| 1. |
- Niessen, Peter, et al.
(author)
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Recent results from the amanda experiment
- 2003
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In: Proceedings of 38th Rencontres de Moriond on Electroweak Interactions and Unified Theories 15-22 Mar 2003. Les Arcs, France.
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Conference paper (peer-reviewed)abstract
- AMANDA (Antarctic Muon And Neutrino Detector Array) is a neutrino telescope built under the southern polar icecap and its scope is to explore the possibility to detect high energy cosmic neutrinos. This should generate insight into the powerful celestial objects where acceleration mechanisms can bring up to 10 20 eV. We describe the achievements and results from the AMANDA-B10 prototype and the preliminary results from the current AMANDA-II detector which show dramatic increase in sensitivity.
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| 2. |
- Tinetti, Giovanna, et al.
(author)
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The science of EChO
- 2010
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In: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 6:S276, s. 359-370
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Journal article (peer-reviewed)abstract
- The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spitzer, Hubble, and large ground-based telescopes the spectra of bright close-in massive planets can be obtained and species like water vapour, methane, carbon monoxide and dioxide have been detected. With transit science came the first tangible remote sensing of these planetary bodies and so one can start to extrapolate from what has been learnt from Solar System probes to what one might plan to learn about their faraway siblings. As we learn more about the atmospheres, surfaces and near-surfaces of these remote bodies, we will begin to build up a clearer picture of their construction, history and suitability for life. The Exoplanet Characterisation Observatory, EChO, will be the first dedicated mission to investigate the physics and chemistry of Exoplanetary Atmospheres. By characterising spectroscopically more bodies in different environments we will take detailed planetology out of the Solar System and into the Galaxy as a whole. EChO has now been selected by the European Space Agency to be assessed as one of four M3 mission candidates. © International Astronomical Union 2011.
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| 3. |
- Mentuch, Erin, et al.
(author)
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Lithium Depletion of Nearby Young Stellar Associations
- 2008
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 689, s. 1127-1140
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Journal article (peer-reviewed)abstract
- We estimate cluster ages from lithium depletion in five pre-main-sequence groups found within 100 pc of the Sun: the TW Hydrae association, η Chamaeleontis cluster, β Pictoris moving group, Tucanae-Horologium association, and AB Doradus moving group. We determine surface gravities, effective temperatures, and lithium abundances for over 900 spectra through least-squares fitting to model-atmosphere spectra. For each group, we compare the dependence of lithium abundance on temperature with isochrones from pre-main-sequence evolutionary tracks to obtain model-dependent ages. We find that the η Cha cluster and the TW Hydrae association are the youngest, with ages of 12+/-6 Myr and 12+/-8 Myr, respectively, followed by the β Pic moving group at 21+/-9 Myr, the Tucanae-Horologium association at 27+/-11 Myr, and the AB Dor moving group at an age of at least 45 Myr (whereby we can only set a lower limit, since the models-unlike real stars-do not show much lithium depletion beyond this age). Here the ordering is robust, but the precise ages depend on our choice of both atmospheric and evolutionary models. As a result, while our ages are consistent with estimates based on Hertzsprung-Russell isochrone fitting and dynamical expansion, they are not yet more precise. Our observations do show that with improved models, much stronger constraints should be feasible, as the intrinsic uncertainties, as measured from the scatter between measurements from different spectra of the same star, are very low: around 10 K in effective temperature, 0.05 dex in surface gravity, and 0.03 dex in lithium abundance.
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| 4. |
- Ludwig, Hans-Günter, et al.
(author)
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Convection and Dust in Cool Stellar Atmospheres
- 2003
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In: Stars as Suns: Activity, Evolution and Planets, International Astronomical Union. Symposium no. 219, held 21-25 July, 2003 in Sydney, Australia, meeting abstract. ; 219, s. 41-41
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Conference paper (peer-reviewed)abstract
- We report on recent progress in hydrodynamical modelling of the surfacelayers of late M- and L-type main- as well as pre-main-sequence objects.Despite the complex chemistry encountered in the cool atmospheres ofsuch objects a reasonably accurate representation of the radiativetransfer is possible - even within time-dependent multi-dimensionalmodels. The detailed treatment of the interplay between radiation andconvection in the hydrodynamical models allows us to study processesusually not accessible within the framework of conventional modelatmospheres. In particular we derive the efficiency of the convectiveenergy transport expressed in terms of an equivalent mixing-lengthparameter e.g. suitable to construct global stellar structure models.The models also provide an estimate of convective overshooting into theatmospheric layers which are formally stable according to theSchwarzschild criterion. Preliminary brown dwarf models incorporatingthe atmospheric condensation transport and evaporation of dust cloudswill be presented.
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| 5. |
- Lynch, David K., et al.
(author)
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NOVA V2362 CYGNI (NOVA CYGNI 2006): SPITZER, SWIFT, AND GROUND-BASED SPECTRAL EVOLUTION
- 2008
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In: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 136:number 5, 2008 November, s. 1815-1827
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Journal article (peer-reviewed)abstract
- Nova V2362 Cygni has undergone a number of very unusual changes. Ground-based spectroscopy initially revealed a normal sequence of events: the object faded and its near-infrared emission lines gradually shifted to higher excitation conditions until about day 100 when the optical fading reversed and the object slowly brightened. This was accompanied by a rise in the Swift X-ray telescope flux and a sudden shift in excitation of the visible and IR spectrum back to low levels. The new lower excitation spectrum revealed broad line widths and many P-Cygni profiles, all indicative of the ejection of a second shell. Eventually, dust formed, the X-ray brightness—apparently unaffected by dust formation—peaked and then declined, and the object faded at all wavelengths. The Spitzer dust spectra revealed a number of solid-state emission features that, at this time, are not identified.
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