298 research outputs found
Young planets under extreme UV irradiation. I. Upper atmosphere modelling of the young exoplanet K2-33b
The K2-33 planetary system hosts one transiting ~5 R_E planet orbiting the
young M-type host star. The planet's mass is still unknown, with an estimated
upper limit of 5.4 M_J. The extreme youth of the system (<20 Myr) gives the
unprecedented opportunity to study the earliest phases of planetary evolution,
at a stage when the planet is exposed to an extremely high level of high-energy
radiation emitted by the host star. We perform a series of 1D hydrodynamic
simulations of the planet's upper atmosphere considering a range of possible
planetary masses, from 2 to 40 M_E, and equilibrium temperatures, from 850 to
1300 K, to account for internal heating as a result of contraction. We obtain
temperature profiles mostly controlled by the planet's mass, while the
equilibrium temperature has a secondary effect. For planetary masses below 7-10
M_E, the atmosphere is subject to extremely high escape rates, driven by the
planet's weak gravity and high thermal energy, which increase with decreasing
mass and/or increasing temperature. For higher masses, the escape is instead
driven by the absorption of the high-energy stellar radiation. A rough
comparison of the timescales for complete atmospheric escape and age of the
system indicates that the planet is more massive than 10 M_E.Comment: 11 pages, 7 figure
A grid of upper atmosphere models for 1--40 MEARTH planets: application to CoRoT-7 b and HD219134 b,c
There is growing observational and theoretical evidence suggesting that
atmospheric escape is a key driver of planetary evolution. Commonly, planetary
evolution models employ simple analytic formulae (e.g., energy limited escape)
that are often inaccurate, and more detailed physical models of atmospheric
loss usually only give snapshots of an atmosphere's structure and are difficult
to use for evolutionary studies. To overcome this problem, we upgrade and
employ an already existing upper atmosphere hydrodynamic code to produce a
large grid of about 7000 models covering planets with masses 1 - 39 Earth mass
with hydrogen-dominated atmospheres and orbiting late-type stars. The modeled
planets have equilibrium temperatures ranging between 300 and 2000 K. For each
considered stellar mass, we account for three different values of the
high-energy stellar flux (i.e., low, moderate, and high activity). For each
computed model, we derive the atmospheric temperature, number density, bulk
velocity, X-ray and EUV (XUV) volume heating rates, and abundance of the
considered species as a function of distance from the planetary center. From
these quantities, we estimate the positions of the maximum dissociation and
ionisation, the mass-loss rate, and the effective radius of the XUV absorption.
We show that our results are in good agreement with previously published
studies employing similar codes. We further present an interpolation routine
capable to extract the modelling output parameters for any planet lying within
the grid boundaries. We use the grid to identify the connection between the
system parameters and the resulting atmospheric properties. We finally apply
the grid and the interpolation routine to estimate atmospheric evolutionary
tracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c...Comment: 21 pages, 4 Tables, 15 Figure
The Kepler-11 system: evolution of the stellar high-energy emission and {initial planetary} atmospheric mass fractions
The atmospheres of close-in planets are strongly influenced by mass loss
driven by the high-energy (X-ray and extreme ultraviolet, EUV) irradiation of
the host star, particularly during the early stages of evolution. We recently
developed a framework to exploit this connection and enable us to recover the
past evolution of the stellar high-energy emission from the present-day
properties of its planets, if the latter retains some remnants of their
primordial hydrogen-dominated atmospheres. Furthermore, the framework can also
provide constraints on planetary initial atmospheric mass fractions. The
constraints on the output parameters improve when more planets can be
simultaneously analysed. This makes the Kepler-11 system, which hosts six
planets with bulk densities between 0.66 and 2.45g cm^{-3}, an ideal target.
