NGC 6397 with a scatter that is most likely due to photometric errors, but may also reflect real differences in mass or chemical composition.
The Stellar Populations in the Disk of M31
Authors: Morris P.W. , Griffiths W. , Reid I.N. , Penny A.J. , Dickens R.J.
Published: June 2019

CCD observations have been carried on 4 fields in the outer disk and one in the halo of M31 on the 5m Hale telescope, and reduced using the Starman stellar photometry package (Penny, 1992). CMDs for all fields show the brightest 3 magnitudes of the Red Giant Branch. AGB luminosity functions were constructed for each field and corrected for incompletness. Full details are given in Morris et al (1994).
Disks and Dark Haloes of Dwarf Spirals
Authors: Friese V. , Fuchs B. , Wielen R.
Published: June 2019

We have investigated the dynamical state of the disks of a set of 9 spiral galaxies fainter than MB = −18 and with Hubble types Scd or later for which rotation curves are available in the literature. The rotation curve of each galaxy is decomposed in disk and dark halo contributions in order to determine the mass distributions of both components. The velocity dispersion of dwarf spirals is not known, but we use the vertical scale heights of the disks assuming vertical hydrostatic equilibrium to derive estimates of the velocity dispersions. For this purpose we have performed a statistical flattening analysis of faint dwarf spirals in the ESO-Uppsala catalogue. We find that the intrinsic ratio of vertical to radial scalelengths of these types of galaxies is z0/h = 0.2 corresponding to an intrinsic flattening of q0 = 0.14.
Two Different Stellar Populations in the Large Magellanic Cloud?
Authors: Frantsman JU. , Shmeld I.
Published: June 2019

The evolution of stars on the AGB has been explained as episodic helium burning and neutron capture nucleosynthesis in the stellar interior, followed by the mixing of a portion of the processed material into the envelope of a star. The simple stellar evolutionary scheme M–MS–S–SC–N had been accepted. However in recent years extensive observations of AGB stars have shown that evolution of the AGB is more complicated than painted in such a simple picture.
The Resolved Stellar Populations of Leo A & GR 8
Authors: Tolstoy Eline
Published: June 2019

The complex effects that determine the shape of an observed Colour Magnitude Diagram (CMD) are best disentangled through numerical simulation. We make synthetic CMDs by randomly extracting stars from theoretical stellar evolution tracks using a series of adopted initial conditions, including an Initial Mass Function. Utilizing reliable error estimates on our photometry provided by the program DoPHOT we apply a Maximum Likelihood technique to quantitatively determine which of the numerous different possible models is the most probable match to the data. From these comparisons we obtain a better understanding of how star formation proceeds in the relatively simple environments provided by Dwarf galaxies.
The Vertical Age Distribution of Stellar Disk Populations in Edge-on Galaxies
Authors: Just A. , Fuchs B. , Wielen R.
Published: June 2019

The scale height of the disk stars in our Galaxy increases continously with age, which is also seen in the age-velocity dispersion relation of the solar vicinity. In external galaxies a similar evolution of stellar disks can be deduced from the colour distribution of the light in edge-on galaxies. Using physical disk models and stellar population synthesis we compute the luminosity and colour profiles in optical and infrared bands. For diffusion coefficient and SFR constant in time the vertical density profile is exponential. The colour profiles are mainly affected by dust extinction, and the age and metallicity distribution of the stars. The comparison of a basic model with the observed profiles of IC 2531 shows, that these influences can be disentangled by analyzing the systmatic deviations in the colour profiles.
Surface Brightness Fluctuations and the Stellar Population in Elliptical Galaxies
Authors: Sodemann Marianne , Thomsen Bjarne
Published: June 2019

The Surface Brightness Fluctuation (SBF) method introduced by Tonry & Schneider (1988) is known as a distance indicator. However, we focus on another aspect. Our aim is to obtain new information on the stellar population that constitutes an elliptical galaxy by comparing radial gradients in SBF magnitudes with traditional broad-band colours. We have obtained I–band images of NGC 3379 with the NTT/SUSI, 0″.8–1″.2 FWHM, Sodemann & Thomsen (1994). An analysis similar to that of Tonry & Schneider (1988) is applied. However, the smoothed galaxy is obtained from (Thomsen & Baum, 1989). For NGC 3379 we find a SBF signal of 3.39 ± 0.02 ADU, see Figure 1, corresponding to an object with apparent magnitude Ī = 28m.62 ± 0m.03. If the image is subdivided into 4 annular regions, we find the gradient in I in Figure 2. As both fluctuation ‘noise’ and photon noise raise towards the centre of the galaxy, it is difficult to correct for globular clusters in a position independent way. Dealing with gradients of the SBF signal, the task is even more delicate. The weakening of Ī towards the galaxy centre is foreseen by the stellar population models of Worthey (1994).
Metallicity of NGC 5128 Globular Clusters
Authors: Jablonka P. , Bica B. , Pelat D. , Alloin D.
Published: June 2019

