3,414 research outputs found
An L Band Spectrum of the Coldest Brown Dwarf
The coldest brown dwarf, WISE 0855, is the closest known planetary-mass,
free-floating object and has a temperature nearly as cold as the solar system
gas giants. Like Jupiter, it is predicted to have an atmosphere rich in
methane, water, and ammonia, with clouds of volatile ices. WISE 0855 is faint
at near-infrared wavelengths and emits almost all its energy in the
mid-infrared. Skemer et al. 2016 presented a spectrum of WISE 0855 from 4.5-5.1
micron (M band), revealing water vapor features. Here, we present a spectrum of
WISE 0855 in L band, from 3.4-4.14 micron. We present a set of atmosphere
models that include a range of compositions (metallicities and C/O ratios) and
water ice clouds. Methane absorption is clearly present in the spectrum. The
mid-infrared color can be better matched with a methane abundance that is
depleted relative to solar abundance. We find that there is evidence for water
ice clouds in the M band spectrum, and we find a lack of phosphine spectral
features in both the L and M band spectra. We suggest that a deep continuum
opacity source may be obscuring the near-infrared flux, possibly a deep
phosphorous-bearing cloud, ammonium dihyrogen phosphate. Observations of WISE
0855 provide critical constraints for cold planetary atmospheres, bridging the
temperature range between the long-studied solar system planets and accessible
exoplanets. JWST will soon revolutionize our understanding of cold brown dwarfs
with high-precision spectroscopy across the infrared, allowing us to study
their compositions and cloud properties, and to infer their atmospheric
dynamics and formation processes.Comment: 19 pages, 21 figures. Accepted for publication in Ap
A transmission spectrum of the sub-Earth planet L98-59~b in 1.1-1.7 m
With the increasing number of planets discovered by TESS, the atmospheric
characterization of small exoplanets is accelerating. L98-59 is a M-dwarf
hosting a multi-planet system, and so far, four small planets have been
confirmed. The innermost planet b is smaller and lighter
than Earth, and should thus have a predominantly rocky composition. The Hubble
Space Telescope observed five primary transits of L98-59b in m,
and here we report the data analysis and the resulting transmission spectrum of
the planet. We measure the transit depths for each of the five transits and, by
combination, we obtain a transmission spectrum with an overall precision of
ppm in for each of the 18 spectrophotometric channels. With this level
of precision, the transmission spectrum does not show significant modulation,
and is thus consistent with a planet without any atmosphere or a planet having
an atmosphere and high-altitude clouds or haze. The scenarios involving an
aerosol-free, H-dominated atmosphere with HO or CH are inconsistent
with the data. The transmission spectrum also disfavors, but does not rules
out, an HO-dominated atmosphere without clouds. A spectral retrieval
process suggests that an H-dominated atmosphere with HCN and clouds or haze
may be the preferred solution, but this indication is non-conclusive. Future
James Webb Space Telescope observations may find out the nature of the planet
among the remaining viable scenarios.Comment: 17 pages, 5 figures, 7 tables, accepted for publication in A
Vacuum polarization on topological black holes
We investigate quantum effects on topological black hole space-times within the framework of quantum field theory on curved space-times. Considering a quantum scalar field, we extend a recent mode-sum regularization prescription for the computation of the renormalized vacuum polarization to asymptotically anti-de Sitter black holes with nonspherical event horizon topology. In particular, we calculate the vacuum polarization for a massless, conformally-coupled scalar field on a four-dimensional topological Schwarzschild–anti-de Sitter black hole background, comparing our results with those for a spherically-symmetric black hole
Improving recruitment to a study of telehealth management for long-term conditions in primary care: two embedded, randomised controlled trials of optimised patient information materials
Background: Patient understanding of study information is fundamental to gaining informed consent to take part in a randomised controlled trial. In order to meet the requirements of research ethics committees, patient information materials can be long and need to communicate complex messages. There is concern that standard approaches to providing patient information may deter potential participants from taking part in trials. The Systematic Techniques for Assisting Recruitment to Trials (MRC-START) research programme aims to test interventions to improve trial recruitment. The aim of this study was to investigate the effect on recruitment of optimised patient information materials (with improved readability and ease of comprehension) compared with standard materials. The study was embedded within two primary care trials involving patients with long-term conditions.
