762 research outputs found
All along the line of sight: a closer look at opening angles and absorption regions in the atmospheres of transiting exoplanets
Transmission spectra contain a wealth of information about the atmospheres of transiting exoplanets. However, large thermal and chemical gradients along the line of sight can lead to biased inferences in atmospheric retrievals. In order to determine how far from the limb plane the atmosphere still impacts the transmission spectrum, we derive a new formula to estimate the opening angle of a planet. This is the angle subtended by the atmospheric region that contributes to the observation along the line of sight, as seen from the planet centre. We benchmark our formula with a 3D Monte Carlo radiative transfer code and we define an opening angle suitable for the interpretation of JWST observations, assuming a 10-ppm noise floor. We find that the opening angle is only a few degrees for planets cooler than ca. 500 Kelvins, while it can be as large as 25 degrees for (ultra-)hot Jupiters and 50 degrees for hot Neptunes. Compared to previous works, our more robust approach leads to smaller estimates for the opening angle across a wide range scale heights and planetary radii. Finally, we show that ultra-hot Jupiters have an opening angle that is smaller than the angle over which the planet rotates during the transit. This allows for time-resolved transmission spectroscopy observations that probe independent parts of the planetary limb during the first and second half of the transit
Modelling the effect of 3D temperature and chemistry on the cross-correlation signal of transiting ultra-hot Jupiters: A study of 5 chemical species on WASP-76b
Ultra-hot Jupiters are perfect targets for transmission spectroscopy.
However, their atmospheres feature strong spatial variations in temperature,
chemistry, dynamics, cloud coverage, and scale height. This makes transit
observations at high spectral resolution challenging to interpret. In this
work, we model the cross-correlation signal of five chemical species (Fe, CO,
HO, OH, and TiO) on WASP-76b, a benchmark ultra-hot Jupiter. We
compute phase-dependent high-resolution transmission spectra of 3D SPARC/MITgcm
models. The spectra are obtained with gCMCRT, a 3D Monte-Carlo
radiative-transfer code. We find that, on top of atmospheric dynamics, the
phase-dependent Doppler shift of the absorption lines in the planetary rest
frame is shaped by the combined effect of planetary rotation and the unique 3D
spatial distribution of chemical species. For species probing the dayside
(e.g., refractories or molecules like CO and OH), the two effects act in
tandem, leading to increasing blueshifts with orbital phase. For species that
are depleted on the dayside (e.g., HO and TiO), the two effects act
in an opposite manner, and could lead to increasing redshifts during the
transit. This behaviour yields species-dependent offsets from a planet's
expected value that can be much larger than planetary wind speeds.
The offsets are usually negative for refractory species. We provide an
analytical formula to estimate the size of a planet's offsets,
which can serve as a prior for atmospheric retrievals. We conclude that
observing the phase-resolved absorption signal of multiple species is key to
constraining the 3D thermochemical structure and dynamics of ultra-hot
Jupiters.Comment: 21 pages, 14 figures, resubmitted to MNRAS after minor revision
The star cluster formation history of the LMC
The Large Magellanic Cloud is one of the nearest galaxies to us and is one of
only few galaxies where the star formation history can be determined from
studying resolved stellar populations. We have compiled a new catalogue of
ages, luminosities and masses of LMC star clusters and used it to determine the
age distribution and dissolution rate of LMC star clusters. We find that the
frequency of massive clusters with masses M>5000 Msun is almost constant
between 10 and 200 Myr, showing that the influence of residual gas expulsion is
limited to the first 10 Myr of cluster evolution or clusters less massive than
5000 Msun. Comparing the cluster frequency in that interval with the absolute
star formation rate, we find that about 15% of all stars in the LMC were formed
in long-lived star clusters that survive for more than 10 Myr. We also find
that the mass function of LMC clusters younger than 1 Gyr can be fitted by a
power-law mass function with slope \alpha=-2.3, while older clusters follow a
significantly shallower slope and interpret this is a sign of the ongoing
dissolution of low-mass clusters. Our data shows that for ages older than 200
Myr, about 90% of all clusters are lost per dex of lifetime. The implied
cluster dissolution rate is significantly faster than that based on analytic
estimates and N-body simulations. Our cluster age data finally shows evidence
for a burst in cluster formation about 1 Gyr ago, but little evidence for
bursts at other ages.Comment: 18 pages, 6 figures, MNRAS in pres
Decomposing the Iron Cross-Correlation Signal of the Ultra-Hot Jupiter WASP-76b in Transmission using 3D Monte-Carlo Radiative Transfer
Ultra-hot Jupiters are tidally locked gas giants with dayside temperatures
high enough to dissociate hydrogen and other molecules. Their atmospheres are
vastly non-uniform in terms of chemistry, temperature and dynamics, and this
makes their high-resolution transmission spectra and cross-correlation signal
difficult to interpret. In this work, we use the SPARC/MITgcm global
circulation model to simulate the atmosphere of the ultra-hot Jupiter WASP-76b
under different conditions, such as atmospheric drag and the absence of TiO and
VO. We then employ a 3D Monte-Carlo radiative transfer code, HIRES-MCRT, to
self-consistently model high-resolution transmission spectra with iron (Fe I)
lines at different phases during the transit. To untangle the structure of the
resulting cross-correlation map, we decompose the limb of the planet into four
sectors, and we analyse each of their contributions separately. Our experiments
demonstrate that the cross-correlation signal of an ultra-hot Jupiter is
primarily driven by its temperature structure, rotation and dynamics, while
being less sensitive to the precise distribution of iron across the atmosphere.