We have analyzed a selection of globular clusters based on the indications of high metallicity from previous photometric studies.
Formation of Structures of cD Galaxies and Gravitational Lenses: Computer Simulations
Authors: Anosova J. , Namboodiri P.M.S. , Deshpande M.R.
Published: June 2019

The tidal effects of disruption and merger of a massive perturber-quasar on a galaxy cluster have been studied by computer simulations using Aarseth's NBODY2 code. The model consists of a spherical N-body galaxy cluster and a point-mass perturber. A wide range of initial conditions (mass ratio of the galaxy and the perturber, the virial coefficient q of the N-body system, and the pericentric distances of orbits) have been considered.
Determination of Young Population Ages in Cluster Galaxies
Authors: Poggianti B.M. , Barbaro G.
Published: June 2019

The “Butcher–Oemler” effect was originally defined as the excess of blue galaxies observed in distant rich clusters when compared to local counterparts. Subsequent observations revealed that a larger fraction of objects in clusters between 0.1 < z < 1 show signs in their spectra of the presence of young stars, i.e. of a recent (during the last 2 Gyrs) or current burst of star formation.
Relative orientation of VLBI celestial reference frames
Authors: Arias E. F. , Lestrade J.- F. , Feissel M.
Published: June 2019

Several series of celestial reference frames have been produced during the past few years as part of VLBI geodynamic programs. They consist in coordinates of 20 to 150 extragalactic radio sources with a precision at the level of 0.001″. The relative orientations of these frames and the evolution of each series of catalogs are studied.
The oceans and the Earth's rotation
Authors: Brosche P.
Published: June 2019

In the long run, the tidal interaction between the Moon and the solid Earth is mediated by the oceans. It produces the retardation of the Earth's rotation known as ‘tidal friction’. Due to the changing configuration of the continents, it is a non-monotonic function of time. Tides of the solid Earth dominate the short-periodic tidal effects while the exchange with the atmosphere is preponderant in climatic changes, especially with an annual signature. It is shown that the influences of the oceans within such short time-scales must be taken into account for tidal and for non-tidal variations as well if one wants to model the Earth's rotation at the cm-level corresponding to the most advanced observational techniques.
Effect of earthquakes on observations of time and latitude
Authors: Zheng Y.
Published: June 2019

According to a vast amount of both seismological and astronomical data obtained from China, it has been understood that: 1, A large number of anomalies may appear before and after the major earthquake and the anomalous area is usually very large; 2, And therefore the anomalous residuals in the observations of time and latitude before the shock are of profound significance in geophysics.
The RS Canum Venaticorum Stars
Authors: Rodonò Marcello
Published: June 2019

The picture emerging from recent studies of RS CVn-type systems indicates the presence of very active stars showing typical solar-like activity phenomena, such as spots and flares, and possibly mutual interactions. The binary nature of RS CVns is certainly important in enforcing high stellar rotation rates, but the actual clue to the understanding of the intrinsic variability of the component stars resides in their internal structure, where the appropriate physical conditions are met for the generation and intensification of strong magnetic fields, as prescribed by the αω-dynamo models. The most significant results have been derived from multi-wavelength, coordinated observations and long-term monitoring programs.

Recent highlights include: a) the mapping of compact atmospheric structures at various temperature regimes by light curve modelling and spectral (Doppler) imaging techniques; b) clear evidence of long-term activity cycles on RS CVn and other types of interacting binaries; c) the detection and measurement of surface magnetic fields, as derived from the differential Zeeman splitting of spectral lines.

