My Science

Dust ionises usually quit easily. But what is ‘usual’ with respect to dust ionisation in the very cold atmospheres of Brown Dwarfs and planets? Intuitively, such cold gases should be rather neutral … but why do planets than produce lightning?

I am interested in the physics and chemistry of substellar atmospheres, that are atmospheres of Brown Dwarfs and Giant Gas Planets. These objects have the particularity of forming dust clouds in their atmosphere much as we know it from our Earth, except that the chemistry is very different. This different chemistry makes it quit a challenge since the one-to-one translation of terrestrial cloud and atmosphere models does not work. Also turbulence plays a role, a topic with which already Heisenberg struggled during his PhD.

The need to predict the spectral appearance of Brown Dwarfs and planets has lead to a variety of cloud model approaches. Our kinetic approach (DRIFT + more details below) that combines phase-non-equilibrium dust formation and drift (rain!) has lead to the development of DRIFT-PHOENIX in collaboration with the PHOENIX-group in Hamburg and to DRIFT-MARCS with the exoplanet/cool stars group at the University of Copenhagen/Niels-Bohr-Insitute. For more details and possible downloads see “My Science” (below) and the LEAP Blog for the World . I’ve organised a workshop comparing the respective model atmosphere results which are published here .

Applying our kwowledge in a variety of fields is key to progress, for example,  the irradiated planet WASP-12b and its assymetric ingress , linking to laboratory knowledge that can help understand other worlds with their glittery clouds , or substellar atmospheres at very low metalicities in the early universe.

Material quantities are importent input parameter for models of all kinds (atmospheres, winds, disks, stellar evolution). I’ve worked on statistical methods (opacity sampling), modelling of time-dependent AGB-stars wind and disk structures, all related to the treatment of molecular opacities. The mean opacity tables were updated for recent solar abundances and extended into the low-metalicity regime.

Ionisation and lightning in dusty atmospheres of low-mass objects

Dust ionised usually quit easily. But what is usual with respect to dust ionisation in the very cold atmospheres of Brown Dwarfs and planets? Intuitively, one would expect such cold gases to be rather neutral …


Helling Ch., Harrison R.G., Honary F., Diver D.A., Aplin K., Dobbs-Dixon I., Ebert U., Inutsuka S., Gordillo-Vazquez F.J.. Littlefair S. (2016)
Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

Ardaseva A., Rimmer P. B., Waldmann I., Rocchetto M., Yurchenko S. N., Helling Ch., Tennyson J. (2017)
Lightning chemistry on Earth-like exoplanets

Helling Ch., Rimmer P.B., Rodriguez-Barrera I.M., Wood K., Robertson G.B., Stark C.R. (2016)
Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets

Hodosan G., Helling Ch., Asensio-Torres R., Vorgul I., Rimmer P.B. (2016):
Lightning climatology of exoplanets and brown dwarfs guided by Solar System data

Hodosán G., Rimmer P.B., Helling Ch. (2016):
Is lightning a possible source of the radio emission on HAT-P-11b?

Helling Ch., Rimmer P.B., Rodriguez-Barrera I.M., Wood Kenneth, Robertson G.B., Stark C.R. (2016):
Ionisation and discharge in cloud-forming atmospheres of brown dwarfs and extrasolar planets

Vorgul I., Helling, Ch. (2016):
Flash ionisation signature in coherent cyclotron emission from Brown Dwarfs

Rodríguez-Barrera M. I., Helling Ch., Stark C. R., Rice A. M. (2015):
Reference study to characterize plasma and magnetic properties of ultracool atmospheres

Stark C. R., Helling Ch., Diver D. A. (2015):
Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres

Casewell S. L., Lawrie K. A., Maxted P. F. L., Marley M. S., Fortney J. J., Rimmer P. B., Littlefair S. P., Wynn G., Burleigh M. R., Helling, Ch. (2014)
Multiwaveband photometry of the irradiated brown dwarf WD0137-349B

