bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecules in Novae and Supernovae
Authors: Rawlings J.M.C.
Published: June 2019

Molecular observations and models of the chemical processes in the ejecta of novae and supernovae are reviewed. Although only a few molecular species have been identified, the information that they give has provided great insight into the physical and chemical conditions. We now have quite a detailed understanding of the processes at work in both novae and supernovae.
Lithium Abundance and Spacial Distribution of T Tauri Stars
Authors: Gregorio-Hetem Jane , Lépine Jacques R.D.
Published: June 2019

We determined temperatures and Lithium 6707 A resonance line equivalent width of a sample of 62 T Tauri stars. Lithium abundances were then estimated by using a grid of curves of growth. The lithium abundance is shown to decrease with the distance of the stars to the nearest dense core of a molecular cloud. This effect is interpreted as being due to the ages of the stars, the youngest ones being closer to still active star formation regions.
A Molecular Line Survey of the Carbon Star IRAS 15194-5115
Authors: Nyman L.-Å. , Booth R. S. , Carlström U. , Johansson L.E.B. , Olofsson H. , Wolstencroft R.
Published: June 2019

IRAS 15194-5115 was discovered by IRAS and identified as a carbon star by Meadows et al. (1987). It is the third brightest carbon star at 12 μm, the brighter ones are IRC+10216 and CIT6. Its infrared properties are similar to those of IRC+10216. Le Bertre and Epchtein (1990) have monitored the star in the near-infrared and derived a period of 578 days. The distance to IRAS 15194-5115 is estimated to about 1 kpc from infrared observations, and also by comparing its bolometric luminosity with that of IRC+10216.
Radioactive Isotope 26Al in the Interstellar Matter (Resulting From a Mass Loss by AGB Stars)
Authors: L. Frantsman Ju
Published: June 2019

Several calculations of the Asymptotic Giant Branch star evolution have been performed with the aim of explaining the synthesis of interstellar 26Al in these stars. The agreement of theoretically calculated mass of interstellar 26Al and observations is rather satisfactory, the best for the abrupt tenfold jump in the mass-loss rate for the stars reaching the luminosity log(L/L⊙) ⋍ 4.0.
Cometary Origin of Carbon and Water on the Terrestrial Planets
Authors: H. Delsemme A.
Published: June 2019

The origin of carbon and water on the terrestrial planets is not trivial, because their presence seems to be excluded by the high temperatures requested by the accretion disk models (Morfill 1988) as well as by Lewis' (1973) adiabat that can explain the different densities of the planets. These high temperatures imply that all dust was outgassed and dehydrated and most carbon stored in CO, that is in the gas phase, before the separation of dust from gas, that occurred by dust sedimentation to the mid-plane of the accretion disk. Thermochemical equilibrium was easily reached, since chemical kinetics (Lewis & Prinn 1980) had time constants shorter than the time needed to agglomerate the first planetesimals (Weidenschilling 1988).
The Possible Orbital Evolution of the Near-Earth Asteroids
Authors: Timoshkova E.I.
Published: June 2019

The subject of this paper is a study of a possible orbital evolution for near-Earth asteroids. The investigation is fulfilled in the frame of the restricted circular three body problem. It is based on the calculations of the Jacobi constant. The osculating elements of some real Apollo-Amor-Aten asteroids are used as the starting parameters. The comparison with the results of other authors is given.
A Synthetic Theory of Motion for Titan-Hyperion
Authors: Duriez L.
Published: June 2019

We present an iterative method allowing to synthetize a semi-numerical solution for the equations of motion of the resonant Saturn's satellites Titan-Hyperion (limited now to the planar problem). The current theory of Hyperion by Taylor, Sinclair & Message (1987) gives the greatest terms of the long-period part of the solution (depending on two angles: the libration angle τ, and the angular distance of the pericenters ζ). Using it as a first approximation, this solution is substituted numerically in the exact Lagrange equations of motion for Titan and Hyperion, computed for many values of the three angles: τ, ζ and ϕ (the mean synodic longitude). Then, a multivariable Fourier transform allows to reconstruct the equations in these three angles, that is in same form as the initial one with, in addition, the short-period terms. Then, a solution may be obtained and used as a better approximation in an iterative process. Besides a complete determination of the short-period perturbations of Hyperion obtained here completely for the first time, some long-period perturbations of Titan by Hyperion are also found which would be non negligible at the 10 km level.
The Solar Motion, the Galaxy and the Aphelia Distribution of Long Period Comets
Authors: Brunini A. , Canosa D.M.
Published: June 2019

We analyze the incoming direction of 180 long period comets, taken into account the gravitational influence of the planets and the Galaxy as a whole. We have made an improvement of some previous works on the matter, by inclusion of comets observed up to 1989. An asymmetry of aphelia is detected that cannot be explained as due to observational selection. We conclude that the so called Dynamical Friction induced by the solar motion through the interstellar medium could be the proper answer to this observed fact.
Dynamics of the Zodiacal Cloud
Authors: Dermott S. F. , Gomes R. S. , Durda D. D. , Gustafson B. Å. S. , Jayaraman S. , Xu Y. L. , Nicholson P. D.
Published: June 2019