These results clearly demonstrate that the study of RS CVn stars can play a very fundamental role in the understanding of basic stellar physics, as well as in interpreting the characteristic variability of interacting binaries.
Binary Be Stars and Be Binaries
Authors: Baade Dietrich
Published: June 2019

Two hypotheses have been put forward for the rôle of binarity in Be stars: (1) All Be stars are interacting binaries. (2) Roughly one-half of the observed Be stars are post-mass exchange binaries with compact companions. Contrary to (1), (2) does not attempt to explain also the existence of disks in Be stars. After the spin-up by mass and angular momentum transfer, the B star somehow has to succeed to form and maintain the disk. Since rapid rotation is only necessary but not sufficient for this transformation, the effect of duplicity would merely be to give more stars the opportunity to become a Be star. Model (1) is not nearly realistic as is also underlined by a new spectroscopic survey for cool companions. The verification of (2) on the basis of theROSATAll-Sky Survey has just begun; but a serious deficiency of white dwarf companions is already apparent. Binarity currently provides no extra clue on the origin of the Be phenomenon.
Wind Accretion by Compact Objects: The “Flip-Flop” Instability
Authors: Livio Mario
Published: June 2019

The problem of the stability of wind accretion onto compact objects is examined. Recent analytical and numerical calculations show that in two dimensions, Bondi-Hoyle accretion flows are unstable to a “flip-flop” instability. The instability can manifest itself as bursts in the accretion rate and as a random walk-type spin-up, spin-down behaviour of the accreting compact object. The nature of the flow in three dimensions needs further clarification. Possible observational implications are reviewed.
Accretion Disc Instabilities
Authors: King A.R.
Published: June 2019

I give a brief discussion of accretion disc instabilities, concentrating mainly on tidal instabilities caused by the presence of a binary companion. The superhumps observed in superoutbursts of SU UMa dwarf novae probably result from the excitation of a resonance in the accretion disc near the 3:1 commensurability with the binary orbit. This resonance can only appear for mass ratios q = M2/M1 < qerit ≃ 0.25 – 0.33: for larger mass ratios the available resonances are considerably weaker. Application of this picture to other types of binary suggests that the condition q < qerit may be necessary but not sufficient. Further, some cataclysmic systems show phenomena which could be tidal in origin even though the condition evidently fails.
Binary Star Research: Where We Are Now and Future Prospects
Authors: Guinan E. F.
Published: June 2019

A review of IAU Symposium 151 on Interacting Binary Stars is given along with discussions of the present and future prospects of research in close binary stars.
H-Alpha and OI 7774 Spectroscopy of Algol-Type Binaries
Authors: Etzel Paul B. , Olson Edward C.
Published: June 2019

Spectroscopic observations are presented showing evidence of mass transfer activity in Algol-type eclipsing binaries. Traditional Hα emission line spectroscopy is discussed along with absorption line spectroscopy of the O I 7774 A multiplet. Eclipse effects in both lines are discussed, along with a new non-LTE model for Hydrogen line spectrum synthesis.
Observations of CNO Processed Matter in Massive Interacting Binary Systems
Authors: Polidan Ronald S. , Wade Richard A.
Published: June 2019

Ultraviolet observations for nine massive Algol systems (DH Her, TU Mon, AU Mon, Z Ori, RY Per, IZ Per, V356 Sgr, RZ Sct and ET Tau) obtained during their primary eclipses with the IUE spacecraft are discussed. Four systems, AU Mon, Z Ori, IZ Per, and RZ Sct, yielded no useful data on the presence of UV emission lines. Four binary systems DH Her, TU Mon, RY Per, and V356 Sgr, displayed a prominent emission spectrum with the notable exception of carbon lines; only one of the studied systems, ET Tau, showed carbon emission. Analysis of these data strongly supports the suggestion that the lack of carbon emission lines in these systems is the product of an inherent carbon deficiency in the transferred material and not due to any ionization effects in the gas. This carbon deficiency is the result of the CNO processed layers of the secondary being exposed as a result of mass transfer. The IUE data on TU Mon also indicates that this system undergoes a total, rather than partial, eclipse.
Atmospheric Eclipsing Binary Zeta Aurigae in the 1987–1988 Eclipse
Authors: Nha Il-Seong
Published: June 2019

A total of 1,037 UBV observations was made for the latest eclipse of Zeta Aur in 1987–1988 at Yonsei University Observatory. These observations furnish UBV light curves which cover the phases before, during, and after the eclipse. The current issues regarding the radius variations of K supergiant component are discussed.
FK Comae and the Evolution of Close Binaries
Authors: Huenemoerder David P. , Ramsey Lawrence W. , Buzasi Derek L. , Nations Harold L.
Published: June 2019

FK Com is an enigma among active cool stars. A rotationally driven magnetic dynamo is an explanation for activity. Youth and binarity are two causes of rapid rotation, but FK Com is old, single, and rotating near breakup. Much studied optical and ultraviolet data have not revealed the cause of its unusual activity. It is an important object in a more complete understanding of close binary star evolution and of the dynamo theory of magnetic activity. In 1989, we executed a coordinated ultraviolet and intensive optical spectroscopic and photometric campaign to better elucidate its characteristics. Data relevant to its evolutionary status, namely its radial velocity variations, will be discussed here, while an in depth study of the chromospheric activity will be deferred to a more detailed publication.
Orbital Elements of a Sample of S Stars: Testing the Barium - S Evolutionary Connection
Authors: Jorissen A. , Mayor M.
Published: June 2019

