Now showing items 1-20 of 43

    • An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet 

      Nikolov, N.; Sing, D. K.; Fortney, J. J.; Goyal, J. M.; Drummond, B.; Evans, T. M.; Gibson, N. P.; De Mooj, E. J. W.; Rustamkulov, Z.; Wakeford, H. R.; Smalley, B.; Burgasser, A. J.; Hellier, C.; Helling, Christiane; Mayne, N. J.; Madhusudhan, N.; Kataria, T.; Baines, J.; Carter, A. L.; Ballester, G. E.; Barstow, J. K.; McCleery, J.; Spake, J. J. (2018-05-07) - Journal article
      Broad absorption signatures from alkali metals, such as the sodium (Na i) and potassium (K i) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1,2,3. ...
    • Atmospheres of brown dwarfs 

      Helling, Christiane; Casewell, Sarah (2014) - Journal item
      Brown Dwarfs are the coolest class of stellar objects known to date. Our present perception is that Brown Dwarfs follow the principles of star formation, and that Brown Dwarfs share many characteristics with planets. Being ...
    • Atmospheric electrification in dusty, reactive gases in the solar system and beyond 

      Helling, Christiane; Harrison, R. Giles; Honary, Farideh; Diver, Declan A.; Aplin, Karen; Dobbs-Dixon, Ian; Ebert, Ute; Inutsuka, Shu-ichiro; Gordillo-Vazquez, Francisco J.; Littlefair, Stuart (2016-07) - Journal item
      Detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. Astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar ...
    • A chemical kinetics network for lightning and life in planetary atmospheres 

      Rimmer, Paul; Helling, Christiane (2016-05) - Journal article
      There are many open questions about prebiotic chemistry in both planetary and exoplanetary environments. The increasing number of known exoplanets and other ultra-cool, substellar objects has propelled the desire to detect ...
    • Comparison Catalogue of Gas-Equilibrium Constants, Kp 

      Worters, Megan; Millard, Drew; Hunter, Glen; Helling, Christiane; Woitke, Peter (University of St Andrews, 2017) - Other
    • Direct Imaging discovery of a second planet candidate around the possibly transiting planet host CVSO 30 

      Schmidt, T. O. B.; Neuhäuser, R.; Briceño, C.; Vogt, N.; Raetz, St; Seifahrt, A.; Ginski, C.; Mugrauer, M.; Buder, S.; Adam, C.; Hauschildt, P. H.; Witte, S.; Helling, Christiane; Schmitt, J. H. M. M. (2016-09) - Journal article
      We surveyed the 25 Ori association for direct-imaging companions. This association has an age of only few million years. Among other targets, we observed CVSO 30, which has recently been identified as the first T Tauri ...
    • Dust cloud lightning in extraterrestrial atmospheres 

      Helling, Christiane; Jardine, Moira Mary; Diver, Declan; Witte, Sören (2013-03-01) - Journal article
      Lightning is present in all solar system planets which form clouds in their atmospheres. Cloud formation outside our solar system is possible in objects with much higher temperatures than on Earth or on Jupiter: Brown ...
    • Dust in brown dwarfs and extra-solar planets : VI. Assessing seed formation across the brown dwarf and exoplanet regimes 

      Lee, Graham K. H.; Blecic, Jasmina; Helling, Christiane (2018) - Journal article
      Context. The cloud formation process starts with the formation of seed particles, after which, surface chemical reactions grow or erode the cloud particles. If seed particles do not form, or are not available by another ...
    • Dust in brown dwarfs and extra-solar planets. IV. Assessing TiO2 and SiO nucleation for cloud formation modelling 

      Lee, G.; Helling, Christiane; Giles, H.; Bromley, S. T. (2015-03) - Journal article
      Clouds form in atmospheres of brown dwarfs and planets. The cloud particle formation processes are similar to the dust formation process studied in circumstellar shells of AGB stars and in Supernovae. Cloud formation ...
    • Electron acceleration above thunderclouds 

      Fuellekrug, Martin; Kolmasova, Ivana; Santolik, Ondrej; Farges, Thomas; Bor, Jozsef; Bennett, Alec; Parrot, Michel; Rison, William; Zanotti, Ferruccio; Arnone, Enrico; Mezentsev, Andrew; Lan, Radek; Uhlir, Ludek; Harrison, Giles; Soula, Serge; van der Velde, Oscar; Pincon, Jean-Louis; Helling, Christiane; Diver, Declan (2013-08-13) - Journal article
      The acceleration of electrons results in observable electromagnetic waves which can be used for remote sensing. Here, we make use of similar to 4 Hz-66 MHz radio waves emitted by two consecutive intense positive lightning ...
    • Electrostatic activation of prebiotic chemistry in substellar atmospheres 