Advances in infrared astronomy and in computing power have recently opened up an interesting area of the solar system for dynamical exploration. The survey of the sky made by The Infrared Astronomical Satellite (IRAS) in 1983 revealed the complex structure of the zodiacal dust cloud. We now know the inclination and nodes of the plane of symmetry of the cloud with respect to the ecliptic and we have evidence that the cloud is not rotationally symmetric with respect to the Sun. Of even more interest is the discovery by IRAS of prominent dust bands that circle the Sun in planes near-parallel to the ecliptic. In 1984, we suggested (Dermott et al., Nature, 312, 505-509) that the solar system dust bands discovered by IRAS are produced by the gradual comminution of the asteroids in the major Hirayama asteroid families. The confirmation of this hypothesis has involved: (1) The development of a new secular perturbation theory that includes the effects of Poynting-Robertson light drag on the evolution of the dust particle orbits; (2) The production of a new high resolution Zodiacal History File by IPAC (the Infrared Processing and Analysis Center at Caltech); (3) The development of the SIMUL code: a three-dimensional numerical model that allows the calculation of the thermal flux produced by any particular distribution of dust particle orbits. SIMUL includes the effects of planetary perturbations and PR drag on the dust particle orbits and reproduces the exact viewing geometry of the IRAS telescope. We report that these tools allow us to account in detail for the observed structure of the dust bands. They also allow us to show that there is evidence in the IRAS data for the transport of asteroidal dust from the main belt to the Earth by Poynting-Robertson light drag.
Dynamics of the Moon
Authors: Jeffreys Sir Harold
Published: June 2019

Koziel's results on the librations have been rediscussed. Some serious departures from independence of the errors were detected and have been allowed for. The results are

β = 0.0006271 ± 0.0000010

γ = 0.0002362 ± 0.0000082

These do not differ much from Koziel's values but the uncertainties are larger. Both are consistent with results previously derived by comparison of results of different authors, and γ is consistent with a reinterpretation of a result of Yakovkin.

The effect of elasticity is considered. It is shown that the elastic strain does not contribute to the librations but would affect the perturbations of a satellite. Allowance for this difference reduces Michael's estimate of 0.4015 for C/Ma2 to 0.4001 ± 0.0030, which would be consistent with either uniform density or with the value I found in 1936 after allowance for compressibility and a possible thin surface layer, namely 0.3971 ± 0.0007.
The Geomorphic Evolution of the Lunar Surface
Authors: Ronca L. B.
Published: June 2019

Fundamental parameters of the geomorphology of a lunar surface are (i) the number and size distribution of craters, (ii) the degree of erosion of the craters and (iii) thickness and other characteristics of the regolith. These parameters are not independent of one another; as one changes through time, the other two will also change in a statistically predictable way.

In the continuous degradation sequence, the relationship between the number of craters per unit area and the degree of erosion of the craters is continuous and monotonic. This sequence occurs in areas subjected to intermediate to small impacts, and eroded mainly by the impacts themselves plus other small-scale erosional processes. In areas subjected to large impacts and mare flooding the discontinuous degradation sequence is predominant.

The relationship of the first two parameters, the number of craters and the degree of erosion, with the third parameter, the regolith, is not simple and is not yet understood. It appears, however, that the geomorphological stage is more important than the mare-versus-highland dichotomy of the lunar surface.

The solution of the function relating craters of the continuous degradation sequence with degree of erosion was defined as the geomorphic index of the area. Studies of the geomorphic index of stratigraphic surfaces show that areas covered by considerable ballistic sediments have a geomorphic index which is not a monotonic function of time. On the other hand, areas covered almost exclusively by mare flooding show an index which is a monotonic function of the age of the flooding. As each mare surface shows a considerable range in indices, it is concluded that maria are covered by surfaces formed through a considerable length of time. By using Apollo 11 and 12 radiometric ages it is suggested that the time of mare flooding lasted on the order of one billion (109) years.

The geomorphic index of highland surfaces shows a remarkable degree of order; i.e., the farther an area is inland from the mare shores, the higher will be the index. No explanation is given to this phenomenon, but is suggested that lunar erosion is not just a localized phenomenon centered on the locus of an impact, but has lateral trends of regional dimensions. Electrostatic transportation as suggested by Gold is a possible mechanism.
Introductory Remarks: The Apollo 14 Mission
Authors: Newell Homer E.
Published: June 2019

To set the context of our current exploration of the Moon, it is well to recall: Apollo 11 landed near the equator and was capable of affording the astronauts only a few hours on the lunar surface; Apollo 12 checked out pin-point landing which then permitted going to more difficult, nonequatorial sites; in Apollo 14 enlarged propellant tanks permitted some 42 kg of samples to be brought back. Three more Apollo missions follow Apollo 14. The Apollo missions, complemented by unmanned missions to the various planets, form a program to explore the solar system.

Captain Scherer will elaborate on the significant increase in Apollo capability in the last three missions. Of note are the lunar heat flow experiments, the lunar surface gravimeter, and, for Apollo 15, the laser ranging retroreflector which will be three times the area of and four times as efficient as retroreflectors in the previous Apollo missions. In the lunar orbital equipment will be the sub-satellite with instruments for measuring various physical properties of the Moon and its environment. Also noteworthy is the lunar sounder, for Apollo 17, which will use radar for probing a large fraction of the lunar surface to considerable depth.