Orbital elements for 8 non-Mira S stars (derived from CORAVEL observations and from Griffin 1984) are compared with those of barium stars. In all but one case, the mass functions are compatible with white dwarf companions. No periods shorter than 600 d are found, while the 5 orbits with 600 < P(d) < 900 all have e ≤ 0.1, in contrast with the situation prevailing for barium stars. It is suggested that the hypothesis of an evolutionary link between barium and non-Mira (no Tc) S stars can be reconciled with these differences provided that these S stars are low-mass stars populating the first giant branch instead of the asymptotic giant branch, as usually thought.
A 3-D hydrodynamical simulation of wind accretion
Authors: Boffin Henri M.J.
Published: June 2019

Using a 3-dimensional hydrodynamical code, based on the Smooth Particle Hydrodynamics (SPH) method, we have simulated the case of wind accretion. Several configurations were studied:

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homogeneous mass flow

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wind with a density gradient

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wind with a velocity gradient

In each case, the accretion rate as well as the accreted angular momentum has been calculated. Comparisons were done with other simulations published in the literature and especially with the two currently existing 3-D simulations. According to one of these group (Matsuda et al., 1990) resolution is very critical in determining the accretion rate as well as to determine if the flow is stationary or not. We have done simulation at various resolutions and we confirm its importance for the deduced accretion rate. However, our simulations do not seem to show any non- stationary behaviour.
Absolute Dimensions and Distance Modulus for HV 2226 in the SMC
Authors: Bell S.A. , Hill G. , Hilditch R.W. , Clausen J.V. , Reynolds A.P. , Giménez A.
Published: June 2019

Absolute dimensions and the distance modulus have been established for the early-type eclipsing binary HV 2226 in the SMC. Analyses of the new radial velocities reported here, and CCD light curves published by Jensen et al. (1988) yield component masses of 9.3 ± 0.7 and 5.6 ± 0.5 M⊙, respectively. The radii are 5.6 ± 0.2 and 5.3 ± 0.2 R⊙ with the secondary component filling its Roche lobe which implies that HV 2226 must have evolved through a case A mass-transfer process. A distance modulus of (mv – Mv)0 = 18m.6 ± 0m.3 is derived, marginally lower than the adopted mean of 18m.9 for the SMC. The position of HV 2226, however, indicates that it is in fact situated in the near side of the SMC. In the present case, the accuracy of this estimate is limited mainly by the uncertainties of ≈ 2000 K in the effective temperatures. We point out that distance moduli with uncertainties of ± 0m.15 can be achieved from accurate radial velocities, light curves and colour indices of eclipsing binaries; such systems in the SMC and LMC are therefore promising distance indicators and work on further selected candidates is in progress.
The Cold Heart of the Solar Chromosphere
Authors: Ayres T. R.
Published: June 2019

The early 1990's heralded the deployment of vastly improved space instruments in the ultraviolet (HST) and X-ray (ROSAT) bands, where thermal inhomogeneities in high-excitation chromospheres and coronae are seen in their most favorable light. The infrared spectrum provides a key complementary view of inhomogeneities, but only recently has begun to be seriously exploited for studies of the solar chromosphere and the outer atmospheres of other late-type stars.
Interpreting Recent Observations of He I 10830 Å
Authors: Jones Harrison P.
Published: June 2019

Spectra-spectroheliograms obtained in the 10830 Å line with the NASA/NSO Spectromagnetograph are analyzed to produce images in equivalent width, line depth, velocity, and continuum intensity. These and other images imply that if large-scale deficits in coronal irradiation induce weakening of the 10830 line, the ionizing radiation must be produced in close enough spatial proximity to the region of formation for 10830 to allow sharply defined spatial boundaries. The complex morphology of the images shows the importance of underlying chromospheric structure in providing a highly variable “substrate” which is modulated by varying illumination. Clear evidence is seen of He I 10830 Å formation in magnetic loops where the velocity field, particularly at footpoints, directly affects the excitation of the line. Steady flows as seen by Lites et al. (1985) are also observed, particularly near the limb. The observations and radiative transfer calculations are consistent with a simple, optically thin “cloud” model of line formation, and observed line profiles in weak network elements compare favorably with predictions from mean models.
Variability of the Solar He I 10830 Å Triplet
Authors: Harvey J. W. , Livingston W. C.
Published: June 2019

