391 research outputs found
Structuring the HD 141569 A circumstellar dust disk. Impact of eccentric bound stellar companions
Scattered light images of the optically thin dust disk around the 5 Myr old
star HD141569 have revealed its complex asymmetric structure. We show in this
paper that the surface density inferred from the observations presents
similarities with that expected from a circumprimary disk within a highly
eccentric binary system. We assume that either the two M stars in the close
vicinity of HD141569 are bound companions or at least one of them is an
isolated binary companion. We discuss the resulting interaction with an
initially axisymmetric disk. This scenario accounts for the formation of a
spiral structure, a wide gap in the disk and a broad faint extension outside
the truncation radius of the disk after 10-15 orbital periods with no need for
massive companion(s) in the midst of the disk resolved in scattered light. The
simulations match the observations and the star age if the perturber is on an
elliptic orbit with a periastron distance of 930 AU and an eccentricity from
0.7 to 0.9. We find that the numerical results can be reasonably well
reproduced using an analytical approach proposed to explain the formation of a
spiral structure by secular perturbation of a circumprimary disk by an external
bound companion. We also interpret the redness of the disk in the visible
reported by Clampin et al.(2003) and show that short-lived grains one order of
magnitude smaller than the blow-out size limit are abundant in the disk. The
most probable reason for this is that the disk sustains high collisional
activity. Finally we conclude that additional processes are required to clear
out the disk inside 150 AU and that interactions with planetary companions
possibly coupled with the remnant gas disk are likely candidates.Comment: 13 pages. Accepted for publication in A&A. MPEG amd AVI animations +
paper available at : http://www.strw.leidenuniv.nl/~augereau/newresults.htm
Modeling the gas-phase chemistry of the transitional disk around HD 141569A
Aims: The chemistry, distribution and mass of the gas in the transitional
disk around the 5 Myr old B9.5 V star HD 141569A are constrained.
Methods: A quasi 2-dimensional (2D) chemistry code for photon dominated
regions (PDR) is used to calculate the chemistry and gas temperatures in the
disk. The calculations are performed for several gas distributions, PAH
abundances and values of the total gas mass. The resulting CO J=2-1 and J=3-2
emission lines are computed with a 2D radiative transfer code and are compared
to observations.
Results: The CO abundance is very sensitive to the total disk mass because
the disk is in a regime where self-shielding just sets in. The observed CO
emission lines are best fit by a power-law gas distribution of 80 M_earth
starting at 80 AU from the central star, indicating that there is some gas in
the inner hole. Predictions are made for intensities of atomic fine-structure
lines. [C I], which is the dominant form of carbon in large parts of the disk,
is found to be a good alternative tracer of the gas mass.Comment: 11 pages, 9 figures. Accepted for publication in A&
Does partial tear repair of adjacent tendons improve the outcome of supraspinatus tendonfull-thickness tear reinsertion?
AbstractBackgroundPartial tearing of the infraspinatus and/or subscapularis tendon(s) is frequently associated with supraspinatus full-thickness tears. However, limited data regarding its influence on supraspinatus surgical repair is available.PurposeOur aim was to assess the functional and anatomical outcomes of open repair of supraspinatus full-thickness tears combined with adjacent partial tearing, comparatively to a control.MethodsWe retrospectively identified 22 patients (22 shoulders) with a partial tear, most of them being a delamination tear, of the infraspinatus and/or subscapularis tendons associated with a complete detachment of the supraspinatus tendon. Twenty-seven patients (27 shoulders) treated for an isolated complete detachment of the supraspinatus tendon by open repair served as controls. The mean age was 58 years. A proximalized trans-osseous reinsertion of the supraspinatus tendon was combined with a curettage-closure of the delamination tear. Patients were evaluated with standardized MRI at last follow-up.ResultsAt a mean of 75-month follow-up, the presence of a partial tear of either infraspinatus or subscapularis, or both, did not influence function and healing rates of supraspinatus tendon repair. Conversely to the control, when a retear occurred, the functional score tended to worsen. Preoperatively, fatty muscular degeneration was more pronounced when a partial tear was present. Fatty degeneration worsened regardless of repair healing.ConclusionOpen reinsertion of a supraspinatus full-thickness tear associated with a thorough treatment of partial tear of adjacent tendons led to optimal functional and anatomical mid term outcomes. Our results suggest the presence of a partial tear of adjacent tendons could be associated with poorer function in case of supraspinatus tendon re-rupture.Level of evidenceLevel III case-control study
