Relationship of groups of submillimeter starless condensations to radial systems of dark globules

The recently discovered groups of submillimeter starless condensations at the junction of HII regions and molecular clouds, which are invisible in the optical and near IR ranges, are similar in many ways to visible radial systems of dark globules, specifically, in their densities of molecular hydrogen, sizes, proximity to bright stars of early classes (which may be responsible for their formation), etc. It is proposed that the groups of submm starless condensations are radial systems of dark globules that are optically invisible because they lie behind dark clouds. Thus, it is shown that these groups of condensations are not a new type of object.     

Growth of planetesimals and clearance of disks around the T-tauri stars

A growth and contraction of dust condensations formed as a result of development of gravitation instability in a dust subdisk is discussed within the framework of the generally accepted scheme of evolution of a circumsolar pre-planetary disk. The time of evolution of condensations necessary for clearing the hypothetical disks around young stars of the Sun type is estimated.     

Arcsecond radio jets in Cygnus X–3

A deep VLA map of the X-ray binary Cygnus X–3, obtained at 6 cm wavelength in B configuration, is presented. The map clearly shows the symmetric ejection of plasma condensations along a position angle close to the North–South direction. An overall jet-like bipolar morphology, with a full size of about 5 arcsec is evident. The jet condensations are detected at the 0.3 mJy level with a very high significance (SNR>10), and they are very likely to be the remnant of the strong Cygnus X–3 radio flare that occurred three months before our observing run. Accepting this association, the ejection velocity derived for both condensations is 0.6c.     

Stability of protoplanets around RU Lupi

It is shown that the protoplanetary dust condensations around the T-Tauri star RU Lup, proposed by Gahmet al. (1974), would be unstable to tidal disruption if they are bound only by gravitational forces. There are extreme conditions under which the condensations would be stable, but such conditions would easily be verifiable observationally.     

Statistical mechanics of Keplerian orbits

A statistical theory of Keplerian orbits is constructed for a system of particles, which are subject to partially elastic collisions. If the elasticity decreases with collisional velocity, the system shows an increased tendency to form condensations. Near the central body they are concentric rings, which are separated by gaps void of matter. At larger distances outside the Roche limit, the condensations probably form larger bodies. An application to Saturn's rings suggests that at least rings A and C would consist of separate ringlets.     

A study on the asymmetries in flare lines

We calculate the H and CaII K profiles under different velocity models with chromospheric condensations and investigate the effect of the velocity in different layers on the profiles from a semi-empirical standpoint. The results show that the short-time, H blue asymmetry in the early stage of the flare can be caused by condensations in the transition zone, that the subsequent red asymmetry is the result of the downward motion of matter in the upper chromosphere, while the later CaII K asymmetries can be explained by downward velocities of 10–20 km/s in the middle and lower chromosphere.     

Formation of trans-Neptunian satellite systems at the stage of condensations

The formation of trans-Neptunian satellite systems at the stage of rarefied preplanetesimals (i.e., condensations of dust and/or objects less than 1 m in diameter) is discussed. It is assumed that trans-Neptunian objects (including those with satellites) could form as a result of compression of parental rarefied preplanetesimals. The formulas for calculating the angular momentum of two colliding condensations with respect to their center of mass, which were applied earlier in (Ipatov, 2010) in the comparison of such momenta with the angular momenta of observed satellite systems, are used to estimate the angular momenta of condensations needed to form satellite systems. It is demonstrated that the angular velocities of condensations used in (Nesvorny et al., 2010) as the initial data in the computer simulation of compression of rarefied preplanetesimals and subsequent formation of trans-Neptunian satellite systems may be obtained in collisions of preplanetesimals with their radii comparable to the corresponding Hill radii. For example, these angular velocities are in the range of possible values of angular velocities of a parental rarefied preplanetesimal formed as a result of a merger of two colliding rarefied preplanetesimals that moved in circular heliocentric orbits before a collision. Some rarefied preplanetesimals formed as a result of collision of preplanetesimals in the region of formation of solid small bodies acquire such angular momenta that are sufficient to form satellite systems of small bodies. It is likely that the ratio of the number of rarefied preplanetesimals with such angular momenta to the total number of rarefied preplanetesimals producing classical trans-Neptunian objects with diameters larger than 100 km was 0.45 (the initial fraction of satellite systems among all classical trans-Neptunian objects).     