The He I 10830 Å triplet gives a unique view of the solar chromosphere. Digital spectroheliograms have been made regularly since early 1974 using this line and the NSO Vacuum Telescope on Kitt Peak. For many purposes (detection of coronal holes, giant two-ribbon flares, and dark point events) these images are sufficient. A Sun-as-a-star signal is also produced by averaging all the pixels in each daily image. To calibrate this ‘irradiance’ signal in terms of line equivalent width, a comparison is made with integrated sunlight spectrophotometric measurements obtained less frequently. After correction for the effects of water vapor blends, we find a linear relation between the two measurements. The daily averages have been assembled into a time series covering nearly two solar cycles. This time series shows cycle modulation of about ±30% and rotational modulation of about ±10%. The general variation is similar to that of other activity indices but with some interesting small differences. Since images are available, it has been possible to decompose the full disk index into components due to plages, filaments, coronal holes and background. At all times during the cycle, most of the signal comes from the background but most of the variability from plages.
Far Infrared and Submillimeter Continuum Observations of Solar Flares: Justifications and Prospects for Ground-Based Experiments
Authors: Kaufmann P. , Correia E. , Costa J. E. R. , Zodi A. M.
Published: June 2019

Solar flare observations in the sub-mm spectral bands are essentially non-existent. There is evidence that some solar bursts exhibit a spectral component rising in intensity towards wavelengths shorter than 3 mm, displaying fast sub-second pulses at different repetition rates. On the other hand, the spectral features of white light flares are also unknown in the infra-red range of frequencies. In both wavelength ranges the physics of the emission processes may involve particles accelerated to high energies. The diagnostics of solar flare continuum emission in the IR and sub-mm spectral regions will provide crucial tests on various flare models and bring some clues on the initial primary energy release mechanisms. We propose the construction and operation of a ground-based telescope, operating at two sub-millimeter wavelengths (at about 210 GHz and 405 GHz), with high time resolution (one millisecond), capable of determining the spatial position of burst emission centroids with high definition (a few arcseconds) using the multiple beam technique. Final installation and operation at a high-altitude site in the Argentinian Andes mountains are planned in a joint cooperation with Argentina's Instituto de Astronomia y Fisica del Espacio, IAFE (M. Rovira and associates) and Complejo Astronomico El Leoncito, CASLEO, San Juan (H. Levato and associates); and Switzerland's University of Bern, Institute of Applied Physics, IAP, Bern (A. Magun and associates).
Eclipse Observations of the Extreme Solar Limb at Submillimeter Wavelengths
Authors: Clark T. A.
Published: June 2019

This paper will review the use of solar eclipses in the study of the extreme solar limb at sub-millimeter and millimeter wavelengths. This approach has been used to overcome the severe limitation imposed by diffraction upon the resolution attainable by direct solar limb scans at these wavelengths. Strong absorption by water vapor in the Earth's lower atmosphere has necessitated the use of telescopes at high altitude sites or in jet aircraft. Data from several of these experiments will be reviewed, including those from the recent James Clerk Maxwell Telescope observation at a wavelength of 1.3 mm of the eclipse of 11 July 1991. In view of the success of recent measurements in improving the spatial resolution with this technique, several of the ultimate limitations placed upon it by lunar surface roughness and by diffraction at the lunar limb are outlined.

These observations have demonstrated the inadequacy of present phenomenological solar atmospheric models at sub-millimetric source heights. Newer models have been developed to fit the observed extension, brightening and detailed structure of the solar limb by attempting to include the structure of the chromospheric network and its spicular field, and their relative success in doing so will be discussed.
Near IR Observations of the 11 July 1991 Total Solar Eclipse from Mauna Kea, Hawaii
Authors: Clark T. A. , Naylor D. A. , Tompkins G. J. , Lindsey C.
Published: June 2019

Near IR total eclipse measurements have provided clear evidence during both 2nd and 3rd contacts for a limb extension of about 125 km for wavelengths in the range containing the CO fundamental vibration-rotation bands between 4.3 and 5.5 μm, when compared to the limb at nearby shorter wavelengths. This is interpreted as a “flash” spectrum in the CO lines, with the above extension representing the outer level of the CO emission layer. This height can be compared to the τCO = 1.0 level incorporated into recent representative atmospheric models (Ayres and Wiedemann, 1989) which is 90 km above the visible limb for a semi-empirical “hot chromosphere” model (Avrett, 1985) and 220 km for a “cool” radiative equilibrium model based upon work by Anderson (1989).
The White-Light, Far-Red (600-700 nm) and Emission Coronae at the July 11, 1991 Eclipse
Authors: Rušin V. , Rybanský M. , Minarovjech M , Pintér T.
Published: June 2019