Hardware changes will allow the astronauts to remain on the lunar surface for up to 66 hrs – an increase of 100%; thus the landed scientific payload may be doubled to approximately 550 kg. Increased range and efficiency of surface operations will result from improved suit mobility, an improved life support system, and a Lunar Roving Vehicle capable of up to 90 km traverses. Changes in the Command and Service Modules will allow for up to 16 days total flight duration.

We will again welcome proposals for analysis of the new samples, but now that the initial exploratory work has been done we intend to be far less duplicative in choosing proposals to support. We are particularly pleased with the growing attention being given by the scientific societies to the results of lunar research.

In the last talk of this series, Mr. Burke will describe some of the future possibilities that have been studied for exploration of the Moon and planets. We will particularly welcome suggestions as to how to improve the value of future missions.
Petrochemistry and Chemical Features of Lunar Glassy Spherules
Authors: Trigila R.
Published: June 2019

The major elements of glassy spherules from samples 12001.73, 12057.60 and 12070.37 of lunar fines have been determined by electron probe analysis. The bulk chemistry of these spherules (which are between 200 μm and 62 μm in size) falls in most cases within the range of gabbro-peridotite and gabbro-anorthosite.

In individual spherules, the grade of chemical homogeneity is highly variable and can be related to the possible presence of small inclusions or sometimes to slight concentration gradients evident near the peripheries of the particles. These features, together with the presence of vesicles of different size in association with strong alkali enrichment along the boundaries of such cavities can account for relationships between the chemistry of the particles and their genetic history.
The Solar Irradiation Record in Lunar Dust Grains
Authors: Borg J. , Vassent B.
Published: June 2019

Comparative studies of the distribution of latent and etched tracks in lunar grains from five different size fractions of three lunar fine samples and of six lunar dust samples taken at different depths in core tube 12028 have been performed by using transmission and scanning electron microscopies. Two very different sets of etching conditions were used: a slight etching was applied for transmission microscopy but a much stronger etching was used for scanning microscopy. We observed: (1) a definite stratigraphy in the core tube, both in the latent and etched track distributions; (2) striking differences between the densities of the latent and slightly etched tracks (≥ 1010 tracks cm−2) and those of the strongly etched tracks, ranging from ⋍ 108 to 5.109 tracks cm−2; (3) a lack of correlation between the grain size and the density of strongly etched tracks observed on the external surface of grains from sample 12032; (4) no variation of the density of the tracks with the depth inside a grain. Some implications of the present results concerning the ancient low energy solar cosmic rays and the fabric of the lunar soil will be briefly discussed.
The Origin of the Moon and Solar System
Authors: Urey Harold C.
Published: June 2019

The Rb87-Sr87ages of many of the lunar rocks suggest that the fundamental differentiation took place 4.5 × 109yr ago and that remelting occurred without exchange of the rubidium and strontium with the surroundings. The Apollo A rocks are an exception to this. They appear to have acquired rubidium without all of the Sr87produced during the first aeon. Also in the remelting about half of the radiogenic leads were lost to the surroundings probably the soil by a vaporization process. We interpret these results to mean that remelting occurred in a system that was nearly closed to the surroundings and that the high early concentrations of radioactive elements in highly insulating surroundings made this possible.
The global properties of planetary nebulae in the Galactic Bulge
Authors: Stasińska G.
Published: June 2019

After a discussion of the methods used to derive the physical parameters of planetary nebulae and their central stars, the global properties of planetary nebulae in the Galactic bulge are reviewed, and compared to those of planetary nebulae in different contexts.
Stellar population synthesis: Application To Galactic Bulges
Authors: Arimoto N.
Published: June 2019

The stellar populations give traces of the formation history of the bulges. The metallicity distribution of K-giants in the Galactic bulge resembles to that of the giant ellipticals. There seems to be no conspicuous colour-magnitude relation intrinsic to the bulges. This can be explained if the bulges formed by the dissipative collapse of central regions of proto-galaxies followed by the supernova-driven bulge wind which was induced later than the dwarf ellipticals of the similar mass (the biased wind). Unfortunately, the observational data available at present of stellar populations of the bulges are not yet sufficient to get a firm conclusion on the origin of the bulges.
Formation and evolution of stars in galactic bulges
Authors: Renzini Alvio
Published: June 2019

A fair fraction of stars in the Galactic Bulge (a possibly in bulges in general) appears to be more metal rich than the sun. Some of the current limitations in quantitatively modelling such super metal rich (SMR) stars are briefly recalled, including the question of the helium enrichment, of the metallicity dependence of mass loss, and of the metal opacity. Recent color-magnitude diagrams for stars in the Galactic Bulge are show that the bulk of Bulge stars must be very old, although current data do not allow to determine the age with sufficient accuracy to establish the relative age of the Halo and of the Bulge. The question of the nature of the most luminous (AGB) stars in bulges and in M32 is then addressed in some detail, discussing a series of methodological aspects which would need careful consideration before using bright AGB stars as age indicators. It is concluded that — for the time being — none of the claims for the presence of an intermediate age component in the Galactic Bulge, in M32, and in the bulge of M31 is completely exempt from ambiguities, and ways for elimitating such ambiguities are suggested. Finally, from the evidence that bulges are dominated by a very old stellar population it is concluded that star formation in bulges probably started and was essentially completed before the completion of star formation in the halo: bulges are likely to on average older than halos.
Kinematics of extragalactic bulges: evidence that some bulges are really disks
Authors: Kormendy John
Published: June 2019

