1,926 research outputs found
IRC+10216 in Action: Present Episode of Intense Mass-Loss Reconstructed by Two-Dimensional Radiative Transfer Modeling
We present two-dimensional (2D) radiative transfer modeling of IRC+10216 at
selected moments of its evolution in 1995-2001, which correspond to three
epochs of our series of 8 near-infrared speckle images (Osterbart et al. 2000,
Weigelt et al. 2002). The high-resolution images obtained over the last 5.4
years revealed the dynamic evolution of the subarcsecond dusty environment of
IRC+10216 and our recent time-independent 2D radiative transfer modeling
reconstructed its physical properties at the single epoch of January 1997
(Men'shchikov et al. 2001). Having documented the complex changes in the
innermost bipolar shell of the carbon star, we incorporate the evolutionary
constraints into our new modeling to understand the physical reasons for the
observed changes. The new calculations imply that during the last 50 years, we
have been witnessing an episode of a steadily increasing mass loss from the
central star, from Mdot ~ 10^-5 Msun/yr to the rate of Mdot ~ 3x10^-4 Msun/yr
in 2001. The rapid increase of the mass loss of IRC+10216 and continuing
time-dependent dust formation and destruction caused the observed displacement
of the initially faint components C and D and of the bright cavity A from the
star which has almost disappeared in our images in 2001. Increasing dust
optical depths are causing strong backwarming that leads to higher temperatures
in the dust formation zone, displacing the latter outward with a velocity v_T ~
27 km/s due to the evaporation of the recently formed dust grains. This shift
of the dust density peak in the bipolar shell mimics a rapid radial expansion,
whereas the actual outflow has probably a lower speed v < v_inf ~ 15 km/s. The
model predicts that the star will remain obscured until Mdot starts to drop
back to lower values in the dust formation zone.Comment: 10 pages, 6 figures, accepted by Astronomy and Astrophysics, also
available at
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.htm
Properties of the close binary and circumbinary torus of the Red Rectangle
New diffraction-limited speckle images of the Red Rectangle in the wavelength
range 2.1--3.3 microns with angular resolutions of 44--68 mas and previous
speckle images at 0.7--2.2 microns revealed well-resolved bright bipolar
outflow lobes and long X-shaped spikes originating deep inside the outflow
cavities. This set of high-resolution images stimulated us to reanalyze all
infrared observations of the Red Rectangle using our two-dimensional radiative
transfer code. The new detailed modeling, together with estimates of the
interstellar extinction in the direction of the Red Rectangle enabled us to
more accurately determine one of the key parameters, the distance D=710 pc with
model uncertainties of 70 pc, which is twice as far as the commonly used
estimate of 330 pc. The central binary is surrounded by a compact, massive
(M=1.2 Msun), very dense dusty torus with hydrogen densities reaching
n_H=2.5x10^12 cm^-3 (dust-to-gas mass ratio rho_d/rho~0.01). The bright
component of the spectroscopic binary HD 44179 is a post-AGB star with mass
M*=0.57 Msun, luminosity L*=6000 Lsun, and effective temperature T*=7750 K.
Based on the orbital elements of the binary, we identify its invisible
component with a helium white dwarf with Mwd~0.35 Msun, Lwd~100 Lsun, and
Twd~6x10^4 K. The hot white dwarf ionizes the low-density bipolar outflow
cavities inside the dense torus, producing a small HII region observed at radio
wavelengths. We propose an evolutionary scenario for the formation of the Red
Rectangle nebula, in which the binary initially had 2.3 and 1.9 Msun components
at a separation of 130 Rsun. The nebula was formed in the ejection of a common
envelope after Roche lobe overflow by the present post-AGB star.Comment: 20 pages, 10 figures, accepted by Astronomy and Astrophysics, also
available at
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.htm
Spatially resolved H_2 emission from a very low-mass star
Molecular outflows from very low-mass stars (VLMSs) and brown dwarfs have
been studied very little. So far, only a few CO outflows have been observed,
allowing us to map the immediate circumstellar environment. We present the
first spatially resolved H2 emission around IRS54 (YLW52), a ~0.1-0.2 Msun
Class I source. By means of VLT SINFONI K-band observations, we probed the H2
emission down to the first ~50 AU from the source. The molecular emission shows
a complex structure delineating a large outflow cavity and an asymmetric
molecular jet. Thanks to the detection of several H2 transitions, we are able
to estimate average values along the jet-like structure (from source position
to knot D) of Av~28 mag, T~2000-3000 K, and H2 column density N(H2)~1.7x10^17
cm^-2. This allows us to estimate a mass loss rate of ~2x10^-10 Msun/yr for the
warm H2 component . In addition, from the total flux of the Br Gamma line, we
infer an accretion luminosity and mass accretion rate of 0.64 Lsun and ~3x10^-7
Msun/yr, respectively. The outflow structure is similar to those found in
low-mass Class I and CTTS. However, the Lacc/Lbol ratio is very high (~80%),
and the mass accretion rate is about one order of magnitude higher when
compared to objects of roughly the same mass, pointing to the young nature of
the investigated source.Comment: accepted as a Letter in A&
Nematode communities, plant nutrient economy and life-cycle characteristics jointly determine plant monoculture performance over 12 years
The end-state comfort effect in 3- to 8-year-old children in two object manipulation tasks
