Can the Dragon Make the Lion Breathe Fire? The Links of Chinese Entrepreneurs in the Addis Ababa Economy

China’s increasing role in many African economies has given rise to discussions about the drivers of these economic relations and the benefits that Africa can reap. This article, based on field work carried out in Addis Ababa (Ethiopia), aims to contribute to this discussion by shedding light on a group that is often overlooked: the Chinese small entrepreneurs. Our investigation of five specific economic linkages shows how Chinese entrepreneurs mainly operate in secluded market segments, but also are impactful players in the local economy of Bole Rwanda (Addis Ababa). Their presence has both direct and indirect economic effects: even though focusing mainly on serving the Chinese community, these entrepreneurs play important roles in employment generation, and the transfer of knowledge of particular markets, while simultaneously offering new opportunities for Ethiopian entrepreneurs and transforming the existing vegetable market. The dragon helped the lion to breathe fire—the challenge is to make it a far-reaching and long-lasting breath.</p

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

Time variations of the narrow FeII and HI spectral emission lines from the close vicinity of Eta Carinae during the spectral event of 2003

The spectrum of Eta Carinae and its ejecta shows slow variations over a period of 5.5 years. However, the spectrum changes drastically on a time scale of days once every period called the 'spectral event'. We report on variations in the narrow emission line spectrum of gas condensations (the Weigelt blobs) close to the central star during a spectral event. The rapid changes in the stellar radiation field illuminating the blobs make the blobs a natural astrophysical laboratory to study atomic photoprocesses. The different responses of the HI Paschen lines, fluorescent lines and forbidden [FeII] lines allow us to identify the processes and estimate physical conditions in the blobs. This paper is based on observations from the Pico dos Dias Observatory (LNA/Brazil) during the previous event in June 2003.Comment: Accepted for publication in A&

Analysis of the dust evolution in the circumstellar disks of TTauri stars

We present a compositional analysis of 8-13um spectra of 32 young stellar objects (YSOs). Our sample consists of 5 intermediate-mass stars and 27 low-mass stars. While the spectra and first scientific results have already been published by Przygodda et al. (2003) and Kessler-Silacci et al. (2004) we perform a more detailed analysis of the 10um silicate feature. In our analysis we assume that this emission feature can be represented by a linear superposition of the wavelength-dependent opacity $\kappa_{\rm abs}(\lambda)$ describing the optical properties of silicate grains with different chemical composition, structure, and grain size. The determination of an adequate fitting equation is another goal of this study. Using a restricted number of fitting parameters we investigate which silicate species are necessary for the compositional fitting. Particles with radii of 0.1um- and 1.5um consisting of amorphous olivine and pyroxene, forsterite, enstatite, and quartz have been considered. Only compact, homogeneous dust grains have been used in the presented fitting procedures. In this context we show that acceptable fitting results can also be achieved if emission properties of porous silicate grains are considered instead. Although some previous studies give reasons for the similarity between the dust in circumstellar disks of TTauri stars and Herbig Ae/Be stars, a quantitative comparison has been missing, so far. Therefore, we conclude with a discussion of the results of a 10um spectroscopic survey of van Boekel et al. (2005) who focus on Herbig Ae/Be stars, the higher mass counterparts of T Tauri stars and draw comparisons to this and other studies. We find that the results of our study of T Tauri systems partly agree with previous studies of Herbig Ae/Be stars.Comment: 17 pages, 6 figure

Resonance-Enhanced Two-Photon Ionization (RETPI) of SiII and an Anomalous, Variable Intensity of the 1892A SiIII] Line in the Weigelt Blobs of Eta Carinae

The Si III] 1892A intercombination line shows an anomalously high intensity in spectra of the radiation-rich Weigelt blobs in the vicinity of Eta Carinae. The line disappears during the 100 days long spectral events occurring every 5.5 years. The aim is to investigate whether resonance-enhanced two-photon ionization (RETPI) is a plausible excitation mechanism for the Si III] 1892A line. The possible intensity enhancement of the 1892A line is investigated as regards quasi-resonant intermediate energy levels of Si II. The RETPI mechanism is effective on SiII in the radiation-rich Weigelt blobs where the two excitation steps are provided by the two intense hydrogen lines Ly alpha and Ly gammaComment: 4 pages, Accepted for publication in A&

Why Chromatic Imaging Matters

During the last two decades, the first generation of beam combiners at the Very Large Telescope Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, we present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix we include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, we recovered chromatic images, from simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.Comment: Accepted for publication in Experimental Astronomy as part of the topical collection: Future of Optical-infrared Interferometry in Europ

Discovery of a double ring in the core of η Carinae

We report the discovery of a double ring structure in the waist of the nebula surrounding η Carinae. The rings are detected in the mid-IR dust continuum at wavelengths of 7.9, 11.9, 12.9 and 20 μm. The dust in the rings has a temperature of about 300 K. The orientation of the rings is inclined with respect to the axis of the homunculus by either 37 or 58 degrees. The central star is not in the projected centre of the structure defined by the two rings. This geometry is reminiscent of that seen in SN1987A and some planetary nebulae. We discuss several possible origins for this remarkable geometry and its orientation

Discovery of a double ring in the core of η Carinae

We report the discovery of a double ring structure in the waist of the nebula surrounding η Carinae. The rings are detected in the mid-IR dust continuum at wavelengths of 7.9, 11.9, 12.9 and 20 μm. The dust in the rings has a temperature of about 300 K. The orientation of the rings is inclined with respect to the axis of the homunculus by either 37 or 58 degrees. The central star is not in the projected centre of the structure defined by the two rings. This geometry is reminiscent of that seen in SN1987A and some planetary nebulae. We discuss several possible origins for this remarkable geometry and its orientation

Mid-infrared observations of the transitional disks around DH Tau, DM Tau, and GM Aur

Aims: We present mid-infrared observations and photometry of the transitional disks around the young stellar objects DH Tau, DM Tau, and GM Aur, obtained with VISIR/VLT in N band. Our aim is to resolve the inner region and the large-scale structures of these transitional disks, carrying potential signatures of intermediate or later stages of disk evolution and ongoing planet formation. Methods: We use the simultaneously observed standard-stars as PSF reference to constrain the radial flux profiles of our target objects. Subtracting the obtained standard-star profile from the corresponding science object profile yields the flux residuals produced by the star-disk system. A detection threshold takes into account the background standard deviation and also the seeing variations during the observations to evaluate the significance of these flux residuals. On the basis of a simple model for the dust re-emission, we derive constraints on the inner radius of the dust disk. Results: We spatially resolve the transitional disk around GM Aur and determine an inner-disk hole radius of 20.5(+1.0,-0.5) AU. The circumstellar disks around DH Tau and DM Tau are not spatially resolved but we are able to constrain the inner-disk hole radius to <15.5(+9.0,-2.0) AU and <15.5(+0.5,-0.5) AU, respectively. The performed photometry yields fluxes of 178+-31 mJy for DH Tau, 56+-6 mJy for DM Tau, and 229+-14 mJy for GM Aur.Comment: Accepted for publication in Astronomy & Astrophysics. (6 pages, including 7 figures and 5 tables