152 research outputs found
Calligraphic Stylisation Learning with a Physiologically Plausible Model of Movement and Recurrent Neural Networks
We propose a computational framework to learn stylisation patterns from example drawings or writings, and then generate new trajectories that possess similar stylistic qualities. We particularly focus on the generation and stylisation of trajectories that are similar to the ones that can be seen in calligraphy and graffiti art. Our system is able to extract and learn dynamic and visual qualities from a small number of user defined examples which can be recorded with a digitiser device, such as a tablet, mouse or motion capture sensors. Our system is then able to transform new user drawn traces to be kinematically and stylistically similar to the training examples. We implement the system using a Recurrent Mixture Density Network (RMDN) combined with a representation given by the parameters of the Sigma Lognormal model, a physiologically plausible model of movement that has been shown to closely reproduce the velocity and trace of human handwriting gestures
Chromosphere of K giant stars Geometrical extent and spatial structure detection
We aim to constrain the geometrical extent of the chromosphere of non-binary
K giant stars and detect any spatial structures in the chromosphere. We
performed observations with the CHARA interferometer and the VEGA beam combiner
at optical wavelengths. We observed seven non-binary K giant stars. We measured
the ratio of the radii of the photosphere to the chromosphere using the
interferometric measurements in the Halpha and the Ca II infrared triplet line
cores. For beta Ceti, spectro-interferometric observations are compared to an
non-local thermal equilibrium (NLTE) semi-empirical model atmosphere including
a chromosphere. The NLTE computations provide line intensities and contribution
functions that indicate the relative locations where the line cores are formed
and can constrain the size of the limb-darkened disk of the stars with
chromospheres. We measured the angular diameter of seven K giant stars and
deduced their fundamental parameters: effective temperatures, radii,
luminosities, and masses. We determined the geometrical extent of the
chromosphere for four giant stars. The chromosphere extents obtained range
between 16% to 47% of the stellar radius. The NLTE computations confirm that
the Ca II/849 nm line core is deeper in the chromosphere of ? Cet than either
of the Ca II/854 nm and Ca II/866 nm line cores. We present a modified version
of a semi-empirical model atmosphere derived by fitting the Ca II triplet line
cores of this star. In four of our targets, we also detect the signature of a
differential signal showing the presence of asymmetries in the chromospheres.
Conclusions. It is the first time that geometrical extents and structure in the
chromospheres of non-binary K giant stars are determined by interferometry.
These observations provide strong constrains on stellar atmosphere models.Comment: 10 pages, 12 figure
Spectral and spatial imaging of the Be+sdO binary phi Persei
The rapidly rotating Be star phi Persei was spun up by mass and angular
momentum transfer from a now stripped-down, hot subdwarf companion. Here we
present the first high angular resolution images of phi Persei made possible by
new capabilities in longbaseline interferometry at near-IR and visible
wavelengths. We observed phi Persei with the MIRC and VEGA instruments of the
CHARA Array. Additional MIRC-only observations were performed to track the
orbital motion of the companion, and these were fit together with new and
existing radial velocity measurements of both stars to derive the complete
orbital elements and distance. The hot subdwarf companion is clearly detected
in the near-IR data at each epoch of observation with a flux contribution of
1.5% in the H band, and restricted fits indicate that its flux contribution
rises to 3.3% in the visible. A new binary orbital solution is determined by
combining the astrometric and radial velocity measurements. The derived stellar
masses are 9.6+-0.3Msol and 1.2+-0.2Msol for the Be primary and subdwarf
secondary, respectively. The inferred distance (186 +- 3 pc), kinematical
properties, and evolutionary state are consistent with membership of phi Persei
in the alpha Per cluster. From the cluster age we deduce significant
constraints on the initial masses and evolutionary mass transfer processes that
transformed the phi Persei binary system. The interferometric data place strong
constraints on the Be disk elongation, orientation, and kinematics, and the
disk angular momentum vector is coaligned with and has the same sense of
rotation as the orbital angular momentum vector. The VEGA visible continuum
data indicate an elongated shape for the Be star itself, due to the combined
effects of rapid rotation, partial obscuration of the photosphere by the
circumstellar disk, and flux from the bright inner disk.Comment: 16 pages, 6 figures, 1 Anne
Requirements modelling and formal analysis using graph operations
The increasing complexity of enterprise systems requires a more advanced
analysis of the representation of services expected than is currently possible.