Recent work on the dynamics of galaxy bulges has been dominated by two themes. (1) Bulges share the richness in kinematic structure that is currently being discovered in elliptical galaxies. This includes kinematic evidence for triaxiality and for accretion (counterrotating gas and stellar components). (2) The main subject of this paper is observational and theoretical evidence that some “bulges” are built secularly out of disk material. Many bulges show photometric and kinematic evidence for disklike dynamics. This includes (i) velocity dispersions σ much smaller than those predicted by the Faber-Jackson σ — MB correlation, (ii) rapid rotation V(r) that implies V/σ values well above the “oblate line” describing rotationally flattened, isotropic spheroids in the V/σ — ellipticity diagram, and (iii) spiral structure dominating the r1/4 part of the galaxy. In these galaxies, the steep, r1/4-law central brightness profiles belong not to bulges but to disks. That is, some galaxy disks have central brightness profiles that are much steeper than the inward extrapolation of an exponential fit to the outer parts. These observations and n-body simulations of gas flow in nonaxisymmetric galaxies imply that high-central-concentration, flat components can be formed out of disk gas that is transported toward the center by bars and oval distortions. The n-body models suggest further that some “bulges” are built of disk stars heated in the axial direction by resonant scattering off of bars. These effects are signs that important secular evolution processes are at work in galaxy disks.
3D gas dynamics in triaxial systems
Authors: Friedli D. , Udry S.
Published: June 2019

Depending on the nature of the various components (stars, gas) present in triaxial stellar systems (elliptical galaxies, bulges and bars), the dynamics is expected to be rather different. The stars are collisionless, dissipationless, and dynamically hot; they are mainly trapped by quasi-periodic or chaotic orbits. On the contrary, the gas is collisional, dissipational, and dynamically cold; the cold or warm gas (≲ 104 K) is a powerful orbital tracer, however shocks prevent it from following self-crossing orbits. The hot gas (≲ 106 K) is influenced by “repulsive” pressure forces which prevent in close encounters the flow from being strongly shocked; it rather follows chaotic trajectories. By means of fully self-consistent 3D simulations with stars and gas using PM (Pfenniger & Friedli 1992) and SPH (Friedli & Benz 1992) techniques, we investigate the response of gaseous components in the following situations: 1) slow or fast pattern speed Ωp, 2) direct or retrograde gas motion with respect to the stars, and 3) warm or hot gas temperature T. Initial parameters and final characteristics of each runs are reported in Table I.
Detectability of Bulge stars
Authors: Hernandez-Pajares M. , Cubarsi R. , Sanz-Subirana J. , Juan-Zornoza J.M.
Published: June 2019

Classification algorithms based on neural network techniques are applied to study if the bulge stars can be differentiated from other stars belonging to other Galactic components. A synthetic sample is build as a mixture of four components, thin disk, thick disk, halo and bulge, according to some stellar system models and considering observational errors.
The IR stellar population around the Galactic Centre
Authors: Ruelas-Mayorga A. , Teague P.
Published: June 2019

We present K-counts for a number of stars with K ≤ +9.0 in 3 clear regions near the galactic centre. They are located approximately at l∼0.0 and b ∼ −3.5, −4.0 and −4.5. Their Cumulative Counts Functions (CCF's) are formed, and with the aid of an exponential disc model for the Galaxy are separated into disc and bulge CCF. As for the case in Baade's Window (BW) (Ruelas-Mayorga and Teague, 1992a) the disc is dominant at bright magnitudes whereas the bulge dominates at fainter ones. The slope of the bulge CCF is steeper than that for the disc in all cases corroborating the result obtained for BW. The two colour JHK and the K vs J-K diagrams show that the stellar population in these areas is similar to that studied in BW by us and by Frogel and Whitford (1987). An average E(J-K) ∼0.42 mag for the reddening is obtained. At K ≤ +9.0, the disc may be accounted for by those sources with J-K ≤ +1.6 whereas the bulge population presents values for J-K in excess of +1.6.
The UV and optical reddening law to the Galactic Bulge and CNO abundances in Bulge planetary nebulae
Authors: Walton N.A. , Barlow M.J. , Clegg R.E.S.
Published: June 2019

An analysis of the differential ultraviolet extinction towards four bulge planetary nebulae, based on the observed line ratio of He II 1640/4686Å, shows that the ultraviolet reddening law towards the bulge is much steeper than in the solar neighbourhood. An analysis of the optical reddening law for 42 bulge PN, based upon observed Balmer line ratios and Hβ to radio free-free flux ratios, is presented. The optical reddening law towards the bulge is steeper than in the local ISM, and thus the ratio of total to selective extinction, Rv = 2.29 (± 0.50), is lower than the standard solar neighbourhood value of Rv = 3.10.

