Showing papers in "Astrophysics and Space Science in 2000"

The fractional kinetic equation and thermonuclear functions

Abstract: The paper discusses the solution of a simple kinetic equation of thetype used for the computation of the change of the chemical compositionin stars like the Sun. Starting from the standard form of the kineticequation it is generalized to a fractional kinetic equation and itssolutions in terms of H-functions are obtained. The role of thermonuclearfunctions, which are also represented in terms of G- and H-functions,in such a fractional kinetic equation is emphasized. Results containedin this paper are related to recent investigations of possibleastrophysical solutions of the solar neutrino problem.

A New Database of Astrophysical Interest

Abstract: The aim of the new database D.R.E.A.M. is to supply the astrophysicists with accurate atomic data (wavelengths, energy levels, oscillator strengths, radiative lifetimes) of neutral, singly or multiply ionized lanthanides. Up to now, it contains about 50000 lines but it will be updated and extended in the near future.

Lagrangian Modelling of Dust Admixture in Gas Flows

Abstract: A method of calculating the dispersed-phase concentration in dusty gas flow, based on using the Lagrange form of the particle continuity equation, is developed The method makes it possible to calculate the particle concentration along a fixed particle trajectory and to investigate flow regions with multiple intersection of particle trajectories and particle accumulation zones The use of the method is illustrated by numerical calculations of the near-symmetry-axis region in a hypersonic flow colliding with a two-phase supersonic flow from a point source (the model of evaporation of a comet nucleus) It is demonstrated that, between the bow and termination shock waves, the particle concentration distribution may have a multi-layer structure with alternating layers of high and low particle concentration and sharp particle accumulation near the envelops of the particle trajectories

On the Stability of Colliding Flows: Radiative Shocks, ThinShells, and Supersonic Turbulence

Abstract: High-resolution numerical simulations reveal the turbulent character of the interaction zone of colliding, radiative, hypersonic flows As the shocked gas cools radiatively, the cooled matter is squeezed into thin, high density shells The remaining kinetic energy causes supersonic turbulence within these shells, before it is finally dissipated by internal shocks and vortex cascades The density is far from homogeneous High density filaments and large voids coexist Its mean value is significantly below the stationary value Similarly, areas with supersonic velocities are found next to subsonic regions The mean velocity is slightly below or above the sound speed While quasi uniform flow motions are observed on smaller scales the large scale velocity distribution is isotropic Part of the turbulent shell is occupied by relatively uniform flow-patches, resembling coherent structures Astronomical implications of the turbulent interaction zone are multifarious It probably drives the X-ray variability in colliding wind binaries as well as the surprising dust formation on orbital scales in some WR-binaries It lets us understand the knotty appearance of wind-driven structures as planetary and WR-ring nebulae, symbiotics, supernova remnants, galactic supperbubbles Also, WR and other radiatively driven, clumpy winds, advection dominated accretion, cooling flows and molecular cloud dynamics in star-forming regions may carry its stamp

Hot Neutral H in the Heliosphere: Elastic H-H, H-p Collisions

Abstract: Williams et al. (1997) have suggested that a population of hot hydrogen atoms is created in the heliosphere through elastic H-H collisions between energetic `solar' atoms (neutralized solar wind) and interstellar atoms. They used a BGK-like approximation (Bhatnagar et al., 1954) for the Boltzmann collision term and the collision cross sections suggested by Dalgarno (1960). We show that both assumptions result in a significant overestimation of the the H-H collision effect. On the basis of calculated momentum transfer cross-sections for elastic H-H collisions, we argue that elastic H-H and H-p collisions cannot produce hot H atoms in the heliosphere.

A Photogravitational Hill Problem and Radiation Effects on Hill Stability of Orbits

Abstract: We introduce a photogravitational version of Hill's problem to include the effect of radiation of the primaries, and discuss its equilibrium points and zero velocity curves. As a first application we use this model to study Hill stability of orbits around the small primary. The estimates obtained for the maximum distance of Hill stable orbits are compared to the predicted maximum sizes of accretion disks in binary stars according to recent theories based on periodic orbits as streamlines of the disks.