      Stark, Craig Ronald; Helling, Christiane; Diver, Declan A; Rimmer, Paul (2014-04) - Journal article
      Charged dust grains in the atmospheres of exoplanets may play a key role in the formation of prebiotic molecules, necessary to the origin of life. Dust grains submerged in an atmospheric plasma become negatively charged ...
    • Environmental effects on the ionisation of brown dwarf atmospheres 

      Rodríguez-Barrera, M. Isabel; Helling, Christiane; Wood, Kenneth (2018-10) - Journal article
      Context. Brown dwarfs emit bursts of Hα, white-light flares, and show radio flares and quiescent radio emission. They are suggested to form aurorae, similar to planets in the solar system, but much more energetic. All these ...
    • Equlibrium chemistry down to 100 K : impact of silicates and phyllosilicates on carbon/oxygen ration 

      Woitke, Peter; Helling, Christiane; Hunter, G.H.; Millard, J.D.; Turner, G.E.; Worters, M.; Blecic, J.; Stock, J.W. (2018-06) - Journal article
      We have introduced a fast and versatile computer code, GGchem, to determine the chemical composition of gases in thermo-chemical equilibrium down to 100 K, with or without equilibrium condensation. We have reviewed the ...
    • Expect the unexpected : non-equilibrium processes in brown dwarf atmospheres 

      Helling, Christiane (2014-07-17) - Journal article
      Brown Dwarf atmosphere are a chemically extremely rich, one example being the formation of clouds driven by the phase-non-equilibrium of the atmospheric gas. Cloud formation modelling is an integral part of any atmosphere ...
    • The first millimeter detection of a non-accreting ultracool dwarf 

      Williams, P. K. G.; Casewell, Sarah L.; Stark, Craig Ronald; Littlefair, S. P.; Helling, Christiane; Berger, E. (2015-12-09) - Journal article
      The well-studied M9 dwarf TVLM 513–46546 is a rapid rotator (Prot ∼ 2 hr) hosting a stable, dipolar magnetic field of ∼3 kG surface strength. Here we report its detection with ALMA at 95 GHz at a mean flux density of 56 ± ...
    • First spectroscopic observations of the substellar companion of the young debris disk star PZ Telescopii 

      Schmidt, T.O.B.; Mugrauer, M.; Neuhäuser, R.; Vogt, N.; Witte, S.; Hauschildt, P.H.; Helling, Christiane; Seifahrt, A. (2014-06-20) - Journal article
      Context. In 2010 a substellar companion to the solar analog pre-main sequence star PZ Tel and member of the approximately 12 Myr old beta Pic moving group was found by high-contrast direct imaging independently by two ...
    • Flash ionization signature in coherent cyclotron emission from brown dwarfs 

      Vorgul, Iryna; Helling, Christiane (2016-05-01) - Journal article
      Brown dwarfs (BDs) form mineral clouds in their atmospheres, where charged particles can produce large-scale discharges in the form of lightning resulting in substantial sudden increase of local ionization. BDs are observed ...
    • Glass rain : modelling the formation, dynamics and radiative-transport of cloud particles in hot Jupiter exoplanet atmospheres 

      Lee, Graham Kim Huat (University of St Andrews, 2017-12-07) - Thesis
      The atmospheres of exoplanets are being characterised in increasing detail by observational facilities and will be examined with even greater clarity with upcoming space based missions such as the James Webb Space Telescope ...
    • Graphical Comparison of Mineral Gibbs Free Energy Data 

      Woitke, Peter; Helling, Christiane; Turner, George (University of St Andrews, 2017) - Other
      The following pages show plots of the Gibbs-free energy of formation ΔGӨf [kJ/mol] from free atoms as function of temperature T [K] of 121 solid minerals from the SUPCRTBL database (Zimmer et al., 2016). These thermo-chemical ...
    • The influence of non-isotropic scattering of thermal radiation on spectra of brown dwarfs and hot exoplanets 

      de Kok, R. J.; Stam, D. M.; Woitke, Peter; Witte, S.; Helling, Christiane (2011-07) - Journal article
      Context. Currently, the thermal emission from exoplanets can be measured with either direct imaging or secondary eclipse measurements of transiting exoplanets. Most of these measurements are taken at near-infrared wavelengths, ...