100 research outputs found
Modélisation biomécanique du diaphragme humain : du CT-4D au modèle du mouvement
Session "Articles"National audienceL'hadronthérapie est une technique avancée de traitement du cancer par radiothérapie. Elle offre une balistique d'irradiation bien supérieure à la radiothérapie conventionnelle. Lorsque la tumeur se trouve sur un organe en mouvement, la difficulté majeure est de pouvoir la cibler pendant le traitement. En ce qui concerne la tumeur pulmonaire, le diaphragme joue un rôle majeur et prépondérant dans le mouvement tumoral. Le diaphragme est une membrane musculo-tendineuse en forme de dôme qui sépare le thorax de l'abdomen. Dans ce travail nous présentons un modèle biomécanique permettant de modéliser les mouvements du diaphragme pendant la respiration. Dans cette démarche nous simulons le mouvement du diaphragme entre l'inspiration et l'expiration, à partir d'un modèle de contraction musculaire. Pour cela, un modèle biomécanique 3D personnalisé du diaphragme, basé sur la méthode des éléments finis, a été développé à partir de données expérimentales (4D CT-scan) d'un patient. Les résultats de notre modélisation montrent une bonne concordance entre la simulation et les données expérimentales
Herschel Planetary Nebula Survey (HerPlaNS) - First Detection of OH+ in Planetary Nebulae
We report the first detections of OH emission in planetary nebulae (PNe).
As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the
PACS and SPIRE instruments aboard the Herschel Space Observatory, we performed
a line survey in these PNe over the entire spectral range between 51 and
672m to look for new detections. OH rotational emission lines at
152.99, 290.20, 308.48, and 329.77m were detected in the spectra of three
planetary nebulae: NGC 6445, NGC 6720, and NGC 6781. Excitation temperatures
and column densities derived from these lines are in the range of 27 to 47 K
and 210 to 4 10 cm, respectively. In PNe,
the OH+ rotational line emission appears to be produced in the
photodissociation region (PDR) in these objects. The emission of OH+ is
observed only in PNe with hot central stars (T > 100000 K), suggesting
that high-energy photons may play a role in the OH+ formation and its line
excitation in these objects, as it seems to be the case for ultraluminous
galaxies.Comment: 9 pages, 7 figures; accepted for publication in A&
The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure
Context. The interaction between stellar winds and the interstellar medium
(ISM) can create complex bow shocks. The photometers on board the Herschel
Space Observatory are ideally suited to studying the morphologies of these bow
shocks. Aims. We aim to study the circumstellar environment and wind-ISM
interaction of the nearest red supergiant, Betelgeuse. Methods. Herschel PACS
images at 70, 100, and 160 micron and SPIRE images at 250, 350, and 500 micron
were obtained by scanning the region around Betelgeuse. These data were
complemented with ultraviolet GALEX data, near-infrared WISE data, and radio 21
cm GALFA-HI data. The observational properties of the bow shock structure were
deduced from the data and compared with hydrodynamical simulations. Results.
