The importance of chemical data for the study of interstellar shocks

Shock waves perturb the chemical state of the interstellar gas. We consider the effects of C-shocks on the composition of molecular clouds, for a range of values of the pre-shock gas density and magnetic induction. The time required to re-establish equilibrium in the post-shock gas depends on the initial conditions and can become very large. The significance of the two known chemical phases of dark clouds and of bistability is considered in this context.     

大质量恒星形成的观测和研究

对于大质量的形成，由于区域的遥远和结构的复杂以及过程的特殊，研究相对迟缓，对可能形成大质量得的云核和大质量年轻星体的活动，进行多波段搜寻和研究，取得了相应的进展。     

Presolar grains from meteorites: Remnants from the early times of the solar system

This review provides an introduction to presolar grains - preserved stardust from the interstellar molecular cloud from which our solar system formed - found in primitive meteorites. We describe the search for the presolar components, the currently known presolar mineral populations, and the chemical and isotopic characteristics of the grains and dust-forming stars to identify the grains’ most probable stellar sources.     

Evolution of current loops in space

Ampere's law requires that every magnetic field have an associated current. The analysis of magnetic fields in this paper begins with that current in a circular loop and calculates the forces that make the loop evolve. A circular current generates a dipole field; and a second-order, ordinary differential equation represents the evolving magetic field. The theory describes cases where the conductor shrinks as the loop increases in size. The temperature of the conducting ions and electrons then decreases. The theory also describes cases where the conductor grows as the loop grows. Then the conducting particles heat up.Analysis shows that the magnetic clouds in the solar wind belong to the first type. In the provisional model adopted, the Klein-Burlaga clouds at one astronomical unit have a toroidal shape, centered on the sun, with a conductor radius of .125 au, and temperature (same for conducting electrons and protons) of 10⁵ K. After 26 days the toroid has a radius of 7.1 au, the conductor radius is .025 au, and the temperature is 2600 K.     

The evolution of charged particles in a model of contracting cloud

The evolution of the charged particles are followed during contraction of a model of an interstellar cloud, with initial density number of n = 10 cm^–3. The contraction is followed up to density increase by five orders of magnitude. Special care is given to the details of the negative ions. In addition, we have tested the ambipolar diffusion according to the results of the ion density.The results predict the importance of atomic ions in the diffuse regions. H⁺ and C⁺ are distinctly enhanced in the beginning of contraction but decrease as contraction proceeds. Molecular ions enhance as contraction proceeds and becomes important in dense regions. The most enhanced molecular ions are HCO⁺, O₂ ⁺, C₂H₃ ⁺, H₃O⁺ and SO⁺, H₃ ⁺ is less abundant. The atomic ions (except metalic ions) decrease noticeably as density increases. In general the negative ions are of negligible fractional abundances. It has also been found that the time of ambipolar diffusion is shorter than the dynamical time, hence the magnetic field should be weakened in the central core as the central density increases to n = 10⁴ cm^–3.     

On the origin of stellar aggregates in molecular clouds

A method which provides the possibility to connect the global characteristics of the interstellar medium with that of the young stellar population of the Galaxy is proposed.