4,347 research outputs found
Milli-arcsecond images of the Herbig Ae star HD 163296
The very close environments of young stars are the hosts of fundamental
physical processes, such as planet formation, star-disk interactions, mass
accretion, and ejection. The complex morphological structure of these
environments has been confirmed by the now quite rich data sets obtained for a
few objects by near-infrared long-baseline interferometry. We gathered numerous
interferometric measurements for the young star HD163296 with various
interferometers (VLTI, IOTA, KeckI and CHARA), allowing for the first time an
image independent of any a priori model to be reconstructed. Using the
Multi-aperture image Reconstruction Algorithm (MiRA), we reconstruct images of
HD 163296 in the H and K bands. We compare these images with reconstructed
images obtained from simulated data using a physical model of the environment
of HD 163296. We obtain model-independent and -band images of the
surroundings of HD 163296. The images present several significant features that
we can relate to an inclined asymmetric flared disk around HD 163296 with the
strongest intensity at about 4-5 mas. Because of the incomplete spatial
frequency coverage, we cannot state whether each of them individually is
peculiar in any way. For the first time, milli-arcsecond images of the
environment of a young star are produced. These images confirm that the
morphology of the close environment of young stars is more complex than the
simple models used in the literature so far.Comment: 11 pages, 10 figures, accepted A&A pape
On-chip spectro-detection for fully integrated coherent beam combiners
This paper presents how photonics associated with new arising detection
technologies is able to provide fully integrated instrument for coherent beam
combination applied to astrophysical interferometry. The feasibility and
operation of on-chip coherent beam combiners has been already demonstrated
using various interferometric combination schemes. More recently we proposed a
new detection principle aimed at directly sampling and extracting the spectral
information of an input signal together with its flux level measurement. The
so-called SWIFTS demonstrated concept that stands for Stationary-Wave
Integrated Fourier Transform Spectrometer, provides full spectral and spatial
information recorded simultaneously thanks to a motionless detecting device.
Due to some newly available detection principles considered for the
implementation of the SWIFTS concept, some technologies can even provide
photo-counting operation that brought a significant extension of the
interferometry domain of investigation in astrophysics . The proposed concept
is applicable to most of the interferometric instrumental modes including
fringe tracking, fast and sensitive detection, Fourier spectral reconstruction
and also to manage a large number of incoming beams. The paper presents three
practical implementations, two dealing with pair-wise integrated optics beam
combinations and the third one with an all-in-one 8 beam combination. In all
cases the principles turned into a pair wise baseline coding after proper data
processing.Comment: 12 pages, 6 figures, part of the Optics Express special issue
dedicated to Astrophotonic
Variational data assimilation for 2D fluvial hydraulics simulations
International audienceA numerical method for model parameters identification is presented for a river model based on a finite volume discretization of the bidimensional shallow water equations. We use variational data assimilation to combine optimally physical information from the model and observation data of the physical system in order to identify the value of model inputs that correspond to a numerical simulation which is consistent with reality. Two numerical examples demonstrate the efficiency of the method for the identification of the inlet discharge and the bed elevation. An application to real data on the Pearl River for the identification of boundary conditions is presented
Plan de negocio de la empresa Vapiano
El presente proyecto tiene como objetivo el estudio de viabilidad de una empresa dedicada a la restauración, concretamente la franquicia del restaurante Vapiano. Vapiano es un restaurante especializado en pizzas, pasta fresca y ensaladas gourmet, con un concepto de negocio totalmente innovador. El hecho de haber nacido en el año 2002 y estar actualmente presente en 26 países de 4 continentes hace prever que es una compañía en auge. Por este motivo, la idea principal ha sido estudiar una posible apertura del primer restaurante de esta cadena en España, concretamente en Barcelona. Con esta finalidad se presenta un plan de empresa que abarca desde la definición de la idea a desarrollar hasta la forma concreta de llevarla a la práctica. Para ello, se ha dividido en distintos apartados estructurados de la siguiente manera:
- Presentación de la empresa y concepto de negocio.
- Estudio del modelo de negocio ya existente. Asimismo, se ha realizado un análisis de la oportunidad estudiando el entorno competitivo, las cinco fuerzas de Porter y el análisis DAFO.
- Por otra parte, se ha realizado un Plan de Marketing, Plan de Operaciones y Plan de Organización y Recursos Humanos.
- Desde el punto de vista económico, se ha estudiado la viabilidad del negocio y se ha observado si generaría beneficios comparándolo con los distintos escenarios.
- Por último, se ha elaborado un informe sobre los aspectos jurídicos derivados del proyecto estudiando las ventajas e inconvenientes de la franquicia
Multiplicity of Galactic Cepheids from long-baseline interferometry. II. The Companion of AX Circini revealed with VLTI/PIONIER
Aims: We aim at detecting and characterizing the main-sequence companion of
the Cepheid AX Cir ( 18 yrs). The long-term objective is
to estimate the mass of both components and the distance to the system.
