@article{ArridgeAchilleosAgarwaletal.2014, author = {Arridge, Christopher S. and Achilleos, N. and Agarwal, Jessica and Agnor, C. B. and Ambrosi, R. and Andre, N. and Badman, S. V. and Baines, K. and Banfield, D. and Barthelemy, M. and Bisi, M. M. and Blum, J. and Bocanegra-Bahamon, T. and Bonfond, B. and Bracken, C. and Brandt, P. and Briand, C. and Briois, C. and Brooks, S. and Castillo-Rogez, J. and Cavalie, T. and Christophe, B. and Coates, Andrew J. and Collinson, G. and Cooper, John F. and Costa-Sitja, M. and Courtin, R. and Daglis, I. A. and De Pater, Imke and Desai, M. and Dirkx, D. and Dougherty, M. K. and Ebert, R. W. and Filacchione, Gianrico and Fletcher, Leigh N. and Fortney, J. and Gerth, I. and Grassi, D. and Grodent, D. and Gr{\"u}n, Eberhard and Gustin, J. and Hedman, M. and Helled, R. and Henri, P. and Hess, Sebastien and Hillier, J. K. and Hofstadter, M. H. and Holme, R. and Horanyi, M. and Hospodarsky, George B. and Hsu, S. and Irwin, P. and Jackman, C. M. and Karatekin, O. and Kempf, Sascha and Khalisi, E. and Konstantinidis, K. and Kruger, H. and Kurth, William S. and Labrianidis, C. and Lainey, V. and Lamy, L. L. and Laneuville, Matthieu and Lucchesi, D. and Luntzer, A. and MacArthur, J. and Maier, A. and Masters, A. and McKenna-Lawlor, S. and Melin, H. and Milillo, A. and Moragas-Klostermeyer, Georg and Morschhauser, Achim and Moses, J. I. and Mousis, O. and Nettelmann, N. and Neubauer, F. M. and Nordheim, T. and Noyelles, B. and Orton, G. S. and Owens, Mathew and Peron, R. and Plainaki, C. and Postberg, F. and Rambaux, N. and Retherford, K. and Reynaud, Serge and Roussos, Elias and Russell, C. T. and Rymer, Am. and Sallantin, R. and Sanchez-Lavega, A. and Santolik, O. and Saur, J. and Sayanagi, Km. and Schenk, P. and Schubert, J. and Sergis, N. and Sittler, E. C. and Smith, A. and Spahn, Frank and Srama, Ralf and Stallard, T. and Sterken, V. and Sternovsky, Zoltan and Tiscareno, M. and Tobie, G. and Tosi, F. and Trieloff, M. and Turrini, D. and Turtle, E. P. and Vinatier, S. and Wilson, R. and Zarkat, P.}, title = {The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets}, series = {Planetary and space science}, volume = {104}, journal = {Planetary and space science}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-0633}, doi = {10.1016/j.pss.2014.08.009}, pages = {122 -- 140}, year = {2014}, abstract = {Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99\% of the mass of the Sun's planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus' atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency's call for science themes for its large-class mission programme in 2013.}, language = {en} } @article{SramaKruegerYamaguchietal.2012, author = {Srama, Ralf and Krueger, H. and Yamaguchi, T. and Stephan, T. and Burchell, M. and Kearsley, A. T. and Sterken, V. and Postberg, F. and Kempf, S. and Gr{\"u}n, Eberhard and Altobelli, Nicolas and Ehrenfreund, P. and Dikarev, V. and Horanyi, M. and Sternovsky, Zoltan and Carpenter, J. D. and Westphal, A. and Gainsforth, Z. and Krabbe, A. and Agarwal, Jessica and Yano, H. and Blum, J. and Henkel, H. and Hillier, J. and Hoppe, P. and Trieloff, M. and Hsu, S. and Mocker, A. and Fiege, K. and Green, S. F. and Bischoff, A. and Esposito, F. and Laufer, R. and Hyde, T. W. and Herdrich, G. and Fasoulas, S. and Jaeckel, A. and Jones, G. and Jenniskens, P. and Khalisi, E. and Moragas-Klostermeyer, Georg and Spahn, Frank and Keller, H. U. and Frisch, P. and Levasseur-Regourd, A. C. and Pailer, N. and Altwegg, K. and Engrand, C. and Auer, S. and Silen, J. and Sasaki, S. and Kobayashi, M. and Schmidt, J. and Kissel, J. and Marty, B. and Michel, P. and Palumbo, P. and Vaisberg, O. and Baggaley, J. and Rotundi, A. and Roeser, H. P.