Browsing by Subject "nature"

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    Open Access
    Is GBT 1355+5439 a dark galaxy?
    (2013) Oosterloo, T A; Heald, G H; de Blok, W J G
    We present H i imaging of GBT 1355+5439 performed with the Westerbork Synthesis Radio Telescope. This is a dark H i object recently discovered close to the nearby galaxy M101. We find GBT 1355+5439 to be an H i cloud 5 × 3 arcmin in size. The total H i image and the kinematics show that the cloud consists of condensations that have small (~10 km s-1) motions with respect to each other. The column densities of the H i are low; the observed peak value is 7.1 × 1019 cm-2. The velocity field shows a mild velocity gradient over the body of GBT 1355+5439, possibly due to rotation, but it may also indicate large-scale radial motions. Although our data are limited in sensitivity, at all positions the H i velocity dispersion is higher than 5 km s-1 and no narrow, cold, H i component is seen. Because its distance is not known, we considered various possibilities for the nature of GBT 1355+5439. Both the scenarios that it is a tidal remnant near M101 and that it is a dark dwarf companion of M101 meet difficulties. Neither do the data fit the properties of known compact high-velocity clouds in the Galactic halo exactly, but we cannot entirely exclude this option and deeper observations are required. We also considered the possibility that GBT 1355+5439 is a gas-rich dark minihalo in the outer regions of the Local Group. Interestingly, it would then have similar properties as the clouds of a proposed Local Group population recently found in the ALFALFA survey. In this case, the H i mass of GBT 1355+5439 would be about a few times 105M⊙, its size about 1 kpc, and the dynamical mass Mdyn > 5 × 107M⊙. However, if GBT 1355+5439 is a dark Local Group object, the internal kinematics of the H i appears to be different from that of gas-dominated, almost dark galaxies of similar size.
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    Open Access
    The VLT-FLAMES Tarantula survey: XX. The nature of the X-ray bright emission-line star VFTS 399⋆
    (2015) Clark, J S; Bartlett, E S; Broos, P S; Townsley, L K; Taylor, W D; Walborn, N R; Bird, A J; Sana, H; de Mink, S E; Dufton, P L; Evans, C J; Langer, N; Maíz Apellániz, J; Schneider, F R N; Soszyński, I
    Context: The stellar population of the 30 Doradus star-forming region in the Large Magellanic Cloud contains a subset of apparently single, rapidly rotating O-type stars. The physical processes leading to the formation of this cohort are currently uncertain. Aims. One member of this group, the late O-type star VFTS 399, is found to be unexpectedly X-ray bright for its bolometric luminosity − in this study we aim to determine its physical nature and the cause of this behaviour. Methods. To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. Results. We found VFTS 399 to be an aperiodic photometric variable with an apparent near-IR excess. Its optical spectrum demonstrates complex emission profiles in the lower Balmer series and select He i lines − taken together these suggest an OeBe classification. The highly variable X-ray luminosity is too great to be produced by a single star, while the hard, non-thermal nature suggests the presence of an accreting relativistic companion. Finally, the detection of periodic modulation of the X-ray lightcurve is most naturally explained under the assumption that the accretor is a neutron star. Conclusions. VFTS 399 appears to be the first high-mass X-ray binary identified within 30 Dor, sharing many observational characteristics with classical Be X-ray binaries. Comparison of the current properties of VFTS 399 to binary-evolution models suggests a progenitor mass 25 M for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS 399 is now the second member of the cohort of rapidly rotating “single” O-type stars in 30 Dor to show evidence of binary interaction resulting in spin-up, suggesting that this may be a viable evolutionary pathway for the formation of a subset of this stellar population.
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    Open Access
    Understanding philanthrocapitalism and its impact on private nature reserves: A case study of Gorongosa, Mozambique
    (2022) Ochs, Tobias; Mbatha, Philile
    An increasing body of literature reveals that powerful businesspeople have a long history of using their wealth for the benefit of the greater common good. With philanthrocapitalism, a new generation of hands-on donors that have made incredible fortunes within business sectors like information technology or finance, are taking on the world's most pressuring social and environmental problem, willing to change the way of giving and enhancing traditional philanthropy. The rich entrepreneurs turned philanthropists are applying their skills and talents that have made them successful in business and infusing the charity sector with corporate tools and strategies and are getting personally engaged and using political and social networks to leverage their efforts. Driven to find solutions to the world's most severe problems, philanthrocapitalists tend to target problems that cut across national boundaries, such as AIDS, Malaria, illiteracy, and population growth. Next to these familiar fields such as health and education, philanthropists are also increasingly engaging in nature conservation. By establishing private nature reserves or taking over failed state-run nature reserves, elite donors are increasingly featuring neoliberal conservation and intervene in political ecology particularly in biodiversity hotspots in the global South. Notwithstanding philanthrocapitalism growing prominence and significance, broader public debates and academic literature is just emerging in recent years and the impact on nature conservation has received little scholarly attention. By examining the case of the Gorongosa Project (GP), a transnational nature conservation project that was established by U.S. multimillionaire Greg Carr in Mozambique, this thesis seeks to illustrate: a) how philanthrocapitalism influences nature conservation, b) how philanthrocapitalistic conservation projects work in practice and, c) enhance understanding about the implications of philanthrocapitalism in conservation governance, recognising its advantages and limitations. The thesis further seeks to contribute to the academic discourse as the far-reaching ventures of Western philanthrocapitalists have provoked a controversial debate. Advocates such as economists, journalists and political organisations argue that the financial power, unique business skills, resources and networks enable philanthrocapitalists to contribute to solving global issues more efficiently than other stakeholders. In contrast, critics from political or social sciences or conservation point out the increasing influence that wealthy philanthropists have on global policymaking as well as social and political agendas and have raised concerns about democratic values and power and wealth inequalities.