Methods: We used the PIONIER combiner at the VLT Interferometer to obtain the
first interferometric measurements of the short-period Cepheid AX Cir and its
orbiting component. Results: The companion is resolved by PIONIER at a
projected separation mas and projection angle . We measured -band flux ratios between the companion and
the Cepheid of % and %, respectively at a
pulsation phase for the Cepheid and 0.48. The lower contrast at
is due to increased brightness of the Cepheid compared to the
. This gives an average apparent magnitude mag. The limb-darkened angular diameter of the Cepheid at the
two pulsation phases was measured to be
mas and mas, respectively at and 0.48. A lower limit on the total mass of the system was also derived
based on our measured separation, we found .Comment: Accepted for publication in Astronomy and Astrophysic
MYSTIC: Michigan Young STar Imager at CHARA
We present the design for MYSTIC, the Michigan Young STar Imager at CHARA.
MYSTIC will be a K-band, cryogenic, 6-beam combiner for the Georgia State
University CHARA telescope array. The design follows the image-plane
combination scheme of the MIRC instrument where single-mode fibers bring
starlight into a non-redundant fringe pattern to feed a spectrograph. Beams
will be injected in polarization-maintaining fibers outside the cryogenic dewar
and then be transported through a vacuum feedthrough into the ~220K cold volume
where combination is achieved and the light is dispersed. We will use a C-RED
One camera (First Light Imaging) based on the eAPD SAPHIRA detector to allow
for near-photon-counting performance. We also intend to support a 4-telescope
mode using a leftover integrated optics component designed for the VLTI-GRAVITY
experiment, allowing better sensitivity for the faintest targets. Our primary
science driver motivation is to image disks around young stars in order to
better understand planet formation and how forming planets might influence disk
structures.Comment: Presented at the 2018 SPIE Astronomical Telescopes + Instrumentation,
Austin, Texas, US
Optical volume and mass measurements show that mammalian cells swell during mitosis
International audienceThe extent, mechanism, and function of cell volume changes during specific cellular events, such as cell migration and cell division, have been poorly studied, mostly because of a lack of adequate techniques. Here we unambiguously report that a large range of mammalian cell types display a significant increase in volume during mitosis (up to 30%). We further show that this increase in volume is tightly linked to the mitotic state of the cell and not to its spread or rounded shape and is independent of the presence of an intact actomyosin cortex. Importantly, this volume increase is not accompanied by an increase in dry mass and thus corresponds to a decrease in cell density. This mitotic swelling might have important consequences for mitotic progression: it might contribute to produce strong pushing forces, allowing mitotic cells to round up; it might also, by lowering cytoplasmic density, contribute to the large change of physicochemical properties observed in mitotic cells
Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse
We present high-resolution 4.6micron CO spectra of the circumstellar
environments of two RSGs that are potential SN progenitors: Betelgeuse and VY
CMa. Around Betelgeuse, 12CO emission within 3arcsec follows a mildly clumpy
but otherwise spherical shell, smaller than its 55arcsec shell in KI
lambda7699. In stark contrast, 4.6micron CO emission around VY CMa is
coincident with bright KI in its clumpy asymmetric reflection nebula, within
5arcsec of the star. Our CO data reveal redshifted features not seen in KI
spectra of VY CMa, indicating a more isotropic distribution of gas punctuated
by randomly distributed asymmetric clumps. The relative CO and KI distribution
in Betelgeuse arises from ionization effects within a steady wind, whereas in
VY CMa, KI is emitted from skins of CO cloudlets resulting from episodic mass
ejections 500--1000 yr ago. In both cases, CO and KI trace potential pre-SN
circumstellar matter: we conclude that an extreme RSG like VY CMa might produce
a Type IIn event like SN1988Z if it were to explode in its current state, but
Betelgeuse will not. VY CMa demonstrates that LBVs are not necessarily the only
progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer
enhanced episodic mass loss shortly before exploding.Comment: 16 pages, AJ accepte
Kalman-filter control schemes for fringe tracking. Development and application to VLTI/GRAVITY
The implementation of fringe tracking for optical interferometers is
inevitable when optimal exploitation of the instrumental capacities is desired.
Fringe tracking allows continuous fringe observation, considerably increasing
the sensitivity of the interferometric system. In addition to the correction of
atmospheric path-length differences, a decent control algorithm should correct
for disturbances introduced by instrumental vibrations, and deal with other
errors propagating in the optical trains. We attempt to construct control
schemes based on Kalman filters. Kalman filtering is an optimal data processing
algorithm for tracking and correcting a system on which observations are
performed. As a direct application, control schemes are designed for GRAVITY, a
future four-telescope near-infrared beam combiner for the Very Large Telescope
Interferometer (VLTI). We base our study on recent work in adaptive-optics
control. The technique is to describe perturbations of fringe phases in terms
of an a priori model. The model allows us to optimize the tracking of fringes,
in that it is adapted to the prevailing perturbations. Since the model is of a
parametric nature, a parameter identification needs to be included. Different
possibilities exist to generalize to the four-telescope fringe tracking that is
useful for GRAVITY. On the basis of a two-telescope Kalman-filtering control
algorithm, a set of two properly working control algorithms for four-telescope
fringe tracking is constructed. The control schemes are designed to take into
account flux problems and low-signal baselines. First simulations of the
fringe-tracking process indicate that the defined schemes meet the requirements
for GRAVITY and allow us to distinguish in performance. In a future paper, we
will compare the performances of classical fringe tracking to our Kalman-filter
control.Comment: 17 pages, 8 figures, accepted for publication in A&
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