The infrared Herschel images of the environment around Betelgeuse are
spectacular, showing the occurrence of multiple arcs at 6-7 arcmin from the
central target and the presence of a linear bar at 9 arcmin. Remarkably, no
large-scale instabilities are seen in the outer arcs and linear bar. The dust
temperature in the outer arcs varies between 40 and 140 K, with the linear bar
having the same colour temperature as the arcs. The inner envelope shows clear
evidence of a non-homogeneous clumpy structure (beyond 15 arcsec), probably
related to the giant convection cells of the outer atmosphere. The
non-homogeneous distribution of the material even persists until the collision
with the ISM. A strong variation in brightness of the inner clumps at a radius
of 2 arcmin suggests a drastic change in mean gas and dust density some 32 000
yr ago. Using hydrodynamical simulations, we try to explain the observed
morphology of the bow shock around Betelgeuse. Conclusions: [abbreviated]Comment: 26 page
The detached dust shells of AQ And, U Ant, and TT Cyg
Detached circumstellar dust shells are detected around three carbon variables
using Herschel-PACS. Two of them are already known on the basis of their
thermal CO emission and two are visible as extensions in IRAS imaging data. By
model fits to the new data sets, physical sizes, expansion timescales, dust
temperatures, and more are deduced. A comparison with existing molecular CO
material shows a high degree of correlation for TT Cyg and U Ant but a few
distinct differences with other observables are also found.Comment: Letter accepted for publication on the A&A Herschel Special Issu
Near-IR Spectra of Red Supergiants and Giants. I- Models with Solar and with Mixing-Induced Surface Abundance Ratios
We provide a grid of PHOENIX spectra of red giant and supergiant stars, that
extend through optical and near-IR wavelengths. For the first time, models are
also provided with modified surface abundances of C, N and O, as a step towards
accounting for the changes known to occur due to convective dredge-up (and to
be enhanced in the case of rotation). The aims are (i) to assess how well
current models reproduce observed spectra, (ii) to quantify the effects of the
abundance changes on the spectra, and (iii) to determine how these changes
affect estimates of fundamental stellar parameters.
Observed giant star spectra can be fitted very well at solar metallicity down
to about 3400K. Modified surface abundances are preferred in only a minority of
cases for luminosity class II, possibly indicating mixing in excess of standard
first dredge-up.
Supergiant stars show a larger variety of near-IR spectra, and good fits are
currently obtained for about one third of the observations only. Modified
surface abundances help reproducing strong CN bands, but do not suffice to
resolve all the difficulties. The effect of the abundance changes on the
estimated Teff depends on the wavelength range of observation and can amount
several 100K. Reasons for the remaining discrepancies are discussed.Comment: To be published in A&A. 19 p., 35 postscript figures, uses aa.cls.
Selected model spectra available through CD
The Herschel Planetary Nebula Survey (HerPlaNS) I. Data Overview and Analysis Demonstration with NGC 6781
This is the first of a series of investigations into far-IR characteristics
of 11 planetary nebulae (PNs) under the Herschel Space Observatory Open Time 1
program, Herschel Planetary Nebula Survey (HerPlaNS). Using the HerPlaNS data
set, we look into the PN energetics and variations of the physical conditions
within the target nebulae. In the present work, we provide an overview of the
survey, data acquisition and processing, and resulting data products. We
perform (1) PACS/SPIRE broadband imaging to determine the spatial distribution
of the cold dust component in the target PNs and (2) PACS/SPIRE
spectral-energy-distribution (SED) and line spectroscopy to determine the
spatial distribution of the gas component in the target PNs. For the case of
NGC 6781, the broadband maps confirm the nearly pole-on barrel structure of the
amorphous carbon-richdust shell and the surrounding halo having temperatures of
26-40 K. The PACS/SPIRE multi-position spectra show spatial variations of
far-IR lines that reflect the physical stratification of the nebula. We
demonstrate that spatially-resolved far-IR line diagnostics yield the (T_e,
n_e) profiles, from which distributions of ionized, atomic, and molecular gases
can be determined. Direct comparison of the dust and gas column mass maps
constrained by the HerPlaNS data allows to construct an empirical gas-to-dust
mass ratio map, which shows a range of ratios with the median of 195+-110. The
present analysis yields estimates of the total mass of the shell to be 0.86
M_sun, consisting of 0.54 M_sun of ionized gas, 0.12 M_sun of atomic gas, 0.2
M_sun of molecular gas, and 4 x 10^-3 M_sun of dust grains. These estimates
also suggest that the central star of about 1.5 M_sun initial mass is