Physics and Gasdynamics of the Heliospheric Interface

Abstract: During 30 years, a big theoretical effort to understand the physical processes in the heliospheric interface has followed the pioneer papers by Parker (1961) and Baranov et al. (1971). The heliospheric interface is a shell formed by the solar wind interaction with the ionized component of the circumsolar local interstellar medium (LISM). For fully ionized supersonic interstellar plasma two-shocks (the termination shock and the bow shock) and a contact discontinuity (the heliopause) are formed in the solar wind/LISM interaction. However, LISM consists of at least of three components additional to plasma: H-atoms, galactic cosmic rays and magnetic field. The interstellar atoms that penetrate into the solar wind, are ionized there and form pickup ions. A part of the pickup ions is accelerated to high energies of anomalous cosmic rays (ACRs). ACRs may modify the plasma flow upstream the termination shock and in the heliosheath. In this short review I summarize current understanding of the physical and gasdynamical processes in the heliospheric interface, outline unresolved problems and future perspectives.

Spiral Structure as a Recurrent Instability

Abstract: A long-standing controversy in studies of spiral structure has concerned the lifetimes of individual spiral patterns. Much theoretical work has sought quasi-stationary spiral modes while N-body simulations have consistently displayed recurrent, short-lived patterns. The simulations manifest a recurrent cycle of true instabilities related to small-scale features in the angular momentum distribution of particles, with the decay of each instability seeding the growth of the next. Data from the recent Hipparcos mission seem to offer support for the recurrent transient picture.

Application of the Information Criterion to the Estimation of Galaxy Luminosity Function

Abstract: To determine the exact shape of the luminosity function (LF) of galaxies is one of the central problems in galactic astronomy and observational cosmology. The most popular method to estimate the LF is maximum likelihood, which is clearly understood with the concepts of the information theory. In the field of information theory and statistical inference, great advance has been made by the discovery of Akaike's Information Criterion (AIC). It enables us to perform a direct comparison among different types of model swith different numbers of parameters, and provides us a common basis of the model adequacy. In this paper we applied AIC to the determination of the shape of the LF. We first treated the estimation using stepwise LF(Efstathiou, Ellis and Peterson,1988), and derived a formula to obtain the optimal bin number. In addition, we studied the method to compare the goodness-of-fit of the parametric form (Sandage, Tamman and Yahil, 1979) with stepwise LF.

Cosmic Ray Production Rates in Supernova Remnants

Abstract: Supernova Remnants (SNRs) are the most likely sources of the galactic cosmic rays up to energies of about 1015 eV/nuc. The large scale shock waves of SNRs are almost ideal sites to accelerate particles up to these highly non-thermal energies by a first order Fermi mechanism which operates through scattering of the particles at magnetic irregularities. In order to get an estimate on the total amount of the explosion energy E SNconverted into high energy particles the evolution of a SNR has to be followed up to the final merging with the interstellar medium. This can only be done by numerical simulations since the non-linear modifications of the shock wave due to particle acceleration as well as radiative cooling processes at later SNR stages have to be considered in such investigations. Based on a large sample of numerical evolution calculations performed for different ambient densities n ext, SN explosion energies, magnetic fields etc. we discuss the final ‘yields’ of cosmic rays at the final SNR stage where the Mach number of the shock waves drops below 2. At these times the cosmic rays start to diffuse out of the remnant. In the range of external densities of10-2 ≤ n ext/[cm-3] ≤ 30 we find a the total acceleration efficiency of about 0.15 E SN with an increase up to 0.24 E SN at maximum for an external density of n ext = 10 cm-3. Since for the larger ambient densities radiative cooling can reduce significantly the total thermal energy content of the remnant dissipation of Alfven waves can provide an important heating mechanism for the gas at these later stages. From the collisions of the cosmic rays with the thermal plasma neutral pions are generated which decay subsequently into observable γ-rays above 100 MeV. Hence, we calculate these γ-ray luminosities of SNRs and compare them with current upper limits of ground based γ-raytelescopes. The development of dense shells due to cooling of the thermal plasma increases the γ-ray luminosities and e.g. an external density of n ext = 10 cm-3 with E SN = 1051 erg can lead to a γ-ray flux above 10-6 ph cm-2 s-1 for a remnant located at a distance of 1 kpc.

