Linear spectropolarimetry across the optical spectrum of Herbig Ae/Be stars

We present the results of spectropolarimetric observations of 12 Herbig Ae/Be objects. Our data have the largest spectropolarimetric wavelength coverage, 4560 Å to 9480~Å, published to date. A change in linear polarisation across the Hα line, is detected in all objects. Such a line effect reveals the fact that stellar photons are scattered off free electrons that are not distributed in a spherically symmetric volume, suggesting the presence of small disks around these accreting objects. Thanks to the large wavelength coverage, we can report that Hα is the spectral line in the optical wavelength range that is most sensitive to revealing deviations from spherical symmetry, and the one most likely to show a line effect across the polarisation in such cases. Few other spectral lines display changes in polarisation across the line. In addition, Hα is the only line which shows an effect across its absorption component in some sources. We present a scenario explaining this finding and demonstrate that the detection of the line effect strongly relies on the number of photons scattered into our line of sight. We highlight the special case of R Mon, which is the only object in our sample to show many lines with a polarisation effect, which is much stronger than in all other objects. Given that the object and its nebulosity is spatially resolved, we argue that this is due to scattering of the stellar and emission spectrum off circumstellar dust

A Statistical Spectropolarimetric Study of Herbig Ae/Be Stars

We present Halpha linear spectropolarimetry of a large sample of Herbig Ae/Be stars. Together with newly obtained data for 17 objects, the sample contains 56 objects, the largest such sample to date. A change in linear polarization across the Halpha line is detected in 42 (75 %) objects, which confirms the previous finding that the circumstellar environment around these stars on small spatial scales has an asymmetric structure, which is typically identified with a disk. A second outcome of this research is that we confirm that Herbig Ae stars are similar to T Tauri stars in displaying a line polarization effect, while depolarization is more common among Herbig Be stars. This finding had been suggested previously to indicate that Herbig Ae stars form in the same manner than T Tauri stars through magnetospheric accretion. It appears that the transition between these two differing polarization line effects occurs around the B7-B8 spectral type. This would in turn not only suggest that Herbig Ae stars accrete in a similar fashion as lower mass stars, but also that this accretion mechanism switches to a different type of accretion for Herbig Be stars. We report that the magnitude of the line effect caused by electron scattering close to the stars does not exceed 2%. Only a very weak correlation is found between the magnitude of the line effect and the spectral type or the strength of the Halpha line. This indicates that the detection of a line effect only relies on the geometry of the line-forming region and the geometry of the scattering electrons

Metro Area Network Single Link Failure- Fast Spanning Tree Reconnection

Due to Affordability, ease of maintenance and ubiquity, Ethernet has become a preferred technology to be deployed in to LAN, MAN and WAN networks. Even though Ethernet has being used widely for switched communication it is not meet requirement for Metro Area Networks in terms of network resilience. In this paper, author propose the fast spanning tree re-connection formula, especially for Metro Area Ethernet networks to manage any single link failure, and it has most important feature of fast recovery, backup capacity grantees and ease of fast recovery. If in case of link failure on a spanning tree, a distributed failure recovery protocol is activated to rebuild the broken spanning tree. This is re-connecting the link but not a spanning tree. Author presents the details of the protocol, which including failure notification and forwarding table reconfiguration manual. The Integer linear programming (ILP) is formulated to reconnect-links as it pre-configured. The result of optimization gives the remark of lower implementation cost, fast and effective spanning tree reconnection mechanism can achieve better performance than other resilient technique for Metro Ethernet Network

THE CORONAVIRUS PANDEMIC AND THE TRANSFORMATION OF INTERNATIONAL ORDER: A SHORT OVERVIEW

The Covid-19 pandemic has affected most of the world, adding health security as a new challenge. Instead of facing these challenges, some states move towards a system of competition and intolerance, which forms new patterns in the international order. This questions the impact of the pandemic on the strategic dynamics of the international order. This article argues that the global pandemic transforms the political system and the way of governing liberal democracy more than any other factor. It took the form of a variable, driver, and accelerator, and the established world order transformed into a new form of order. Using the descriptive-analytical method and the theories of international relations, the current study examined the impact of the pandemic on the strategic dynamics of the international order.        &nbsp

