Some secondary indications of gravitational collapse

A stellar core becomes somewhat less massive due to neutrinos radiated away during its collapse in a neutron star or a black hole. The paper deals with the hydrodynamic motion of stellar envelope induced by such a mass loss. Depending on the structure of the outer stellar layers, the motion results either in ejection of an envelope with mass and energy proper for Nova outbursts; or nearly instantaneous excitation of strong pulsations of the star; or lastly in a slow slipping away of the whole stellar envelope. These phenomena are of importance when more powerful events, like supernova outbursts presumably associated with gravitational collapse, are absent. Such secondary indications of gravitational collapse are of special interest, since they may be a single observable manifestation (besides neutrinos and gravitational waves) of massive black hole formation.     

Infrared photometry of the X-ray binary XTE J1118+480 in April 2000

We present the IR photometry of the X-ray binary XTE J1118+480 performed during seven nights in April and two nights in May–June 2000. A significant IR excess has been detected in the object, which may be due to the thermal radiation from a dust envelope/cloud. The observed energy distribution in the range 1.25–3.5 μm can be interpreted in terms of the sum of the fluxes from an accretion disk with a temperature of ～20 000 K and a dust envelope with grains heated to ～900 K. The distance to the X-ray binary estimated from the total flux from the dust envelope is no less than 0.6–3 kpc. The mean optical depth of the dust envelope for the accretion-disk radiation is about 0.06.     

PK 6-2o1, a remarkable nitrogen-rich southern planetary nebula

Photoelectric spectrophotometry with the IDS on the 3.9 m Anglo-Australian Telescope has shown the planetary nebula PK 6-2^o1 to be unique in its overabundance of nitrogen and helium, strong reddening and broad range of excitation conditions. It is suggested that here we see part of the massive envelope of a Wolf-Rayet star of the nitrogen sequence which is still embedded in its placental interstellar cloud.     

The magnetohydrodynamic rotational model of supernova explosion

The calculations of supernova explosion are made, using the one-dimensional nonstationary equations of magnetic hydrodynamics for the case of cylindrical symmetry. The energy source is supposed to be the rotational energy of the system (the neutron star in the centre and the surrounding envelope). The magnetic field plays the role of a mechanism of the transfer of rotational momentum. The calculations show that the envelope split up during the dynamical evolution of the system, the main part of the envelope joins the neutron star and becomes uniformly rotating with it, the outer part of the envelope (10% mass) expands with large velocity, carrying out a considerable part of rotational energy and rotational momentum.These results correspond qualitatively with the observational picture of supernovae explosions.     

Level of electrostatic excitation associated with relativistic beam-plasma system and pulsar radiation

A class of pulsar models which provide a stationary beam-plasma system as the source of radiation is considered. Since the beam-plasma system is stable near the pulsar where the coherent curvature radiation damps the longitudinal mode, we consider the beam-plasma system away from the star so that the effects of curvature radiation may be neglected. We find that the total wave energy density may attain a significant fraction of the beam energy density provided that the beam and plasma carry away a comparable amount of energy from the star. It should be noted that the attained high wave energy density is peculiar to a relativistic beam-plasma interaction.     

暗星云L134的稳定性及热特性

利用暗星云L134的光学观测及分子谱线观测的结果,估算了它的某些基本物理参数,讨论了该星云的稳定性及能量问题。 发现在L134的演化过程中,热压力及转动在制约其自引力坍缩中起一定作用,但不是重要因素,而磁场的支撑作用可能是比较重要的,L134不是在自由下落时间尺度t_(ff)上引力坍缩,而可能是在一个比较长的双极扩散时间尺度t_D上收缩。 本文还计算了L134的冷却率及加热率,表明引力克服热压力作功不是暗星云L134的有效加热源;宇宙线是L134的一个加热源,它能提供所需能量的～20％;磁场通过双极扩散释放能量可能为L134提供了一个重要的加热源。     

