5 research outputs found
Collisional modelling of the debris disc around HIP 17439
We present an analysis of the debris disc around the nearby K2 V star HIP
17439. In the context of the Herschel DUNES key programme the disc was observed
and spatially resolved in the far-IR with the Herschel PACS and SPIRE
instruments. In a first model, Ertel et al. (2014) assumed the size and radial
distribution of the circumstellar dust to be independent power laws. There, by
exploring a very broad range of possible model parameters several scenarios
capable of explaining the observations were suggested. In this paper, we
perform a follow-up in-depth collisional modelling of these scenarios trying to
further distinguish between them. In our models we consider collisions, direct
radiation pressure, and drag forces, i.e. the actual physical processes
operating in debris discs. We find that all scenarios discussed in Ertel et al.
are physically sensible and can reproduce the observed SED along with the PACS
surface brightness profiles reasonably well. In one model, the dust is produced
beyond 120au in a narrow planetesimal belt and is transported inwards by
Poynting-Robertson and stellar wind drag. A good agreement with the observed
radial profiles would require stellar winds by about an order of magnitude
stronger than the solar value, which is not supported, although not ruled out,
by observations. Another model consists of two spatially separated planetesimal
belts, a warm inner and a cold outer one. This scenario would probably imply
the presence of planets clearing the gap between the two components. Finally,
we show qualitatively that the observations can be explained by assuming the
dust is produced in a single, but broad planetesimal disc with a surface
density of solids rising outwards, as expected for an extended disc that
experiences a natural inside-out collisional depletion. Prospects of
discriminating between the competing scenarios by future observations are
discussed.Comment: Astronomy and Astrophysics (accepted for publication). 11 pages, 8
figure
Collisional modelling of the AU Microscopii debris disc
The spatially resolved AU Mic debris disc is among the most famous and
best-studied debris discs. We aim at a comprehensive understanding of the dust
production and the dynamics of the disc objects with in depth collisional
modelling including stellar radiative and corpuscular forces. Our models are
compared to a suite of observational data for thermal and scattered light
emission, ranging from the ALMA radial surface brightness profile at 1.3mm to
polarisation measurements in the visible. Most of the data can be reproduced
with a planetesimal belt having an outer edge at around 40au and subsequent
inward transport of dust by stellar winds. A low dynamical excitation of the
planetesimals with eccentricities up to 0.03 is preferred. The radial width of
the planetesimal belt cannot be constrained tightly. Belts that are 5au and
17au wide, as well as a broad 44au-wide belt are consistent with observations.
All models show surface density profiles increasing with distance from the star
as inferred from observations. The best model is achieved by assuming a stellar
mass loss rate that exceeds the solar one by a factor of 50. While the SED and
the shape of the ALMA profile are well reproduced, the models deviate from the
scattered light data more strongly. The observations show a bluer disc colour
and a lower degree of polarisation for projected distances <40au than predicted
by the models. The problem may be mitigated by irregularly-shaped dust grains
which have scattering properties different from the Mie spheres used. From
tests with a handful of selected dust materials, we derive a preference for
mixtures of silicate, carbon, and ice of moderate porosity. We address the
origin of the unresolved central excess emission detected by ALMA and show that
it cannot stem from an additional inner belt alone. Instead, it should derive,
at least partly, from the chromosphere of the central star.Comment: Astronomy and Astrophysics (accepted for publication), 18 pages, 11
figure
Potential multi-component structure of the debris disk around HIP?17439 revealed by <i>Herschel</i> /DUNES
[abridged]
Aims. Our Herschel Open Time Key Programme DUNES aims at detecting and
characterizing debris disks around nearby, sun-like stars. In addition to the
statistical analysis of the data, the detailed study of single objects through
spatially resolving the disk and detailed modeling of the data is a main goal
of the project.
Methods. We obtained the first observations spatially resolving the debris
disk around the sun-like star HIP 17439 (HD23484) using the instruments PACS
and SPIRE on board the Herschel Space Observatory. Simultaneous
multi-wavelength modeling of these data together with ancillary data from the
literature is presented.
Results. A standard single component disk model fails to reproduce the major
axis radial profiles at 70 um, 100 um, and 160 um simultaneously. Moreover, the
best-fit parameters derived from such a model suggest a very broad disk
extending from few au up to few hundreds of au from the star with a nearly
constant surface density which seems physically unlikely. However, the
constraints from both the data and our limited theoretical investigation are
not strong enough to completely rule out this model. An alternative, more
plausible, and better fitting model of the system consists of two rings of dust
at approx. 30 au and 90 au, respectively, while the constraints on the
parameters of this model are weak due to its complexity and intrinsic
degeneracies.
Conclusions. The disk is probably composed of at least two components with
different spatial locations (but not necessarily detached), while a single,
broad disk is possible, but less likely. The two spatially well-separated rings
of dust in our best-fit model suggest the presence of at least one high mass
planet or several low-mass planets clearing the region between the two rings
from planetesimals and dust.Comment: 12 pages, 4 figures, accepted for publication in A&