The morphology,kinematics and metallicity of blue-core galaxies

We select 107 blue-core galaxies from the MaNGA survey, studying their morphology, kinematics as well as the gas-phase metallicity. Our results are as follows:(i) In our sample, 26% of blue-core galaxies have decoupled gas-star kinematics, indicating external gas accretion;15% have bar-like structure and 8% show post-merger features, such as tidal tails and irregular gas/star velocity field. All these processes/features, such as accreting external misaligned gas, interaction and bar, can trigger gas inflow. Thus the central star-forming activities lead to bluer colors in their centers(blue-core galaxies).(ii) By comparing with the SDSS DR7 star-forming galaxy sample, we find that the blue-core galaxies have higher central gas-phase metallicity than what is predicted by the local mass-metallicity relation. We explore the origin of the higher metallicity, finding that not only the blue-core galaxies, but also the flat-gradient and red-core galaxies all have higher metallicity. This can be explained by the combined effect of redshift and galaxy color.     

The local interstellar medium: A test-bed for the galactic ISM

We outline a method to explore the column density of the Local Interstellar Medium (LISM) using absorptions in the resonance H and K lines of Mgii. The intrinsic strengths of these lines in the temperature and density conditions prevailing in warm clouds (T _eff<10⁴ K) in the LISM allows them to be used to explore many lines of sight where lines such a NaD and Caii H and K are too weak, but where L is saturated. The number of measurable lines-of-sight is greatly enhanced by using cool stars as the background emitters, but this implies reliable separation of the LISM components from stellar chromospheric selfabsorptions. We explain how to do this, and how to use a combination of column density and radial velocity data to measure the spatial extent and the physical parameters of the single cloud in which the Sun is embedded. This proves to be an oblate spheroid, of characteristic diameter 8 pc, withT _eff 10⁴ K,n(Hi) of 0.1 cm^–3 and a mass <5M , streaming in the LSR from a point 1=4°,B=+16° with velocity equal to 16 km s^–1, and is surrounded by the much hotter lower density ionized gas of the local supernova bubble.     

The local complex of high-velocity clouds (geometry and kinematics)

Many HVC - high velocityHi clouds - are added to the known combination of diffuse soft X-rays and radioloops. Among these HVC there are previously examined complexes A, C, Magellanic Stream, etc. Their common composition has a clear geometry and kinematics.Two powerful long HVC filaments form the bridges between Loop I and double Loop II + III. The Bridges join the polarX _max regions in C band. The bridges ends at Loop I side are bounded by the systems of shorter filaments withX _max spots in M₁ and larger energy bands. There are no HVC in the spots themselves. The opposite ends of bridges reach Loops II and III centres. The two structures have the features of rotational symmetry.The isolines X-ray count rates pass along HVC chains with the same _r -velocities. The frequent alternation of different _r on the same filament is better explained by the turbulent gas motion than by the differences of HVC distance.All of the above-mentioned, as well as the _r signs of dependence on the galactical longitude, are the result of HVC interaction with X-rays. The whole composition from HVC-loops-X-rays is a component of the local system (Gould Belt).     

Steady magnetic reconnection in three dimensions

The concepts of magnetic reconnection that have been developed in two dimensions need to be generalised to three-dimensional configurations. Reconnection may be defined to occur when there is an electric field (E) parallel to field lines (known as potential singular lines) which are potential reconnection locations and near which the field has an X-type topology in a plane normal to that field line. In general there is a continuum of neighbouring potential singular lines, and which one supports reconnection depends on the imposed flow or electric field. For steady reconnection the nearby flow and electric field are severely constrained in the ideal region by the condition that E = 0 there. Potential singular lines may occur in twisted prominence fields or in the complex magnetic configuration above sources of mixed polarity of an active region or a supergranulation cell. When reconnection occurs there is dynamic MHD behaviour with current concentration and strong plasma jetting along the singular line and the singular surfaces which map onto them.     

Understanding physical processes in the diffuse ISM using high-resolution UV spectroscopy

Our understanding of the important physical processes operating in the diffuse interstellar medium (ISM) has advanced in recent years from the analysis of high-resolution ultraviolet (UV) spectra obtained with the Hubble Space Telescope (HST) and the Far-Ultraviolet Spectrograph Explorer (FUSE) and from high-fidelity simulations of the kinematics and energetics of the ISM. Nevertheless, much remains to be learned from observations with the Space Telescope Imaging Spectrograph (STIS) instrument on HST and spectrographs on the World Space Observatory (WSO). I will describe several major unanswered questions and suggest how future UV observations can answer these questions. I will also summarize the instrument requirements needed for a future UV spectroscopic mission and recommend how to achieve a successful mission.     