}, title = {SARIM PLUS-sample return of comet 67P/CG and of interstellar matter}, series = {EXPERIMENTAL ASTRONOMY}, volume = {33}, journal = {EXPERIMENTAL ASTRONOMY}, number = {2-3}, publisher = {SPRINGER}, address = {DORDRECHT}, issn = {0922-6435}, doi = {10.1007/s10686-011-9285-7}, pages = {723 -- 751}, year = {2012}, abstract = {The Stardust mission returned cometary, interplanetary and (probably) interstellar dust in 2006 to Earth that have been analysed in Earth laboratories worldwide. Results of this mission have changed our view and knowledge on the early solar nebula. The Rosetta mission is on its way to land on comet 67P/Churyumov-Gerasimenko and will investigate for the first time in great detail the comet nucleus and its environment starting in 2014. Additional astronomy and planetary space missions will further contribute to our understanding of dust generation, evolution and destruction in interstellar and interplanetary space and provide constraints on solar system formation and processes that led to the origin of life on Earth. One of these missions, SARIM-PLUS, will provide a unique perspective by measuring interplanetary and interstellar dust with high accuracy and sensitivity in our inner solar system between 1 and 2 AU. SARIM-PLUS employs latest in-situ techniques for a full characterisation of individual micrometeoroids (flux, mass, charge, trajectory, composition()) and collects and returns these samples to Earth for a detailed analysis. The opportunity to visit again the target comet of the Rosetta mission 67P/Churyumov-Gerasimeenternko, and to investigate its dusty environment six years after Rosetta with complementary methods is unique and strongly enhances and supports the scientific exploration of this target and the entire Rosetta mission. Launch opportunities are in 2020 with a backup window starting early 2026. The comet encounter occurs in September 2021 and the reentry takes place in early 2024. An encounter speed of 6 km/s ensures comparable results to the Stardust mission.}, language = {en} } @inproceedings{MoffatHillierHamannetal.2007, author = {Moffat, Anthony F. J. and Hillier, D. J. and Hamann, Wolf-Rainer and Owocki, S. P.}, title = {General Discussion}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17953}, year = {2007}, abstract = {Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007}, language = {en} } @inproceedings{GrohHillierDamineli2007, author = {Groh, J. H. and Hillier, D. J. and Damineli, A.}, title = {Mass-loss rate and clumping in LBV stars : the impact of time-dependent effects}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17773}, year = {2007}, abstract = {This paper outlines a newly-developed method to include the effects of time variability in the radiative transfer code CMFGEN. It is shown that the flow timescale is often large compared to the variability timescale of LBVs. Thus, time-dependent effects significantly change the velocity law and density structure of the wind, affecting the derivation of the mass-loss rate, volume filling factor, wind terminal velocity, and luminosity. The results of this work are directly applicable to all active LBVs in the Galaxy and in the LMC, such as AG Car, HR Car, S Dor and R 127, and could result in a revision of stellar and wind parameters. The massloss rate evolution of AG Car during the last 20 years is presented, highlighting the need for time-dependent models to correctly interpret the evolution of LBVs.}, language = {en} } @inproceedings{NajarroPulsHerreroetal.2007, author = {Najarro, F. and Puls, Joachim and Herrero, A. and Hanson, M. M. and Mart{\´i}n-Pintado, J. and Hillier, D. J.}, title = {Tracking the Clumping in OB Stars from UV to radio}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17701}, year = {2007}, abstract = {We review different line and continua diagnostics from the UV to radio, which can be utilized to simultaneously constrain the clumping structure throughout the stellar wind of massive OB stars.}, language = {en} } @article{PostbergSchmidtHillieretal.2011, author = {Postberg, Frank and Schmidt, J. and Hillier, J. and Kempf, Sascha and Srama, Ralf}, title = {A salt-water reservoir as the source of a compositionally stratified plume on Enceladus}, series = {Nature : the international weekly journal of science}, volume = {474}, journal = {Nature : the international weekly journal of science}, number = {7353}, publisher = {Nature Publ. Group}, address = {London}, issn = {0028-0836}, doi = {10.1038/nature10175}, pages = {620 -- 622}, year = {2011}, abstract = {The discovery of a plume of water vapour and ice particles emerging from warm fractures ('tiger