On most general exact solution for Vaidya-Tikekar isentropicsuperdense star

Abstract: The energy density of Vaidya-Tikekar isentropic superdense star is found to be decreasing away from the center, only if the parameter K is negative. The most general exact solution for the star is derived for all negative values of K in terms of circular and inverse circular functions. Which can further be expressed in terms of algebraic functions for K = 2-(n/δ)2 < 0 (n being integer andδ = 1,2,3 4). The energy conditions 0 ≤ p ≤ αρc 2, (α = 1 or 1/3) and adiabatic sound speed conditiondp dρ ≤ c 2, when applied at the center and at the boundary, restricted the parameters K and α such that .18 < −K −2287 and.004 ≤ α ≤ .86. The maximum mass of the star satisfying the strong energy condition (SEC), (α = 1/3) is found to be3.82 Mq· at K=−2/3, while the same for the weak energy condition (WEC), (α =1) is 4.57 M_ ⊙ atK=−>5/2. In each case the surface density is assumed to be 2 × 1014 gm cm-3. The solutions corresponding to K>0 (in fact K>1) are also made meaningful by considering the hypersurfaces t= constant as 3-hyperboloid by replacing the parameter R 2 by −R2 in Vaidya-Tikekar formalism. The solutions for the later case are also expressible in terms of algebraic functions for K=2-(n/δ2 > 1 (n being integer or zero and δ =1,2,3 4). The cases for which 0 < K < 1 do not possess negative energy density gradient and therefore are incapable of representing any physically plausible star model. In totality the article provides all the physically plausible exact solutions for the Buchdahl static perfect fluid spheres.

The Evolution of HII Regions

Abstract: Here we review some recent results on the observed properties of UCH IIregions, and on the new class of Super-ultra-compact H II regions, and describe the theoretical scheme for H II region expansion, from star-forming cloud cores to the more diffuse external medium. High-pressure cores can stop the expansion on relatively short time scales, of the order of 3× 104 yr, and the resulting pressure equilibrium UCH II regions have small sizes and large ion densities. If the ionization front enters into the decreasing density gradient of the cloud core, the expansion is accelerated and the H II region“pops” out of the core and becomes a “blister”-like region. The properties of the outflows depend on the cloud density structure, and a variety of different shocks can be formed. Density inhomogeneities inside photoionized regions are smoothed out on short time scales, but new clumps are continuously created at the cool shell generated by the shock front. Instabilities in both the ionization and shock fronts cause the fragmentation of the shell, maintaining the presence of clumps during the whole evolution.

INES: Astronomy Data Distribution for the Future

Abstract: We describe here the structure under which the IUE Project will leave its archive at the completion of the distribution system and final data processing, within the INES systemThe INES system is a total system, which comprises both the data in their final bulk processing mode for direct application to scientific analysis, as well as the software driving the distributed service for data retrieval directly by the end userAs a consequence of the expected long-term usage and support needs, it has been designed to require minimum maintenance costs and will not suffer single point failures because of the distributed nature Integration of the INES system in a more general multi-wavelength archive for specialized analysis is anticipated tobe relatively easy, so further evolution of the data availabilitywill be driven fully by the users community and will evolve as thedata needs of the community develop The long term responsibilitywill be transferred from ESA to the astronomical community throughthe establishment of the INES Principal Centre at the LAEFF Instituteof INTA in Spain

Empirical models for estimating net radiative flux: a case study for three mid-latitude sites with orographic variability

Abstract: Based on a 4-year REKLIP data-set of global solar radiationG, shortwave surface albedo a, air temperature Ta and net radiative flux Rn, four types of regression models for the estimation of net radiative flux for three sites at different altitudes, located in the southern Upper Rhine valley have been proposed. In order to make for the limitation associated with the basic regression model (BRM) which relates net radiative flux over a surface to only incoming shortwave radiation, a longwave exchange coefficient has been introduced thus giving rise to the modified regression model (MRM). During daytime, the longwave exchange coefficient is observed to be negative for all three sites averaging about -0.20. The suitability of MRM over BRM becomes particularly obvious with respect to the mountainous site of Feldberg where the mean absolute error between measured and simulated Rn using MRM amounts to just half of that observed using BRM. Furthermore the role of clearness index and air temperature in the estimation of the net radiative flux have each been examined. The incorporation of the former is to make up for the effect of cloudiness on the net radiative flux budget, while the latter is an independent variable arising from the effective terrestrial radiation which thus allow for the estimation of the net radiative flux during all hours of the day. The regression models been proposed here have each been validated and their efficiency in reproducing actual measurements have been reported.

