Excitation of Sr ii lines in Eta Carinae

We study the nature of the peculiar [Sr  ii ] and Sr  ii emission filament found in the ejecta of Eta Carinae. To this purpose we carry out ab initio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr  ii . Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr  ii optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 10⁷ cm⁻³. Under these conditions, the observed emission can be explained without the need for a large Sr overabundance.     

The 2dF Galaxy Redshift Survey: luminosity dependence of galaxy clustering

We investigate the dependence of the strength of galaxy clustering on intrinsic luminosity using the Anglo-Australian two degree field galaxy redshift survey (2dFGRS). The 2dFGRS is over an order of magnitude larger than previous redshift surveys used to address this issue. We measure the projected two-point correlation function of galaxies in a series of volume-limited samples. The projected correlation function is free from any distortion of the clustering pattern induced by peculiar motions and is well described by a power law in pair separation over the range     . The clustering of     galaxies in real space is well-fitted by a correlation length     and power-law slope     . The clustering amplitude increases slowly with absolute magnitude for galaxies fainter than M *, but rises more strongly at higher luminosities. At low luminosities, our results agree with measurements from the Southern Sky Redshift Survey 2 by Benoist et al. However, we find a weaker dependence of clustering strength on luminosity at the highest luminosities. The correlation function amplitude increases by a factor of 4.0 between     and −22.5, and the most luminous galaxies are 3.0 times more strongly clustered than L * galaxies. The power-law slope of the correlation function shows remarkably little variation for samples spanning a factor of 20 in luminosity. Our measurements are in very good agreement with the predictions of the hierarchical galaxy formation models of Benson et al.     

Modelling line profiles in infalling cores

Results are presented from a model of molecular line formation in collapsing star-forming cores. The study includes, for the first time, a self-consistent chemical and dynamical model which is then directly coupled to an appropriate radiative transfer model. The assumptions of chemical uniformity or simple monotonic variations within such cores are shown to be unacceptable. The results show that the abundance variations and the line profiles are highly sensitive to the assumed values of the free parameters in the chemical model. Extreme caution is therefore advised in the quantitative analysis of emission-line profiles from infall sources. The implied degeneracy can be overcome by multiple line-of-sight observations of many species and transitions.     

Testing tidal-torque theory – I. Spin amplitude and direction

We evaluate the success of linear tidal-torque theory (TTT) in predicting galactic-halo spin using a cosmological N -body simulation with thousands of well-resolved haloes. The protohaloes are identified by tracing today's haloes back to the initial conditions. The TTT predictions for the protohaloes match, on average, the spin amplitudes of the virialized haloes of today, if linear growth is assumed until ∼ t ₀/3, or  55–70  per cent of the halo effective turn-around time. This makes it a useful qualitative tool for understanding certain average properties of galaxies, such as total spin and angular momentum distribution within haloes, but with a random scatter of the order of the signal itself. Non-linear changes in spin direction cause a mean error of ∼50° in the TTT prediction at t ₀, such that the linear spatial correlations of spins on scales ≥1  h ⁻¹ Mpc are significantly weakened by non-linear effects. This questions the usefulness of TTT for predicting intrinsic alignments in the context of gravitational lensing. We find that the standard approximations made in TTT, including a second-order expansion of the Zel'dovich potential and a smoothing of the tidal field, provide close-to-optimal results.     

Comparisons of Infrared Colors and Emission-line Intensities between Two types of Seyfert 2 Galaxies

We study the relation between the infrared colors[ OⅢ] emission lines,gaseous absorbing column density(NH) ,and the detectability of the polarized (hidden)broad-line region(HBLR) in a large sample of 75 Seyfert 2 galaxies(Sy2s).From the indicators of star-formation activity,f60/f100 and LFIR/LB,we find some evidence that the Sy2s without HBLR show higher star-formation activities than those with HBLR,in agreement with previous prediction.Also,we confirm that the HBLR Sy2s tend to have a larger luminosity ratio of the core to the host galaxy,suggesting that the HBLR Sy2s display more powerful AGN activity.Howerver,the level of obscuration found in previous papers in nearly indistinguishable between the two types of Sy2s.The results support the statement that the non-HBLR Sy2s,with a weaker core component and a stronger star-formation activity component,are intrinsically different from the HBLR Sy2s,which are Sy1 systems with a hidden powerful AGN core and a low star-formation activity.The indications are that the non-HBLR Sy2s might be at an earlier evolutionary phase than the HBLR Sy2s.     

Near—Infrared Imaging Observations of the Orion A—W Star Forming Region

We carried out near-infrared imaging observations of the Ori A-W region using the Italian 1.5m TIRGO infrared telescope at Gornergrat. A group of infrared objects is visible on the K band image, including an IRAS source (IRS 1). From its IRAS flux density the IRAS luminosity is derived to be 45L⊙, which shows that IRS 1 is a low-mass protostar. By superimposing the position of the VLA H2O maser on the K image, we can identify the less evolved object IRS 1 as the excitation source of the H2O maser, within a projected distance of 470AU. This would be evidence that the maser effect is associated with the youngest phase of stellar evolution. The first probable HH object candidate in the Ori A-W region is discovered from the H2 S(1) 1-0 observation. Comparing the position of the H2O maser with the direction of the molecular hydrogen emission in the region, we suggest that the observed H2O maser could be tracing the circumstellar disk of IRS 1.     

土地利用分类及其影响因素研究

土地利用分类是研究土地利用的最基础工作，它直接影响着土地利用的科研与实践，本文在全面研究土地利用分类理论与方法的基础上，比较且说明了当前国内外土地利用分类的优劣。并提出多层统一标准的系统分类设想。     

The circumnuclear X-ray reflectors in NGC 1068 and the Circinus galaxy

The ASCA and BeppoSAX spectra of the Circinus galaxy and NGC 1068 are analysed and compared with photoionization models based on cloudy . In the case of Circinus, a single, mildly ionized reflector can account for the line spectrum, while in NGC 1068 at least three different reflectors (with different ionization states) are needed. We suggest that the reflector in Circinus and the low ionized one in NGC 1068 are the inner and visible part of the material responsible for the X-ray absorption. With this assumption, we estimate for the inner radius of the absorber a value of 0.2 pc for Circinus and of a few parsecs for NGC 1068.