Our results indicate that the star has likely evolved as a slow rotator (slower
than 85\% of the stars with similar masses), corresponding to a high-energy
emission at 150 Myr of between 1-10 times that of the current Sun. We also
constrain the initial atmospheric mass fractions for the planets, obtaining a
lower limit of 4.1% for planet c, a range of 3.7-5.3% for planet d, a range of
11.1-14% for planet e, a range of 1-15.6% for planet f, and a range of 4.7-8.7%
for planet g assuming a disc dispersal time of 1 Myr. For planet b, the range
remains poorly constrained. Our framework also suggests slightly higher masses
for planets b, c, and f than have been suggested based on transit timing
variation measurements. We coupled our results with published planet atmosphere
accretion models to obtain a temperature (at 0.25 AU, the location of planet f)
and dispersal time of the protoplanetary disc of 550 K and 1 Myr, although
these results may be affected by inconsistencies in the adopted system
parameters.Comment: 8 pages, 3 figure
Revival of Philozoon Geddes for host-specialized dinoflagellates, âzooxanthellaeâ, in animals from coastal temperate zones of northern and southern hemispheres
The dinoflagellate family Symbiodiniaceae comprises numerous genera and species with large differences in diversity, ecology and
geographic distribution. An evolutionarily divergent lineage common in temperate symbiotic cnidarians and designated in the
literature by several informal names including âtemperateâAâ, AI, Phylotype AÂŽ (A-prime) and âMediterranean Aâ, is here assigned to
the genus Philozoon. This genus was proposed by Geddes (1882) in one of the earliest papers that recognized âyellow cellsâ as distinct
biological entities separate from their animal and protist hosts. Using phylogenetic data from nuclear (rDNA), chloroplast (cp23S)
and mitochondrial genes (cob and cox1), as well as morphology (cell size), ecological traits (host affinity) and geographic
distributions, we emend the genus Philozoon Geddes and two of its species, P. medusarum and P. actiniarum, and describe six
new species. Each symbiont species exhibits high host fidelity for particular species of sea anemone, soft coral, stony coral and
a rhizostome jellyfish. Philozoon is most closely related to Symbiodinium (formerly Clade A), but, unlike its tropical counterpart,
occurs in hosts in shallow temperate marine habitats in northern and southern hemispheres including the Mediterranean Sea,
north-eastern Atlantic Ocean, eastern Australia, New Zealand and Chile. The existence of a species-diverse lineage adapted to
cnidarian hosts living in high latitude habitats with inherently wide fluctuations in temperature calls further attention to the
ecological and biogeographic reach of the Symbiodiniaceae
Baseline Configuration of the Cryogenic System for the International Linear Collider
The paper discusses the main constraints and boundary conditions and describes the baseline configuration of the International Linear Collider (ILC) cryogenic system. The cryogenic layout, architecture and the cooling principle are presented. The paper addresses a plan for study and development required to demonstrate and improve the performance, to reduce cost and to attain the desired reliability
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
Cytisine versus varenicline for smoking cessation in New Zealand indigenous MÄori: a randomized controlled trial
© 2021 The Authors. Aim
To determine whether cytisine was at least as effective as varenicline in supporting smoking abstinence for â„ 6 months in New Zealand indigenous MÄori or whÄnau (extended-family) of MÄori, given the high smoking prevalence in this population.
Design
Pragmatic, open-label, randomized, community-based non-inferiority trial.
Setting
Bay of Plenty, Tokoroa and Lakes District Health Board regions of New Zealand.
Participants
Adult daily smokers who identified as MÄori or whÄnau of MÄori, were motivated to quit in the next 2 weeks, were aged â„ 18 years and were eligible for subsidized varenicline. Recruitment used multi-media advertising.
Interventions
A total of 679 people were randomly assigned (1 : 1) to receive a prescription for 12 weeks of cytisine or varenicline, plus low-intensity cessation behavioural support from the prescribing doctor and community stop-smoking services or a research assistant. Day 5 of treatment was the designated quit date.
Measurements
The primary outcome was carbon monoxide-verified continuous abstinence at 6 months, analysed as intention-to-treat (with multiple imputation for missing data). Secondary outcomes measured at 1, 3, 6 and 12 months post-quit date included: self-reported continuous abstinence, 7-day point prevalence abstinence, cigarettes per day, time to (re)lapse, adverse events, treatment adherence/compliance and acceptability, nicotine withdrawal/urge to smoke and health-care utilization/health-related quality of life.
Findings
Verified continuous abstinence rates at 6 months post-quit date were 12.1% (41 of 337) for cytisine versus 7.9% (27 of 342) for varenicline [risk difference 4.29%, 95% confidence interval (CI) = â0.22 to 8.79; relative risk 1.55; 95% CI = 0.97â2.46]. Sensitivity analyses confirmed that the findings were robust. Self-reported adverse events over 6 months occurred significantly more frequently in the varenicline group (cytisine: 313 events in 111 participants; varenicline: 509 events in 138 participants, incidence rate ratio 0.56, 95% CI = 0.49â0.65, P < 0.001) compared with the cytisine group. Common adverse events were headache, nausea and difficulty sleeping.
Conclusion
A randomized controlled trial found that cytisine was at least as effective as varenicline at supporting smoking abstinence in New Zealand indigenous MÄori or whÄnau (extended-family) of MÄori, with significantly fewer adverse events.Health Research Council of New Zealand. Grant Number: 16/07
Suppressed Far-UV stellar activity and low planetary mass-loss in the WASP-18 system
WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (RâČHK activity parameter lies slightly below the basal level; there is no significant time-variability in the log RâČHK value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of HST aimed at explaining this anomaly. From the starâs spectral energy distribution, we infer the extinction (E(B â V) â 0.01mag) and then the ISM column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg sâ1 cmâ2. We employ the rescaled XUV solar fluxes to model of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10â20MJ Gyrâ1. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape
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