Preliminary results of the analysis of the white-light, emission (green and red), and far red (600-700 nm) corona during the July 11, 1991 eclipse are given. Even though the corona is of nearly-maximum type, four different principal coronal structures are seen, combined with faint, small-scale structures (loops, arches, cavities, voids or plasmoids). Scattered light is seen up to 10 R⊙ in helmet streamers. The Ludendorff index of the corona shape turns out to be a + b = −0.02, and the estimated brightness of JK = 1.47 × 10–6B⊙. Some aspects of multiwavelength observations are discussed.
Analysis of Very High Excitation Fe I Lines (4f–5g) in the Solar Infrared Spectrum
Authors: Johansson S. , Nave G. , Geller M. , Sauval A. J. , Grevesse N.
Published: June 2019

We present a detailed analysis of very high excitation lines (4f–5g) of Fe I which are present in the spectral region 2545–2585 cm–1 in high resolution spectra both in the laboratory and in the ATMOS solar spectra obtained from space. A value of the solar abundance of iron which agrees with the meteoritic value is derived.
Insights on Dust Grain Formation and Destruction Provided by Gas-Phase Element Abundances
Authors: Jenkins Edward B.
Published: June 2019

The abundances of free atoms and ions relative to hydrogen in the interstellar medium indicate how thoroughly different elements have condensed into solid form. Large contrasts in these depletions disclose differences in how tightly various elements are bound to the grains. While most grain nuclei probably form within astrophysical sites where densities are large, a substantial amount of the accretion of heavy elements must occur within interstellar clouds. Interstellar shocks created by supernova explosions or perhaps collisions of clouds destroy or significantly erode the grains. This viewpoint on the formation and destruction of grains is supported by the decrease in the severity of depletions in regions of lower than normal density or parcels of gas moving at high velocity. While depletions in gas away from the plane of the galaxy generally imitate the behavior of low density regions in the plane, mild anomalies for some elements may exist.
Dust towards the Galactic Centre
Authors: Aitken D. K.
Published: June 2019

The observed infrared properties of dust extinction along the line of site to the Galactic Centre are compared with those in the local interstellar medium. Further constraints on the nature of the dust grains are provided by polarimetric observations, which also lead to information on the stratification of the material along the line of sight. Finally some implications of the large polarized emission seen from the central regions are discussed.
Optical Properties of Carbonaceous Materials
Authors: Bussoletti E. , Colangelí L.
Published: June 2019

We discuss the optical properties of carbonaceous materials from the VUV to the FIR. Updated laboratory data on amorphous carbon (HAC) and some PAH mixtures are analysed and compared with relevant literature. We find that the 2175 å hump can be due to very small (< a > ≥ 10 å) HAC grains. The UIR bands seem better explained by mixtures of HAC particles and collections of PAHs.
Dust in Dense Clouds
Authors: Tielens A. G. G. M.
Published: June 2019

Recent observational and theoretical studies of dust in dense clouds are reviewed with an emphasis on the growth of dust grains through accretion and coagulation. IR reflection nebulae around protostellar objects are useful probes of grain sizes in dense clouds. For example, detailed studies of the IR reflection nebula surrounding OMC 2-IRS 1 show that the (scattering) grains are much larger (Ã 5000 å) than in the diffuse interstellar medium. Likewise, the presence of a weak shoulder at 2.95 μm on the 3.08 μm feature in BN indicates the importance of scattering by icy grains and implies a very similar increase in the grain size.

Theoretical studies of grain surface chemistry predict the possible presence of three distinctly different grain mantle components in dense clouds depending on the physical conditions in the gas phase. These are: 1) A hydrogenated mantle dominated by H2O and CH3OH; 2) An inert grain mantle dominated by CO and O2; and 3) An oxidized grain mantle dominated by CO2. Although the importance of H2O dominated grain mantles was known for 10 yrs, the presence of CH3OH was only recently confirmed. Furthermore, recent studies of the solid CO band have revealed the presence of at least two distinctly different interstellar grain mantle components along the line of sights towards most stars: One dominated by polar and one by non-polar molecules. Although specific identification of the molecules mixed in with the CO in these components is difficult, it is quite possible that the former component is dominated by H2O and the latter by CO itself, as suggested by theoretical models. Finally, the photochemical evolution of icy grain mantles is briefly reviewed and it is suggested that the resulting complex molecular mantles may evolve into amorphous carbon mantles in the diffuse ISM.