We also show that the previously published iron signal of WASP-76b can be
reproduced by a model featuring iron condensation on the leading limb.
Alternatively, the signal may be explained by a substantial temperature
asymmetry between the trailing and leading limb, where iron condensation is not
strictly required to match the data. Finally, we compute the
maps of the simulated WASP-76b atmospheres, and we show that rotation and
dynamics can lead to multiple peaks that are displaced from zero in the
planetary rest frame.Comment: Accepted for publication in MNRAS, 25 pages, 24 figure
Can agricultural cultivation methods influence the healthfulness of crops for foods
The aim of the current study was to investigate if there are any health effects of long-term consumption of organically grown crops using a rat model. Crops were retrieved over two years from along-term field trial at three different locations in Denmark, using three different cultivation systems(OA, organic based on livestock manure; OB, organic based on green manure; and C, conventional with mineral fertilizers and pesticides)with two field replicates. The cultivation system had an impact on the nutritional quality, affecting γ-tocopherol, some amino acids, and fatty acid composition. Additionally, the nutritional quality was affected by harvest year and location. However, harvest year and location rather than cultivation system affected the measured health biomarkers. In conclusion, the differences in dietary treatments composed of ingredients from different cultivation systems did not lead to significant differences in the measured health biomarkers, except for a significant difference in plasma IgGl evels
Understanding and Mitigating Biases when Studying Inhomogeneous Emission Spectra with JWST
Exoplanet emission spectra are often modelled assuming that the hemisphere
observed is well represented by a horizontally homogenised atmosphere. However
this approximation will likely fail for planets with a large temperature
contrast in the James Webb Space Telescope (JWST) era, potentially leading to
erroneous interpretations of spectra. We first develop an analytic formulation
to quantify the signal-to-noise ratio and wavelength coverage necessary to
disentangle temperature inhomogeneities from a hemispherically averaged
spectrum. We find that for a given signal-to-noise ratio, observations at
shorter wavelengths are better at detecting the presence of inhomogeneities. We
then determine why the presence of an inhomogeneous thermal structure can lead
to spurious molecular detections when assuming a fully homogenised planet in
the retrieval process. Finally, we quantify more precisely the potential biases
by modelling a suite of hot Jupiter spectra, varying the spatial contributions
of a hot and a cold region, as would be observed by the different instruments
of JWST/NIRSpec. We then retrieve the abundances and temperature profiles from
the synthetic observations. We find that in most cases, assuming a homogeneous
thermal structure when retrieving the atmospheric chemistry leads to biased
results, and spurious molecular detection. Explicitly modelling the data using
two profiles avoids these biases, and is statistically supported provided the
wavelength coverage is wide enough, and crucially also spanning shorter
wavelengths. For the high contrast used here, a single profile with a dilution
factor performs as well as the two-profile case, with only one additional
parameter compared to the 1-D approach.Comment: Accepted for publication by MNRA
How Does Thermal Scattering Shape the Infrared Spectra of Cloudy Exoplanets? A Theoretical Framework and Consequences for Atmospheric Retrievals in the JWST era
Observational studies of exoplanets are suggestive of a ubiquitous presence
of clouds. The current modelling techniques used in emission to account for the
clouds tend to require prior knowledge of the cloud condensing species and
often do not consider the scattering effects of the cloud. We explore the
effects that thermal scattering has on the emission spectra by modelling a
suite of hot Jupiter atmospheres with varying cloud single-scattering albedos
(SSAs) and temperature profiles. We examine cases ranging from simple
isothermal conditions to more complex structures and physically driven cloud
modelling. We show that scattering from nightside clouds would lead to
brightness temperatures that are cooler than the real atmospheric temperature
if scattering is unaccounted for. We show that scattering can produce spectral
signatures in the emission spectrum even for isothermal atmospheres. We
identify the retrieval degeneracies and biases that arise in the context of
simulated JWST spectra when the scattering from the clouds dominates the