Methods: The Healthlines Study involves two linked trials evaluating a telehealth intervention in patients with depression (Healthlines Depression) or raised cardiovascular disease risk (Healthlines CVD). We conducted two trials of a recruitment intervention, embedded within the Healthlines host trials. Patients identified as potentially eligible in each of the Healthlines trials were randomised to receive either the original patient information materials or optimised versions of these materials. Primary outcomes were the proportion of participants randomised (Healthlines Depression) and the proportion expressing interest in taking part (Healthlines CVD).
Results: In Healthlines Depression (n = 1364), 6.3 % of patients receiving the optimised patient information materials were randomised into the study compared to 4.0 % in those receiving standard materials (OR = 1.63, 95 % CI = 1.00 to 2.67). In Healthlines CVD (n = 671) 24.0 % of those receiving optimised patient information materials responded positively to the invitation to participate, compared to 21.9 % in those receiving standard materials (OR = 1.12, 95 % CI = 0.78 to 1.61).
Conclusions: Evidence from these two embedded trials suggests limited benefits of optimised patient information materials on recruitment rates, which may only be apparent in some patient populations, with no effects on other outcomes. Further embedded trials are needed to provide a more precise estimate of effect, and to explore further how effects vary by trial context, intervention, and patient population
Transiting Exoplanet Studies and Community Targets for JWST's Early Release Science Program
The James Webb Space Telescope will revolutionize transiting exoplanet
atmospheric science due to its capability for continuous, long-duration
observations and its larger collecting area, spectral coverage, and spectral
resolution compared to existing space-based facilities. However, it is unclear
precisely how well JWST will perform and which of its myriad instruments and
observing modes will be best suited for transiting exoplanet studies. In this
article, we describe a prefatory JWST Early Release Science (ERS) program that
focuses on testing specific observing modes to quickly give the community the
data and experience it needs to plan more efficient and successful future
transiting exoplanet characterization programs. We propose a multi-pronged
approach wherein one aspect of the program focuses on observing transits of a
single target with all of the recommended observing modes to identify and
understand potential systematics, compare transmission spectra at overlapping
and neighboring wavelength regions, confirm throughputs, and determine overall
performances. In our search for transiting exoplanets that are well suited to
achieving these goals, we identify 12 objects (dubbed "community targets") that
meet our defined criteria. Currently, the most favorable target is WASP-62b
because of its large predicted signal size, relatively bright host star, and
location in JWST's continuous viewing zone. Since most of the community targets
do not have well-characterized atmospheres, we recommend initiating preparatory
observing programs to determine the presence of obscuring clouds/hazes within
their atmospheres. Measurable spectroscopic features are needed to establish
the optimal resolution and wavelength regions for exoplanet characterization.
Other initiatives from our proposed ERS program include testing the instrument
brightness limits and performing phase-curve observations.(Abridged)Comment: This is a white paper that originated from an open discussion at the
Enabling Transiting Exoplanet Science with JWST workshop held November 16 -
18, 2015 at STScI (http://www.stsci.edu/jwst/science/exoplanets). Accepted
for publication in PAS
Hemodynamic Forces Sculpt Developing Heart Valves through a KLF2-WNT9B Paracrine Signaling Axis.