Thermal condensations in coronal magnetic fields

Conditions under which cool condensations can form in the solar corona are investigated using the powerful phase plane method to analyse the energy and hydrostatic balance equations. The importance of the phase plane approach is that the conclusions deduced are not sensitive to the actual choice of boundary conditions adopted which only determine the actual contour. The importance of heating variations and area divergence are studied as well as the influence of gravity for their effect on the formation of cool condensations. The cool temperature at which optically thin radiation and heating balance is important and the links with other cool solutions are mentioned.     

The physics of thermal instability in two dimensions

Previous studies of a thermal (radiative) instability in a sheared magnetic field have shown that, under solar coronal conditions, cool condensations can form in a small neighborhood about the shear layer. Such results have served to model the formation of solar filaments (or prominences) observed to occur above photospheric magnetic polarity-inversion lines. A surprising conclusion of these studies is that the width of the condensation does not depend on the thermal conductivity (). By examining the mass-flow patterns of two-dimensional condensations in the absence of thermal conduction, we demonstrate that local plasma dynamics and the constraints imposed by boundary conditions are together sufficient to explain the size of the condensation width. In addition we present the results of a series of numerical calculations which illustrate the characteristic mode structure of sheared-field condensations.     

Stability of particulate discs

Collisionally-induced amplification of density fluctuations can also produce non-axisymmetric local condensations in particulate discs if the optical thickness is between definite values. Gravitational instability occurs above this interval. The theory of both phenomena is derived from collisional equations. The conventional criterion for gravitational instability in a gaseous medium cannot be used for particulate discs, in which the equilibrium depends on the collisional energy loss. These instabilities can produce an unbounded growth in density or a gravitational coagulation of particles, but the typical consequence is the formation of highly elongated clouds which are denser than the background matter and have a relatively long lifetime before decay. The third type of instability, the thermal one, appears at low values of velocity dispersion. It only affects the random motion of particles without producing condensations.     

Origin of orbits of secondaries in the discovered trans-Neptunian binaries

The dependences of inclinations of orbits of secondaries in the discovered trans-Neptunian binaries on the distance between the primary and the secondary, on the eccentricity of orbits of the secondary around the primary, on the ratio of diameters of the secondary and the primary, and on the elements of heliocentric orbits of these binaries are studied. These dependences are interpreted using the model of formation of a satellite system in a collision of two rarefied condensations composed of dust and/or objects less than 1 m in diameter. It is assumed in this model that a satellite system forms in the process of compression of a condensation produced in such a collision. The model of formation of a satellite system in a collision of two condensations agrees with the results of observations: according to observational data, approximately 40% of trans-Neptunian binaries have a negative angular momentum relative to their centers of mass.     

Zur Bewegung der Kondensationen im Schweif des Kometen MOREHOUSE 1908 III

This paper deals with the motion of condensations within the tail of Comet Morehouse 1908 III as derived from Greenwich- and Yerkes-photographs. For the vicinity of the nucleus the following results are obtained:     

Radially aligned clumps and tails in planetary nebulae

We study the formation of radially aligned condensations and tails through the compression of material inside ionization shadows at early ionization phases of planetary nebulae. A dense clump, formed before ionization starts, forms an ionization shadow behind it. The surroundings, which are ionized before the shadow, have a higher temperature, and as a result compress the material in the shadow, forming a compressed tail. If the compressed tail crosses a dense shell, a dense condensation (clump) is formed there. At later stages this condensation is ionized and observed as a bright knot, radially aligned with the inner clump. We find that for the shadow to be effective, the clump should be already present as the ionization by the central star starts, and its density enhancement should be by a factor of ≳ 5. We propose this mechanism as an explanation for the radially aligned condensations recently found in the planetary nebula IC 4593.     

Dense cores in the L1630 molecular cloud: discovering new protostars with SCUBA

Maps of the 450- and 850-μm dust continuum emission from three star-forming condensations within the Lynds 1630 molecular cloud, made with the SCUBA bolometer array, reveal the presence of four new submillimetre sources, each of a few solar masses (two of which are probably class I and two of which are class 0), as well as several sources the existence of which was previously known. The sources are located in filaments and appear elongated when observed at 450 μm. They probably have dust temperatures in the range 10 to 20 K, in good agreement with previous ammonia temperature estimates. Attempts to fit their structures with power-law and Gaussian density distributions suggest that the central distribution is flatter than expected for a simple singular isothermal sphere.
Although the statistics are poor, our results suggest that the ratio of 'protostellar core' mass to total virial mass may be similar for both large and small condensations.     