Grain-grain collisions can lead to large modifications of the interstellar grain size distribution. At high velocities (v ≳ 1 kms−1) shattering into many small fragments will be important, while at low velocities (v ≲ 10 ms−1) coagulation dominates. Both processes can play a role in dense molecular clouds. The sticking of grains at low velocities is discussed in some detail and it is concluded that coagulation in molecular clouds is only important if the colliding grains are covered by icy grain mantles.

Thus, a model for interstellar dust is proposed in which small (≲ 500 å) silicate and carbonaceous grains are “glued” together in large (Ã 3000å), open conglomerates by a polymerized, all enveloping grain mantle. This structure resembles that of certain interplanetary dust particles collected in the upper stratosphere.
Polarized Infrared Emission from Dust
Authors: Hildebrand Roger H.
Published: June 2019

At the beginning of this decade what we knew about polarization of far-infrared emission from dense clouds was that some very good observers had looked for it and had not found it. Gull et al. (1978) had shown that the degree of polarization in Orion was not more than 2%. That information provided an important guide but very little encouragement for later efforts. There was reason to doubt whether the mechanisms invoked to explain the alignment of dust grains in the diffuse intercloud medium would operate in dense clouds; whether the strengths of the magnetic fields in dense clouds would be sufficiently greater than those in the intercloud medium to overcome the higher rate at which gas collisions would destroy alignment; and whether the field, if sufficient locally, would have enough large-scale order to give measurable polarization in far-infrared observations with large beams and large column depths.
On the Interpretation of the λ2175 Å Feature
Authors: Draine B. T.
Published: June 2019

The interpretation of the interstellar λ2175å feature is reviewed. Various proposed explanations for the feature are examined, and difficulties with each of the proposed interpretations are identified.
Sources of Stardust in the Galaxy
Authors: Gehrz Robert D.
Published: June 2019

Observed mass loss rates and Galactic stellar population distributions are used to estimate the rate of injection of stardust into the ISM. M stars and RLOH/IR Stars produce most of the silicates; most of the carbon and SiC comes from carbon stars. WR stars, novae, and supernovae may eject dust with chemical anomalies. There is little observational evidence for a major stellar source of hydrocarbon grains. The Galactic dust ecology considered by comparing stellar dust injection with depletion by star formation and supernova shocks suggests that dust grains are produced by accretion in molecular clouds at 1 to 5 times the stellar rate.
Recent Measurements of the Cosmic Microwave Radiation
Authors: Wilkinson David T.
Published: June 2019

Recent measurements of the spectrum and anisotropy of the cosmic microwave may be showing deviations from a perfectly homogeneous blackbody flux. Improved spectral measurements at wavelengths of 3 cm and 1.2 cm disagree weakly; and new results from a rocket show large excess flux at wavelengths of 0.71 and 0.48 mm. The same instrument measured a radiation temperature at λ = 1.16 mm of 2.795 ± 0.018 K in good agreement with results at longer wavelengths. The observed excess flux at short wavelengths may be due to: local contaminants; dust emission from active galaxies at high redshift; or inverse Compton scattering of microwave photons from hot electrons at large redshift (Sunyaev-Zel'dovich effect). Anisotropy of ΔT/T = 3.7 × 10−5 has been reported on an angular scale of 8° at a wavelength of 3 cm. Measurements on a similar angular scale at λ = 6 cm (reported at this meeting) do not show the anisotropy at the flux level expected if Galactic emission were the source of the anisotropy at λ = 3 cm. The standard model has not yet predicted anisotropy this large at 8°, but without doubt it soon will. Long integrations with the Very Large Array at λ = 6 cm are showing resolved structures on angular scales of 15 to 30 arcseconds. Observations at another wavelength are needed to see if these are radio sources at high redshift or perturbations in the 2.77 K radiatoin.
The Anisotropy of the Microwave Background: Space Experiment Relict
Authors: Strukov I.A. , Skulachev D.P. , Klypin A.A. , Sazhin M.V.
Published: June 2019

We carried out the first satellite experiment for searching the anisotropies of the microwave background. The main goal of the experiment was to obtain a radio brightness map of the sky at 8 mm. We obtained the direction and amplitude of the dipole component at 90% confidence level

