Now showing items 1-20 of 35

  • 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. 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 ...
  • 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. (2017-12-02) - Journal article
    We introduce a fast and versatile computer code, GG chem, to determine the chemical composition of gases in thermo-chemical equilibrium down to 100 K, with or without equilibrium condensation. We review the data for molecular ...
  • 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, ...
  • Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres 

    Stark, Craig Ronald; Helling, Christiane; Diver, D. A. (2015-07) - Journal article
    Context. Recent observations of brown dwarf spectroscopic variability in the infrared infer the presence of patchy cloud cover. Aims. This paper proposes a mechanism for producing inhomogeneous cloud coverage due to the ...
  • Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets 

    Helling, Christiane; Rimmer, Paul B.; Rodriguez-Barrera, Maria Isabel; Wood, Kenny; Robertson, G. B.; Stark, C. R. (2016-07) - Journal article
    Brown dwarfs and giant gas extrasolar planets have cold atmospheres with a rich chemical compositions from which mineral cloud particles form. Their properties, like particle sizes and material composition, vary with height, ...
  • Ionisation in atmospheres of Brown Dwarfs and extrasolar planets II Dust-induced collisional ionization 

    Helling, Christiane; Jardine, M.; Mokler, F. (2011-08-10) - Journal article
    Observations have shown that continuous radio emission and also sporadic Ha and X-ray emission are prominent in singular, low-mass objects later than spectral class M. These activity signatures are interpreted as being ...