Hemodynamic forces play an essential epigenetic role in heart valve development, but how they do so is not known. Here, we show that the shear-responsive transcription factor KLF2 is required in endocardial cells to regulate the mesenchymal cell responses that remodel cardiac cushions to mature valves. Endocardial Klf2 deficiency results in defective valve formation associated with loss of Wnt9b expression and reduced canonical WNT signaling in neighboring mesenchymal cells, a phenotype reproduced by endocardial-specific loss of Wnt9b. Studies in zebrafish embryos reveal that wnt9b expression is similarly restricted to the endocardial cells overlying the developing heart valves and is dependent upon both hemodynamic shear forces and klf2a expression. These studies identify KLF2-WNT9B signaling as a conserved molecular mechanism by which fluid forces sensed by endothelial cells direct the complex cellular process of heart valve development and suggest that congenital valve defects may arise due to subtle defects in this mechanotransduction pathway.journal articleresearch support, non-u.s. gov'tresearch support, n.i.h., extramural2017 11 062017 10 19importe
Volatility in the Housing Market: Evidence on Risk and Return in the London Sub-market
The impact of volatility in housing market analysis is reconsidered via examination of the risk-return relationship in the London housing market is examined. In addition to providing the first empirical results for the relationship between risk (as measured by volatility) and returns for this submarket, the analysis offers a more general message to empiricists via a detailed and explicit evaluation of the impact of empirical design decisions upon inferences. In particular, the negative risk-return relationship discussed frequently in the housing market literature is examined and shown to depend upon typically overlooked decisions concerning components of the empirical framework from which statistical inferences are drawn
Tentative Evidence for Water Vapor in the Atmosphere of the Neptune-Size Exoplanet HD 106315 c
We present a transmission spectrum for the Neptune-size exoplanet HD 106315 c from optical to infrared wavelengths based on transit observations from the Hubble Space Telescope/Wide Field Camera 3, K2, and Spitzer. The spectrum shows tentative evidence for a water absorption feature in the 1.1−1.7μm wavelength range with a small amplitude of 30 ppm (corresponding to just 0.8±0.04 atmospheric scale heights). Based on an atmospheric retrieval analysis, the presence of water vapor is tentatively favored with a Bayes factor of 1.7 - 2.6 (depending on prior assumptions). The spectrum is most consistent with either enhanced metallicity, high altitude condensates, or both. Cloud-free solar composition atmospheres are ruled out at >5σ confidence. We compare the spectrum to grids of cloudy and hazy forward models and find that the spectrum is fit well by models with moderate cloud lofting or haze formation efficiency, over a wide range of metallicities (1−100× solar). We combine the constraints on the envelope composition with an interior structure model and estimate that the core mass fraction is ≳0.3. With a bulk composition reminiscent of that of Neptune and an orbital distance of 0.15 AU, HD 106315 c hints that planets may form out of broadly similar material and arrive at vastly different orbits later in their evolution
Tentative Evidence for Water Vapor in the Atmosphere of the Neptune-Size Exoplanet HD 106315 c
We present a transmission spectrum for the Neptune-size exoplanet HD 106315 c
from optical to infrared wavelengths based on transit observations from the
Hubble Space Telescope/Wide Field Camera 3, K2, and Spitzer. The spectrum shows
tentative evidence for a water absorption feature in the m
wavelength range with a small amplitude of 30 ppm (corresponding to just atmospheric scale heights). Based on an atmospheric retrieval
analysis, the presence of water vapor is tentatively favored with a Bayes
factor of 1.7 - 2.6 (depending on prior assumptions). The spectrum is most
consistent with either enhanced metallicity, high altitude condensates, or
both. Cloud-free solar composition atmospheres are ruled out at
confidence. We compare the spectrum to grids of cloudy and hazy forward models
and find that the spectrum is fit well by models with moderate cloud lofting or
haze formation efficiency, over a wide range of metallicities (
solar). We combine the constraints on the envelope composition with an interior
structure model and estimate that the core mass fraction is . With
a bulk composition reminiscent of that of Neptune and an orbital distance of
0.15 AU, HD 106315 c hints that planets may form out of broadly similar
material and arrive at vastly different orbits later in their evolution.Comment: Submitted to AAS journals; 19 pages, 12 figure
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