We present abundance determinations, in particular C/H and C/O ratios, for 11 Galactic bulge PN, based on spectrophotometry in the UV from IUE and in the optical from the Anglo-Australian Telescope. The derived abundances are compared with values for PN in the Galactic disk. The mean C/O ratio for bulge PN is significantly lower than that found for Galactic disk PNs. Additionally we present an abundance analysis of the very metal-poor halo population PN M2-29, which is located in the bulge.
Do the OH/IR stars within 100 pc of the Galactic Center belong to the disk population?
Authors: Whitford A.E.
Published: June 2019

The 135 OH/IR stars within 0.8 deg (∼ 100 pc) of the Galactic Center (GC) identified in a search with the VLA (Lindqvist et al. 1991) are in rapid rotation about the center with a regression line showing a velocity gradient of 1.2±0.1 km s−1, equivalent to 178 km s—1 deg−1 for Ro = 8.5 kpc (Lindqvist et al. 1992). This is of the same order as the inward extrapolation of the Galactic rotation curve derived from the terminal velocities of HI for l < 2 deg (Burton and Gordon 1978) and the general trend of the velocities of the CO clouds in the equatorial disk mapped by Dame et al. (1987) (Fig. 1b). These OH/IR stars are located along the ridge of highest projected CO density. This spatial location and the flat configuration argue for assignment to the disk population, a possibility suggested by Feast (1989). The VLA objects are not in general supergiants (Blommaert et al. 1992). On a K-band map of an area 1×2 deg around the GC, Catchpole et al. (1990) found a number of stars brighter than (mK)o = 5. On the assumption that BCK = 3.3, (Frogel and Whitford 1987), and Ro = 8.5 kpc, Mbol < — 6.3, i.e., in the supergiant range.
Proper motions: what dynamical information can we easily extract from them?
Authors: Wybo M. , Dejonghe H.
Published: June 2019

We explore the proper motion distributions of anisotropic Plummer models, and show that information on the orbital structure can be obtained, even if no distance information is available.
The contribution of the Galactic Bulge to the Galactic rotation curve
Authors: Petrovskaya I.V. , Ninković S.
Published: June 2019

It is not always clear what the bulge of the Galaxy is: a region close to the centre, a subsystem formed by a distinct population, or a mixture of populations but characterised by its own mass distribution. We consider the bulge of the Milky Way as a subsystem and thus contributing to the galactic gravitation field. We want to estimate the contribution of the galactic bulge to the rotation curve.
Two–Integral Models with Almost Circular Orbits
Authors: Batsleer P. , Dejonghe H.
Published: June 2019

We present global dynamical models for bulge–disk systems. The phase–space structure is examined by means of two integral models. The models indicate that in the formation merger argument for ellipticals one cannot always assume that the maximum phase–space density occurs in the center of the system.
On the formation mechanisms for ellipticals and bulges
Authors: Fridman A.M. , Polyachenko V.L.
Published: June 2019

We study the formation of elliptical galaxies and the bulges of disk galaxies as a result of the collisionless collapse of a rotating star cloud. At small amounts of rotation, this process is accompanied by the bar mode of the radial orbit instability slightly modified by rotation. We refer this case to (giant) ellipticals. For moderate rotation, when the radial orbit instability is suppressed, another mode takes over, which is the direct continuation of a strongly damping mode at the limit of almost radial orbits; it turns into a practically non-damping and long-lived mode (for many revolutions), and even a slowly rotating bar may eventually be formed. It is natural to refer this case to bulges and dwarf elipticals. Then spirals could be formed from the clouds with large amounts of rotation.
The effect of a bar on the kinematics of a central ring structure in NGC 4736
Authors: Pişmiş P. , Moreno E.
Published: June 2019

We analyze the kinematics of the gaseous ring in the central region of NGC 4736 considering an ejection mechanism for the formation of the ring in a non-axisymmetric potential. A barred spiral of strength 10 or 25 per cent of the axisymmetric background is consistent with van der Kruit (1974) observational data.
Kinematic signatures of triaxial stellar systems
Authors: Arnold Richard , Zeeuw Tim De , Hunter Chris
Published: June 2019

Analytic dynamic models of triaxial stellar systems, such as elliptical galaxies and galactic bulges, can be used to calculate the velocity fields of systems in a wide range of potentials without the need for orbit integrations. We present results from a first application of these models, in the form of velocity fields projected onto the sky. The appearance of the velocity field depends strongly on the viewing angle. Thin orbit models provide a theoretical upper limit to streaming in all possible kinematic models in a given potential.
Colour Gradients in Galaxy Bulges
Authors: Balcells Marc , Peletier R. F.
Published: June 2019

Colour gradients, when due to stellar populations rather than dust, are potential diagnostics on the formation history of galaxy bulges. We have carried out measurements of colour gradients on a sample of 30 bulges, the first such study using CCD detectors.
Hot Stellar Populations in the M31 Bulge
Authors: Ferguson Henry C. , Davidsen Arthur F.
Published: June 2019

We investigate the possibility that the Far-UV spectral energy distributions (SED's) of M31 and NGC 1399 differ only in the relative contribution from classical PAGB stars and in the amount of extinction. A good fit to the M31 spectrum is obtained for E(B-V) = 0.11 if about 65% of the flux comes from PAGB stars and the rest from stars of the type producing the far-UV emission in NGC1399. We speculate that the UV continuum in both galaxies is dominated by stars in post-horizontal branch phases of evolution, with a distribution of post-HB masses governed primarily by the metallicity and metallicity spread of the population. This hypothesis can qualitatively explain both the relative fluxes of UV rising branches in NGC1399 and M31 and the shapes of their SED's.
Line profiles in the bulge of NGC 7217
Authors: Kuijken Konrad , Merrifield Michael R.
Published: June 2019