spectral shape. Finally, we propose a novel method of fitting the SSA spectrum
of the cloud in emission retrievals, using a technique that does not require
any prior knowledge of the cloud chemical or physical properties.Comment: Accepted to MNRA
Switching between dynamic states in intermediate-length Josephson junctions
The appearance of zero-field steps (ZFS’s) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hill’s equation which predicts how the number, locations, and widths of the instability regions depend on the junction parameters. A numerical integration of the PSGE in terms of truncated series of time-dependent Fourier spatial modes verifies that the parametrically excited instabilities of the MCB evolve into the fluxon oscillations characteristic of the ZFS’s. An approximate analysis of the Fourier mode equations in the presence of a small magnetic field yields a field-dependent Hill’s equation which predicts that the major effect of such a field is to reduce the widths of the instability regions. Experimental measurements on Nb-NbxOy-Pb junctions of intermediate length, performed at different operating temperatures in order to vary the junction parameters and for various magnetic field values, verify the physical existence of switching from the MCB to the ZFS’s. Good qualitative, and in many cases quantitative, agreement between analytic, numerical, and experimental results is obtained
Simulating gas giant exoplanet atmospheres with Exo-FMS: Comparing semi-grey, picket fence and correlated-k radiative-transfer schemes
Radiative-transfer (RT) is a fundamental part of modelling exoplanet
atmospheres with general circulation models (GCMs). An accurate RT scheme is
required for estimates of the atmospheric energy transport and for gaining
physical insight from model spectra. We implement three RT schemes for Exo-FMS:
semi-grey, non-grey `picket fence', and real gas with correlated-k. We
benchmark the Exo-FMS GCM using these RT schemes to hot Jupiter simulation
results from the literature. We perform a HD 209458b-like simulation with the
three schemes and compare their results. These simulations are then
post-processed to compare their observable differences. The semi-grey scheme
results show qualitative agreement with previous studies in line with
variations seen between GCM models. The real gas model reproduces well the
temperature and dynamical structures from other studies. After post-processing
our non-grey picket fence scheme compares very favourably with the real gas
model, producing similar transmission spectra, emission spectra and phase curve
behaviours. Exo-FMS is able to reliably reproduce the essential features of
contemporary GCM models in the hot gas giant regime. Our results suggest the
picket fence approach offers a simple way to improve upon RT realism beyond
semi-grey schemes.Comment: MNRAS accepted 22 June 2021 - V2, typos fixe
Two-channel Kondo effect and renormalization flow with macroscopic quantum charge states
Many-body correlations and macroscopic quantum behaviors are fascinating
condensed matter problems. A powerful test-bed for the many-body concepts and
methods is the Kondo model which entails the coupling of a quantum impurity to
a continuum of states. It is central in highly correlated systems and can be
explored with tunable nanostructures. Although Kondo physics is usually
associated with the hybridization of itinerant electrons with microscopic
magnetic moments, theory predicts that it can arise whenever degenerate quantum
states are coupled to a continuum. Here we demonstrate the previously elusive
`charge' Kondo effect in a hybrid metal-semiconductor implementation of a
single-electron transistor, with a quantum pseudospin-1/2 constituted by two
degenerate macroscopic charge states of a metallic island. In contrast to other
Kondo nanostructures, each conduction channel connecting the island to an
electrode constitutes a distinct and fully tunable Kondo channel, thereby
providing an unprecedented access to the two-channel Kondo effect and a clear
path to multi-channel Kondo physics. Using a weakly coupled probe, we reveal
the renormalization flow, as temperature is reduced, of two Kondo channels
competing to screen the charge pseudospin. This provides a direct view of how
the predicted quantum phase transition develops across the symmetric quantum
critical point. Detuning the pseudospin away from degeneracy, we demonstrate,
on a fully characterized device, quantitative agreement with the predictions
for the finite-temperature crossover from quantum criticality.Comment: Letter (5 pages, 4 figures) and Methods (10 pages, 6 figures
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