The aim of the study was to compare 3- to 8-year-old childrenâs propensity to antici- pate a comfortable hand posture at the end of a grasping movement ( end-state comfort effect ) between two different object manipulation tasks, the bar-transport task, and the overturned-glass task. In the bar-transport task, participants were asked to insert a verti- cally positioned bar into a small opening of a box. In the overturned-glass task, participants were asked to put an overturned-glass right-side-up on a coaster. Half of the participants experienced action effects (lights) as a consequence of their movements (AE groups), while the other half of the participants did not (No-AE groups). While there was no differ- ence between the AE and No-AE groups, end-state comfort performance differed across age as well as between tasks. Results revealed a significant increase in end-state comfort performance in the bar-transport task from 13% in the 3-year-olds to 94% in the 8-year- olds. Interestingly, the number of children grasping the bar according to end-state comfort doubled from 3 to 4 years and from 4 to 5 years of age. In the overturned-glass task an increase in end-state comfort performance from already 63% in the 3-year-olds to 100% in the 8-year-olds was significant as well. When comparing end-state comfort performance across tasks, results showed that 3- and 4-year-old children were better at manipulating the glass as compared to manipulating the bar, most probably, because children are more familiar with manipulating glasses. Together, these results suggest that preschool years are an important period for the development of motor planning in which the familiarity with the object involved in the task plays a significant role in childrenâs ability to plan their movements according to end-state comfort
Predicting stochastic community dynamics in grasslands under the assumption of competitive symmetry
International audienceCommunity dynamics is influenced by multiple ecological processes such as environmental spatiotemporal variation, competition between individuals and demographic stochasticity. Quantifying the respective influence of these various processes and making predictions on community dynamics require the use of a dynamical framework encompassing these various components. We here demonstrate how to adapt the framework of stochastic community dynamics to the peculiarities of herbaceous communities, by using a short temporal resolution adapted to the time scale of competition between herbaceous plants, and by taking into account the seasonal drops in plant aerial biomass following winter, harvesting or consumption by herbivores. We develop a hybrid inference method for this novel modelling framework that both uses numerical simulations and likelihood computations. Applying this methodology to empirical data from the Jena biodiversity experiment, we find that environmental stochasticity has a larger effect on community dynamics than demographic stochasticity, and that both effects are generally smaller than observation errors at the plot scale. We further evidence that plant intrinsic growth rates and carrying capacities are moderately predictable from plant vegetative height, specific leaf area and leaf dry matter content. We do not find any trade-off between demographical components, since species with larger intrinsic growth rates tend to also have lower demographic and environmental variances. Finally, we find that our model is able to make relatively good predictions of multi-specific community dynamics based on the assumption of competitive symmetr
Triple-negative breast cancer: the importance of molecular and histologic subtyping, and recognition of low-grade variants
Bispectrum speckle interferometry of IRC+10216: the dynamic evolution of the innermost circumstellar environment from 1995 to 2001
We present new near-infrared (JHK) bispectrum speckle-interferometry
monitoring of the carbon star IRC+10216 obtained between 1999 and 2001 with the
SAO 6m telescope. The J-, H-, and K-band resolutions are 50mas, 56mas, and
73mas, resp. The total sequence of K-band observations covers now 8 epochs from
1995 to 2001 and shows the dynamic evolution of the inner dust shell. The
present observations show that the appearance of the dust shell has
considerably changed compared to the epochs of 1995 to 1998. Four main
components within a 0.2" radius can be identified in the K-band images. The
apparent separation of the two initially brightest components A and B increased
from ~191mas in 1995 to ~351mas in 2001. Simultaneously, component B has been
fading and almost disappeared in 2000 whereas the initially faint components C
and D became brighter (relative to peak intensity). These changes can be
related to changes of the optical depth caused, e.g., by mass-loss variations
or new dust condensation in the wind. Our 2D radiative transfer model suggests
that the observed relative motion of A and B is not consistent with the known
terminal wind velocity of 15 km/s. The apparent motion with a deprojected
velocity of 19 km/s on average and of recently 27 km/s appears to be caused by
adisplacement of the dust density peak due to dust evaporation in the optically
thicker and hotter environment. Our monitoring, covering more than 3 pulsation
periods, shows that the structural variations are not related to the stellar
pulsation cycle in a simple way. This is consistent with the predictions of
hydrodynamical models that enhanced dust formation takes place on a timescale
of several pulsation periods. The timescale of the fading of component B can
well be explained by the formation of new dust in the circumstellar envelope.Comment: 11 pages including 6 PostScript figures; also available from
http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.html;
Astronomy & Astrophysics, in pres
What do we learn from HER2-positive breast cancer genomic profiles?
Patients with a tumor presenting amplification of the HER2 gene are currently proposed trastuzumab (herceptin) and this has greatly changed their outcome. However, a number of HER2-positive cancers show intrinsic or acquired resistance to trastuzumab and there are clear indications that they form a heterogeneous group of tumors. A paper in this issue of Breast Cancer Research addresses this heterogeneity at the genomic level
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