Rimmer P. B., Stark C. R., Helling Ch. (2014)
Jupiter as a Giant Cosmic Ray Detector

Bailey R. L., Helling Ch., Hodosán G., Bilger C., Stark C. R. (2014)
Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets VI: Properties of Large-scale Discharge Events

Füllekrug M., Kolmasova I., Santolik O., Farges T., Bór J., Bennett A., Parrot M., Rison W., Zanotti F., Arnone E., Mezentsev A., Lan R., Uhlir L., Harrison G., Soula S., van der Velde O., Pinçon J.-L., Helling Ch., Diver D. (2013)
Electron acceleration above thunderclouds

Rimmer P. B., Helling Ch., Bilger, C. (2013, The Int. Journal of Astrobiology)
The Influence of Galactic Cosmic Rays on Ion-Neutral Hydrocarbon Chemistry in the Upper Atmospheres of Free-Floating Exoplanets

Stark C. R., Helling Ch., Diver D. A., Rimmer, P. B. (2013, The Int. Journal of Astrobiology)
Electrostatic activation of prebiotic chemistry in substellar atmospheres

Stark C. R., Helling Ch., Diver D. A., Rimmer, P. B. (2013, ApJ)
Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets V: Alfven Ionization

Rimmer P., Helling Ch. (2013, ApJ):
Ionization in atmospheres of Brown Dwarfs and extrasolar planets IV. The Effect of Cosmic Rays

Helling Ch., Jardine M., Stark C., Diver D. (2013):
Ionisation in atmospheres of Brown Dwarfs and extrasolar planets
III. Breakdown conditions for mineral clouds

Füllekrug M., Diver D., Pinçon J.-L., Phelps A. D. R., Bourdon A., Helling Ch., Blanc E., Honary F., Harrison R. G., Sauvaud J.-A., Renard J.-B., Lester M., Rycroft M., Kosch M., Horne R. B., Soula S., Gaffet S. (2013)
Energetic Charged Particles Above Thunderclouds

Helling Ch., Jardine M., Diver D., Witte S. (2012):
Dust cloud lightning in extraterrestrial atmospheres 2013 , P&SS, 77, 152 (part of EPSC-DPS Joint Meeting 2011)

Helling Ch., Jardine M., Mockler F (2011):
Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets
II Dust-induced collisional ionization

Helling Ch., Jardine M., Witte F., Diver (2010):
Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets
I. The Role of Electron Avalanche

Gas-phase chemistry

Woitke P., Helling Ch., Hunter G. H., Millard J. D., Turner G. E., Worters M., Blecic J., Stock J. W. (2017):
Equilibrium chemistry down to 100 K – Impact of silicates and phyllosilicates on carbon/oxygen ratio

Rimmer P.B, Helling Ch. (2015):
A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres (STAND2015)

Bilger C., Rimmer P., Helling Ch. (2013, MNRAS):
Small hydrocarbon molecules in cloud-forming Brown Dwarf and giant gas planet atmospheres

Pluto’s atmosphere

Greaves J. S., Helling Ch., Friberg P. (2011):
Discovery of carbon monoxide in the upper atmosphere of Pluto

Light-curve asymmetries in transiting planet-star systems

WASP-12b is the first planet showing an early ingress in the near-UV (Fossati et al. 2010) compared to the optical transit light curve (Hebb et al. 2009 ).
Here are arguments for the appearance of an early ingress and potential uses of it:

Llama J., Wood K., Jardine M., Vidotto A. A., Helling Ch., Fossati L., Haswell C. A. (2011)
The shocking transit of WASP-12b: modelling the observed early ingress in the near-ultraviolet

Vidotto A.A., Llama J., Jardine M., Helling Ch., Wood K. (2011):
Shock formation around planets orbiting M-dwarf stars

Vidotto A.A., Jardine M., Helling Ch. (2011):
Transit variability in bow shock-hosting planets

