4 research outputs found
Can dead zones create structures like a transition disk?
[Abridged] Regions of low ionisation where the activity of the
magneto-rotational instability is suppressed, the so-called dead zones, have
been suggested to explain gaps and asymmetries of transition disks. We
investigate the gas and dust evolution simultaneously assuming simplified
prescriptions for a dead zone and a magnetohydrodynamic (MHD) wind acting on
the disk. We explore whether the resulting gas and dust distribution can create
signatures similar to those observed in transition disks. For the dust
evolution, we included the transport, growth, and fragmentation of dust
particles. To compare with observations, we produced synthetic images in
scattered optical light and in thermal emission at mm wavelengths. In all
models with a dead zone, a bump in the gas surface density is produced that is
able to efficiently trap large particles ( mm) at the outer edge of
the dead zone. The gas bump reaches an amplitude of a factor of , which
can be enhanced by the presence of an MHD wind that removes mass from the inner
disk. While our 1D simulations suggest that such a structure can be present
only for 1 Myr, the structure may be maintained for a longer time when
more realistic 2D/3D simulations are performed. In the synthetic images,
gap-like low-emission regions are seen at scattered light and in thermal
emission at mm wavelengths, as previously predicted in the case of planet-disk
interaction. As a conclusion, main signatures of transition disks can be
reproduced by assuming a dead zone in the disk, such as gap-like structure in
scattered light and millimetre continuum emission, and a lower gas surface
density within the dead zone. Previous studies showed that the Rossby wave
instability can also develop at the edge of such dead zones, forming vortices
and also creating asymmetries.Comment: Minor changes after language edition. Accepted for publication in A&
M&m's: An error budget and performance simulator code for polarimetric systems
Although different approaches to model a polarimeter's accuracy have been
described before, a complete error budgeting tool for polarimetric systems has
not been yet developed. Based on the framework introduced by Keller & Snik, in
2009, we have developed the M&m's code as a first attempt to obtain a generic
tool to model the performance and accuracy of a given polarimeter, including
all the potential error contributions and their dependencies on physical
parameters. The main goal of the code is to provide insight on the combined
influence of many polarization errors on the accuracy of any polarimetric
instrument. In this work we present the mathematics and physics based on which
the code is developed as well as its general structure and operational scheme.
Discussion of the advantages of the M&m's approach to error budgeting and
polarimetric performance simulation is carried out and a brief outlook of
further development of the code is also given.Comment: Publ. date: 09/201