423 research outputs found
Signals of exomoons in averaged light curves of exoplanets
The increasing number of transiting exoplanets sparked a significant interest
in discovering their moons. Most of the methods in the literature utilize
timing analysis of the raw light curves. Here we propose a new approach for the
direct detection of a moon in the transit light curves via the so called
Scatter Peak. The essence of the method is the valuation of the local scatter
in the folded light curves of many transits. We test the ability of this method
with different simulations: Kepler "short cadence", Kepler "long cadence",
ground-based millimagnitude photometry with 3-min cadence, and the expected
data quality of the planned ESA mission of PLATO. The method requires ~100
transit observations, therefore applicable for moons of 10-20 day period
planets, assuming 3-4-5 year long observing campaigns with space observatories.
The success rate for finding a 1 R_Earth moon around a 1 R_Jupiter exoplanet
turned out to be quite promising even for the simulated ground-based
observations, while the detection limit of the expected PLATO data is around
0.4 R_Earth. We give practical suggestions for observations and data reduction
to improve the chance of such a detection: (i) transit observations must
include out-of-transit phases before and after a transit, spanning at least the
same duration as the transit itself; (ii) any trend filtering must be done in
such a way that the preceding and following out-of-transit phases remain
unaffected.Comment: 9 pages, 5 figures, accepted for publication in MNRAS. Typos
correcte
Methods for exomoon characterisation: combining transit photometry and the Rossiter-McLaughlin effect
It has been suggested that moons around transiting exoplanets may cause
observable signal in transit photometry or in the Rossiter-McLaughlin (RM)
effect. In this paper a detailed analysis of parameter reconstruction from the
RM effect is presented for various planet-moon configurations, described with
20 parameters. We also demonstrate the benefits of combining photometry with
the RM effect. We simulated 2.7x10^9 configurations of a generic transiting
system to map the confidence region of the parameters of the moon, find the
correlated parameters and determine the validity of reconstructions. The main
conclusion is that the strictest constraints from the RM effect are expected
for the radius of the moon. In some cases there is also meaningful information
on its orbital period. When the transit time of the moon is exactly known, for
example, from transit photometry, the angle parameters of the moon's orbit will
also be constrained from the RM effect. From transit light curves the mass can
be determined, and combining this result with the radius from the RM effect,
the experimental determination of the density of the moon is also possible.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Total Chiral Symmetry Breaking during Crystallization: Who needs a "Mother Crystal"?
Processes that can produce states of broken chiral symmetry are of particular
interest to physics, chemistry and biology. Chiral symmetry breaking during
crystallization of sodium chlorate occurs via the production of secondary
crystals of the same handedness from a single "mother crystal" that seeds the
solution. Here we report that a large and "symmetric" population of D- and
L-crystals moves into complete chiral purity disappearing one of the
enantiomers. This result shows: (i) a new symmetry breaking process
incompatible with the hypothesis of a single "mother crystal"; (ii) that
complete symmetry breaking and chiral purity can be achieved from an initial
system with both enantiomers. These findings demand a new explanation to the
process of total symmetry breaking in crystallization without the intervention
of a "mother crystal" and open the debate on this fascinating phenomenon. We
present arguments to show that our experimental data can been explained with a
new model of "complete chiral purity induced by nonlinear autocatalysis and
recycling".Comment: 5 pages, 4 figures, Added reference
Exomoon simulations
We introduce and describe our newly developed code that simulates light
curves and radial velocity curves for arbitrary transiting exoplanets with a
satellite. The most important feature of the program is the calculation of
radial velocity curves and the Rossiter-McLaughlin effect in such systems. We
discuss the possibilities for detecting the exomoons taking the abilities of
Extremely Large Telescopes into account. We show that satellites may be
detected also by their RM effect in the future, probably using less accurate
measurements than promised by the current instrumental developments. Thus, RM
effect will be an important observational tool in the exploration of exomoons.Comment: 5 pages, 2 figures with 9 figure panels, accepted by EM&
Bayesian Methods for Exoplanet Science
Exoplanet research is carried out at the limits of the capabilities of
current telescopes and instruments. The studied signals are weak, and often
embedded in complex systematics from instrumental, telluric, and astrophysical
sources. Combining repeated observations of periodic events, simultaneous
observations with multiple telescopes, different observation techniques, and
existing information from theory and prior research can help to disentangle the
systematics from the planetary signals, and offers synergistic advantages over
analysing observations separately. Bayesian inference provides a
self-consistent statistical framework that addresses both the necessity for
complex systematics models, and the need to combine prior information and
heterogeneous observations. This chapter offers a brief introduction to
Bayesian inference in the context of exoplanet research, with focus on time
series analysis, and finishes with an overview of a set of freely available
programming libraries.Comment: Invited revie
(5RS,10SR,15RS)-Trimethyltruxene1
The title molecule, C30H24, was prepared as a possible precursor to buckminsterfullerene cages. The two enantiomers adopt the anti configuration, with one S/R and two R/S methyl groups, one anti to the other two. The truxene framework is slightly non-planar: with respect to the central six-ring mean plane, the three methyl C atoms are 1.377 (3), −1.475 (3) and 1.515 (3) Å distant, whereas the respective proximate peripheral six-ring mean planes make dihedral angles of 6.27 (6), 3.45 (7) and −7.37 (7)°
Chiral Crystal Growth under Grinding
To study the establishment of homochirality observed in the crystal growth
experiment of chiral molecules from a solution under grinding, we extend the
lattice gas model of crystal growth as follows. A lattice site can be occupied
by a chiral molecule in R or S form, or can be empty. Molecules form
homoclusters by nearest neighbor bonds. They change their chirality if they are
isolated monomers in the solution. Grinding is incorporated by cutting and
shafling the system randomly. It is shown that Ostwald ripening without
grinding is extremely slow to select chirality, if possible. Grinding alone
also cannot achieve chirality selection. For the accomplishment of
homochirality, we need an enhanced chirality change on crystalline surface.
