64 research outputs found
Retrieval Analysis of the Emission Spectrum of WASP-12b: Sensitivity of Outcomes to Prior Assumptions and Implications for Formation History
We analyze the emission spectrum of the hot Jupiter WASP-12b using our HELIOS-R retrieval code and HELIOS-K opacity calculator. When interpreting Hubble and Spitzer data, the retrieval outcomes are found to be prior-dominated. When the prior distributions of the molecular abundances are assumed to be log-uniform, the volume mixing ratio of HCN is found to be implausibly high. A VULCAN chemical kinetics model of WASP-12b suggests that chemical equilibrium is a reasonable assumption even when atmospheric mixing is implausibly rigorous. Guided by (exo)planet formation theory, we set Gaussian priors on the elemental abundances of carbon, oxygen, and nitrogen with the Gaussian peaks being centered on the measured C/H, O/H, and N/H values of the star. By enforcing chemical equilibrium, we find substellar O/H and stellar to slightly superstellar C/H for the dayside atmosphere of WASP-12b. The superstellar carbon-to-oxygen ratio is just above unity, regardless of whether clouds are included in the retrieval analysis, consistent with Madhusudhan et al. Furthermore, whether a temperature inversion exists in the atmosphere depends on one's assumption for the Gaussian width of the priors. Our retrieved posterior distributions are consistent with the formation of WASP-12b in a solar-composition protoplanetary disk, beyond the water iceline, via gravitational instability or pebble accretion (without core erosion) and migration inward to its present orbital location via a disk-free mechanism, and are inconsistent with both in situ formation and core accretion with disk migration, as predicted by Madhusudhan et al. We predict that the interpretation of James Webb Space Telescope WASP-12b data will not be prior-dominated
Orbital Architectures of Planet-Hosting Binaries:I. Forming Five Small Planets in the Truncated Disk of Kepler-444A
We present the first results from our Keck program investigating the orbital
architectures of planet-hosting multiple star systems. Kepler-444 is a
metal-poor triple star system that hosts five sub-Earth-sized planets orbiting
the primary star (Kepler-444A), as well as a spatially unresolved pair of M
dwarfs (Kepler-444BC) at a projected distance of 1.8" (66 AU). We combine our
Keck/NIRC2 adaptive optics astrometry with multi-epoch Keck/HIRES RVs of all
three stars to determine a precise orbit for the BC pair around A, given their
empirically constrained masses. We measure minimal astrometric motion
( mas yr, or km s), but our RVs reveal
significant orbital velocity ( km s) and acceleration
( m s yr). We determine a highly eccentric stellar
orbit () that brings the tight M dwarf pair within
AU of the planetary system. We validate that the system is
dynamically stable in its present configuration via n-body simulations. We find
that the ABC orbit and planetary orbits are likely aligned (98%) given that
they both have edge-on orbits and misalignment induces precession of the
planets out of transit. We conclude that the stars were likely on their current
orbits during the epoch of planet formation, truncating the protoplanetary disk
at 2 AU. This truncated disk would have been severely depleted of
solid material from which to form the total 1.5 of
planets. We thereby strongly constrain the efficiency of the conversion of dust
into planets and suggest that the Kepler-444 system is consistent with models
that explain the formation of more typical close-in Kepler planets in normal,
not truncated, disks.Comment: accepted to Ap
THE TRENDS HIGH-CONTRAST IMAGING SURVEY. VI. DISCOVERY OF A MASS, AGE, AND METALLICITY BENCHMARK BROWN DWARF
Neurovascular unit dysfunction with blood-brain barrier hyperpermeability contributes to major depressive disorder: a review of clinical and experimental evidence
About one-third of people with major depressive disorder (MDD) fail at least two antidepressant drug trials at 1 year. Together with clinical and experimental evidence indicating that the pathophysiology of MDD is multifactorial, this observation underscores the importance of elucidating mechanisms beyond monoaminergic dysregulation that can contribute to the genesis and persistence of MDD. Oxidative stress and neuroinflammation are mechanistically linked to the presence of neurovascular dysfunction with blood-brain barrier (BBB) hyperpermeability in selected neurological disorders, such as stroke, epilepsy, multiple sclerosis, traumatic brain injury, and Alzheimer’s disease. In contrast to other major psychiatric disorders, MDD is frequently comorbid with such neurological disorders and constitutes an independent risk factor for morbidity and mortality in disorders characterized by vascular endothelial dysfunction (cardiovascular disease and diabetes mellitus). Oxidative stress and neuroinflammation are implicated in the neurobiology of MDD. More recent evidence links neurovascular dysfunction with BBB hyperpermeability to MDD without neurological comorbidity. We review this emerging literature and present a theoretical integration between these abnormalities to those involving oxidative stress and neuroinflammation in MDD. We discuss our hypothesis that alterations in endothelial nitric oxide levels and endothelial nitric oxide synthase uncoupling are central mechanistic links in this regard. Understanding the contribution of neurovascular dysfunction with BBB hyperpermeability to the pathophysiology of MDD may help to identify novel therapeutic and preventative approaches
Autoimmune psychosis: an international consensus on an approach to the diagnosis and management of psychosis of suspected autoimmune origin
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