Cometary-like bodies in the protoplanetary disk aroundβ pictoris

Repeated spectroscopic observations of Pictoris have been performed since 1985 and revealed the presence, in many metallic lines likeCa II, Mg II, Fe II, ..., of strong sporadic circumstellar absorption, redshifted by tens to hundreds of km s^–1 with respect to the star, and highly time-variable (time-scales of days or hours).We have tentatively interpreted these variable events as the spectral signature of infalling cometary-like bodies, when evaporating in the vicinity of the star. This scenario has been furthermore theoretically studied, and we showed that it could indeed explain correctly the observations with their peculiar characteristics, like (1) the behavior difference between visible and UV lines, (2) the unusual line ratios, (3) the surprising presence of Al III absorption lines. Constraints deduced from both observational data and theoretical study allowed us to suggest that a planet within the disk could be responsible, by perturbations, of this high rate infall of small bodies towards the star (> 100 per year).Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

New observations of theβ pictoris circumstellar disk with the JHU Adaptive Optics Coronagraph

We present a simple model for interactions between the slow and fast phases of mass ejection in classical nova outbursts. A situation develops in which a layer of hot gas sandwiched between two shocks progresses through the slow wind until it blows-out, expanding and cooling adiabatically. We calculate the X-ray emission from this model and find that the dynamical timescale is at least as important as the radiative cooling time in determining the form of the X-ray light curves. Models of this type may help to explain the origin of X-ray emission in some classical nova outbursts.This author is supported by the SERC     

Properties of theβ pictoris disc deduced from optical imaging polarimetry

The asymmetries in the brightness structure and levels of polarization between the two sides of the Pic disc are discussed. The possibility of these differences being caused by a planet, or planets, within the circumstellar disc is investigated.     

Sub-arcsec 10 μm imaging of β pictoris and other star disk candidates

We have used the ESO 10 m camera, TIMMI, to image with a very high angular resolution (PFoV: 0.3; FWHM:0.9) several main-sequence star disk candidates. Information on the -Pictoris dust disk has been obtained in a region largely inaccessible to previous observations: 0–80 AU, with a resolution of about 5 AU after deconvolution. Another promising target for 10 m imaging, 51 Ophiuchi, appears point-like.based on data collected at the European Southern Observatory (ESO), La Silla, Chile     

Area-preserving Poincaré mappings of the unit disk

The best way to investigate the long-time behaviour of dynamical systems is to introduce an appropriate Poincaré mapping P and study its iterates.Two cases of physical interest arise: Conservative and dissipative systems. While the latter has been considered by a great many authors, much less is known for the first one (according to Liouville's theorem, here the mapping leaves a certain measure in phase space invariant). In this paper, we concentrate our attention on compact phase spaces (or, rather, surfaces of section). This assumption is mathematically useful and physically reasonable.We consider the simplest possible (2-dimensional) systems whehre the phase space is the compact unit disk D in ². A family of simple area-preserving mappings from D onto itselves will be given and discussed in detail.It is shown that general characteristics of the dynamics are quite similar to those of e.g. the Hénon-Heiles system, while other features, as the structure of invariant curves, are different.     

On the formation of superdense gaseous cores in the nuclei of disk galaxies — I

A model for the formation of superdense gaseous cores by accretion in the nuclei of disk galaxies has been proposed. Equations for radial flow of gas into the nucleus in the presence of aweak galactic magnetic field have been solved, and time scales for the accretion of an exploding mass in the nucleus (10⁹ M ) have been obtained under several different situations in the absence of any rotation. The time scales are found to lie in the range between a few times 10⁷ yr and 10⁸ yr. Such time scales have been proposed by some authors for repeated explosions in the nuclei of galaxies; they have also proposed that spiral arms in disk galaxies are repeatedly formed and destroyed over such time scales. It is shown that the presence of rotational velocities in the infalling gas practically destroys the efficiency of the accretion process unless such velocities are dissipated by frictional forces within the system. Viscosity of gas is the most obvious dissipative agent. The problem of accretion of a rotating viscous gas will be discussed in a subsequent paper.     