Vidotto A.A., Jardine M., Helling Ch. (2010b):
Prospects for detection of exoplanet magnetic fields through bow-shock observations during transits

Vidotto A.A., Jardine M., Helling Ch. (2010a):
Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields

Lai D., Helling Ch., van den Heuvel E.P.J. (2010):
Mass Transfer, Transiting Stream, and Magnetopause in Close-in Exoplanetary Systems with Applications to WASP-12

Influence of stellar atmosphere modelling on disk detection and visa versa

Helling Ch., Woitke P., Rimmer P. B., Kamp I., Thi W.-F., Meijerink R. (2014)
Disk evolution, element abundances and cloud properties of young gas giant planets

Sinclair J.A., Helling Ch., Greaves J.S. (2010)
The impact of stellar model spectra in disc detection

Cloud formation in atmospheres (e.g. Brown Dwarfs, giant gas planets)

This is about describing condensation processes while a seed is moving through a gas, hence while it is drifting compared to the surounding gas.

Christiane Helling (Review paper for Annual Review of Earth and Planetary Sciences)
Exoplanet Clouds

Christiane Helling & Sarah Casewell (The A&A Review, 2014)
Atmospheres of Brown Dwarfs

Helling Ch. & Fomins A. (2012, Philosophical Transactions A of The Royal Society):
Modelling the formation of atmospheric dust in brown dwarfs and planetary atmospheres

Helling Ch. (2009):
The Chemical Evolution of Dust and Gas in Substellar Atmospheres (how to cite )


Mahapatra G., Helling Ch., Miguel Y. (2017)
Cloud formation in metal-rich atmospheres of hot super-Earths like 55 Cnc e and CoRoT7b

Helling Ch., Tootill D., Woitke P., Lee, G. (2017)
Dust in brown dwarfs and extrasolar planets. V. Cloud formation in carbon- and oxygen-rich environments

Woitke & Helling (2003):
Dust in brown dwarfs. II. The coupled problem of dust formation and sedimentation

Woitke & Helling (2004):
Dust in brown dwarfs. III. Formation and structure of quasi-static cloud layers

Helling, Thi, Woitke, Fridlund (2006):
Detectability of dirty dust grains in brown dwarf atmospheres

Helling & Rietmeijer (2008):
Glittery clouds in exo-planetary atmospheres ? (how to cite)

Helling, Woitke & Thi (2008):
Dust in brown dwarfs and extra-solar planets. I. Chemical composition and spectral appearance of quasi-static cloud layers

Dust and cloud formation in oxygen-rich environments

We needed a model that was capable of describing the formation of dust grains made of more then one species, hence the formation of heterogeneous dust grains that have not simple onion-like shells of different materials but a mixture of all possible materials.

Lee G.K.H., Blecic J., Helling Ch. (2018)
Dust in brown dwarfs and extra-solar planets VI. Assessing seed formation across the brown dwarf and exoplanet regimes

Lee, Helling, Giles, Bromley (2014):
Dust in brown dwarfs and extra-solar planets IV. Assessing TiO2 and SiO nucleation for cloud formation modeling

Helling & Woitke (2006):
Dust in brown dwarfs. V. Growth and evaporation of dirty dust grains

Helling & Woitke (2006):
Time-dependent modelling of oxygen-rich dust formation

Micro-physics of cloud formation for 1D & 3D model atmospheres

The stationary version of the model for oxygen-rich, heterogeneous dust formation (see Publications) is now part of a radiative transfer atmosphere code (PHOENIX ), and that version of PHOENIX was named DRIFT-PHOENIX. The home of PHOENIX is Hamburg.

The DRIFT-PHOENIX spectra are available via the Virtual Observatory.