Stability and thermal properties of dark cloud L134

Using the results of optical and molecular line observations of the dark cloud L134, some basic cloud parameters are obtained and the stability and energy of the cloud are discussed.It is found that thermal pressure and rotation are unimportant, while internal magnetic field may be effective for supporting the cloud against gravitational collapse. And the cloud could not collapse on the free-fall time scale but on the longer time scale of ambipolar diffusion.The cooling and heating rates in L134 are also calculated. The results show that the work done by gravitation against thermal pressure is not an effective heating source; cosmic rays, however, may provide as much as 20% heating energy required. Calculation shows that internal magnetic energy released through the processes of ambipolar diffusion can supply the most part of the energy required, therefore, it may be the most important source.     

Collapse and explosion in a rotating star

The collapse, bounce, shock wave and expansion of the envelope of a rotating star have been analysed in the adiabatic approximation using the particle-in-cell method. The bounce takes place first in the equatorial plane and a shock wave arises there which shortly afterwards crosses the surface of the star. In the envelope, and to a less extent in the remainder of the star, there is a fast and lasting meridional motion the direction of which changes. As a consequence of the fast meridional motion in the envelope, mass and angular momentum are transported towards the axis of rotation. If the initial star rotates fast enough this will cause a secondary radial expansion in the polar region and a mass ejection. These motions reduce the strong anisotropy caused originally by the equatorial expansion. Strong whirls may arise along the axis of rotation. In the remainder of the star the meridional motion becomes supersonic. The temperature in the envelope depends to a high degree on the choice of the equation of state. Massloss is proportional to the energy initially added. The final loss of angular momentum and of energy is quite large, both losses being about 25%.     

Formation of bipolar flow by the stellar wind embeded in molecular disk

The interaction of the isotropic stellar wind with the rotating isothermal cloud surrounding the young star is investigated. The density distribution of the cloud is taken as that for the equilibrium state of the rotating isothermal cloud modified by adding the rarefied interstellar gas in the polar region. The development of the shock envelope and the structure of the shell induced by the stellar wind are obtained. It is shown that the envelope of the shock front elongates and opens to the polar direction with half opening angle of about 20 degrees resulting the bipolar flow which is able to reproduce well the observed properties for the outflow in the bipolar sources.     

A Study of Star Formation in BRC18

Using the 13.7m radio telescope at Delingha, the millimeter-wave radio observatory of Purple Mountain Observatory, we made mapping observations in 12CO J = 1 - 0 line towards IRAS 05417+0907, located in the bright-rimmed cloud (BRC) BRC18. We used a 7 × 7 grid with 1' spacing, a finer and larger grid than the one used by Myers et al. Our results show that there is a bipolar outflow near IRAS 05417+0907. Combining with the observations at other wave bands, we find that the star formation process in this region is triggered by radiation-driven implosion. The significant difference between the masses of BRC18 and the cores and the relatively large ratio of associated source bolometric luminosity to the mass show that the star formation in BRC18 may be taking place in a sequence.     

The first CO(1-0) mapping of the globule IC 1396 W

Near-infrared observations indicate that three H₂ outflows and their driving sources are present in the globule IC 1396 W, where the existence of molecular outflows has also been suggested by some authors. We made the first CO(1-0) map of IC 1396 W, and found that its CO molecular cloud may consist of three physically distinct components with different velocities. We detected neither molecular outflows nor the dense cores associated with candidate driving sources. One possible reason is that CO(1-0) and its isotopes cannot trace high density gas, and another is that the beam of our observation is too large to observe them. The CO cloud may be one part of the natal molecular cloud of IC 1396 W, in the process of disrupting and blowing away. The CO cloud seems to be in the foreground of the H₂ outflows.     