Unfreezing 'the Transnistria Conflict' from the Lens of Regional Security Complex Theory

ABABAKR, Amer. Unfreezing 'the Transnistria Conflict' from the Lens of Regional Security Complex Theory. Eastern European Journal of Regional Studies. June 2022, vol. 8, issue 1, pp. 5-20. ISSN 2537-6179, E-ISSN 1857-436X.Transnistrian is a frozen geopolitical conflict extends back to the dissolution of the Soviet Union and the formation of an independent Moldovan state. However, there has been little real movement toward a long-term conflict resolution until recently. The aim of this study is to find out why, despite the efforts of the European Union, the Transnistrian conflict remains inactive and there is no clear prospect for resolving it. To answer this question, the integrated theory of regional security by Buzan and Weaver has been used. The results of this study show that Transnistria is part of a regional security complex under Russian influence, and its intersection with the security complex designed in the Eastern Partnership plan does not allow the EU to resolve the conflict. The difference in the power structures in the two complexes has an effect on the failure of this process. The matrix of regional security complexes in this area is centralized with sub-branches of superior power and superior institutions, and this has added to the complexity of conflict resolution. JEL: F02; DOI: https://doi.org/10.53486/2537-6179.8-1.0

The Obstacles of Rural Women Participation in Agricultural Development in Erbil Province of Iraq

The role of rural women’s in agricultural activities is substantial in Iraq, especially in Erbil province. The aim of the study is to determine the problems of rural women faced during agricultural activities. This study is conducted in Erbil province which is located in the North of Iraq. The data is collected from 250 women from through face to face interviews. Results show that the obstacles of women’s role in agricultural development are lack of literacy due to their poor academic background, increased work inside and outside of activities of rural women, family obstacles, whereby women always face disagreement with their family while attending to social and economic activities. Furthermore, the women also have obstacles in the agricultural development due to the gender discriminations as well as due to low attendance of women NGOs to track their problems

A spectroscopic survey of Herbig Ae/Be stars with X-shooter – I. Stellar parameters and accretion rates

Herbig Ae/Be stars (HAeBes) span a key mass range that links low- and high-mass stars, and thus provide an ideal window from which to explore their formation. This paper presents Very Large Telescope/X-shooter spectra of 91 HAeBes, the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultraviolet are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within Herbig Be mass range

The accretion rates and mechanisms of Herbig Ae/Be stars

This work presents a spectroscopic study of 163 Herbig Ae/Be stars. Amongst these, we present new data for 30 objects. Stellar parameters such as temperature, reddening, mass, luminosity, and age are homogeneously determined. Mass accretion rates are determined from Hα emission line measurements. Our data is complemented with the X-Shooter sample from previous studies and we update results using Gaia DR2 parallaxes giving a total of 78 objects with homogeneously determined stellar parameters and mass accretion rates. In addition, mass accretion rates of an additional 85 HAeBes are determined. We confirm previous findings that the mass accretion rate increases as a function of stellar mass, and the existence of a different slope for lower and higher mass stars, respectively. The mass where the slope changes is determined tobe 3.98+1.37−0.94M⊙⁠. We discuss this break in the context of different modes of disc accretion for low- and high-mass stars. Because of their similarities with T Tauri stars, we identify the accretion mechanism for the late-type Herbig stars with the Magnetospheric Accretion. The possibilities for the earlier-type stars are still open, we suggest the Boundary Layer accretion model may be a viable alternative. Finally, we investigated themass accretion–age relationship. Even using the superior Gaia based data, it proved hard to select a large enough sub-sample to remove the mass dependence in this relationship. Yet, it would appear that the mass accretion does decline with age as expected from basic theoretical considerations