Galactic and Anomalous Cosmic Rays in the Heliosphere

Abstract: We discuss the present status of our understanding of the transport and acceleration of anomalous cosmic rays and the transport of galactic and CIR-accelerated particles in the heliosphere. Currently, two- and three-dimensional numerical codes can accurately model many of the observed phenomena – with the major current uncertainties being the values of the parameters such as the diffusion coefficients and the effects of the poorly understood structure beyond the termination shock. We illustrate the nature of the phenomena by discussing in detail the response of energetic particles to co-rotating interaction regions, the acceleration of singly- and multiply-charged anomalous cosmic rays, and the effects of galactic cosmic rays on the structure of the solar wind and its termination shock.

Impact Vaporization and Ionization of Cosmic Dust Particles

Abstract: We report on theoretical efforts to understand the process of vaporization and ion formation upon hypervelocity impact of small cosmic dust particles on a solid surface. Such collisions occur at the surface of solid bodies within the planetary system, which do not have an atmosphere as well as in various actual and upcoming space missions for in-situ measurements of interplanetary, interstellar and cometary dust. The investigation uses Godunov's method to simulate the impact. For the very high velocitites investigated, the impacting dust particle as well as parts of the target vaporize and some of the vapor cloud may change to partially ionized. Numerical results of the impact process are communicated for an 80 kms-1impact of a slightly porous SiO2 particle on a compact SiO2surface. Values of the amount of vapor and liquid excavated from the target are given. Ionization rates are calculated for the example investigated and an estimate is given how this extrapolates to the highest conceivable velocities in the planetary system (above 100 km s-1).

Pick-up Ion Measurements in the Heliosphere – A Review

Abstract: Measurements of the composition and spatial distribution of pick-up ions inside the heliosphere are reviewed. The first interstellar 4He+pick-up ions were detected with the SULEICA instrument on the AMPTE spacecraft near Earth's orbit. Most data on pick-up ions were taken in the solar-wind and suprathermal energy range of SWICS on Ulysses while the spacecraft cruised from 1.4 to 5.4 AU and explored the high-latitude heliosphere and solar wind from the ecliptic to ± 80° heliolatitude. This includes the discovery of H+, 4He++, 3He+, N+,O+, and Ne+ pick-up ions that originate from the interstellar neutralgas penetrating the heliosphere. From their fluxes properties of the interaction region between the heliosphere and the Local Interstellar Cloud such as the limits on filtration and the strength of the interstellar magnetic field have been revealed. Detailed analysis of the velocity distributions of pick-up ions led to 1) the discovery of a new distinct source, the so-called Inner Source, consisting of atoms released from interstellar and interplanetary dust inside the heliosphere, 2) the determination of pick-up ion transport parameters such as the long mean free path for pitch-angle scattering of order1 AU, and 3) detailed knowledge on the very preferential injection and acceleration of pick-up ions during interplanetary energetic particle events such as Co-rotating Interaction Regions and Coronal Mass Ejections. SWICS measurements have fully confirmed the theory of Fisk, Koslovsky, and Ramaty that pick-up ions derived from the interstellar gas are the dominant source of the Anomalous Cosmic Rays; they are pre-accelerated inside the heliosphere and re-accelerated at the solar-wind Termination Shock according to Pesses, Eichler, and Jokipii. The data indicate that the Inner Source of pick-up ionsis largely responsible for the occurence of C+ in the Anomalous Cosmic Rays. The abundances of recently discovered Inner-Source Mg+ and Si+ are solar-wind like and consistent with their abundances in the energetic particles associated with Co-rotating Interaction Regions. Knowledge on the injection and acceleration processes in Co-rotating Interaction Regions is applied to discuss the current observational evidence for the Interplanetary Focusing Cone of the interstellar neutral gas due to the Sun's gravitational force. The 25–150 keV/amu suprathermal 4He+ pick-up ion fluxes measured by CELIAS/STOF on board SOHO over 360° of ecliptic longitude represent a `local' ionization and acceleration of interstellar atoms at 1 AU or smaller heliocentric distances. Completing the first limited data set of SULEICA/AMPTE on 4He+ pick-up ions they indicate a density enhancement in the Interplanetary Focusing Cone which is confirmed by recent SWICS/ACE data. Clear evidence for signatures in ecliptic longitude are found in the data on energetic neutral H fluxes observed with the CELIAS/HSTOF sensor on board SOHO. These fluxes are enhanced in the upstream and downstream directions of the interstellar wind. Detection of energetic H atoms, which propagate unaffected by the Heliospheric Magnetic Field, provided for the first time a diagnostic tool for observations near Earth to analyze the structure in ecliptic longitude of the interface region between the heliosphere and the Local Interstellar Cloud.