With this "autocatalytic effect" and the recycling of monomers due to rinding,
an exponential increase of crystal enantiomeric excess to homochiral state is
realized.Comment: 10 pages, 5 figure
Methane in the atmosphere of the transiting hot Neptune GJ436b?
We present an analysis of seven primary transit observations of the hot
Neptune GJ436b at 3.6, 4.5 and m obtained with the Infrared Array Camera
(IRAC) on the Spitzer Space Telescope. After correcting for systematic effects,
we fitted the light curves using the Markov Chain Monte Carlo technique.
Combining these new data with the EPOXI, HST and ground-based and
published observations, the range m can be covered. Due to
the low level of activity of GJ436, the effect of starspots on the combination
of transits at different epochs is negligible at the accuracy of the dataset.
Representative climate models were calculated by using a three-dimensional,
pseudo-spectral general circulation model with idealised thermal forcing.
Simulated transit spectra of GJ436b were generated using line-by-line radiative
transfer models including the opacities of the molecular species expected to be
present in such a planetary atmosphere. A new, ab-initio calculated, linelist
for hot ammonia has been used for the first time. The photometric data observed
at multiple wavelengths can be interpreted with methane being the dominant
absorption after molecular hydrogen, possibly with minor contributions from
ammonia, water and other molecules. No clear evidence of carbon monoxide and
dioxide is found from transit photometry. We discuss this result in the light
of a recent paper where photochemical disequilibrium is hypothesised to
interpret secondary transit photometric data. We show that the emission
photometric data are not incompatible with the presence of abundant methane,
but further spectroscopic data are desirable to confirm this scenario.Comment: 19 pages, 10 figures, 1 table, Astrophysical Journal in pres
Study protocol for First Dental Steps Intervention: feasibility study of a health visitor led infant oral health improvement programme.
BACKGROUND: Dental caries in childhood is a burden on the daily lives of children and their families, and associated with poor oral health in adulthood. In England, dental caries is the most common reason for young children to be admitted to hospital. It is believed that most tooth extractions (due to decay) for children aged 10 years and under, could be avoided with improved prevention and early management. National public health policy recommendations in England include specific oral health initiatives to tackle tooth decay. One of these initiatives is delivered as part of the Healthy Child Programme and includes providing workforce training in oral health, integrating oral health advice into home visits, and the timely provision of fluoride toothpaste. This protocol seeks to assess the delivery of the First Dental Steps intervention and uncertainties related to the acceptability, recruitment, and retention of participants. METHODS: This study seeks to explore the feasibility and acceptability of the First Dental Steps intervention and research methods. First Dental Steps intervention will be delivered in local authority areas in South West England and includes oral health training for health visitors (or community nursery nurses) working with 0-5-year-olds and their families. Further, for vulnerable families, integrating oral health advice and the provision of an oral health pack (including a free flow cup, an age appropriate toothbrush, and 1450 ppm fluoride toothpaste) during a mandated check by a health visitor. In this study five local authority areas will receive the intervention. Interviews with parents receiving the intervention and health visitors delivering the intervention will be undertaken, along with a range of additional interviews with stakeholders from both intervention and comparison sites (four additional local authority areas). DISCUSSION: This protocol was written after the start of the COVID-19 pandemic, as a result, some of the original methods were adjusted specifically to account for disruptions caused by the pandemic. Results of this study will primarily provide evidence on the acceptability and feasibility of both the First Dental Steps intervention and the research methods from the perspective of both families and stakeholders
A systems map of the determinants of child health inequalities in England at the local level
Children and young people in the UK have worse health outcomes than in many similar western countries and child health inequalities are persistent and increasing. Systems thinking has emerged as a promising approach to addressing complex public health issues. We report on a systems approach to mapping the determinants of child health inequalities at the local level in England for young people aged 0–25, and describe the resulting map. Qualitative group concept mapping workshops were held in two contrasting English local authorities with a range of stakeholders: professionals (N = 35); children and young people (N = 33) and carers (N = 5). Initial area maps were developed, and augmented using data from qualitative interviews with professionals (N = 16). The resulting local maps were reviewed and validated by expert stakeholders in each area (N = 9; N = 35). Commonalities between two area-specific system maps (and removal of locality-specific factors) were used to develop a map that could be applied in any English local area. Two rounds of online survey (N = 21; N = 8) experts in public health, local governance and systems science refined the final system map displaying the determinants of child health inequalities. The process created a map of over 150 factors influencing inequalities in health outcomes for children aged 0–25 years at the local area level. The system map has six domains; physical environment, governance, economic, social, service, and personal. To our knowledge this is the first study taking a systems approach to addressing inequalities across all aspects of child health. The study shows how group concept mapping can support systems thinking at the local level. The resulting system map illustrates the complexity of factors influencing child health inequalities, and it may be a useful tool in demonstrating to stakeholders the importance of policies that tackle the systemic drivers of child health inequalities beyond those traditionally associated with public health
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