The ISM in nearby galaxies

The SKA will revolutionise the study of the principles underlying star formation (SF), resolving interstellar cloud complexes which are the birthplaces of stars and answering such questions as which are the sufficient and necessary conditions for SF to commence. Also, massive SF is intimately related to stellar death. The SKA will be able to study the structure of the ISM at 100 pc resolution out to distances of up to 20 Mpc and will quantify the impact the demise of massive stars has on their environment. Importantly, the SKA will probe the transition region between ISM and IGM, linking star formation and stellar death in the disks of galaxies to faint HI structures further afield, such as “anomalous gas” and (Compact) High Velocity Clouds. Lastly, the superb sensitivity of the SKA will result in some hundred background sources per square degree against which HI absorption lines can be searched for, probing not only the relative importance of the different phases of the gas in galaxies but also the low density gas in the outskirts and between galaxies.     

Variation of physical properties across the green valley for local galaxies

We selected a sample of nearby galaxies from the Sloan Digital Sky Survey Data Release 7(SDSS DR7) to investigate the variation of physical properties from the blue cloud to green valley to red sequence.The sample is limited to a narrow range in the color-stellar mass diagram. After splitting green valley galaxies into two parts—a bluer green valley(green 1) and a redder one(green 2) and three stellar mass bins,we investigate the variation of physical properties across the green valley region. Our main results are as follows:(i) The percentages of pure bulge and bulge-dominated/elliptical galaxies increase gradually from blue cloud to red sequence while the percentages of pure disk and disk-dominated/spiral galaxies decrease gradually in all stellar mass bins and different environments.(ii) With the analysis of morphological and structural parameters(e.g., concentration(C) and the stellar mass surface density within the central 1 kpc(Σ1)), red galaxies show more luminous and compact cores than both green valley and blue galaxies, while blue galaxies show the opposite behavior in all stellar mass bins.(iii) A strong negative(positive) relationship between bulge-to-total light ratio(B/T) and specific star formation rate(sSFR)(D_(4000)) is found from blue to red galaxies. Our results indicate that the growth in bulge plays an important role when the galaxies change from the blue cloud, to the green valley and to the red sequence.     

Dynamical structure of planetary nebulae in three dimensions

The interacting of two winds model and a nonspherical density functionin three dimensions is introduced to study the dynamical structure ofplanetary nebulae. A fast wind with a mechanical energy interacts with asuper wind mass-loss rate of 2 × 10^-10 M yr and avelocity of 10 km s^-1. As a result it produces a dense and luminosmedium.Taking into account the above assumptions, we introduce the code(DS3D),and numerically we calculate the following physical quantities:the shell velocity, the shell radious and thickness, and other physicalquantities throughout the entire nebula.     

The Roche Coordinates in three dimensions and their application to problems of double-star astronomy

In a preceding paper (Kopal, 1969; in what follows referred to as Paper I) we introduced a new system of curvilinear coordinates-hereafter referred to as Roche Coordinates — in which spheres of constant radius in spherical polars have been replaced by surfaces of constant potential of a rotating gravitational dipole; while the angular coordinates are orthogonal to the equipotentials. In Paper I we established an explicit form of such a transformation, and related the Roche coordinates with polar coordinates (with which they coalesce in the immediate neighbourhood of each one of the two finite mass-points) in the plane case. The aim of the present investigation will be to generalize the definition of the Roche coordinates to three dimensions.The opening Section 1 of this paper will contain a general outline of the proposed three-dimensional transformation; and in Section 2 details of this transformation will be explicitly worked out correctly to quantities of first order in superficial distortion — an approximation which should prove adequate in regions surrounding the two finite masses; while in Section 3 we shall evaluate (to this degree of accuracy) the metric coefficients of the respective transformation, and its direction cosines, in both polar and curvilinear coordinates. Section 4 will then contain a formulation of the fundamental equations of hydrodynamics in terms of the three-dimensional Roche coordinates; and their advantages for a treatment of certain classes of dynamical problems encountered in doublestar astronomy will be illustrated in the concluding Section 5 by an investigation of the vibrational stability of the Roche model. We shall show that this model is capable of performing free radial oscillations which remain barotropic only if its equilibrium form is spherical (i.e., in the absence of any external mass in the neighbourhood); but not if it is distorted to any extent by rotation or tides.     

The physical and chemical properties of circumstellar envelopes

An overview is given of recent results on some basic properties of the circumstellar envelopes of evolved stars. The focus is on well studied examples which illustrate envelopes of different types and at different stages of evolution. The close connection between the physical and chemical properties of the envelopes is emphasized.     