Non-Linear Amplification of a Magnetic Field Driven by Cosmic Ray Streaming

Abstract: One dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large amplitude Alfvenic waves. The cosmic ray streaming energy is very efficiently transfered to the perturbed magnetic field of the Alfven waves. Thus a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy galactic cosmic ray problem were the cosmic rays themselves provide the fields necessary for their acceleration.

On the dynamical evolution of the brown dwarf populationin open clusters

Abstract: It is by now well established that open clusters contain a considerable fraction of brown dwarfs (BDs). This paper investigates the dynamical evolution of this substellar population by using simulations with Aarseth's (1994) NBODY5 code. A noticeable preferential escape of BDs is found, which may influence the determination of the IMF of substellar objects in dynamically evolved open clusters. This small dynamical-in-origin depletion may not explain, however, the scarcity of BDs observed in some evolved clusters, as the Hyades. On the other hand, BD cooling processes are able to reduce our ability to detect BDs in old clusters in a very significant way. Our results confirm that the probability of observing BDs in open clusters is almost the same over the whole cluster area because they are distributed quite uniformly even at late stages of the evolution of the cluster. This is expected to be a general feature as observed for low-mass stars in well studied open clusters (Pleiades, Praesepe). Our present calculations show that clusters as old as the Pleiades may have lost about 10% of their initial BD population but the number ratio of BDs to normal (not substellar) stars must remain almost unchanged. However, the long-term behavior of the relative percentage of BDs depends strongly on the initial mass function (IMF) assumed in the calculations. Clusters with a Salpeterian IMF evolve to reach relative percentages of BDs as low as 40% for a starting value around 70%. Our results suggest that BDs in clusters escape preferentially by evaporation.

The Multifluid Character of the `Baranov' Interface

Abstract: Since about three decades now it is clearly recognized that the interaction of the solar system with the ambient interstellar medium flow mainly is characterized by its hydrodynamic nature invoking structures like the inner shock, the heliopause and the outer shock with plasma sheath regions in between. After the pioneering works by Eugene Parker and Vladimir Baranov the main outlines of this interaction scenario were established, while some discussion on location and geometry of these structures is still going on till now. Fundamentally new aspects of this interaction problem have meanwhile appeared calling for new and more consistent calculations. The revisions of the earlier interaction concept starts with the neutral LISM gas component passing through the solar system. At the occasion of ionizations of this component a medium-energetic plasma component in form of keV-energetic pick-up ions is created. This component changes the distant solar wind properties by mass-, momentum-, and energy-loading, by wave generation and lowering the solar wind Mach numbers. Furthermore pick-up ions serve as a seed population for a high-energetic plasma population with energies between 10 and 100 MeV/nuc called anomalous cosmic rays. This latter component by means of its pressure gradient not only modifies the solar wind flow but also modulates its termination shock. In this paper it is shown how the main features of the enlarged interaction scenario change if the above mentioned multifluid character of the scenario is taken into account. While now we present a `multicolour vision' of the interacting heliosphere, it should never be forgotten that these modern views only were possible due to the fundamental `black-and-white vision' already presented by Baranov in the seventieths.

ASTROPHYSICAL MOLECULES AlD AND CaH: TRANSITION PROBABILITIES AND DISSOCIATION ENERGY

Abstract: The Franck-Condon (FC) factors andr-centroids for the bands system C 1 6 C ! X 1 6 C of AlD andE 2 5! X 2 6 C of CaH have been evaluated by means of a reliable numerical integration procedure by using a suitable potential. The dissociation energy, De, for the electronic ground states of AlD and CaH have been estimated by the curve fitting method to the RKRV experimental potential curve turning out to be 3.01 eV and 2.32 eV, respectively.