Theory papers:

Lines S., Mayne N.J., Boutle I.A., Manners J., Lee G.K.H., Helling, Ch., Drummond B., Amundsen D.S. Royal J., Acreman D.M., Trembling P., Kerslake M.
Simulating the cloudy atmospheres of HD 209458 b and HD 189733 b with the 3D Met Office Unified Model

Juncher D., Jørgensen U.G., Helling Ch. (2017)
Self-consistent atmosphere modeling with cloud formation for low-mass stars and exoplanets

Lee G.K.H., Wood K., Dobbs-Dixon I., Rice A., Helling Ch. (2017)
Dynamic mineral clouds on HD 189733b. II. Monte Carlo radiative transfer for 3D cloudy exoplanet atmospheres: combining scattering and emission spectra

Lee G., Dobbs-Dixon I., Helling Ch., Bognar K., Woitke, P. (2016)
Dynamic mineral clouds on HD 189733b. I. 3D RHD with kinetic, non-equilibrium cloud formation

Helling Ch., Lee G., Dobbs-Dixon I., Mayne N., Amundsen D.S., Khaimova J., Unger A.A., Manners J., Acreman D., Smith C. (2016):
The mineral clouds on HD 209458b and HD 189733b

Lee G., Helling Ch., Dobbs-Dixon I., Juncher, D. (2015):
Modelling the local and global cloud formation on HD 189733b

de Kok R. J., Helling Ch., Stam D. M., Woitke P., Witte S. (2011):
The influence of non-isotropic scattering of thermal radiation on spectra of
brown dwarfs and hot exoplanets

Witte S.; Helling Ch.; Barman T.; Heidrich N.; Hauschildt P. (2011):
Dust in brown dwarfs and extra-solar planets. III. Testing synthetic spectra on

Witte S., Helling Ch., Hauschildt P. (2009):
Dust in brown dwarfs and extra-solar planets. II. Cloud formation for cosmologically evolving abundances

Johnas, Helling Ch., Dehn M., Woitke P., Hauschildt P. (2008):
The influence of dust formation modelling on Na I and K I line profiles in substellar atmospheres

Helling Ch., Dehn M., Woitke P., Hauschildt P. (2008):
Consistent Simulations of Substellar Atmospheres and Nonequilibrium Dust Cloud Formation

Observational papers:

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 Ch., Schmitt J.H.M.M. (2016):
Direct Imaging discovery of a second planet candidate around the possibly transiting planet host CVSO 30

Bonnefoy M., Marleau G.-D., Galicher R., Beust H., Lagrange A.-M., Baudino J.-L., Chauvin G., Borgniet S., Meunier N., Rameau J., Boccaletti A., Cumming A., Helling C., Homeier D., Allard F., Delorme P. (2014)
Physical and orbital properties of β Pictoris b

Schmidt T.O.B , Mugrauer M., Neuhäuser R., Vogt N., Witte S., Hauschildt P.H., Helling Ch. and Seifahrt A. (2014)
First spectroscopic observations of the sub-stellar companion of the young debris disk star PZ Telescopii

Bonnefoy M., Currie T. et al. (2014)
Characterization of the gaseous companion κ Andromedae b. New Keck and LBTI high-contrast observations

Rajpurohit A. S., Reyle C., Schultheis M., Leinert Ch., Allard F., Homeier D., Ratzka T., Abraham P., Moster B., Witte S., Ryde N. (2012)
The very low mass multiple system LHS 1070 — a testbed for model atmospheres for the lower end of the main sequence

Patience J., King R.R., De Rosa R.J., Vigan A., Witte S., Rice E., Helling Ch., Hauschildt P. (2012)
Spectroscopy across the brown dwarf/planetary mass boundary – I. Near-infrared JHK spectra

Lafrenière D., Jayawardhana R., Janson M., Helling Ch.,Witte S., Hauschildt P. (2011):
Discovery of an ~23 M Jup Brown Dwarf Orbiting ~700 AU from the Massive Star
HIP 78530 in Upper Scorpius

Rodler F., del Burgo C., Witte S., Helling Ch.,Hauschildt P., Martin E.L., Alvarez C. (2011):
Detecting Planets around Very Cool Dwarfs at Near Infrared Wavelengths with the
Radial Velocity Technique

