Stellar winds and globules in Hii regions

The interaction of a plane-parallel hypersonic stellar wind with a globule in an Hii region is considered in two approximations. In both approximations, the ionization front on the globule remains strong-D type, and a flow pattern containing two oppositely facing shock waves results. In the first approximation, the structure of the shocked region is calculated assuming that globule gas and stellar wind gas mix well and move at the same velocity. However, this assumption results in a very thick shocked layer and the assumption of good mixing is consequently not well justified. This approximation provides an upper limit on the gas velocities expected in the shocked gas which originated at the globule. In the second approximation, the stellar wind merely applies pressure to balance the momentum flux in the globule gas. The structure of the shocked region is calculated on the assumption that a tangential discontinuity exists between shocked stellar wind and shocked glubule gas. Structures may be produced having velocities ～10 km s^?1 and emission measures ～10³ cm^?6 pc with reasonable stellar luminosities and mass loss rates.     

Distance estimate of M31 based on the size distribution of Hii regions and dark clouds

The size distribution of dark clouds and of H II regions were used to derive a distance of 440±22 kpc for M31. Some galactic H II regions and dark clouds were combined with the same ingredients in M31 to study the mass spectrum of both phenomena. A gas to dust ratio of 10001 has been derived for M31. Radii of the classical H II regions as derived in this work using distance of 440 kpc agrees with the galactic classical H II region radii.     

The physical parameters and exciting stars of six Hii regions

The radio spectra of particular radio sources (mainly Hii regions) are plotted on the same graph for comparison. Various physical parameters of these objects are obtained from the radio data through a model. Predictions about the number and the nature of the exciting stars of six Hii regions are made. A comparison with the so far identified exciting stars is also presented.     

Grains and the galactic electron temperature gradient of Hii regions

The effect of dust on the electron temperature gradient of galactic Hii regions is investigated taking into account the photoelectric heating mechanism and using a recent galactic rotation curve. It is shown that the grains are unable to contribute substantially to the observed gradient of electron temperature.     

The structure of the dense cores of Hii regions

The latest observational and theoretical evidence which suggests the existence of a large number of partially ionized globules (PIG's) in the cores of Hii regions is presented. The consequences of this proposition to the structure of the Orion Nebula are then considered. It is suggested that the dense ionized core of M42 is caused by two major ionization fronts eating into a large mass of neutral material which contains many dense neutral globules. The ‘Hourglass’ in M8 is shown to be very similar.     

Sampling effects in the emission-line spectra of Hii regions

We show that sampling effects in the initial mass function are very important in the low-mass cluster case. To this aim, we compute photoionization models ionized by realistic clusters made up of various combinations of individual stars and clusters built with a synthesis model. We discuss the differences in the position on diagnostic diagrams, their implications, and future and ongoing applications of the present work.     

W28-A possible association of supernova remnants and Hii regions

The nature of various components of the W28 complex region is investigated. The radio spectra of W28-A1 (G 6.4-0.2), M20 (G 7.0-0.2), W28-A2 (G 5.9-0.4), W28-A4 (G 5.3-1.1), KE59 (G 6.6-0.3) and G 6.4-0.5 are established over a wide range of frequencies. The W28-A1 (G 6.4-0.2) source is a SNR (sp. index –0.41), the M20, W28-A2 and KE59 seem to be thermal sources (sp. indexes –0.06, –0.15 and –0.04 respectively) whereas the W28-A4 and G 6.4-0.5 are possibly mixed sources containing thermal and non-thermal features. Certain physical parameters of the thermal components are derived by adopting a model. The physical properties of the W28-A1 SNR are investigated. The possibility of a SNR-Hii regions association in the W28 region is also discussed.     

A review of recent observations of dust in Hii regions

The upper limit for the absorption cross section σ _H ^ext , of dust in Hii regions in the wave-length range 912–504 Å derived by Mezgeret al. (1974), is compatible with that expected for large dust grains, and a gas-to-dust ratio equal to that in the general interstellar medium. The albedo of the small grains must be high for λ>504 Å. This restriction is lifted if the visual extinction cross section of the grains in Hii regions is less than that for grains in the general interstellar medium. New observations of the Orion Nebula indicate that the visual extinction cross section is within a factor 2 of the value in the general interstellar medium.     

