Spectral line profiles changed by dust scattering in heavily obscured young stellar objects

It is known that scattering of radiation by circumstellar dust can strongly change the line profiles in stellar spectra. This hampers the analysis of spectral lines originating in the emitting regions of heavily obscured young stars. To calculate the line profile of the scattered radiation, we suggest to use the approximation of remote scattering particles. This approximation assumes that the scattering dust grains are at a distance from the star that is much larger than the characteristic size of the emitting region. Using this method, we calculated the line profiles of several simple models. They show the H alpha line profiles of Herbig AeBe stars in the presence and absence of motionless or moving dust

Will the Explosive Growth of China Continue?

The role of China in the world economy is constantly growing. In particular we observe that it plays more and more important role in the support of theworld economic growth (as well as high prices of certain very important commodities). In the meantime the perspectives of the Chinese economy (as well as possible fates of the Chinese society) remain unclear, whereas respective forecasts look rather contradictory. That is why the search for new aspects and modes of analysis of possible development of China turns out to be rather important for the forecasting of global futures. This article employs a combination of scientific methods that imply (a) the analysis at the level of Chinese economic model; (b) the analysis at regional level (at this level the Chinese economic model is compared with the regional East Asian model); (c) the analysis at the global level that relies on the modified world-system approach that allows to answer the question whether China will replace the USA as the global leader. It is important that the analysis is conducted simultaneously in economic, social, demographic, and political dimensions. As regards the analysis of specific features of the Chinese model as an especial type of the East Asian model (that is based on the export orientation, capital & technology importation, as well as cheap labor force), we note as organic features of the Chinese model the totalitarian power of the Communist Party and the immenseness of resources. As regards special features of the Chinese model, we note (in addition to “cheap ecology” and cheap labor force) and emphasize that China has a multilevel (in a way unique) system of growth driving forces, where, as opposed to developed states, the dominant role belongs not to native private capital, but to state corporations, local authorities and foreign business. This explains the peculiarities of the Chinese investment (or rather overinvestment), which determines high growth rate up to a very significant degree. A unique feature of the Chinese model is the competition of provinces and territories for investments and high growth indicators. As regards perspectives of the global hegemony of China, we intend to demonstrate that, on the one hand, economic and political positions of China will strengthen in the forthcoming decades, but, on the other hand, China, assuming all possible future success, will be unable to take the USA position in the World System. We believe that in a direct connection with the development of globalization processes the hegemony cycle pattern is likely to come to its end, which will lead to the World System reconfiguration and the emergence of its new structure that will allow the World System to continue its further development without a hegemon. Finally, the article describes some possible scenarios of the development of China. We demonstrate that China could hardly avoid serious difficulties and critical situations (including those connected with demographic problems); however, there could be different scenarios of how China will deal with the forthcoming crisis. We also come to the conclusion that it would be better for China to achieve a slowdown to moderate growth rates (that would allow China to go through the forthcoming complex transition period with less losses) than to try to return at any cost to explosive growth rates attested in the 2000s

Disc wind in the HH 30 binary models

Recent interferometric observations of the young stellar object(YSO) HH 30 have revealed a low velocity outflow in the $^{12}$CO J=1-2 molecule line (Pety et al. 2006). We present here two models of the low velocity disc winds with the aim of investigating an origin of this molecular outflow. Following Andlada et al. (2006) we treated HH 30 as a binary system. Two cases have been considered: i) the orbital period $P$ = 53 yrs and ii) $P \le$ 1 yr. Calculations showed that in the first case the outflow cone had a spiral-like structure due to summing the velocities of the orbital motion and the disc wind. Such a structure contradicts the observations. In the second case, the outflow cone demonstrates a symmetry relatively to the system axis and agrees well with the observations.Comment: 5 pages, 4 figures. accepted by Mon. Not. R. Astron. So

Structures in circumbinary disks: Prospects for observability

During the past decade circumbinary disks have been discovered around various young binary stars. Hydrodynamical calculations indicate that the gravitational interaction between the central binary star and the surrounding disk results in global perturbations of the disk density profile. We study the observability of characteristic large-scale disk structures resulting from the binary-disk interaction in the case of close binary systems. We derived the structure of circumbinary disks from smoothed-particle hydrodynamic simulations. Subsequently, we performed radiative transfer simulations to obtain scattered light and thermal reemission maps. We investigated the influence of the binary mass ratio, the inclination of the binary orbit relative to the disk midplane, and the eccentricity of the binary orbit on observational quantities. We find that ALMA will allow tracing asymmetries of the inner edge of the disk and potentially resolving spiral arms if the disk is seen face-on. For an edge-on orientation, ALMA will allow detecting perturbations in the disk density distribution through asymmetries in the radial brightness profile. Through the asymmetric structure of the disks, areas are formed with a temperature $2.6$ times higher than at the same location in equivalent unperturbed disks. The time-dependent appearance of the density waves and spiral arms in the disk affects the total re-emission flux of the object by a few percent.Comment: 8 pages, 9 figures, to appear in A&

