10 research outputs found
Hydrodynamic simulations of captured protoatmospheres around Earth-like planets
Young terrestrial planets, when they are still embedded in a circumstellar
disk, accumulate an atmosphere of nebula gas. The evolution and eventual
evaporation of the protoplanetary disk affect the structure and dynamics of the
planetary atmosphere. These processes, combined with other mass loss
mechanisms, such as thermal escape driven by extreme ultraviolet and soft X-ray
radiation (XUV) from the young host star, determine how much of the primary
atmosphere, if anything at all, survives into later stages of planetary
evolution. Our aim is to explore the structure and the dynamic outflow
processes of nebula-accreted atmospheres in dependency on changes in the
planetary environment. We integrate stationary hydrostatic models and perform
time-dependent dynamical simulations to investigate the effect of a changing
nebula environment on the atmospheric structure and the timescales on which the
protoatmosphere reacts to these changes. We find that the behavior of the
atmospheres strongly depends on the mass of the planetary core. For planets of
about Mars-mass the atmospheric structure, and in particular the atmospheric
mass, changes drastically and on very short timescales whereas atmospheres
around higher mass planets are much more robust and inert
Interaction of infalling solid bodies with primordial atmospheres of disk-embedded planets
Planets that form early enough to be embedded in the circumstellar gas disk
accumulate thick atmospheres of nebular gas. Models of these atmospheres need
to specify the surface luminosity (i.e. energy loss rate) of the planet. This
luminosity is usually associated with a continuous inflow of solid bodies,
where the gravitational energy released from these bodies is the source of
energy. However, if these bodies release energy in the atmosphere instead of at
the surface, this assumption might not be justified. Our aim is to explore the
interactions of infalling planetesimals with primordial atmospheres at an
embedded phase of evolution. We investigate effects of atmospheric interaction
on the planetesimals (mass loss) and the atmosphere (heating/cooling). We used
atmospheric parameters from a snapshot of time-dependent evolution simulations
for embedded atmospheres and simulated purely radial, infall events of
siliceous planetesimals in a 1D, explicit code. We implemented energy transfer
between friction, radiation transfer by the atmosphere and the body and thermal
ablation; this gives us the possibility to examine the effects on the
planetesimals and the atmosphere. We find that a significant amount of
gravitational energy is indeed dissipated into the atmosphere, especially for
larger planetary cores, which consequently cannot contribute to the atmospheric
planetary luminosity. Furthermore, we examine that planetesimal infall events
for cores, M, which actually result in a local
cooling of the atmosphere; this is totally in contradiction with the classical
model
ALMA observations of the "fresh" carbon-rich AGB star TX Piscium. The discovery of an elliptical detached shell
Aims. The carbon-rich asymptotic giant branch (AGB) star TX Piscium (TX Psc)
has been observed multiple times during multiple epochs and at different
wavelengths and resolutions, showing a complex molecular CO line profile and a
ring-like structure in thermal dust emission. We investigate the molecular
counterpart in high resolution, aiming to resolve the ring-like structure and
identify its origin. Methods. Atacama Large Millimeter/submillimeter Array
(ALMA) observations have been carried out to map the circumstellar envelope
(CSE) of TX Psc in CO(2-1) emission and investigate the counterpart to the
ring-like dust structure. Results. We report the detection of a thin,
irregular, and elliptical detached molecular shell around TX Psc, which
coincides with the dust emission. This is the first discovery of a
non-spherically symmetric detached shell, raising questions about the shaping
of detached shells. Conclusions. We investigate possible shaping mechanisms for
elliptical detached shells and find that in the case of TX Psc, stellar
rotation of 2 km/s can lead to a non-uniform mass-loss rate and velocity
distribution from stellar pole to equator, recreating the elliptical CSE. We
discuss the possible scenarios for increased stellar momentum, enabling the
rotation rates needed to reproduce the ellipticity of our observations, and
come to the conclusion that momentum transfer of an orbiting object with the
mass of a brown dwarf would be sufficient