The Submillimeter Probe of the Evolution of Cosmic Structure (SPECS)

Abstract: Following Mather et al. (1999) we describe a concept for a future space mission called SPECS, a spatial and spectral Michelson interferometer with Hubble Telescope-class angular resolution and sensitivity that operates in the far infrared and submillimeter spectral range. SPECS enables detailed studies of the physical conditions in high-redshift galaxies and has the potential to revolutionize our understanding of galaxy formation and evolution.

Are HVCs Produced in Galactic Fountains

Abstract: Three-dimensional simulations of the disk-halo interaction show the formation of a thick HI and HII gas disk with different scale heights. The thick HI disk prevents the disk gas from expanding freely upwards, unless some highly energetic event such as chimneys occurs, whereas the thick HII disk acts as a disk-halo interaction region from where the hot ionized gas flows freely into the halo. The upflowing gas reaches the maximum height at z ∼ 9.3 ± 1 kpc becoming thermally unstable due to radiative losses, and condenses into HI clouds. Because the major fraction of the gas is gravitationally bound to the Galaxy, the cold gas returns to the disk. The descending clouds will have at some height high velocities. In a period of 200 Myr of fountain evolution, some 10 percent of the total number of clouds are HVCs.

The chemistry and prospects for interstellar detection of somedicyanoacetylenes and other cyanoacetylene-related species

Abstract: Recent cryochemical and photochemical findings for cyanoacetylene and cyanopolyacetylene-related molecules (including various isomeric species), backed up with quantum-chemical predictions, are analysed. A new class of interstellar molecules, distinguished by bare (hydrogen-less), unsaturated carbon-nitrogen chains of the general formula C n N2 is postulated. It is recommended to look for some relevant IR spectral features in space.

Time dependent wormholes in an expanding universe dominated by traceless matter

Abstract: Time-dependent wormhole solutions are found which evolve in a cosmological background. Solutions are presented both for GR and Brans-Dicke field equations. Conditions are derived for the supporting matter to be non-exotic. The traceless energy-momentum tensor needed to support the geometry is in the form of an anisotropic fluid. Far from the wormhole, the equation of state rapidly approaches that of an isotropic perfect fluid with p = 1/3 ρ. For the BD wormholes we obtain ρ = 0everywhere, except for the π = const. limit, in which case the GR results are reproduced.

Light Pollution and its Energy Loss

Abstract: Data obtained by US DMSP satellites were analyzed to obtain light energyin order to monitor light pollution at different countries. Light detectedby the satellites is one ejected to space and is not mostly used toilluminate objects to be seen. This light is energy loss and produce lightpollution for astronomical observation. We should reduce such energy lossand light pollution.

3D Hydrodynamical Simulations of Colliding Wind Binaries: TheoryConfronts Observations

Abstract: The link between gas dynamical models and observations is crucial. The general progress in numerical simulations must be accompanied by predictions for observable quantities, which not only allow to test the models or parts of them against observations but which also improve the understanding of observational data. In this paper we focus on predictions for observations, for three examples of 3Dhydrodynamical simulations of binary star systems, and the techniques required for their derivation. The examples include synthetic, optically thin Doppler broadened line profiles for colliding wind symbiotic binaries, the UV light curve of an accretion model for the symbiotic binary RW Hya, and the X-ray light curve of the WR+O binaryγ Velorum. The main purpose is to emphasize the importance of such studies and to illustrate the capabilities of the emploiedtools. The tools are all contained in the A-MAZE code package we have developed and are publicly available.