Дефляция как болезнь современных развитых стран

В последние два-три года среди многочислен- ных проблем в отношении европейской и американской экономики все чаще стала упоминаться опасность дефляции. При этом в каче- стве примера рассматривается японская экономика, которая уже два десятилетия страдает от дефляции, несмотря на огромные раз- меры финансовых вливаний и усилия правительства разогнать ин- фляцию. В западных экономиках инфляция также низкая, времена- ми нулевая, переходящая в дефляцию. В целом есть основания счи- тать, что страны Европы заболевают «японской болезнью», а также что эта «болезнь» может прогрессировать либо носить хрониче- ский характер. В США, хотя и в меньшей степени, также имеются признаки этой «болезни». В результате финансовые вливания мо- гут стать, как и в Японии, постоянными. В разделе показаны при- чины этой проблемы, объяснена неравномерность процессов инфляции – дефляции в мире, сделаны прогноз

Bimodal Brightness Oscillations in Models of Young Binary Systems

We consider a model for the cyclic activity of young binary stars that accrete matter from the remnants of a protostellar cloud. If the orbit of such a binary system is inclined at a small angle to the line of sight, then the streams of matter and the density waves excited in the circumbinary disk can screen the primary component of the binary from the observer. To study these phenomena by the SPH (smoothed particle hydrodynamics) method, we have computed grids of hydrodynamic models for binary systems based on which we have constructed the light curves as a function of the orbital phase.The main emphasis is on investigating the properties of the brightness oscillations. Therefore, the model parameters were varied within the following ranges: the component mass ratio q = M2 : M1 = 0.2 - 0.5 and the eccentricity e = 0 - 0.7. The parameter that defined the binary viscosity was also varied. We adopted optical grain characteristics typical of circumstellar dust. Our computations have shown that bimodal oscillations are excited in binaries with eccentric orbits, provided that the binary components do not differ too much in mass. In this case, the ratios of the periods and amplitudes of the bimodal oscillations and their shape depend strongly on the inclination of the binary plane and its orientation relative to the observer. Our analysis shows that the computed light curves can be used in interpreting the cyclic activity of UX Ori stars.Comment: 14 pages, 5 figures, 1 tabl

Explaining UXOR variability with self-shadowed disks

In this Letter we propose a new view on UX Orionis type variability. The idea is based on the earlier proposal by various authors that UXORs are nearly-edge-on disks in which hydrodynamic fluctuations could cause clumps of dust and gas to cross the line of sight. However, because the standard disk models have a flaring geometry, it is mostly the outer regions of the disk that obscure the star. The time scales for such obscuration events would be too long to match the observed time scales of weeks to months. Recent 2-D self-consistent models of Herbig Ae/Be protoplanetary disks (Dullemond et al. 2002,2003 henceforth D02/DD03), however, have indicated that for Herbig Ae/Be star disks there exists, in addition to the usual flared disks, also a new class of disks: those that are fully self-shadowed. Only their puffed-up inner rim (at the dust evaporation radius) is directly irradiated by the star, while the disk at larger radius resides in the shadow of the rim. For these disks there exist inclinations at which the line of sight towards the star skims the upper parts of the puffed-up inner rim, while passing high over the surface of outer disk regions. Small hydrodynamic fluctuations in the puffed-up inner rim could then be held responsible for the extinction events seen in UXORs. If this idea is correct, it makes a prediction for the shape of the SEDs of these stars. It was shown by D02/DD03 that flared disks have a strong far-IR excess and can be classified as `group I' (in the classification of Meeus et al. 2001), while self-shadowed disks have a relatively weak far-IR excess and are classified as `group II'. Our model therefore predicts that UXORs belong to the `group II' sources. We show that this correlation is indeed found within a sample of 86 Herbig Ae/Be stars.Comment: Accepted for publication in ApJ Letters (a few lines added to original version to accommodate comments of referee

Parameters of Herbig Ae/Be and Vega-type stars

This work presents the determination of the effective temperature, gravity, metallicity, mass, luminosity and age of 27 young early-type stars, most of them in the age range 1-10 Myr, and three -suspected- hot companions of post-T Tauri stars belonging to the Lindroos binary sample. Most of these objects show IR excesses in their spectral energy distributions, which are indicative of the presence of disks. The work is relevant in the fields of stellar physics, physics of disks and formation of planetary systems. Spectral energy distributions and mid-resolution spectra were used to estimate the effective temperature. The comparison of the profiles of the Balmer lines with synthetic profiles provides the value of the stellar gravity. High-resolution optical observations and synthetic spectra are used to estimate the metallicity, [M/H]. Once these three parameters are known for each star, evolutionary tracks and isochrones provide estimations of the mass, luminosity, age and distance (or upper limits in some cases). The method is original in the sense that it is distance-independent, i.e. the estimation of the stellar parameters does not require, as it happens in other works, the knowledge of the distance to the object. A detailed discussion on some individual objects, in particular VV Ser, RR Tau, 49 Cet and the three suspected hot companions of post-T Tauris, is presented. The paper also shows the difficulty posed by the morphology and behaviour of the system star+disk in the computation of the stellar parameters.Comment: 18 pages, 11 figure