24,707 research outputs found
A new view on exoplanet transits: Transit of Venus described using three-dimensional solar atmosphere Stagger-grid simulations
Stellar activity and, in particular, convection-related surface structures,
potentially cause fluctuations that can affect the transit light curves.
Surface convection simulations can help the interpretation of ToV. We used
realistic three-dimensional radiative hydrodynamical simulation of the Sun from
the Stagger-grid and synthetic images computed with the radiative transfer code
Optim3D to provide predictions for the transit of Venus in 2004 observed by the
satellite ACRIMSAT. We computed intensity maps from RHD simulation of the Sun
and produced synthetic stellar disk image. We computed the light curve and
compared it to the ACRIMSAT observations and also to the light curves obtained
with solar surface representations carried out using radial profiles with
different limb-darkening laws. We also applied the same spherical tile imaging
method to the observations of center-to-limb Sun granulation with HINODE. We
managed to explain ACRIMSAT observations of 2004 ToV and showed that the
granulation pattern causes fluctuations in the transit light curve. We
evaluated the contribution of the granulation to the ToV. We showed that the
granulation pattern can partially explain the observed discrepancies between
models and data. This confirms that the limb-darkening and the granulation
pattern simulated in 3D RHD Sun represent well what is imaged by HINODE. In the
end, we found that the Venus's aureole contribution during ToV is less intense
than the solar photosphere, and thus negligible. Being able to explain
consistently the data of 2004 ToV is a new step forward for 3D RHD simulations
that are becoming essential for the detection and characterization of
exoplanets. They show that the granulation have to be considered as an
intrinsic incertitude, due to the stellar variability, on precise measurements
of exoplanet transits of, most likely, planets with small diameters.Comment: Accepted for publication in Astronomy and Astrophysic
What is the Mass of a Gap-Opening Planet?
High contrast imaging instruments such as GPI and SPHERE are discovering gap
structures in protoplanetary disks at an ever faster pace. Some of these gaps
may be opened by planets forming in the disks. In order to constrain planet
formation models using disk observations, it is crucial to find a robust way to
quantitatively back out the properties of the gap-opening planets, in
particular their masses, from the observed gap properties, such as their depths
and widths. Combing 2D and 3D hydrodynamics simulations with 3D radiative
transfer simulations, we investigate the morphology of planet-opened gaps in
near-infrared scattered light images. Quantitatively, we obtain correlations
that directly link intrinsic gap depths and widths in the gas surface density
to observed depths and widths in images of disks at modest inclinations under
finite angular resolution. Subsequently, the properties of the surface density
gaps enable us to derive the disk scale height at the location of the gap ,
and to constrain the quantity , where is the
mass of the gap-opening planet and characterizes the viscosity in the
gap. As examples, we examine the gaps recently imaged by VLT/SPHERE,
Gemini/GPI, and Subaru/HiCIAO in HD 97048, TW Hya, HD 169142, LkCa 15, and RX
J1615.3-3255. Scale heights of the disks and possible masses of the gap-opening
planets are derived assuming each gap is opened by a single planet. Assuming
, the derived planet mass in all cases are roughly between
0.1-1 .Comment: 40 pages (single column), 14 figures, 2 tables, ApJ publishe
Toward high-content/high-throughput imaging and analysis of embryonic morphogenesis
In vivo study of embryonic morphogenesis tremendously benefits from recent advances in live microscopy and computational analyses. Quantitative and automated investigation of morphogenetic processes opens the field to high-content and high-throughput strategies. Following experimental workflow currently developed in cell biology, we identify the key challenges for applying such strategies in developmental biology. We review the recent progress in embryo preparation and manipulation, live imaging, data registration, image segmentation, feature computation, and data mining dedicated to the study of embryonic morphogenesis. We discuss a selection of pioneering studies that tackled the current methodological bottlenecks and illustrated the investigation of morphogenetic processes in vivo using quantitative and automated imaging and analysis of hundreds or thousands of cells simultaneously, paving the way for high-content/high-throughput strategies and systems analysis of embryonic morphogenesis
- …