Consequently, the specification stage, which could be facilitated by formal
verification, becomes very important to the system life-cycle. This paper presents
a formal modelling approach, which may be used in order to better represent
the reality of the system and to verify the awaited or existing system’s properties,
taking into account the environmental characteristics. For that, we firstly propose
a formalization process based upon properties specification, and secondly we
use Conceptual Graphs operations to develop reasoning mechanisms of verifying
requirements statements. The graphic visualization of these reasoning enables us
to correctly capture the system specifications by making it easier to determine if
desired properties hold. It is applied to the field of Enterprise modelling
Grown-up stars physics with MATISSE
MATISSE represents a great opportunity to image the environment around
massive and evolved stars. This will allow one to put constraints on the
circumstellar structure, on the mass ejection of dust and its reorganization ,
and on the dust-nature and formation processes. MATISSE measurements will often
be pivotal for the understanding of large multiwavelength datasets on the same
targets collected through many high-angular resolution facilities at ESO like
sub-millimeter interferometry (ALMA), near-infrared adaptive optics (NACO,
SPHERE), interferometry (PIONIER, GRAVITY), spectroscopy (CRIRES), and
mid-infrared imaging (VISIR). Among main sequence and evolved stars, several
cases of interest have been identified that we describe in this paper.Comment: SPIE, Jun 2016, Edimbourgh, Franc
Time, spatial, and spectral resolution of the Halpha line-formation region of Deneb and Rigel with the VEGA/CHARA interferometer
BA-type supergiants are amongst the most optically-bright stars. They are
observable in extragalactic environments, hence potential accurate distance
indicators. Emission activity in the Halpha line of the BA supergiants Rigel
(B8Ia) and Deneb (A2Ia) is indicative of presence of localized time-dependent
mass ejections. Here, we employ optical interferometry to study the Halpha
line-formation region in these stellar environments. High spatial- (0.001
arcsec) and spectral- (R=30 000) resolution observations of Halpha were
obtained with the visible recombiner VEGA installed on the CHARA
interferometer, using the S1S2 array-baseline (34m). Six independent
observations were done on Deneb over the years 2008 and 2009, and two on Rigel
in 2009. We analyze this dataset with the 1D non-LTE radiative-transfer code
CMFGEN, and assess the impact of the wind on the visible and near-IR
interferometric signatures, using both Balmer-line and continuum photons. We
observe a visibility decrease in Halpha for both Rigel and Deneb, suggesting
that the line-formation region is extended (1.5-1.75 R*). We observe a
significant visibility decrease for Deneb in the SiII6371 line. We witness time
variations in the differential phase for Deneb, implying an inhomogeneous and
unsteady circumstellar environment, while no such variability is seen in
differential visibilities. Radiative-transfer modeling of Deneb, with allowance
for stellar-wind mass loss, accounts fairly well for the observed decrease in
the Halpha visibility. Based on the observed differential visibilities, we
estimate that the mass-loss rate of Deneb has changed by less than 5%
Multi-epoch Near-Infrared Interferometry of the Spatially Resolved Disk Around the Be Star Zeta Tau
We present interferometric observations of the Be star Zeta Tau obtained
using the MIRC beam combiner at the CHARA Array. We resolved the disk during
four epochs in 2007-2009. We fit the data with a geometric model to
characterize the circumstellar disk as a skewed elliptical Gaussian and the
central Be star as a uniform disk. The visibilities reveal a nearly edge-on
disk with a FWHM major axis of ~ 1.8 mas in the H-band. The non-zero closure
phases indicate an asymmetry within the disk. Interestingly, when combining our
results with previously published interferometric observations of Zeta Tau, we
find a correlation between the position angle of the disk and the spectroscopic
V/R ratio, suggesting that the tilt of the disk is precessing. This work is
part of a multi-year monitoring campaign to investigate the development and
outward motion of asymmetric structures in the disks of Be stars.Comment: Accepted for publication in the Astronomical Journal. 27 pages, 7
Figure
High-dispersion spectroscopic monitoring of the Be/X-ray binary A0535+26/V725 Tau I: The long-term profile variability
We report on optical high-dispersion spectroscopic monitoring observations of
the Be/X-ray binary A0535+26/V725 Tau, carried out from November 2005 to March
2009. The main aim of these monitoring observations is to study spectral
variabilities in the Be disc, on both the short (a week or so) and long (more
than hundreds of days) timescales, by taking long-term frequent observations.
