2,982 research outputs found
TESS unveils the phase curve of WASP-33b. Characterization of the planetary atmosphere and the pulsations from the star
We present the detection and characterization of the full-orbit phase curve
and secondary eclipse of the ultra-hot Jupiter WASP-33b at optical wavelengths,
along with the pulsation spectrum of the host star. We analyzed data collected
by the Transiting Exoplanet Survey Satellite (TESS) in sector 18. WASP-33b
belongs to a very short list of highly irradiated exoplanets that were
discovered from the ground and were later visited by TESS. The host star of
WASP-33b is of delta Scuti-type and shows nonradial pulsations in the
millimagnitude regime, with periods comparable to the period of the primary
transit. These completely deform the photometric light curve, which hinders our
interpretations. By carrying out a detailed determination of the pulsation
spectrum of the host star, we find 29 pulsation frequencies with a
signal-to-noise ratio higher than 4. After cleaning the light curve from the
stellar pulsations, we confidently report a secondary eclipse depth of 305.8
+/- 35.5 parts-per-million (ppm), along with an amplitude of the phase curve of
100.4 +/- 13.1 ppm and a corresponding westward offset between the region of
maximum brightness and the substellar point of 28.7 +/- 7.1 degrees, making
WASP-33b one of the few planets with such an offset found so far. Our derived
Bond albedo, A_B = 0.369 +/- 0.050, and heat recirculation efficiency, epsilon
= 0.189 +/- 0.014, confirm again that he behavior of WASP-33b is similar to
that of other hot Jupiters, despite the high irradiation received from its host
star. By connecting the amplitude of the phase curve to the primary transit and
depths of the secondary eclipse, we determine that the day- and nightside
brightness temperatures of WASP-33b are 3014 +/- 60 K and 1605 +/- 45 K,
respectively. From the detection of photometric variations due to gravitational
interactions, we estimate a planet mass of M_P = 2.81 +/- 0.53 M$_J.Comment: 19 pages, 15 figure
Biomechanical models and mechanisms of cellular morphogenesis and cerebral cortical expansion and folding
Morphogenesis of the nervous system involves a highly complex spatio-temporal pattern of physical forces (mainly tension and pressure) acting on cells and tissues that are pliable but have an intricately organized cytoskeletal infrastructure. This review begins by covering basic principles of biomechanics and the core cytoskeletal toolkit used to regulate the shapes of cells and tissues during embryogenesis and neural development. It illustrates how the principle of \u27tensegrity\u27 provides a useful conceptual framework for understanding how cells dynamically respond to forces that are generated internally or applied externally. The latter part of the review builds on this foundation in considering the development of mammalian cerebral cortex. The main focus is on cortical expansion and folding - processes that take place over an extended period of prenatal and postnatal development. Cortical expansion and folding are likely to involve many complementary mechanisms, some related to regulating cell proliferation and migration and others related to specific types and patterns of mechanical tension and pressure. Three distinct multi-mechanism models are evaluated in relation to a set of 18 key experimental observations and findings. The Composite Tension Plus (CT+) model is introduced as an updated version of a previous multi-component Differential Expansion Sandwich Plus (DES+) model (Van Essen, 2020); the new CT+ model includes 10 distinct mechanisms and has the greatest explanatory power among published models to date. Much needs to be done in order to validate specific mechanistic components and to assess their relative importance in different species, and important directions for future research are suggested
Kepler-210: An active star with at least two planets
We report the detection and characterization of two short-period,
Neptune-sized planets around the active host star Kepler-210. The host star's
parameters derived from those planets are (a) mutually inconsistent and (b) do
not conform to the expected host star parameters. We furthermore report the
detection of transit timing variations (TTVs) in the O-C diagrams for both
planets. We explore various scenarios that explain and resolve those
discrepancies. A simple scenario consistent with all data appears to be one
that attributes substantial eccentricities to the inner short-period planets
and that interprets the TTVs as due to the action of another, somewhat longer
period planet. To substantiate our suggestions, we present the results of
N-body simulations that modeled the TTVs and that checked the stability of the
Kepler-210 system.Comment: 8 pages, 8 Encapsulated Postscript figure
Exploring Digital Transformations of Community, Culture and Welfare in Austere Times: the Case of Leeds. Interim Report
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