stripes') in Saturn's small, icy moon Enceladus(1-6) raised the question of whether the plume emerges from a subsurface liquid source(6-8) or from the decomposition of ice(9-12). Previous compositional analyses of particles injected by the plume into Saturn's diffuse E ring have already indicated the presence of liquid water(8), but the mechanisms driving the plume emission are still debated(13). Here we report an analysis of the composition of freshly ejected particles close to the sources. Salt-rich ice particles are found to dominate the total mass flux of ejected solids (more than 99 per cent) but they are depleted in the population escaping into Saturn's E ring. Ice grains containing organic compounds are found to be more abundant in dense parts of the plume. Whereas previous Cassini observations were compatible with a variety of plume formation mechanisms, these data eliminate or severely constrain non-liquid models and strongly imply that a salt-water reservoir with a large evaporating surface(7,8) provides nearly all of the matter in the plume.}, language = {en} } @inproceedings{BouretLanzHillieretal.2007, author = {Bouret, J.-C. and Lanz, T. and Hillier, D. J. and Foellmi, C.}, title = {Clumping in O-type Supergiants}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17662}, year = {2007}, abstract = {We have analyzed the spectra of seven Galactic O4 supergiants, with the NLTE wind code CMFGEN. For all stars, we have found that clumped wind models match well lines from different species spanning a wavelength range from FUV to optical, and remain consistent with Hα data. We have achieved an excellent match of the P V λλ1118, 1128 resonance doublet and N IV λ1718, as well as He II λ4686 suggesting that our physical description of clumping is adequate. We find very small volume filling factors and that clumping starts deep in the wind, near the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more compared to those obtained from smooth-wind models.}, language = {en} } @inproceedings{Hillier2007, author = {Hillier, D. J.}, title = {On the influence of clumping on O and Wolf-Rayet spectra}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17903}, year = {2007}, abstract = {Overwhelming observational and theoretical evidence suggests that the winds of massive stars are highly clumped. We briefly discuss the influence of clumping on model diagnostics and the difficulties of allowing for the influence of clumping on model spectra. Because of its simplicity, and because of computational ease, most spectroscopic analyses incorporate clumping using the volume filling factor. The biases introduced by this approach are uncertain. To investigate alternative clumping models, and to help determine the validity of parameters derived using the volume filling factor method, we discuss results derived using an alternative model in which we assume that the wind is composed of optically thick shells.}, language = {en} } @article{GraefenerHamannHillieretal.1998, author = {Gr{\"a}fener, G{\"o}tz and Hamann, Wolf-Rainer and Hillier, D. J. and Koesterke, Lars}, title = {Spectral analyses of WC stars in the LMC}, year = {1998}, language = {en} } @article{Hillier2015, author = {Hillier, D. J.}, title = {Spectrum formation in Wolf-Rayet stars}, series = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015}, journal = {Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.-5. June 2015}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-87669}, pages = {65 -- 70}, year = {2015}, abstract = {We highlight the basic physics that allows fundamental parameters, such as the effective temperature, luminosity, abundances, and mass-loss rate, of Wolf-Rayet (W-R) stars to be determined. Since the temperature deduced from the spectrum of a W-R star is an ionization temperature, a detailed discussion of the ionization structure of W-R winds, and how it is set, is given. We also provide an overview of line and continuum formation in W-R stars. Mechanisms that contribute to the strength of different emission lines, such as collisional excitation, radiative recombination, dielectronic recombination, and continuum uorescence, are discussed.}, language = {en} }