Line-of-sight velocity distributions are becoming increasingly important for our understanding of galactic structure. We present results obtained for the bulge of NGC7217 with a new deconvolution technique.
On the photometric characteristics of ellipticals and bulges of spirals in interacting systems
Authors: Reshetnikov V.P.
Published: June 2019

The results of the study of the global photometric parameters of ellipticals and bulges of spiral galaxies are presented.
Nuclear molecular gas in the Virgo Cluster S0 galaxy NGC 4710
Authors: Wrobel J.M. , Kenney J.D.P.
Published: June 2019

The CO(J=1→0) emission from NGC 4710, a star–forming S0 galaxy in the Virgo Cluster, was synthesized with spatial and velocity resolutions of 7″ and 26 km s—1, respectively. The CO shows a compact morphology and co–rotates with the galaxy's stars and nuclear optical emission line gas. Analysis of the CO distribution and kinematics indicates that the nuclear molecular gas is probably gravitationally unstable, and this may explain why the galaxy is presently forming stars. Four possible origins for the nuclear molecular gas are considered. An origin via bulge star ejecta being deposited into a residual interstellar medium is favored.
Grains, or Molecules? Thermal, or non-Thermal?
Authors: Barker John R. , Cherchneff Isabelle
Published: June 2019

The effects of size and energy on infrared fluorescence (IRF) and on chemical reaction rates are investigated, using polycyclic aromatic hydrocarbons (PAHs) as examples. The range of validity of the Thermal Approximation (TA) is examined. It is found that for properties that have a near-linear dependence on the internal energy, the TA provides an adequate description of the non-thermal, time-dependent processes associated with ultraviolet photon absorption. Since IRF at high energy is nearly linear, the TA is adequate for IRF at high excitation energies, but care must be taken, because the TA fails at low energies. The TA is never adequate for chemical reactions under these conditions.
Interstellar Grains in Meteorites: Diamond and Silicon Carbide
Authors: Anders Edward , Lewis Roy S. , Ming Tang , Zinner Ernst
Published: June 2019

Well-preserved interstellar grains occur in carbonaceous chondrites. Diamond (10-100å) contains r- and p-process Xe (suggesting a supernovae connection), and appears to have formed by stellar condensation, not by interstellar shocks. SiC (mainly 0.1-1 μm) is labeled either with s-process Xe, Kr (red giant?) or with Ne22, N15 (nova?), and shows large isotopic variations in N (100x), C (16x), and Si (1.3x). As Si is unaffected by H, He-burning, the Si variations reflect the isotopic heterogeneity of the ISM on the scale of individual stars; the Si compositions found thus far require at least 6 separate stars.
Hertz and Michelson
Authors: Shapiro Irwin I.
Published: June 2019

I have mixed feelings about giving the opening talk at this symposium. On the one hand I am delighted to welcome you to this conference on the impact of VLBI on astrophysics and geophysics. On the other hand I am very sad that Ed Purcell is bothered by a bad back and cannot give the introduction as originally scheduled. Ed is one of the truly great of the world's physicists and one of the nicest persons ever born. My substituting for Ed is somewhat like Bill Buckner pinch hitting for Lou Gehrig. (Those who do not understand this reference to American baseball might have a better appreciation after viewing tonight's Red Sox game.)
Superluminal Motion in the Largest Known Quasar
Authors: Barthel P. D. , Schilizzi R. T. , Miley G. K. , Preuss E. , Hooimeyer J. R.
Published: June 2019

We discuss VLBI observations of the bright core in the large, triple radio source 4C 34.37, associated with a quasar at z = 0.206. We have discovered superluminal motion in this quasar, which is the largest quasar known. We comment on the implications of these findings, and subsequently examine the projected size distributions of lobe and core dominated quasars in general. The results of these investigations lead us to conclude that neither superluminal motion, nor core prominence can simply be translated into an orientation of the overall radio source.
Superluminal Motion of 3C273B and the Apparent Right Ascension Shift
Authors: Kawaguchi N. , Takahashi Y.
Published: June 2019

The effect of the superluminal motion of 3C273b was observed on the fringe amplitudes obtained in VLBI experiments which have been conducted on the baselines between Japan and United States since 1984 under the Crustal Dynamics Project. The speed was 0.7 mas/year and the direction was −83 degrees in the position angle. It was also confirmed as the apparent right ascention shift of the source.
Shockwaves in Extended Near-Relativistic Jets
Authors: Biermann Peter L. , Strittmatter Peter A.
Published: June 2019

The origin of the sharp near infrared cutoff in the continuous energy distribution of many compact non-thermal sources (active nuclei or knots in jets) is considered under the assumption that particle acceleration takes place in shockwaves. Energy losses due to synchrotron emission and Compton interactions set upper limits to both electron and proton energies. In this case the upstream disturbance of the flow is dominated by the most energetic protons which are postulated, by analogy with the solar wind, to excite a turbulent wave spectrum of Kolmogorov type in this region. We predict for near relativistic flows a spectral cutoff near 3 1014 Hz independent of magnetic field. The observation of a sharp spectral cutoff near 3 1014 Hz is thus independent evidence for near–relativistic flows in jets.
Superluminal Accelerations Along a Helically Twisted Jet
Authors: Hardee Philip E.
Published: June 2019

