Observing Magnetic Fields in Star-Forming Regions

Magnetic field strengths and directions can be estimated using many different observational techniques that span a wide range of wavelengths. Each observational method favours different regimes of scale size, density and other physical conditions. The available techniques and their ranges of applicability are briefly described and the current status of observations is reviewed, with particular emphasis on high-resolution observations of star-forming regions.     

河南省电子政务空间信息服务系统建设与典型应用

介绍了河南省电子政务空间信息服务系统的项目背景、系统总体设计，论述了数据处理与集成建库所涉及的一些关键技术，并以中原城市群空间信息服务系统为典型应用，作了进一步的探讨。     

New giant H ii regions in the southern sky

We present results of a search for giant H  ii regions in southern galaxies. Using high-resolution spectra, obtained with the Magellan Inamori Kyocera Echelle (MIKE) at the Las Campanas Magellan II telescope, we were able to resolve the emission-line profiles and determine the intrinsic velocity dispersion of the ionized gas. Out of four observed regions, selected from previous CCD narrow-band photometry, we detected three H  ii regions showing supersonic velocity dispersion, characteristic of giant H  ii regions, and their location in diagnostic diagrams suggests that a powerful starburst is the source of ionization energy.     

Stability Regions and Quasi-Periodic Motion in the Vicinity of Triangular Equilibrium Points

The regions of quasi-periodic motion around non-symmetric periodic orbits in the vicinity of the triangular equilibrium points are studied numerically. First, for a value of the mass parameter less than Routh's critical value, the stability regions determined by quasi-periodic motion are examined around the existing families of short (L^s ₄) and long (L^l ₄) period solutions. Then, for two values of μ greater than the Routh value, the unified family L^sl ₄, to which, in these cases, L^s ₄ and L^l ₄ merge, is considered. It is found that such regions surround in general the linearly stable segments of the corresponding families and become smaller as the mass ratio increases. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the maximum value of the cosmic abundance of oxygen and the oxygen yield

We search for the maximum oxygen abundance in spiral galaxies. Because this maximum value is expected to occur in the centres of the most luminous galaxies, we have constructed the luminosity – central metallicity diagram for spiral galaxies, based on a large compilation of existing data on oxygen abundances of H  ii regions in spiral galaxies. We found that this diagram shows a plateau at high luminosities  (−22.3 ≲ M _B ≲−20.3)  , with a constant maximum value of the gas-phase oxygen abundance  12 + log (O/H) ∼ 8.87  . This provides strong evidence that the oxygen abundance in the centres of the most luminous metal-rich galaxies reaches the maximum attainable value of oxygen abundance. Since some fraction of the oxygen (about 0.08 dex) is expected to be locked into dust grains, the maximum value of the true gas + dust oxygen abundance in spiral galaxies is 12 + log(O/H) ∼ 8.95. This value is a factor of ∼2 higher than the recently estimated solar value. Based on the derived maximum oxygen abundance in galaxies, we found the oxygen yield to be about 0.0035, depending on the fraction of oxygen incorporated into dust grains.     

Near-infrared and optical emission-line structure of the Keyhole Nebula in NGC 3372

Narrow-band infrared and optical images of the Keyhole Nebula in NGC 3372 reveal which structures are caused by extinction, and show the underlying morphology of photoionized and shock-excited gas. Dark clouds conspire with ionized gas to create the apparent keyhole shape, which is prominent at blue wavelengths and less apparent in the infrared. The  Pa β /H α   line ratio shows the spatial distribution of foreground extinction. The wavelength dependence of this extinction indicates a reddening law with   R ≈4.8  , different from the normal interstellar medium. This confirms previous estimates of reddening toward the Carina Nebula determined from stellar photometry, and reveals that the anomalous extinction is patchy and within the H  ii region. The morphology of the ionized gas is different from the extinction clouds; it shows an edge-on ionization front running NE to SW, with a limb-brightened indentation that forms the upper outline of the keyhole shape. A fast polar wind from η Carinae may have punctured the ionization front, since the indentation is directly along a projection of the polar axis of the star. This is supported by the morphology of shock-excited gas revealed by a high  [S  ii ]/H α   ratio. High-excitation gas emitting [O  iii ] and He  i has a smoother distribution. Molecular clumps in the region are also discussed.     

Extragalactic Astronomy with the VLTI: a new window on the Universe

Interferometry in the optical and near infrared has so far played a marginal role in Extragalactic Astronomy. Active Galactic Nuclei are the brightest and most compact extragalactic sources, nonetheless only a very limited number could be studied with speckle interferometry and none with long baseline interferometry. The VLTI will allow the study of moderately faint extragalactic objects with very high spatial resolution thus opening a new window on the universe. With this paper we focus on three scientific cases to show how AMBER and MIDI can be used to tackle open issues in extragalactic astronomy. This revised version was published online in July 2006 with corrections to the Cover Date.     

The key‐group method

This paper proposes an extension to the key‐block method, called ‘key‐group method’, that considers not only individual key blocks but also groups of collapsable blocks into an iterative and progressive analysis of the stability of discontinuous rock slopes. The basics of the key‐block method are recalled herein and then used to prove how key groups can be identified. We reveal that a key group must contain at least one basic key block, yet this condition is not entirely sufficient. The second block candidate for grouping must be another key block or a block whose movement‐preventing faces are common to one or more single key blocks. We also show that the proposed method yields more realistic results than the basic key‐block method and a comparison with results obtained using a distinct element analysis demonstrates the ability of this new method. Copyright © 2003 John Wiley & Sons, Ltd.