Dupuy, Liu, Bowler, Cushing, Helling Ch,, Witte S., Hauschildt P. (2010):
Studying the Physical Diversity of Late-M Dwarfs with Dynamical Masses

Burgasser, Witte S., Helling Ch., Sanderson, Bochanski, Hauschildt P. (2009):
Optical and Near-Infrared Spectroscopy of the L Subdwarf SDSS J125637.13-022452.4

Schmidt, Neuhäuser, Seifahrt, Vogt, Bedalov, Helling Ch., Witte S., Hauschildt P.(2008):
Direct evidence of a sub-stellar companion around CT Chamaeleontis

DRIFT-PHOENIX substellar atmosphere data for download:

some are here: Spanish Virtual Observatory

Andreas Seifahrt / Tobias Schmidt
Adam Burgasser
Ray Jayawardhana / David Lafrenière
Mickael Bonnefoy -0.5 +0.5
Remco de Kok
Carlos del Burgo / Florian Rodler
Carsten Weidner +0.5 -0.5 -1.0 -1.5 -2.0 -2.5 -3.0 -3.5 -4.0 -5.0 -6.0
James Sinclair +0.5 0.0 -0.5 -1.0 -1.5
Brenden Bowler / Trent Dupuy +0.5 0.0 -0.5 -1.0 -1.5 -2
Jenny Patience / Robert King (Univ of Exeter–> University of Arizona)
Vanessa Bailey / Phil Hinz (Univ of Arizona)
A.S. Rajpurohit / C. Reyle (Observatoire de Besancon)
Oleksii Kuzmychov/ Svetlana Berdyugina (Kiepenheuer-Institut für Sonnenphysik, Freiburg)
Ben Burningham (University of Hertfortshire)

Comparing model atmosphere simulation results

M-dwarf model atmosphere comparison

Bozhinova I., Helling Ch. Stark C. (2013)
The impact of M-dwarf atmosphere modelling on planet detection

Test case study on Cloud Formation in Brown Dwarfs

The whole workshop idea is motivated by the present situation in substellar atmosphere modelling: different model approaches yield partially very satisfying results and the increasing observational power will need an ever increasing understanding of the models applied. We further encounter the need for massive grids of model atmospheres e.g. in the frame of “automated derivation of stellar atmosphere parameters” (Bailer-Jones et al. 1996, Recio-Blanco et al. 2006 astro-ph/0604385). Such methods need to be able to rely on atmospheric models for which a certain trust-range is available.

Test case page
Workshop page

Helling Ch., Ackerman A., Allard F., Dehn M., Hauschildt P., Homeier D., Lodders K., Marley M., Rietmeijer F., Tsuji T., Woitke P. (2008):
A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres

Turbulent dust formation

Turbulence and dust formation are interacting on the smallest scale inside an atmosphere. Turbulence might foster the formation of seed particles but also destroy it. Dust formation in turbulent gases (like atmospheres) can cause the formation of large-scale structures (like clouds). For an introduction, see my Everyone’s Understanding of Turbulent Dust Formation.

Helling Ch (2005):
The need for small-scale turbulence in atmospheres of substellar objects

Helling Ch., Klein R., Woitke P., Nowak U., Sedlmayr E. (2004):
Dust in brown dwarfs. IV. Dust formation and driven turbulence on mesoscopic scales

Helling Ch., Oevermann M., Luettke M.J.H., Klein R., Sedlmayr E. (2001):
Dust in brown dwarfs. I. Dust formation under turbulent conditions on microscopic scales

Molecular opacity calculations

I have performed molecular mean opacity calculations based on the Copenhangen SCAN and the HITRAN data base. These data were applied to modelling AGB star winds, protoplanetary disks, and are provided for stellar evolution in the early universe.

Data and literature can be obtained here: Data Services
opacity data for: Antonella, Stan

AGB star winds