Spectral observations of HH 448

Spectra of five condensations in the Herbig-Haro object HH 448 are presented for the first time. The emission line intensities indicate a low degree of ionization, 3–5%, with an electron density of 10³–10⁴ cm⁻³. The relative intensities of the emission lines of the individual condensations show that their physical properties differ. We classify the two stars closest to HH 448 as main sequence dwarfs which are, most likely, not coupled to HH 448. The absorption in the region of HH 448 is at least 4^m.3. __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 229–237 (May 2008).     

Dark matter-systematics of its distribution

The dynamical masses of dwarf-spheroidals, spiral and elliptical galaxies, dwarf irregular binaries, groups of galaxies and clusters are shown to lie in a band about the M ∼ ρR³ line. The value of ρ is approximately the same as that estimated for unseen matter in the solar neighbourhood. The clusters themselves lie about theM ∼ R ^-3 line derived for a self-gravitating neutrino gas; their masses are distributed around the maximum Jeans-mass, M_Jmax. corresponding to m_v - 10 eV in an expanding universe. The present day length scales of clusters and the dispersion in the velocities observed within them are understood in terms of a 100-fold expansion subsequent to the initial growth of the fluctuations at M_Jmax. These systematics on theR-M plane imply that the initial condensations in the expanding universe are on the scale of the rich clusters of galaxies, these condensations were triggered dominantly by the gravitation of the neutrinos and the constant density of al systems arises naturally due to the embedding of these systems in the large scale neutrino condensations. If the neutrino density falls off asr ^-2 beyond the cluster edge till the distributions from different clusters overlap, then the mean density of the neutrinos approximately equals the closure density of the universe.     

THE FRAGMENTS OF COMET HYAKUTAKE (C/1996 B2)

Several fragments of Comet Hyakutake were observed in March and April of 1996. This leads to the impression that the splitting of Comet Hyakutake on a small scale occurred frequently. Data analysis points to a rotation period of about 6.18hr if the fragments of Apr. 11 are the condensations within a jet.     

The origin of interplanetary sectors from radio observations

The interplanetary sectors have been correlated to observations of solar coronal active centers and condensations in the metric wavelengths. We have found that (1) a sector boundary is always located to the west of a coronal condensation, and (2) the effect of active centers is to displace systematically the boundary toward the east, thus enlarging the sector. A physical interpretation is discussed.     

Saturn's rings: II. Condensations of light and optical thickness of Cassini's division

“Condensations” of light have been observed when Saturn's rings are seen almost edge on, and the Sun and the Earth are on opposite sides of the ring plane. These condensations are associated with ring C and Cassini's division. If the relative brightness between the two condensations and the optical thickness of ring C are known, we can calculate the optical thickness of Cassini's division, τ_CASS. Using Barnard's and Sekiguchi's measurements, we have obtained 0.01 ? τ_CASS ? 0.05. A brightness profile of the condensations which agrees well with visual observations is also presented.We are able to set an upper limit of about 0.01 for the optical thickness of any hypothetical outer ring. This rules out a ring observed by C. Cragg in 1954, but does not eliminate the D′ ring observed by Feibelman in 1967.It is known that the outer edge of ring B is almost at the position of the 1/2 resonance with Mimas. Franklin, Colombo, and Cook explained this fact in 1971, postulating a total mass of ring B of 10^?6M_SATURN. We have derived a formula for the mass of the rings, which is a linear function of the mean particle size. We find that 10^?6M_SATURN implies large particles (～70m). If the particles are small (～10cm), as currently believed, the total mass of ring B is not enough to shift the outer edge. We conclude that the above explanation and current size estimates are inconsistent.     

Submillimetre co rotational lines from dense cores in molecular clouds

A simple, spherically-symmetric, centrally-condensed model is constructed for a dense core in a molecular cloud. Optical depths and peak brightness temperatures are calculated for the 10 lowest rotational transitions of carbon monoxide. The cloud, using parameters given by observation for dark condensations in molecular clouds, turns out to be optically thin in these transitions, which allows the maximum density and density distribution to be estimated.