The variance analysis gives the most stringent constraints on fluctuations of the relic background. For the model with the Zeldovich spectrum of primordial fluctuations we found an upper limit on the quadrupole as 1.6×10−5 at 95% level. We are first to obtain model-independent estimates of the first 15 multipole components. We obtained upper limits on correlation function of angular fluctuations 〈ΔT1ΔT2〉 = 0.005 mK2 for the angular range from 20° to 160°. Intense galactic emission was observed over longitude interval from 90° to 270° and latitudes ±5°. The total flux from this longitude interval is approximately 56,000 Jy. The experiment studies confirmed that a space experiment gives a possibility to reach sensitivities high enough to estimate an anisotropy that is less than the values predicted by modern cosmological models.
The Edinburgh/Durham Southern Galaxy Catalogue
Authors: Collins C.A. , Heydon-Dumbleton N. , Macgillivray H.T. , Shanks T.
Published: June 2019

We review the current status of the Edinburgh/Durham southern galaxy catalogue. The aim of this project is to use COSMOS measurements of the UK Schmidt J survey to produce a unique data base of galaxies, complete down to bj ∼ 20.5 mag and covering ∼ 100 survey fields. We have developed the optimum procedures to classify objects as stars or galaxies and calibrate the galaxy magniudes on individual plates. We are confident that residual systematics will be ∼ 5%, thereby ensuring that this catalogue will substantially contribute to our understanding of the Universe at large. One initial finding of the survey is a probable 6 sigma density fluctuation in the galaxy distribution.
A Redshift Survey of IRAS Galaxies
Authors: Strauss Michael A. , Davis Marc
Published: June 2019

We have completed a redshift survey of approximately 2200 IRAS galaxies, flux limited at 60μ. The survey covers 76% of the sky and has a characteristic depth of ≈ 6000 km s−1, making it ideal for large scale structure studies requiring whole sky coverage. We have calculated the gravitational acceleration on us due to the inhomogeneous distribution of galaxies in the sample by summing the dipole acceleration in successive shells centered on us. The acceleration converges at ≈ 4000 km s−1 and we derive density estimates in the range 0.4 < Ω < 0.9. We discuss the various biases of the sample in detail: the paucity of elliptical galaxies, the problem of extended sources, and hysteresis, and suggest ways to accommodate them and thus decrease the uncertainty in Ω. Finally, we discuss the use of the survey to make predictions for the peculiar velocity flowfield in space.
Theories of Large Scale Structure
Authors: Shandarin S. F.
Published: June 2019

This talk is concerned with one of the most important class of theories of Large Scale Structure (hereafter LSS) based on two principal assumptions. It is supposed that (i) the main process is gravitational instability in expanding universe and (ii) the primordial perturbations a r e small Gaussian density fluctuations. Both assumptions are natural in inflationary model of the very early universe as well as in cosmological models dominated by Dark Matter (DM) in the form of Weakly Interacting Massive Particles (WIMPs). Other possible models of LSS formation are discussed by N. Turok, J. Ostriker and A. Dekel.
Is Cosmic String Domination of the Universe Avoidable?
Authors: Bouchet François R. , Bennett David P.
Published: June 2019

We address, by means of Numerical Simulations, one of the main issues of the Cosmic String Galaxy Formation Scenario, namely the existence of a scaling solution, which is crucial to the very existence of the scenario. After a brief discussion of our numerical technique, we present our results which, though still preliminary, offer the best support to date of this scaling hypothesis.
Dark Matter and Cooling Flows
Authors: Carr B. J. , Ashman K. M.
Published: June 2019

Cosmological arguments suggest that a large fraction of the baryons in the Universe are dark. Although the background dark matter required to make up the critical density would have to consist of some kind of elementary particle, the dark matter in galactic halos could be baryonic. In particular, we argue that it could consist of jupiters made in pregalactic or protogalactic cooling flows. These would be analagous to the cluster cooling flows observed at the present epoch but on a smaller scale.
Summary
Authors: Peebles P. J. E.
Published: June 2019

This conference has been marked by our willingness to entertain grand schemes of synthesis of theoretical ideas and the observational evidence on how galaxies and large-scale structure might have formed. At IAU Symposium 104 on this subject held in Crete just 5 years ago there was little discussion of how all the pieces of the puzzle might fit together. Now we have at least three candidate grand syntheses that have been worked out in some detail and have been discussed here: scale-invariant cold dark matter, by Frenk; massive cosmic strings, by Turok; and exploding magnetized superconducting cosmic strings, by Ostriker. I have accordingly placed each of the topics I want to review under the heading of the grand scheme for which it seems most embarrassing. This negative approach is a little unfair, but I think we can take it as given that we would not be considering a scheme that did not have many good points, and that the real interest is the probing of weak points by which we hope to learn which schemes might be strengthened, which might safely be abandoned.