66 research outputs found
Testing the predicted mass-loss bi-stability jump at radio wavelengths
In this study, we test the theoretically predicted mass-loss behaviour as a
function of stellar effective temperature across the so-called `bi-stability'
jump (BSJ). We gathered radio observations of 30 OB supergiants (O8-B3). We
derived the radio mass-loss rates and wind efficiencies, and compared our
results with Halpha mass-loss rates and predictions based on radiation-driven
wind models. he wind efficiency shows the possible presence of a local maximum
around an effective temperature of 21~000 K -- in qualitative agreement with
predictions. We also find that the radio mass-loss rates show good agreement
with empirical Halpha rates. However, the empirical mass-loss rates are larger
than the predicted rates from radiation-driven wind theory for objects above
the BSJ temperature, whilst they are smaller for the rest. A new wind
momenta-luminosity relation for O8-B0 stars has been derived.Comment: 13 pages, 13 figures, A&
Natural Diagonal Riemannian Almost Product and Para-Hermitian Cotangent Bundles
We obtain the natural diagonal almost product and locally product structures
on the total space of the cotangent bundle of a Riemannian manifold. We find
the Riemannian almost product (locally product) and the (almost) para-Hermitian
cotangent bundles of natural diagonal lift type. We prove the characterization
theorem for the natural diagonal (almost) para-K\"ahlerian structures on the
total spaces of the cotangent bundle.Comment: 10 pages, will appear in Czechoslovak Mathematical Journa
Managerial Views of Corporate Impacts and Dependencies on Ecosystem Services : A Case of International and Domestic Forestry Companies in China
A line of research is emerging investigating the private sector impacts and dependencies on critical biodiversity and ecosystem services, and related business risks and opportunities. While the ecosystem services narrative is being forwarded globally as a key paradigm for promoting business sustainability, there is scarce knowledge of how these issues are considered at managerial level. This study thus investigates managerial views of corporate sustainability after the ecosystem services concept. We analyse interviews conducted with 20 managers from domestic and international forestry companies operating with a plantation-based business model in China. Content analysis was employed to analyse the data, with a focus on four key areas: (1) interviewee familiarity with the ecosystem services concept; (2) their views of corporate dependencies and impacts on ecosystem services; (3) related business risks and opportunities; and (4) viability of existing instruments and practices that can be employed in detecting and addressing business impacts and dependencies on ecosystem services. Through an inductive approach to the empirical findings, we refined a framework that holds operational value for developing company response strategies to ecosystem services impact/dependence assessment, ensuring that all issues are addressed comprehensively, and that related risks and opportunities are properly acknowledged.Peer reviewe
Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)
Aims: We look for new regions for the search of substellar objects. Methods:
Two circular areas, 45 arcmin-radius each, centred on the young massive star
systems Alnilam and Mintaka in the Orion Belt, have been explored. The regions
are very young (less than 10 Ma), have low extinction, and are neighbours to
sigma Orionis (~3 Ma), a young open cluster very rich in brown dwarfs and
planetary-mass objects. We have used Virtual Observatory tools, the
astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at
similar galactic latitudes, and X-ray, mid-infrared and spectroscopic data from
the literature. Results: We have compiled exhaustive lists of known young stars
and new candidate members in the Ori OB1b association, and of fore- and
background sources. A total of 136 stars display features of extreme youth,
like early spectral types, lithium in absorption, or mid-infrared flux excess.
Other two young brown dwarf and 289 star candidates have been identified from
an optical/near-infrared colour-magnitude diagram. We list additional 74 known
objects that might belong to the association. This catalogue can serve as an
input for characterisation of the stellar and high-mass substellar populations
in the Orion Belt. Finally, we have investigated the surface densities and
radial distributions of young objects surrounding Alnilam and Mintaka, and
compared them with those in the sigma Orionis cluster. We report a new open
cluster centred on Mintaka. Conclusions: Both regions can be analogs to the
sigma Orionis cluster, but more massive, more extended, slightly older, and
less radially concentrated.Comment: Accepted for publication in A&A. It will be published on line in
Sect. 14 (Catalogs and data). Tables in Appendix A will soon be available at
the CD
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