A massive circumstellar envelope around the type-IIn supernova SN 1995G

We model the interaction of the supernova SN 1995G with a dense circumstellar (CS) gas in a thin-shell approximation. A model fit to the observed bolometric light curve combined with data on the supernova expansion velocity gives estimates for the density, mass (≈1 M_⊙), and age (≈8 yr) of the CS envelope. The determined CS-envelope density is shown to be virtually independent of the assumed mass of the supernova envelope because of the high CS-gas density at which the forward shock wave is essentially radiative. The derived CS-envelope density is consistent with the Hα luminosity and with the presence of distinct Thomson scattering in the red wing of this line. The mass of the CS envelope together with its expansion velocity and age indicate that the CS envelope was ejected by the presupernova eight years before the supernova explosion through violent energy release (～6×10⁴⁸ erg).     

Magnetohydrodynamic effects on radiation-driven shock waves

A similarity solution for the flow variables behind a radiation-driven magnetohydrodynamic shock wave has been obtained. Owing to absorption of radiation incident on the shock layer, it is assumed that the total energy contained behind the shock surface is increasing. The ambient medium in which shock wave moves is non-uniform and it is optically thin so that there is no interaction with the incident radiation. A comparison has been made between the results with and without the magnetic field when the density and azimuthal magnetic field distributions are variable.While this paper was in press, Professor Verma passed away on 4 April 1985, without being able to read its proofs.     

The high-latitude cloud MBM 7. I. H I and CO observations

The high-latitude cloud (HLC) MBM 7 has been observed in the 21 cm H I line and the 12CO(1-0) and 13CO(1-0) lines with similar spatial resolutions. The data reveal a total mass approximately 30 M solar for MBM 7 and a complex morphology. The cloud consists of a cold dense core of 5 M solar surrounded by atomic and molecular gas with about 25 M solar, which is embedded in hotter and more diffuse H I gas. We derive a total column density N(H I + 2H2) of 1 x 10(21) cm-2 toward the center and 1 x 10(20) cm-3 toward the envelope of MBM 7. The CO line indicates the existence of dense cores [n(H2) > or = 2000 cm-3] of size (FWHM) approximately 0.5 pc. The morphology suggests shock compression from the southwest direction, which can form molecular cores along the direction perpendicular to the H I distribution. The H I cloud extends to the northeast, and the velocity gradient appears to be about 2.8 km s-1 pc-1 in this direction, which indicates a systematic outward motion which will disrupt the cloud in approximately 10(6) yr. The observed large line widths of approximately 2 km s-1 for CO suggest that turbulent motions exist in the cloud, and hydrodynamical turbulence may dominate the line broadening. Considering the energy and pressure of MBM 7, the dense cores appear not to be bound by gravity, and the whole cloud including the dense cores seem to be expanding. The distance to HLCs suggest that they belong to the galactic plane, since the scale height of the cloud is < or approximately equal to 100 pc. Compared to the more familiar dense dark clouds, HLCs may differ only in their small mass and low density, with their proximity reducing the filling factor and enhancing the contrast of the core and envelope structure.     

Thermal waves in stars

Conclusions In this paper I have set forth in detail the theory of thermal waves in inhomogeneous media; it has, I believe, independent theoretical interest. I wish also to point out the fact that the mechanism of separation of an envelope in a nova explosion has hitherto remained obscure, since it strongly depends on the nature of the energy source of the explosion. Thus, if this energy is liberated by thermonuclear reactions, it is more probable that the time of development of the phenomenon reaches hundreds or even thousands of seconds. In such a case, the ejection of an envelope of the star is the result of the total effect of an infinite series of acoustic and weak shock waves that, added together, give a powerful pressure wave [6]. But if the energy of the explosion is gravitational in nature, its liberation may be virtually instantaneous, and the mechanism that transports the energy to infinity could be either a shock wave or a thermal wave. Moreover, if the explosion is due to a rearrangement of only the outer shell of the star, a thermal wave is more probable. And although the velocities of the thermal waves themselves are high, the rate of expansion of the matter of the shell will be appreciably less, since the time (of the order of a few seconds) is too short for interaction between radiation and matter. This distribution of velocities of the matter behind the thermal front can be obtained by a numerical solution of the equations of gas dynamics with allowance for the effects of radiative thermal conductivity; I hope to find such a solution in the future.Astronomical Observatory, L'vov University. Translated from Astrofizika, Vol. 9, No. 2, pp. 307–317, April–June, 1973.     