The relativistic dispersion relation describing the spatial growth of a helical perturbation to a relativistic supersonic jet is applied to observations of the nonlinear superluminal acceleration of component C4 along the inner jet in 3C345.
Kinematic Properties of the Ejected Matter in NGC 1275
Authors: Marr J. M. , Backer D. C. , Wright M. C. H. , Readhead A. C. S. , Moore R.
Published: June 2019

We have mapped the nearby (z=0.018), active galaxy NGC 1275 (3C84) at 6 different epochs from 1981 to 1986 at 1.3 cm (22.3 GHz) with a global VLBI array of seven telescopes. We find a long-lived knot of emission separating from the brightest radio component with a projected velocity = 0.4 6±0.12 h−1 c. This knot moves through diffuse emission that also moves away from the main component with a slower projected velocity of 0.33±0.12 h−1 c. We show that the knot and diffuse emission result from two separate events that occurred around 1959 and 1968.
WSRT Observations of Hourly Flux Variations in OJ287 at 6cm Wavelength
Authors: de Bruyn A.G.
Published: June 2019

Observations of short term flux variations provide one of the few means of determining the smallest scale sizes in compact radio sources. The fastest variations are generally found in BL Lac-type objects, OJ287 being one of the best studied. In 1985 Valtaoja et al. (Nature 314, 148) found evidence for variations at a level of (typically) a few % with a period of in OJ287 at frequencies of 22 and 37 GHz. [Such periodic variability was, however, not detected at 5 GHz during one of their observations by Dreher et al. (Nature 320, 239, 1986)].
Radio Galaxies and Relativistic Beaming
Authors: Saikia D. J.
Published: June 2019

There have been recent suggestions and suspicions that the earlier unified scheme, which largely involved quasars, could be enlarged upon to include galaxies as well. In this scheme, the extended radio galaxies are believed to be close to the plane of the sky while the lobe and core-dominated quasars are seen at progressively smaller angles to the line-of-sight. In this paper, we study the correlations of the degree of core prominence with optical properties as well as radio structures on VLBI and larger scales for the both radio galaxies and quasars, in order to investigate whether they are consistent with the enlarged unified scheme. From earlier statistical studies of quasar samples, the degree of core prominence has been shown to be a reasonable statistical indicator of source orientation (cf., Saikia 1985 and references therein). Saikia (1984) also showed that jets in quasars are more easily detected in the ones with more prominent cores, consistent with the unified scheme. In the present paper, we present the results of our observations of 30 low-luminosity radio galaxies and investigate whether such a result holds for galaxies as well.
Morphology of Steep Spectrum Radio Sources Showing Variability at Low Frequency
Authors: Mantovani Franco , Muxlow Tom , Padrielli Lucia
Published: June 2019

The observed variability at low frequency of the radio sources can be explained within the framework of the generally accepted models either extrinsic (refractive scintillation in the interstellar medium) or intrinsic (bulk relativistic motion along direction near the line of sight) for variability. Both explanations require a large fraction of the source flux density to be contained in a small high brightness component, of tens of m.a.s. in size. Radio sources with steep straight spectral index are usually tens of Kpc sized, with weak central components and they do not generally show low frequency variability.
Milliarcsecond Polarization Properties of Several BL Lacertae Objects
Authors: Gabuzda D. C. , Roberts D. H. , Wardle J. F. C. , Brown L. F.
Published: June 2019

We discuss the λ6 cm total intensity and polarization structures of a number of BL Lacertae objects at milliarcsecond resolution. 0235+164 was unresolved and weakly polarized at each of two epochs a year apart; each of the other objects displays structure in polarized flux. 0735+178 and 1749+096 can be adequately modeled by two or three point components—a “core” plus one or two “knots.” The core components were moderately polarized (≃ 5%), while “knots” may be polarized at 8% or more, consistent with these components being optically thin. Preliminary results for BL Lac indicate that the total intensity structure can be modeled well by a set of four gaussian components; the polarization structure is complex, but is dominated by the northernmost knot in the jet.
Masers and the Cosmic Distance Scale
Authors: Reid Mark J. , Moran James M. , Gwinn Carl R.
Published: June 2019

Studies of H2O masers have demonstrated the power of VLBI techniques to measure relative positions with sufficient accuracy (∼ 10 μas) to determine proper motions and to estimate distances to maser sources throughout the Galaxy. The distance to four H2O masers have been determined, and the distance to the center of the Galaxy has been determined to be 7.1 ± 1.5 kpc from observations of the H2O masers in Sgr-B2. Proper motion distances for other H2O masers, and possibly for OH masers, may allow the determination of the fundamental parameters describing the size (Ro) and rotation rate (Θo) of the Galaxy with accuracies of better than 10%. Finally, the measurement of the proper motions of H2O masers in nearby galaxies (< 10 Mpc) is feasible and offers the possibility of direct calibration of the extragalactic distance scale.
Initial Radio Observations of SN1987a in the Large Magellanic Cloud
Authors: Turtle A. J. , Campbell-Wilson D. , Bunton J. D. , Jauncey D. L. , Kesteven M. J. , Manchester R. N. , Norris R. P. , Storey M. C. , White G. L. , Reynolds J. E. , Malin D. F.
Published: June 2019