On the observed infrared fluxes from extragalactic Hii regions

We have calculated for extragalactic Hii regions, the expected relationship between the radio flux at 11 cm and the infrared flux at 11 and 20 m based on the grain models and the parameters which fit the observations of galactic Hii regions. It is shown that the measured infrared fluxes of extragalactic Hii regions are consistent with the expected infrared fluxes for these objects.     

The forbidden line spectrum in the edges of Hii regions

The influence of a relative motion between a hot star and the surrounding medium on the forbidden lines emission spectrum of the latter is described in an example.     

Radio observations of small Hii regions with identified exciting stars

The radio maps of ten small Hii regions at λλ=2.8, 6 and 11 cm, obtained with the 100-m MPIR radiotelescope, are given. A comparison of the radio fluxes obtained with parameters of exciting stars is carried out. For four compact Hii regions — namely, S146, S152, S237 and S297 — we present the results of observations with the radiotelescope of the U.S.S.R. Academy of Sciences, RATAN-600. The paper also presents estimates of the physical conditions in nebulae, and conclusions are drawn about the possible stage of their evolution.     

A classification of the available astrophysical data of particular Hii regions

A detailed classification of the available data on W3 is presented. Radio, optical and infrared maps of the object are shown in order of increasing angular resolution. The physical parameters and energy spectra of the various components of W3 and their sources are presented. A summary of the current theories on W3 is also included.     

A classification of the available astrophysical data of particular Hii regions

The physical parameters of the object compiled from various authors are classified in a separate table. Line ratios are presented for their significance in determining the density and temperature of the nebula. Data for the electron temperature of the object are also presented. A correlation of several interesting features of the core of the nebular complex is also shown.     

A classification of the available astrophysical data of particular Hii regions

Various contour maps of the object are presented. The physical parameters of the nebula are also classified and presented either in separate tables or in contour map form.     

On the effect of collisional ionization during the time evolution of Hii regions

The set of equations describing the time evolution ofHii regions, accounting for collisional ionization, are presented. Differential forms of these equations are deduced, and it is shown that it is not necessary within this context to consider changes in the potential energy due to ionization of the gas.     

Burst of star formation in detached extragalactic Hii regions: A qualitative analysis

A calibration previously determined for the evolution of the equivalent width of the emission line H with age for Hii regions (Dottori, 1981) is applied to detached extragalactic Hii regions. The frequency distribution of ages seems to indicate that some of these regions had other bursts of star formation so important as the observed last one.     

A classification of the available astrophysical data of particular Hii regions — IX NGC 2264

A classification of the observational data on NGC 2264 is presented. Optical, infrared and radio data for the Hii region are tabulated, and maps of the molecular cloud structure are shown. The observations of the NGC 2264 star cluster are also summarized. The role of star formation in this young region is briefly assessed.     

天文潮汐与地震

从三个方面综述了天文潮汐与地震关纱的研究，内容包括，日、月、地球的相对位置与地震，天文潮汐的周期，相位与地震，天文潮汐应力与地震，日、月、地球的相对位置与地震和天文潮汐周期与地城的研究均属于从体积力的角度考虑问题，主要是从宏观角度揭示地震发生时的日月位置分布有何规律性，揭示地震发生时间丛集在潮汐周期变化过程中的相位或时段以及地城牟潮汐周期，天文潮汐应力与震的研究从引潮力在地震内部地震源处产生的潮汐应力角度出发，着重研究不同类型性质的发震断层与潮汐应力触发的关系，从物理意义上讲，该研究较深 次地切入了问题的实质，分析了采用某些方法和样本研究结果不一致性的原因，并提出了进一步研究的方向。     

The radio spectrum and physical parameters of the W80 Hii complex

The radio continuum spectrum of the W80 nebular complex (NGC 7000 and IC 5070 nebulae mainly) is established over a wide range of frequencies. The resultant spectrum shows a thermal shape and the spectral index established for the optically thin part of it is –0.04. Certain physical parameters of the complex (rms densities, mass, emission measure, excitation parameter) are derived for adopted models. The possible exciting star is located. Limitations of the models involved and uncertainties of the results are also discussed.