HH 111 STIS Observations and their Analysis using Analytical and Numerical Models

The internal structure of stellar jets arising from young stellar objects is characterized by a series of `knots' or condensations which have highly supersonic proper motions. These structures, we believe, are the result of a variable ejection from the source, which leads to the formation of internal working surfaces or small bowshock within the jet beam. In this paper we present a long-slit spectrum of Herbig-Haro object HH 111 obtained with STIS and an interpretation of this observation in terms of an ejection velocity variability model.     

Non-local diffusion and the chemical structure of molecular clouds

Observations of fluctuations in the redshifted 21-cm radiation from neutral hydrogen (H  i ) are perceived to be an important future probe of the universe at high redshifts. Under the assumption that at redshifts   z ≤ 6  (post-reionization era) the H  i traces the underlying dark matter with a possible bias, we investigate the possibility of using observations of redshifted 21-cm radiation to detect the bispectrum arising from non-linear gravitational clustering and from non-linear bias. We find that the expected signal is ∼ 0.1  mJy at  325  MHz ( z = 3.4)  for the small baselines at the Giant Metrewave Radio Telescope, the strength being a few times larger at higher frequencies  (610 MHz, z = 1.3)  . Further, the magnitude of the signal from the bispectrum is predicted to be comparable to that from the power spectrum, allowing a detection of both in roughly the same integration time. The H  i signal is found to be uncorrelated beyond frequency separations of ∼1.3 MHz whereas the continuum sources of contamination are expected to be correlated across much larger frequencies. This signature can in principle be used to distinguish the H  i signal from the contamination. We also consider the possibility of using observations of the bispectrum to determine the linear and quadratic bias parameters of the H  i at high redshifts, this having possible implications for theories of galaxy formation.     

南海南部SA09-040孔孢粉记录及古气候

依据南海低纬地区SA09-040孔高分辨率的孢粉记录,自下至上划分了4个孢粉组合带。从孢粉成分的变化,重建了22.25ka B P以来的植被与气候变化历史。结果表明:孢粉主要来源于婆罗洲和周围岛屿,孢粉1带(22.25～16.6ka B P),低山雨林植被发育,为暖热气候,从测年时间看,当时为末次冰期晚期。孢粉2带(16.6～10.82ka B P,为末次冰消期),植被以热带低山雨林和低地雨林为主,针叶的松数量较多,当时的气温比现在低。孢粉3带(全新世早期,10.82～6.43ka B P),植被以热带低山雨林和低地雨林为主,针叶松属数量减少,气温比前期升高,海平面也上升。孢粉4带(全新世中晚期,6.43ka B P至今),全新世中期为炎热、湿润的气候环境,全新世晚期可能与婆罗洲现今的植被景观相近,为热、湿的气候环境。     

The properties of convective storms in central Mexico: A radar and lightning approach

Radar data from Cerro Catedral (a peak close to Mexico City) were used to investigate the properties of convective storms over central Mexico, a region with complex orography. The spatial distribution shows a preference for storms to form and move to the west of radar, over a narrow band of high terrain. However, the storms with the higher volumes and echo-top heights tend to be located southwestward over lower terrain. Each radar feature was matched with the number of cloud-to-ground (CG) lightning produced inside it, as retrieved from the World Wide Lightning Location Network dataset. The storms in which lightning was detected, with an average of more than six lightning bolts, clearly outperform in size and intensity the group of storms in which lightning was not detected, and tend to lie over lower terrain. The sample of over 98 000 identified cells was divided into four elevation groups to look for elevation trends in the mean properties, as reported for other Mexican regions. While the number of storms per unit area increases with terrain height, the average values for properties related to both size (area, volume, echo-top height) and intensity (maximum reflectivity, number of CG bolts, height of maximum reflectivity, maximum height of 30 dBZ echo) decrease. These results could be related to the possible shallower warm-cloud depths over the higher elevations. The diurnal cycles of convection and lightning north of the radar show a nearly typical continental regime of precipitation in that zone, with maxima at 18:00 LT in both variables. However, south of the radar, a maximum in lightning activity occurs during late night and early morning, which is linked with the deeper nocturnal convection over the lower terrain in that zone.     

The emergence of a neutral Herbig–Haro jet into a photoionized nebula

Recent observations show the existence of an increasing number of collimated outflows ejected by young, low-mass stars which are embedded in H  ii regions. At distances of a few tens of au from the star, at least one lobe of these outflows will be shielded from the ambient ionizing radiation by the compact, high-extinction circumstellar disc. Within these shielded regions, the jets are probably mostly neutral, similar to the jets in 'normal' Herbig–Haro (HH) objects. At larger distances, these jets emerge into the photoionized nebula, and start to be photoionized by the radiation from the ionizing photon source of the nebula.
In this paper, we model the photoionization of an initially neutral HH jet. This process begins as an ionization front at the side of the jet, which is directed towards the ionizing star of the nebula, and progresses into the beam of the jet. There are two possible solutions. In the first solution, the jet beam becomes fully ionized through the passage of an R-type ionization front. In the second solution, the ionization front slows down enough to become a D-type front (or is already a D-type front at the point in which the jet emerges into the photoionized nebula), forming a partially ionized jet beam, with an expanding photoionized region and a compressed neutral region.
We explore these two types of solutions both analytically and numerically, and discuss the observational effects introduced by this jet photoionization process, concentrating in a region of parameter space that straddles the parameters deduced for HH 444 (the jet from V 510 Orionis).     

大兴安岭中南段中生代成矿物质的深部来源与背景

大兴安岭是我国北方一个重要的多金属成矿带。本文从成矿的物质来源和构造作用两方面讨论大兴安岭的成矿系统。Sr、Nd、O、Pb同位素的研究显示大兴安岭成矿物质的深部来源,大兴安岭晚中生代壳幔混熔花岗质岩石组成及其构造环境的研究,表明它们是在板内非造山的伸展环境下形成的A型花岗岩。与南岭花岗岩及其成矿作用的对比研究,将加深对大兴安岭中生代成矿特征的认识。深部构造特征也进一步印证了大兴安岭的成岩-成矿的背景。     

The dynamics of velocity fluctuations in the solar wind – I. Coronal mass ejections

In this paper we present a simple, analytic model for the dynamical evolution of supersonic velocity fluctuations at the base of the ambient solar wind. These fluctuations result in the formation of dense working surfaces that travel down the wind. It is shown how the initial parameters of the fluctuations (velocity, density and duration) are related to the characteristics of the working surfaces far from the Sun (for instance at the Earth). We apply the model to the evolution of the coronal mass ejections in the IP medium, finding that the model is in good agreement with satellite observations of these phenomena, thus providing physical insight into their dynamical evolution. Our model may contribute to future 'space weather forecasting' on the Earth, based on detailed satellite monitoring of the solar corona.