Our four-year spectroscopic observations indicate that the V/R ratio, i.e., the
relative intensity of the violet (V) peak to the red (R) one, of the
double-peaked H-alpha line profile varies with a period of 500 days. The H-beta
line profile also varies in phase with the H-alpha profile. With these
observations covering two full cycles of the V/R variability, we reconstruct
the 2-D structure of the Be disc by applying the Doppler tomography method to
the H-alpha and H-beta emission line profiles, using a rigidly rotating frame
with the V/R variability period. The resulting disc structure reveals
non-axisymmetric features, which can be explained by a one-armed perturbation
in the Be disc. It is the first time that an eccentric disc structure is
directly detected by using a method other than the interferometric one.Comment: (10 pages, 9 figures, accepted to MNRAS
An investigation of the close environment of beta Cep with the VEGA/CHARA interferometer
High-precision interferometric measurements of pulsating stars help to
characterize their close environment. In 1974, a close companion was discovered
around the pulsating star beta Cep using the speckle interferometry technique
and features at the limit of resolution (20 milli-arcsecond or mas) of the
instrument were mentioned that may be due to circumstellar material. Beta Cep
has a magnetic field that might be responsible for a spherical shell or
ring-like structure around the star as described by the MHD models. Using the
visible recombiner VEGA installed on the CHARA long-baseline interferometer at
Mt. Wilson, we aim to determine the angular diameter of beta Cep and resolve
its close environment with a spatial resolution up to 1 mas level. Medium
spectral resolution (R=6000) observations of beta Cep were secured with the
VEGA instrument over the years 2008 and 2009. These observations were performed
with the S1S2 (30m) and W1W2 (100m) baselines of the array. We investigated
several models to reproduce our observations. A large-scale structure of a few
mas is clearly detected around the star with a typical flux relative
contribution of 0.23 +- 0.02. Our best model is a co-rotational geometrical
thin ring around the star as predicted by magnetically-confined wind shock
models. The ring inner diameter is 8.2 +- 0.8 mas and the width is 0.6 +- 0.7
mas. The orientation of the rotation axis on the plane of the sky is PA = 60 +-
1 deg, while the best fit of the mean angular diameter of beta Cep gives UD[V]
= 0.22 +- 0.05 mas. Our data are compatible with the predicted position of the
close companion of beta Cep. These results bring additional constraints on the
fundamental parameters and on the future MHD and asteroseismological models of
the star.Comment: Paper accepted for publication in A&A (in press
The Carlina-type diluted telescope: Stellar fringes on Deneb
Context. The performance of interferometers has largely been increased over
the last ten years. But the number of observable objects is still limited due
to the low sensitivity and imaging capability of the current facilities.
Studies have been done to propose a new generation of interferometers. Aims.
The Carlina concept studied at the Haute-Provence Observatory consists in an
optical interferometer configured as a diluted version of the Arecibo radio
telescope: above the diluted primary mirror made of fixed co-spherical
segments, a helium balloon or cables suspended between two mountains and/or
pylons, carries a gondola containing the focal optics. This concept does not
require delay lines. Methods. Since 2003, we have been building a technical
demonstrator of this diluted telescope. The main goals of this project were to
find the opto-mechanical solutions to stabilize the optics attached under
cables at several tens of meters above the ground, and to characterize this
diluted telescope under real conditions. In 2012, we have obtained metrology
fringes, and co-spherized the primary mirrors within one micron accuracy. In
2013, we have tested the whole optical train: servo loop, metrology, and the
focal gondola. Results. We obtained stellar fringes on Deneb in September 2013.
In this paper, we present the characteristics of these observations: quality of
the guiding, S /N reached, and possible improvements for a future system.
Conclusions. It is an important step that demonstrates the feasibility of
building a diluted telescope using cables strained between cliffs or pylons.
Carlina, like the MMT or LBT, could be one of the first members of a new class
of telescopes named Large Diluted Telescopes. Its optical architecture has many
advantages for future projects: Planet Formation Imager, Post-ELTs,
Interferometer in space.Comment: 8 pages, 7 figures, Astronomy & Astrophysic
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