Variation of the inner disk radius during the onset of the 2010 outburst of MAXI J1659–152

Low mass black hole binaries are generally transient sources and spend most of their time in the quiescent state. It is believed that the inner accretion flow in the quiescent state is in the form of advection dominated accretion flow and the cold outer accretion disk is truncated far away from the central black hole. During the onset of an outburst, the disk gradually extends towards the central black hole.However, the observational evidence for this general picture is indirect at best. Here we present the results of a study performed to understand the variation of the inner disk radius during the early phase of an outburst. We investigated the variation of the inner disk radius during the 2010 outburst of the black hole candidate MAXI J1659-152 using the method of simultaneous spectral fitting. We found that the inner edge of the disk is truncated at a large radius in the beginning of the outburst when the source was in the hard state. We found a systematic decrease in the inner disk radius as the outburst progressed. We also estimated an upper limit on the mass of the black hole to be 8.1 ± 2.9 M within the uncertainty of the distance and inclination angle.     

Soft X-ray observation of theϱ ophiuchus dark cloud region

Soft X-rays (0.1–0.8 keV) from the region including the Oph dark cloud were observed with the SAS-3 low-energy X-ray telescope. No X-ray absorption by the cloud was observed. This indicates that the diffuse component of soft X-rays in this region is mostly from the foreground of the Oph cloud which is located at a distance of 160–200 pc.     

On the fine structure of the Fe I λ532.4185-nm line profile in the spectrum of the solar disk center

Based on the digital spectra taken with double monochromators of high spectral resolution, we have constructed the profile of the Fe I λ532.4185-nm line in the spectrum of the solar disk center. Basic spectrophotometric characteristics of the line profile have been determined with a high accuracy. The fine structure of the line profile is studied in detail. The profile asymmetry parameters have been determined.     

Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere

A method for the full three-dimensional (3-D) reconstruction of the trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations Observatory (STEREO) data is presented. Four CMEs that were simultaneously observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and Behind STEREO satellites were analysed. These observations were used to derive CME trajectories in 3-D out to ～?15?R _⊙. The reconstructions using COR1/2 data support a radial propagation model. Assuming pseudo-radial propagation at large distances from the Sun (15?–?240?R _⊙), the CME positions were extrapolated into the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in the different fields-of-view. It was found that CMEs slower than the solar wind were accelerated, while CMEs faster than the solar wind were decelerated, with both tending to the solar wind velocity.     

UVbYβ electrophotometry of the RR Lyrae stars

The behaviour of the spectral metallicity parameters S of the RR Lyrae stars in the course of light change is considered. Electrophotometry results of 9 stars of the given class inUVbY are presented. Analysis of the data obtained shows that the variables for which variation of S with the light phase was established do not show any real variations of metallicity indexm ₁.     

2.5-dimensional solution of the advective accretion disk： a self-similar approach

We provide a 2.5-dimensional solution to a complete set of viscous hydrodynamical equations describing accretion-induced outflows and plausible jets around black holes/compact objects. We prescribe a self-consistent advective disk-outflow coupling model, which explicitly includes the information of vertical flux. Inter-connecting dynamics of an inflow-outflow system essentially upholds the conservation laws. We provide a set of analytical family of solutions through a self-similar approach. The flow parameters of the disk-outflow system depend strongly on the viscosity parameter α and the cooling factor f.     

The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anticenter(LSS-GAC) to determine the radial and vertical gradients of stellar metallicity,△[Fe/H]/△R and △[Fe/H]/△|Z | of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages( 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages( 11 Gyr)are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R.After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum(steepest) at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are significant radial flows of gas in the disk, and the rate of gas inflow near the solar neighborhood reaches a maximum around a lookback time of 7–8 Gyr.The transition between the two phases occurs around a lookback time between 8 and11 Gyr. The two phases may be responsible for the formation of the Milky Way's thick and thin disks, respectively. Also, as a consequence, we recommend that stellar age is a natural, physical criterion to distinguish stars from the thin and thick disks. From an epoch earlier than 11 Gyr to one between 8 and 11 Gyr, there is an abrupt, significant change in magnitude of both the radial and vertical metallicity gradients, suggesting that stellar radial migration is unlikely to play an important role in the formation of the thick disk.     