terminating its PN evolution onto the white dwarf cooling track.Comment: 27 pages, 16 figures, accepted for publication in A&
HD 174884: a strongly eccentric, short-period early-type binary system discovered by CoRoT
Accurate photometric CoRoT space observations of a secondary seismological
target, HD 174884, led to the discovery that this star is an astrophysically
important double-lined eclipsing spectroscopic binary in an eccentric orbit (e
of about 0.3), unusual for its short (3.65705d) orbital period. The high
eccentricity, coupled with the orientation of the binary orbit in space,
explains the very unusual observed light curve with strongly unequal primary
and secondary eclipses having the depth ratio of 1-to-100 in the CoRoT 'seismo'
passband. Without the high accuracy of the CoRoT photometry, the secondary
eclipse, 1.5 mmag deep, would have gone unnoticed. A spectroscopic follow-up
program provided 45 high dispersion spectra. The analysis of the CoRoT light
curve was performed with an adapted version of PHOEBE that supports CoRoT
passbands. The final solution was obtained by simultaneous fitting of the light
and the radial velocity curves. Individual star spectra were derived by
spectrum disentangling. The uncertainties of the fit were derived by bootstrap
resampling and the solution uniqueness was tested by heuristic scanning. The
results provide a consistent picture of the system composed of two late B
stars. The Fourier analysis of the light curve fit residuals yields two
components, with orbital frequency multiples and an amplitude of about 0.1
mmag, which are tentatively interpreted as tidally induced pulsations. An
extensive comparison with theoretical models is carried out by means of the
Levenberg-Marquardt minimization technique and the discrepancy between models
and the derived parameters is discussed. The best fitting models yield a young
system age of 125 million years which is consistent with the eccentric orbit
and synchronous component rotation at periastron.Comment: 15 pages, 12 figures. Accepted for publication by A&
Near-IR spectroscopic ages of massive star clusters in M82
Like other starburst galaxies, M82 hosts compact, massive young star clusters
that are interesting both in their own right and as benchmarks for population
synthesis models. Can spectral synthesis models at resolutions around 1000
adequately reproduce the near-IR spectral features and the energy distribution
of these clusters between 0.8 and 2.4 microns? How do the derived cluster
properties compare with previous results from optical studies?
We analyse the spectra of 5 massive clusters in M82, using data acquired with
the spectrograph SpeX on the InfraRed Telescope Facility (NASA/IRTF) and a new
population synthesis tool with a highly improved near-IR extension, based on a
recent collection of empirical and theoretical spectra of red supergiant stars.
We obtain excellent fits across the near-IR with models at quasi-solar
metallicity and a solar neighbourhood extinction law. Spectroscopy breaks a
strong degeneracy between age and extinction in the near-IR colours in the red
supergiant-dominated phase of evolution. The estimated near-IR ages cluster
between 9 and 30 Myr, i.e. the ages at which the molecular bands due to
luminous red supergiants are strongest in the current models. They do not
always agree with optical spectroscopic ages. Adding optical data sometimes
leads to the rejection of the solar neighbourhood extinction law. This is not
surprising considering small-scale structure around the clusters, but it has no
significant effect on the near-IR based spectroscopic ages. [abridged]Comment: 14 pages, 20 figures, uses aa.cl
Fundamental parameters and infrared excesses of Hipparcos stars
We derive the fundamental parameters (temperature and luminosity) of 107 619
Hipparcos stars and place these stars on a true Hertzsprung-Russell diagram.
This is achieved by comparing BT-Settl model atmospheres to spectral energy
distributions (SEDs) created from Hipparcos, Tycho, SDSS, DENIS, 2MASS, MSX,
AKARI, IRAS and WISE data. We also identify and quantify from these SEDs any
infrared excesses attributable to circumstellar matter. We compare our results
to known types of objects, focussing on the giant branch stars. Giant star dust
production (as traced by infrared excess) is found to start in earnest around
680 Lsun.Comment: 16 pages, 8 figures, accepted MNRA
Planetary Nebula dust haloes revealed by Herschel
Herschel Planetary Nebula Survey (HerPlaNS) is a far-IR imaging and spectroscopic survey of planetary nebulae, performedwith the Herschel Space Observatory, aiming at (1) establishing the spatially-resolved far-IR characteristics of the target nebulae and (2) understanding the energetics and shaping history of the circumstellar nebulae. Below we briefly demonstrate the breadth and depth of the HerPlaNS data set using one of the targets, NGC6781, as an example, and explore expectations in the era of SPICA, the next-generation far-IR mission
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