A new observation of C18O (J=1−0) line emission in W31

Using the 13.7-m millimeter wave telescope of Purple Mountain Observatory, we for the first time observed in C¹⁸O(J=1−0), the northwest region (size 16′ × 25′) of the molecular cloud W31. We constructed contour maps in different velocity ranges (grid separation 1′). Three compact molecular clumps are identified and their physical parameters are derived from the observed temperature and line width; they are found to be rather young and stable. We discuss their distribution with respect to the associated HII regions, in regard to star formation.     

Automated cloud tracking system for the Akatsuki Venus Climate Orbiter data

Japanese Venus Climate Orbiter, Akatsuki, is cruising to approach to Venus again although its first Venus orbital insertion (VOI) has been failed. At present, we focus on the next opportunity of VOI and the following scientific observations.We have constructed an automated cloud tracking system for processing data obtained by Akatsuki in the present study. In this system, correction of the pointing of the satellite is essentially important for improving accuracy of the cloud motion vectors derived using the cloud tracking. Attitude errors of the satellite are reduced by fitting an ellipse to limb of an imaged Venus disk. Next, longitude–latitude distributions of brightness (cloud patterns) are calculated to make it easy to derive the cloud motion vectors. The grid points are distributed at regular intervals in the longitude–latitude coordinate. After applying the solar zenith correction and a highpass filter to the derived longitude–latitude distributions of brightness, the cloud features are tracked using pairs of images. As a result, we obtain cloud motion vectors on longitude–latitude grid points equally spaced. These entire processes are pipelined and automated, and are applied to all data obtained by combinations of cameras and filters onboard Akatsuki. It is shown by several tests that the cloud motion vectors are determined with a sufficient accuracy. We expect that longitude–latitude data sets created by the automated cloud tracking system will contribute to the Venus meteorology.     

Insolation of a cometary crater at the stage of dust-jet formation

An important cause of the activation and development of active processes on the surface of a cometary nucleus is direct solar radiation illuminating a part of the surface that is not shielded by dust. The intensity of solar radiation near the surface of a cometary nucleus depends on the thickness of the dust cloud above the active area. If the size of the dust cloud noticeably changes, the intensity considerably depends on time. In the present paper, we consider the nonlinear equation of radiative transfer in a dust cloud growing towards the incident wave front with a constant velocity. The change in the intensity of direct solar radiation along the dust jet originating from the active surface area of a cometary nucleus has been found. For the sake of comparison, the linear equation of radiative transfer was solved in the framework of this task. It turns out that the linear approach to the solution of the considered problem suggests a noticeable loss in the amount of direct radiation participating in the dust-jet formation. This loss is comparable with the intensity of solar radiation incident to the active area of a cometary nucleus after scattering in the cometary atmosphere.     

On the Envelope Soliton – Like Fine Structure in Solar Radio Emission

Several quasi-periodic, milliseconds fine structures in the metric wave band occurring during the evolution of solar type IV bursts have been observed by Yunnan Radio Telescope, Trieste Radio Telescope and IZMIRAN dynamic spectrometer. The envelope of these quasi-period modulational fine structures have a soliton pattern, so it is called an envelope soliton-like fine structure. A modulational instability model of electromagnetic wave has been adopted here. It is found that the longitudinal modulational instability can occur only in the solar coronal region of low magnetic field and high temperature, as well as high density plasma, which will give rise to the envelope soliton-like fine structures in the solar metric and decimetric radio emission. The propagation effects of envelope soliton-like fine structure from corona to the observer on the Earth have been briefly considered. This revised version was published online in July 2006 with corrections to the Cover Date.