4,712 research outputs found
Prospects of using simulations to study the photospheres of brown dwarfs
We discuss prospects of using multi-dimensional time-dependent simulations to
study the atmospheres of brown dwarfs and extrasolar giant planets, including
the processes of convection, radiation, dust formation, and rotation. We argue
that reasonably realistic simulations are feasible, however, separated into two
classes of local and global models. Numerical challenges are related to
potentially large dynamic ranges, and the treatment of scattering of radiation
in multi-D geometries.Comment: 6 pages, 3 figures, to appear in the Proceedings of the IAU Symposium
239 "Convection in Astrophysics", eds. F. Kupka, I.W. Roxburgh, and K.L. Cha
Dust cloud lightning in extraterrestrial atmospheres
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 dwarfs and
giant extrasolar gas planets form clouds made of mixed materials and a large
spectrum of grain sizes. These clouds are globally neutral obeying dust-gas
charge equilibrium which is, on short timescales, inconsistent with the
observation of stochastic ionization events of the solar system planets. We
argue that a significant volume of the clouds in brown dwarfs and extrasolar
planets is susceptible to local discharge events and that the upper cloud
layers are most suitable for powerful lightning-like discharge events. We
discuss various sources of atmospheric ionisation, including thermal ionisation
and a first estimate of ionisation by cosmic rays, and argue that we should
expect thunderstorms also in the atmospheres of brown dwarfs and giant gas
planets which contain mineral clouds.Comment: refereed conference paper accepted for publication in PSS Special
Issue: Outer Planets VIII, 16 page
Expect the unexpected: non-equilibrium processes in brown dwarf atmospheres
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 simulation used
to interpret spectral observations of ultra-cool objects and to determine
fundamental parameters like log(g) and Teff. This proceeding to the workshop
'GAIA and the Unseen: The Brown Dwarf Question' first summarizes what a model
atmosphere simulation is, and then advocates two ideas: A) The use of a
multitude of model families to determine fundamental parameters with realistic
confidence interval. B) To keep an eye on the unexpected, like for example,
ionisation signatures resulting plasma processesComment: 5 pages, proceeding to the workshop 'GAIA and the Unseen: The Brown
Dwarf Question
Cloud formation in giant planets
We calculate the formation of dust clouds in atmospheres of giant
gas-planets. The chemical structure and the evolution of the grain size
distribution in the dust cloud layer is discussed based on a consistent
treatment of seed formation, growth/evaporation and gravitational settling.
Future developments are shortly addressed.Comment: 4 pages, Proceeding to "Extreme solar systems", eds. Fischer, Rasio,
Thorsett, Wolszcza
Beyond Eikonal Scattering in M(atrix)-Theory
We study the problem of more general kinematics for the finite N
M(atrix)-Model than the simple straight line motion that has been used before.
This is supposed to be related to momentum transferring processes in the dual
super-gravity description. We find a negative result for classical,
perturbative processes and discuss briefly the possibility of instianton like
quantum mechanical tunneling processes
- …