Attractors in a dissipative dynamical system with three dimensions

We study an extension of the Hénon mapping to a dissipative dynamical system with three-dimensions and discuss the behavior of the attractors of the Hénon mapping in the extended mapping $$T:\left\{ {\begin{array}{*{20}c} {X_{i + 1} = Y_i + 1 - AX_i^2 + C cos Z_i } \\ {Y_{i + 1} = BX_i + D \sin Z_i } \\ {Z_{i + 1} = Z_i + E \sin Y_{i + 1} + F, (\bmod 2\pi ).} \\ \end{array} } \right.$$ The results show that the strange attractor is destroyed by perturbed extension more easily than the trivial attractor and the invariant manifold of the conservative dynamical system.     

A numerical investigation of coorbital stability and libration in three dimensions

Motivated by the dynamics of resonance capture, we study numerically the coorbital resonance for inclination \(0\le I\le 180^\circ \) in the circular restricted three-body problem. We examine the similarities and differences between planar and three dimensional coorbital resonance capture and seek their origin in the stability of coorbital motion at arbitrary inclination. After we present stability maps of the planar prograde and retrograde coorbital resonances, we characterize the new coorbital modes in three dimensions. We see that retrograde mode I (R1) and mode II (R2) persist as we change the relative inclination, while retrograde mode III (R3) seems to exist only in the planar problem. A new coorbital mode (R4) appears in 3D which is a retrograde analogue to an horseshoe-orbit. The Kozai–Lidov resonance is active for retrograde orbits as well as prograde orbits and plays a key role in coorbital resonance capture. Stable coorbital modes exist at all inclinations, including retrograde and polar obits. This result confirms the robustness the coorbital resonance at large inclination and encourages the search for retrograde coorbital companions of the solar system’s planets.     

MHD Simulations of the ISM: The Importance of the Galactic Magnetic Field on the ISM “Phases”

We have carried out 1.25 pc resolution MHD simulations of the ISM, on a Cartesian grid of 0 ≤ (x, y) ≤ 1 kpc size in the galactic plane and ?10 ≤ z ≤ 10 kpc into the halo, thus being able to fully trace the time-dependent evolution of the galactic fountain. The simulations show that large scale gas streams emerge, driven by SN explosions, which are responsible for the formation and destruction of shocked compressed layers. The shocked gas can have densities as high as 800 cm^?3 and lifetimes up to 15 Myr. The cold gas is distributed into filaments which tend to show a preferred orientation due to the anisotropy of the flow induced by the galactic magnetic field. Ram pressure dominates the flow in the unstable branch 10² < T ≤ 10^3.9 K, whereas for T ≤ 100 K (stable branch) magnetic pressure takes over. Near supernovae thermal and ram pressures determine the dynamics of the flow. Up to 80% of the mass in the disk is concentrated in the thermally unstable regime 10² < T ≤ 10^3.9 K with ～30% of the disk mass enclosed in the T ≤ 10³ K gas. The hot gas in contrast is controlled by the thermal pressure, since magnetic field lines are swept towards the dense compressed walls.     

Weak gravitational lensing in different cosmologies, using an algorithm for shear in three dimensions

We present the results of weak gravitational lensing statistics in four different cosmological N -body simulations. The data have been generated using an algorithm for the three-dimensional shear, which makes use of a variable softening facility for the N -body particle masses, and enables a physical interpretation for the large-scale structure to be made. Working in three dimensions also allows the correct use of the appropriate angular diameter distances.
Our results are presented on the basis of the filled-beam approximation in view of the variable particle softening scheme in our algorithm. The importance of the smoothness of matter in the Universe for the weak lensing results is discussed in some detail.
The low-density cosmology with a cosmological constant appears to give the broadest distributions for all the statistics computed for sources at high redshifts. In particular, the range in magnification values for this cosmology has implications for the determination of the cosmological parameters from high-redshift type Ia supernovae. The possibility of determining the density parameter from the non-Gaussianity in the probability distribution for the convergence is discussed.     

Asymptotic series for planetary motion in periodic terms in three dimensions

For the planetary case of the gravitationaln-body problem in three dimensions, a sequence of Lie series contact transformations is used to construct asymptotic series representations for the canonical parameters of the instantaneous orbits in a Jacobi formulation. The series contain only periodic terms, the frequencies being linear combinations of those of the planetary orbits and those of the secular variations of the apses and nodes, and the series are in powers of the masses of the planets in terms of that of the primary, and of a quantity of the order of the excursions of the eccentricities and inclinations of the orbits. The treatment avoids singularities for circular and coplanar orbits. It follows that the major axes are given by series of periodic terms only, to all orders in the planetary masses.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980.