The equivalent width of the Hβ emission line and the evolution of the Hii regions

The synthetic equivalent width (W _H) of the line H in emission is obtained for Hii regions opaque to the Lyman photon flux, with embedded OB associations with different initial chemical compositions and initial mass functions. The variation ofW _H as a function of the evolution of the ionizing stars is analysed. The observations ofW _H for M33, M101, and M51 by Searle (1971) are discussed.     

uvbyβ Electrophotometry of the components of trapezium multiple star systems

The results of electrophotometric observations of the 19 components of six Trapezium multiple star systems with primary stars of class M are presented. The Strömgren spectral intervals are determined. Of the 19 components, 18 belong to interval 3 ("late group").Translated fromAstrofizika, Vol. 39, No. 3, pp. 407–410, July–September, 1996.     

Variations of the λ525.02 nm FeI line profile over the solar disk and observations of large-scale magnetic fields

This paper examines the question of the influence of the 525.02 nm Fei line profile (slope of its wings) variations over the solar disk upon observations of large-scale magnetic fields (LSMF) made in this line. The study has shown that depending on the position on the disk (center-limb effect) and magnetic field parameters at the place of the observation, values of magnetic field strengths determined with proper account of the real line profile and in the usual way (by calibration using the line profile at the center of the solar disk only) can differ by 25% or more, which is of crucial importance. Observations at the Solar Telescope for Operative Predictions (STOP) of the Sayan Observatory have been used to accomplish this work.     

Vertical structure of the volume scattering coefficient of aerosol in latitude belts of Jupiter’s disk

Pressure dependences of the volume scattering coefficient of aerosol in the atmosphere of Jupiter σ _a (P) are presented. In calculations carried out with separating the gaseous and aerosol absorption, the absorption of light in the continuous spectrum was taken into account. In the analysis, the spectrophotometric data of Jupiter for the absorption bands of methane at 727 and 619 nm—the geometric albedo (measured in 1993) and the reflectivity of some latitudinal details (measured in 2013)—were used. At high tropospheric levels, in the pressure range from 0.4 to 2 bar, the dependences σ _a (P) for the integral disk and latitude belts of the giant planet turned out to be similar. In this part of the atmosphere, the three thickest cloud layers were found; in these layers, within the pressure range from 0.8 to 1.33 bar in the North and South Temperature Belts (NTB and STB), respectively, the values of the coefficient σ _a (P) are maximum. In the pressure interval from 2 to 4 bar, in the analyzed latitude belts except the NTB and STB, the forth aerosol layer was found; its altitude position and vertical structure substantially differ from belt to belt. One more aerosol layer probably exists deeper in the atmosphere; its initial level and extension differ in different latitude belts. Most of the investigated latitude belts exhibit the spectral dependence of σ _a (P) at the atmospheric levels, where the pressure exceeds 3 bar. This probably points to the change in size or nature of aerosol particles.     

The pulsation period of theβ Cephei-star NU Centauri

The radial velocity measurements of the single line spectroscopic binary and Cephei star NU Centauri made during 1985, 1987, and 1988 are presented. New ephemeris with a pulsation period of 0^d.1696401 has been derived by combining the three season data. The new ephemeris also fits well for the earlier data published in the literature.     

Galactic bar: Normal mode of the stellar disk or a superposition of transient spirals?

Several mechanisms of bar mode formation in stellar galactic disks, including the Toomre swing amplification mechanism and modal approaches, are considered. Using the well-known Kuzmin-Toomre stellar disk model as an example, it has been shown through numerical simulations that the stellar bar results from the development of an unstable normal mode. The pattern speed and the spiral wave growth rate found from a numerical experiment agree well with the linear perturbation theory. The nonlinear evolution of the bar is traced. The possible role of growing transient spirals in the formation of bars is discussed.     

The Magnetic Field at the Inner Boundary of the Heliosphere Around Solar Minimum

STEREO A and B observations of the radial magnetic field between 1 January 2007 and 31 October 2008 show significant evidence that in the heliosphere, the ambient radial magnetic field component with any dynamic effects removed is uniformly distributed. Based on this monopolar nature of the ambient heliospheric field we find that the surface beyond which the magnetic fields are in the monopolar configuration must be spherical, and this spherical surface can be defined as the inner boundary of the heliosphere that separates the monopole-dominated heliospheric magnetic field from the multipole-dominated coronal magnetic field. By using the radial variation of the coronal helmet streamers belts and the horizontal current – current sheet – source surface model we find that the spherical inner boundary of the heliosphere should be located around 14 solar radii near solar minimum phase.