201 research outputs found
Limb Darkening and Planetary Transits II: Intensity profile correction factors for a grid of model stellar atmospheres
The ability to observe extrasolar planets transiting their stars has
profoundly changed our understanding of these planetary systems. However, these
measurements depend on how well we understand the properties of the host star,
such as radius, luminosity and limb darkening. Traditionally, limb darkening is
treated as a parameterization in the analysis, but these simple
parameterizations are not accurate representations of actual center-to-limb
intensity variations (CLIV) to the precision needed for interpreting these
transit observations. This effect leads to systematic errors for the measured
planetary radii and corresponding measured spectral features. We compute
synthetic planetary transits using model stellar atmosphere CLIV and
corresponding best-fit limb-darkening laws for a grid spherically symmetric
model stellar atmospheres. From these light curves we measure the differences
in flux as a function of the star's effective temperature, gravity, mass, and
the inclination of the planet's orbit.Comment: 10 pages, 8 figures, submitted to AAS journals. Comments welcom
Control interface concepts for CHARA 6-telescope fringe tracking with CHAMP+MIRC
Cophasing six telescopes from the CHARA array, the CHARA-Michigan
Phasetracker (CHAMP) and Michigan Infrared Combiner (MIRC) are pushing the
frontiers of infrared long-baseline interferometric imaging in key scientific
areas such as star- and planet-formation. Here we review our concepts and
recent improvements on the CHAMP and MIRC control interfaces, which establish
the communication to the real-time data recording & fringe tracking code,
provide essential performance diagnostics, and assist the observer in the
alignment and flux optimization procedure. For fringe detection and tracking
with MIRC, we have developed a novel matrix approach, which provides
predictions for the fringe positions based on cross-fringe information.Comment: 6 pages, 4 figures, published in SPIE conference proceedings
(http://dx.doi.org/10.1117/12.926559
The 2010 Interferometric Imaging Beauty Contest
We present the results of the fourth Optical/IR Interferometry Imaging Beauty
Contest. The contest consists of blind imaging of test data sets derived from
model sources and distributed in the OI-FITS format. The test data consists of
spectral data sets on an object "observed" in the infrared with spectral
resolution. There were 4 different algorithms competing this time: BSMEM the
Bispectrum Maximum Entropy Method by Young, Baron & Buscher; RPR the Recursive
Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo
algorithm by Baron, Monnier & Kloppenborg; and, WISARD the Weak-phase
Interferometric Sample Alternating Reconstruction Device by Vannier & Mugnier.
The contest model image, the data delivered to the contestants and the rules
are described as well as the results of the image reconstruction obtained by
each method. These results are discussed as well as the strengths and
limitations of each algorithm.Comment: To be published in SPIE 2010 "Optical and infrared interferometry II
Fringe tracking and spatial filtering: phase jumps and dropouts
Fringe tracking in interferometers is typically analyzed with the implicit
assumption that there is a single phase associated with each telescope in the
array. If the telescopes have apertures significantly larger than r0 and only
partial adaptive optics correction, then the phase measured by a fringe sensor
may differ significantly from the "piston" component of the aperture phase. In
some cases, speckle noise will cause "branch points" in the measured phase as a
function of time, causing large and sudden jumps in the phase. We present
simulations showing these effects in order to understand their implications for
the design of fringe tracking algorithms.Comment: 9 pages, to be published in Proc. SPIE conference 7013 "Optical and
Infrared Interferometry", Schoeller, Danchi, and Delplancke (eds.
The importance of material used in speech therapy : two case studies in minimally conscious state patients
Speech therapy can be part of the care pathway for patients recovering from comas and presenting a disorder of consciousness (DOC). Although there are no official recommendations for speech therapy follow-up, neuroscientific studies suggest that relevant stimuli may have beneficial effects on the behavioral assessment of patients with a DOC. In two case studies, we longitudinally measured (from 4 to 6 weeks) the behavior (observed in a speech therapy session or using items from the Coma Recovery Scale—Revised) of two patients in a minimally conscious state (MCS) when presenting music and/or autobiographical materials. The results highlight the importance of using relevant material during a speech therapy session and suggest that a musical context with a fast tempo could improve behavior evaluation compared to noise. This work supports the importance of adapted speech therapy for MCS patients and encourages larger studies to confirm these initial observations
Why Chromatic Imaging Matters
During the last two decades, the first generation of beam combiners at the
Very Large Telescope Interferometer has proved the importance of optical
interferometry for high-angular resolution astrophysical studies in the near-
and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v
coverage per pointing increases significantly, providing an opportunity to use
reconstructed images as powerful scientific tools. Therefore, interferometric
imaging is already a key feature of the new generation of VLTI instruments, as
well as for other interferometric facilities like CHARA and JWST. It is thus
imperative to account for the current image reconstruction capabilities and
their expected evolutions in the coming years. Here, we present a general
overview of the current situation of optical interferometric image
reconstruction with a focus on new wavelength-dependent information,
highlighting its main advantages and limitations. As an Appendix we include
several cookbooks describing the usage and installation of several state-of-the
art image reconstruction packages. To illustrate the current capabilities of
the software available to the community, we recovered chromatic images, from
simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we
aim at showing the importance of selecting good regularization functions and
their impact on the reconstruction.Comment: Accepted for publication in Experimental Astronomy as part of the
topical collection: Future of Optical-infrared Interferometry in Europ
Compositional and mechanical properties of growing cortical bone tissue: a study of the human fibula
International audienc
Interferometry of Aurigae: Characterization of the asymmetric eclipsing disk
We report on a total of 106 nights of optical interferometric observations of
the Aurigae system taken during the last 14 years by four beam
combiners at three different interferometric facilities. This long sequence of
data provides an ideal assessment of the system prior to, during, and after the
recent 2009-2011 eclipse. We have reconstructed model-independent images from
the 10 in-eclipse epochs which show that a disk-like object is indeed
responsible for the eclipse. Using new 3D, time-dependent modeling software, we
derive the properties of the F-star (diameter, limb darkening), determine
previously unknown orbital elements (, ), and access the global
structures of the optically thick portion of the eclipsing disk using both
geometric models and approximations of astrophysically relevant density
distributions. These models may be useful in future hydrodynamical modeling of
the system. Lastly, we address several outstanding research questions including
mid-eclipse brightening, possible shrinking of the F-type primary, and any
warps or sub-features within the disk.Comment: 105 pages, 57 figures. This is an author-created, un-copyedited
version of an article accepted for publication in Astrophysical Journal
Supplement Series. IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
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