Cosmic Masks Still Dance

Abstract: The Hubble classification scheme of galaxies is based on their optical appearance or ‘masks’. As one goes from early to late type spirals, both barred and unbarred, the optical appearance will be dominated more and more by the young Population I, i.e., blue stars and dust. Atlases reveal the rich variety of responses of the Population I component of gas and dust (the mask) to the underlying, older, stellar population. However, the gaseous Population I component, may only constitute 5 percent of the dynamical mass of the galaxy. Masks of negligible mass may conceal the human face — and that of galaxy. In the near-infrared, the morphology of older star-dominated disk indicates a simple classification scheme: the dominant Fourier m-mode in the dust penetrated regime, and the associated pitch angle. A ubiquity of low m=1 and m=2 modes is confirmed. On the basis of deprojectcd H (1.65µm) and K’ (2.1µm) images, we propose that the evolved stellar disks may be grouped into three principal dust penetrated archetypes: those with tightly wound stellar arms characterised by pitch angles at K’ of ∼ 10° (the α class), an intermediate group with pitch angles of ∼25° (the β class) and thirdly, those with open spirals demarcated by pitch angles at K’ of ∼ 40° (the γ bin). Flat or falling rotation curves give rise to the tightly wound γ class; rising rotation curves are associated with the open y class. The observed dust penetrated classes are inextricably related to the rate of shear in the stellar disk, as determined by \(\tfrac{A}{\omega }\). Here A is the first Oort constant and w denotes the angular velocity. There is no correlation between our dust penetrated classes and optical Hubble binning: the Hubble tuning fork does not constrain the morphology of the old stellar Population II disks. NGC 3223 and NGC 7083 (both SbI-II and almost the same absolute blue magnitude) have identical Hubble types and identical luminosity classes; the dust penetrated disk of NGC 3223 has tightly wrapped arms of class a, whereas the near-infrared disk of NGC 7083 has open arms of class y. This is in turn associated with their very different rotation curve shapes yielding different rates of shear \(\tfrac{A}{\omega }\). in their stellar disks. Any specific dust penetrated archetype may be the resident disk of both an early or late type galaxy. The number of arms and the pitch angle of the arms at K’ of the early-type ‘a’ spiral NGC 718 are almost identical to those for the late-type ‘c’ spiral NGC 309. We demonstrate that galaxies on opposite ends of the tuning fork can display remarkably similar evolved disk morphologies and belong to the same dust penetrated class. In this sense, there is no differentiation between an early and late type galaxy: the Hubble tuning fork becomes a circle. Furthermore, a prototypically flocculent galaxy such as NGC 5055 (Elmegreen arm class 3) can have an evolved disk morphology almost identical to that of NGC 5861, characterised in the optical as having one of Permanent address: Instituto Nacional de Astrofisica, Optica y Electronica, Calle Luis Enrique Erro 1, 72840 Tonantzintla, Puebla, Mexico the most regular spiral patterns known and of Elmegreen class 12. Both optically flocculent or grand design galaxies can reside within the same dust penetrated morphological hin. As was suggested by Block et al. (1994a), it is the gas dominated Population I component which determines the optical types (a, b, c). This may be partially or even fully decoupled from the Population II disk. Those L=lopsided galaxies (where m=1 is a dominant mode) are designated La, Ls and Ly according to the dust penetrated pitch angle; E=evensided galaxies (where m=2 is the dominant Fourier mode) are classified into classes Eα, Eβ and Eγ, according to our three principal dust penetrated archetypes. The L and E modes arc the most common morphologies in our sample, which spans a range of Hubble types from early (a) to late (irregular).

Nonstationary Phenomena in the Solar Wind and InterstellarMedium Interaction

Abstract: We discuss the results of numerical modeling of the solar wind with the inhomogeneous interstellar medium. The density of the plasma component in the interstellar cloud is supposed to be space periodic. The interaction pattern is shown to be highly unsteady with hydrodynamic instabilities developing on the side portion of the heliopause.

Cosmological Constant and the Final Anthropic Hypothesis

Abstract: The influence of recent detections of a finite vacuum energy(`cosmological constant') on our formulation of anthropic conjectures,particularly the so-called Final Anthropic Principle is investigated. Itis shown that non-zero vacuum energy implies the onset of a quasi-exponentialexpansion of our causally connected domain (`the universe') at some point inthe future, a stage similar to the inflationary expansion at the verybeginning of time. The transition to this future inflationary phase ofcosmological expansion will preclude indefinite survival of intelligentspecies in our domain, because of the rapid shrinking of particle horizonsand subsequent depletion of energy necessary for information processes withinthe horizon of any observer. Therefore, to satisfy the Final AnthropicHypothesis (reformulated to apply to the entire ensemble of universes), itis necessary to show that (i) chaotic inflation of Linde (or some similarmodel) provides a satisfactory description of reality, (ii) migration betweencausally connected domains within the multiverse is physically permitted, and(iii) the time interval left to the onset of the future inflationary phaseis sufficient for development of the technology necessary for suchinter-domain travel. These stringent requirements diminish the probabilityof the Final Anthropic Hypothesis being true.