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- Weigelt, G., et al.
(author)
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VLTI-MATISSE chromatic aperture-synthesis imaging of eta Carinae's stellar wind across the Br alpha line Periastron passage observations in February 2020
- 2021
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 652
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Journal article (peer-reviewed)abstract
- Context. Eta Carinae is a highly eccentric, massive binary system (semimajor axis similar to 15.5 au) with powerful stellar winds and a phase-dependent wind-wind collision (WWC) zone. The primary star, eta Car A, is a luminous blue variable (LBV); the secondary, eta Car B, is a Wolf-Rayet or O star with a faster but less dense wind. Aperture-synthesis imaging allows us to study the mass loss from the enigmatic LBV eta Car. Understanding LBVs is a crucial step toward improving our knowledge about massive stars and their evolution. Aims. Our aim is to study the intensity distribution and kinematics of eta Car's WWC zone. Methods. Using the VLTI-MATISSE mid-infrared interferometry instrument, we perform Br alpha imaging of eta Car's distorted wind. Results. We present the first VLTI-MATISSE aperture-synthesis images of eta Car A's stellar windin several spectral channels distributed across the Br alpha 4.052 mu m line (spectral resolving power R similar to 960). Our observations were performed close to periastron passage in February 2020 (orbital phase similar to 14.0022). The reconstructed iso-velocity images show the dependence of the primary stellar wind on wavelength or line-of-sight (LOS) velocity with a spatial resolution of 6 mas (similar to 14 au). The radius of the faintest outer wind regions is similar to 26 mas (similar to 60 au). At several negative LOS velocities, the primary stellar wind is less extended to the northwest than in other directions. This asymmetry is most likely caused by the WWC. Therefore, we see both the velocity field of the undisturbed primary wind and the WWC cavity. In continuum spectral channels, the primary star wind is more compact than in line channels. A fit of the observed continuum visibilities with the visibilities of a stellar wind CMFGEN model (CMFGEN is an atmosphere code developed to model the spectra of a variety of objects) provides a full width at half maximum fit diameter of the primary stellar wind of 2.84 +/- 0.06 mas (6.54 +/- 0.14 au). We comparethe derived intensity distributions with the CMFGEN stellar wind model and hydrodynamic WWC models.
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| 4. |
- Rajpurohit, A. S., et al.
(author)
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The very low mass multiple system LHS 1070. A testbed for model atmospheres for the lower end of the main sequence
- 2012
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 545
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Journal article (peer-reviewed)abstract
- Context. LHS 1070 is a nearby multiple system of low mass stars. It is an important source of information for probing the low mass end of the main sequence, down to the hydrogen-burning limit. The primary of the system is a mid-M dwarf and two components are late-M to early L dwarfs, at the star-brown dwarf transition. Hence LHS 1070 is a valuable object to understand the onset of dust formation in cool stellar atmospheres. Aims. This work aims at determining the fundamental stellar parameters of LHS 1070 and to test recent model atmospheres: BT-Dusty, BT-Settl, DRIFT, and MARCS models. Methods. Unlike in previous studies, we have performed a chi(2)-minimization comparing well calibrated optical and infrared (IR) spectra with recent cool star synthetic spectra leading to the determination of the physical stellar parameters T-eff, radius, and log g for each of the three components of LHS 1070. Results. With exception of the MARCS models which do not include dust formation, the models are able to reproduce the observations and describe the main features of the visible to IR spectra. This is consistent with the fact that dust formation prevails in the B and C component atmospheres. The parameters obtained with the DRIFT models confirm the values determined in earlier studies. But important differences between models are observed, where the MARCS model is too bright in the H and K bands, and the BT-Settl and BT-Dusty models systematically yield up to 100 K higher T-eff in the case of the B and C components. This confirms a trend for models without, or with less efficient cloud formation, to predict higher T-eff than models richer in dust (DRIFT). Even models including cloud physics however still produce slightly too bright J band flux, showing as too blue J - K colors. The onset of dust formation remains therefore a particularly challenging regime to understand.
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| 5. |
- Stoll-Kleemann, S., et al.
(author)
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The role of community participation in the effectiveness of UNESCO Biosphere Reserve management : evidence and reflections from two parallel global surveys
- 2010
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In: Environmental Conservation. - 0376-8929 .- 1469-4387. ; 37:3, s. 227-238
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Journal article (peer-reviewed)abstract
- Biodiversity management has traditionally followed two contradictory approaches. One champions ecosystem protection through rigorous law enforcement and exclusion of humans. The other promotes community-based sustainable use of natural resources. Participatory conservation, a major paradigm shift, nowadays strongly guides the concept of UNESCO Biosphere Reserves (BRs). In this paper, the rationale for community participation, and the perception of its effectiveness among BR managers are analysed. Within the World Network of BRs (553 sites in 107 countries) diverse participatory approaches are being tried to advance community-based natural resource management (CBNRM). Data from two parallel surveys, involving managers from 276 BRs worldwide, reveal how far this participation paradigm shift has really occurred, and its influence on managers' self-evaluated effectiveness. There is substantial regional disparity, although in general BR managers endorse inclusive conservation, despite critical implementation hurdles. The process of participatory conservation carries new dangers for effective biosphere reserve management, when the aspirations of communities and other stakeholders do not 'fit' with a predetermined interpretation of sustainable development.
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