Interpreting the extended emission around three nearby debris disc host stars
Cool debris discs are a relic of the planetesimal formation process around
their host star, analogous to the solar system's Edgeworth-Kuiper belt. As
such, they can be used as a proxy to probe the origin and formation of
planetary systems like our own. The Herschel Open Time Key Programmes "DUst
around NEarby Stars" (DUNES) and "Disc Emission via a Bias-free Reconnaissance
in the Infrared/Submillimetre" (DEBRIS) observed many nearby, sun-like stars at
far-infrared wavelengths seeking to detect and characterize the emission from
their circumstellar dust. Excess emission attributable to the presence of dust
was identified from around 20% of stars. Herschel's high angular
resolution ( 7" FWHM at 100 m) provided the capacity for resolving
debris belts around nearby stars with radial extents comparable to the solar
system (50 to 100 au). As part of the DUNES and DEBRIS surveys, we obtained
observations of three debris disc stars, HIP 22263 (HD 30495), HIP 62207 (HD
110897), and HIP 72848 (HD 131511), at far-infrared wavelengths with the
Herschel PACS instrument. Combining these new images and photometry with
ancilliary data from the literature, we undertook simultaneous multi-wavelength
modelling of the discs' radial profiles and spectral energy distributions using
three different methodologies: single annulus, modified black body, and a
radiative transfer code. We present the first far-infrared spatially resolved
images of these discs and new single-component debris disc models. We
characterize the capacity of the models to reproduce the disc parameters based
on marginally resolved emission through analysis of two sets of simulated
systems (based on the HIP 22263 and HIP 62207 data) with the noise levels
typical of the Herschel images. We find that the input parameter values are
recovered well at noise levels attained in the observations presented here.Comment: 13 pages, 5 figures, 5 tables, accepted for publication in A&
Inner disk clearing around the Herbig Ae star HD\,139614: Evidence for a planet-induced gap ?
Spatially resolving the inner dust cavity of the transitional disks is a key
to understanding the connection between planetary formation and disk dispersal.
The disk around the Herbig star HD 139614 is of particular interest since it
presents a pretransitional nature with an au-sized gap, in the dust, that was
spatially resolved by mid-IR interferometry. Using new NIR interferometric
observations, we aim to characterize the 0.1-10~au region of the HD~139614 disk
further and identify viable mechanisms for the inner disk clearing. We report
the first multiwavelength radiative transfer modeling of the interferometric
data acquired on HD~139614 with PIONIER, AMBER, and MIDI, complemented by
Herschel/PACS photometries. We confirm a gap structure in the um-sized dust,
extending from about 2.5 au to 6 au, and constrained the properties of the
inner dust component: e.g., a radially increasing surface density profile, and
a depletion of 10^3 relative to the outer disk. Since self-shadowing and
photoevaporation appears unlikely to be responsible for the au-sized gap of
HD~139614, we thus tested if dynamical clearing could be a viable mechanism
using hydrodynamical simulations to predict the gaseous disk structure. Indeed,
a narrow au-sized gap is expected when a single giant planet interacts with the
disk. Assuming that small dust grains are well coupled to the gas, we found
that a ~ 3~Mjup planet located at 4.5 au from the star could, in less than 1
Myr, reproduce most of the aspects of the dust surface density profile, while
no significant depletion in gas occurred in the inner disk, in contrast to the
dust. However, the dust-depleted inner disk could be explained by the expected
dust filtration by the gap and the efficient dust growth/fragmentation in the
inner disk regions. Our results support the hypothesis of a giant planet
opening a gap and shaping the inner region of the HD~139614 disk.Comment: Version accepted in A&A, with typos corrections in the tex
Probing protoplanetary disks with silicate emission: Where is the silicate emission zone?