A prompt radio burst has been observed from the supernova 1987a in the Large Magellanic Cloud. Observations were made at 0.843, 1.415, 2.29, and 8.41 GHz. At frequencies around 1 GHz, the peak flux density reached about 150 mJy and occurred within four days of the supernova. This event may be a weak precursor to a major radio outburst of the type previously observed in other extragalactic supernovae. Radio monitoring of the supernova is continuing at each of the above frequencies, and coordination is underway of a southern hemisphere VLBI array to map the radio outburst region as it expands. Differential astrometry carried out on prime-focus plates taken with the Anglo-Australian telescope indicates that the component, star 1, of Sanduleak's star SK-69202 is within 0.05 ± 0.13 arcsec of the supernova.
VLBI Observations of Gravitational Lens Systems
Authors: Turner Edwin L.
Published: June 2019

Four specific and particularly powerful types of possible VLBI lens studies are discussed. First, comparison of mas scale structure in putative pairs of images separated by arc seconds can provide a powerful additional test of the lens hypothesis in specific candidate systems. Second, VLBI searches for lens systems with image separations too small for resolution by optical or VLA searches will limit (or even determine!) the cosmological density of condensed objects with individual masses ∼ 106M⊙. Third, study of multiply imaged superluminal expansion events will allow a determination of the light travel time delay between different images in a lens system, a quantity which is quite difficult to measure by other means but which would allow profound cosmological tests. Fourth, VLBI data can be used to determine relative image parities and even the full magnification matrix of various images in a lens system, thus providing powerful additional constraints on detailed lens models. Finally, the speculative possibility of detecting Galactic stellar lensing events using VLBI techniques is discussed.
Can We Measure H0 with VLBI Observations of Gravitational Images?
Authors: Falco E. E. , Gorenstein M. V. , Shapiro I. I.
Published: June 2019

We have used the relative positions and magnifications of the A and B images in the gravitational lens system 0957+561, obtained from VLBI observations, to constrain a model for the surface mass distribution of the lens. With measurements of the difference ΔτBA in propagation times associated with A and B (the “relative time delay”) and of the velocity dispersion of the main lensing galaxy, both to be obtained, our model will yield a value for H0 with an uncertainty of ∼ 20% due mainly to uncertainties in our assumptions.
VLBI Observations of Radio Stars
Authors: Lestrade Jean-François
Published: June 2019

In recent years, observations of stars across the whole electromagnetic spectrum have yielded a wealth of information on their atmospheres and borne out new insights on their internal structures. Indirect evidences for chromospheres, coronae and winds were discovered in stars other than the Sun. For instance, ultra-violet and optical emission lines from collisionally excited atoms are evidences for chromospheric activity with temperatures between 104and 2 × 105K. Soft X-ray emission with thermal spectrum is evidence for hot coronae with temperatures between 106and 3 × 107K. The spindown of stars with age is best interprated by loss of mass and of angular momentum via magneticly coupled stellar winds originating in hot stellar coronae.
VLBI and Extreme Scattering Events
Authors: Dennison Brian , Fiedler R. L. , Johnston K. J.
Published: June 2019

Ray tracing numerical simulations of extreme scattering events result in light curves that display many of the qualitative features observed in such events. The apparent images of an affected source show strong and variable distortions, which could be readily discerned with VLBI observations.
Celestial Reference Frames: Definitions and Accuracies
Authors: Standish E M
Published: June 2019

The determination of a specific catalogue or ephemeris reference frame is a highly over-determined problem, depending on the particular selection of which coordinates, which objects and at what time(s) the determination is made. The consistency which various determinations exhibit is dependent upon the accuracy of the catalogue or ephemeris itself. This paper discusses the accuracies of the three most prominent celestial reference frames: stellar catalogues, the lunar and planetary ephemerides and the radio source catalogues.

The FK4 stellar catalogue contains known systematic errors amounting to a few tenths of an arcsecond; the FK5 will yield nearly an order of magnitude improvement; HIPPARCOS and Space Telescope expectby the mid 1990's optical interferometry should approachwithin a couple of years, tens of micro(!)arcseconds after a couple of decades. Present-day lunar and planetary ephemerides have accuracies at the level offor the moon and inner four planets;for the outer planets. Further observational data will permit continued improvement. Radio source catalogues now show internal consistency of
VLBI geodesy: 2 parts-per-billion precision in length determinations for transcontinental baselines
Authors: Davis J. L. , Herring T. A. , Shapiro I. I.
Published: June 2019

We have used very-long-baseline interferometry (VLBI) to make twenty-two independent measurements, between September 1984 and December 1986, of the length of the 3900-km baseline between the Mojave site in California and the Haystack/Westford site in Massachusetts. These experiments differ from the typical geodetic VLBI experiments in that a large fraction of observations are obtained at elevation angles between 4° and 10°. Data from these low elevation angles allows the vertical coordinate of site position, and hence the baseline length, to be estimated with greater precision. For the sixteen experiments processed thus far, the weighted root-mean-square scatter of the estimates of the baseline length is 8 mm. We discuss these experiments, the processing of the data, and the resulting baseline length estimates.