Recent results indicate that the grain size and crystallinity inferred from observations of silicate features may be correlated with the spectral type of the central star and/or disk geometry. In this paper, we show that grain size, as probed by the 10 ÎŒm silicate feature peak-to-continuum and 11.3 to 9.8 ÎŒm flux ratios, is inversely proportional to log Lsstarf. These trends can be understood using a simple two-layer disk model for passive irradiated flaring disks, CGPLUS. We find that the radius, R10, of the 10 ÎŒm silicate emission zone in the disk goes as (L*/Lâ)^0.56, with slight variations depending on disk geometry (flaring angle and inner disk radius). The observed correlations, combined with simulated emission spectra of olivine and pyroxene mixtures, imply a dependence of grain size on luminosity. Combined with the fact that R10 is smaller for less luminous stars, this implies that the apparent grain size of the emitting dust is larger for low-luminosity sources. In contrast, our models suggest that the crystallinity is only marginally affected, because for increasing luminosity, the zone for thermal annealing (assumed to be at T > 800 K) is enlarged by roughly the same factor as the silicate emission zone. The observed crystallinity is affected by disk geometry, however, with increased crystallinity in flat disks. The apparent crystallinity may also increase with grain growth due to a corresponding increase in contrast between crystalline and amorphous silicate emission bands
Dust Distribution in Gas Disks. A Model for the Ring Around HR 4796A
There have been several model analyses of the near and mid IR flux from the
circumstellar ring around HR4796A. In the vicinity of a young star, the
possibility that the dust ring is embedded within a residual protostellar gas
disk cannot be ruled out. In a gas-rich environment, larger sizes () are needed for the particles to survive the radiative blow out. The total
dust mass required to account for the IR flux is . The
combined influence of gas and stellar radiation may also account for the
observed sharp inner boundary and rapidly fading outer boundary of the ring.
The pressure gradient induced by a small (10%) amplitude variation in the
surface density distribution of a low-mass gaseous disk would be sufficient to
modify the rotation speed of the gas.Comment: proof read version, 26 pages, LaTex, 11 figures. To appear in The
Astronomical Journal June 200
Dynamical modeling of large scale asymmetries in the beta Pictoris dust disk
We report a new and complete model of the beta Pictoris disk, which succeeds
in accounting for both the surface brightness distribution, warp
characteristics, the outer ``butterfly'' asymmetry as observed by HST/STIS in
scattered light, as well as the infrared emission. Our model includes the
presence of a disk of planetesimals extending out to 120-150 AU, perturbed
gravitationally by a giant planet on an inclined orbit, following the approach
of Mouillet et al. (1997b). At any time, the planetesimal disk is assumed to be
the source of a distribution of grains produced through collisional evolution,
with the same initial orbital parameter distribution. The steady state spatial
grain distribution is found incorporating the effects of radiation pressure
which can cause the distribution of the smallest particles to become very
distended. With realistic assumptions about the grains' chemical properties,
the modeling confirms the previously evident need for an additional population
of hot grains close to the star, to account for the 12 microns fluxes at short
distances from the star. It also indicates that this population cannot explain
the outer 12 microns flux distribution when the effects of gravity and
radiation pressure determine the distribution. Very small grains, produced by
collisions among aggregates, are tentatively proposed to account for this 12
microns outer emission
The Circumstellar Disk of HD 141569 Imaged with NICMOS
Coronagraphic imaging with the Near Infrared Camera and Multi Object
Spectrometer on the Hubble Space Telescope reveals a large, ~400 AU (4'')
radius, circumstellar disk around the Herbig Ae/Be star HD 141569. A reflected
light image at 1.1 micron shows the disk oriented at a position angle of 356
+/- 5 deg and inclined to our line of sight by 51 +/- 3 deg; the intrinsic
scattering function of the dust in the disk makes the side inclined toward us,
the eastern side, brighter. The disk flux density peaks 185 AU (1.''85) from
the star and falls off to both larger and smaller radii. A region of depleted
material, or a gap, in the disk is centered 250 AU from the star. The dynamical
effect of one or more planets may be necessary to explain this morphology.Comment: 4 pages, LaTeX with emulateapj.sty and epsfig.sty, 4 postscript
figures, Accepted to ApJ Letter
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