45,071 research outputs found
Validation of a Temperate Fourth Planet in the K2-133 Multi-planet System
We present follow-up observations of the K2-133 multi-planet system.
Previously, we announced that K2-133 contained three super-Earths orbiting an
M1.5V host star - with tentative evidence of a fourth outer-planet orbiting at
the edge of the temperate zone. Here we report on the validation of the
presence of the fourth planet, determining a radius of
R. The four planets span the radius gap of the exoplanet population,
meaning further follow-up would be worthwhile to obtain masses and test
theories of the origin of the gap. In particular, the trend of increasing
planetary radius with decreasing incident flux in the K2-133 system supports
the claim that the gap is caused by photo-evaporation of exoplanet atmospheres.
Finally, we note that K2-133 e orbits on the edge of the stars temperate zone,
and that our radius measurement allows for the possibility that this is a rocky
world. Additional mass measurements are required to confirm or refute this
scenario.Comment: Accepted for publication in MNRA
Three small transiting planets around the M dwarf host star LP 358-499
We report on the detection of three transiting small planets around the
low-mass star LP 358-499 (K2-133), using photometric data from the Kepler-K2
mission. Using multiband photometry, we determine the host star to be an early
M dwarf with an age likely older than a Gigayear. The three detected planets
K2-133 b, c, and d have orbital periods of ca. 3, 4.9 and 11 days and transit
depths of ca. 700, 1000 and 2000 ppm, respectively. We also report a planetary
candidate in the system (EPIC 247887989.01) with a period of 26.6 days and a
depth of ca. 1000 ppm, which may be at the inner edge of the stellar habitable
zone, depending on the specific host star properties. Using the transit
parameters and the stellar properties, we estimate that the innermost planet
may be rocky. The system is suited for follow-up observations to measure
planetary masses and JWST transmission spectra of planetary atmospheres.Comment: Accepted for publication in MNRAS Letters. Replaced previous arXiv
version with final submitted versio
The impact of stochastic physics on climate sensitivity in EC-Earth
Stochastic schemes, designed to represent unresolved sub-grid scale
variability, are frequently used in short and medium-range weather forecasts,
where they are found to improve several aspects of the model. In recent years,
the impact of stochastic physics has also been found to be beneficial for the
model's long term climate. In this paper, we demonstrate for the first time
that the inclusion of a stochastic physics scheme can notably affect a model's
projection of global warming, as well as its historical climatological global
temperature. Specifically, we find that when including the 'stochastically
perturbed parametrisation tendencies' scheme (SPPT) in the fully coupled
climate model EC-Earth v3.1, the predicted level of global warming between 1850
and 2100 is reduced by 10% under an RCP8.5 forcing scenario. We link this
reduction in climate sensitivity to a change in the cloud feedbacks with SPPT.
In particular, the scheme appears to reduce the positive low cloud cover
feedback, and increase the negative cloud optical feedback. A key role is
played by a robust, rapid increase in cloud liquid water with SPPT, which we
speculate is due to the scheme's non-linear interaction with condensation.Comment: Under review in Journal of Geophysical Research: Atmosphere
Advanced Computer Dormant Reliability Study Final Report
Reliability of integrated circuits and discrete components of electronics for computer and dormant module for Minuteman
Possible isotopic fractionation effects in sputtered minerals
A model which makes definite predictions for the fractionation of isotopes in sputtered material is discussed. The fractionation patterns are nonlinear, and the pattern for a particular set of isotopes depends on the chemical matrix within which those isotopes are contained. Calculations are presented for all nonmonoisotopic elements contained in the minerals perovskite, anorthite, ackermanite, enstatite, and troilite. All isotopes are fractionated at the level of approximately 4-6 deg/o per atomic mass unit. Oxygen is always positively fractionated (heavier isotopes sputtered preferentially), and heavier elements are generally negatively fractioned (light isotopes sputtered preferentially). The value of Delta (O-18:O-16) is always less by about 1.8 deg/o than a linear extrapolation based upon the calculated delta (O-17:O-16) value would suggest. The phenomenon of both negative and positive fractionation patterns from a single target mineral are used to make an experimental test of the proposed model
High Redshift Standard Candles: Predicted Cosmological Constraints
We investigate whether future measurements of high redshift standard candles
(HzSCs) will be a powerful probe of dark energy, when compared to other types
of planned dark energy measurements. Active galactic nuclei and gamma ray
bursts have both been proposed as potential HzSC candidates. Due to their high
luminosity, they can be used to probe unexplored regions in the expansion
history of the universe. Information from these regions can help constrain the
properties of dark energy, and in particular, whether it varies over time.
We consider both linear and piecewise parameterizations of the dark energy
equation of state, , and assess the optimal redshift distribution a
high-redshift standard-candle survey could take to constrain these models.
The more general the form of the dark energy equation of state being
tested, the more useful high-redshift standard candles become. For a linear
parameterization of , HzSCs give only small improvements over planned
supernova and baryon acoustic oscillation measurements; a wide redshift range
with many low redshift points is optimal to constrain this linear model.
However to constrain a general, and thus potentially more informative, form of
, having many HzSCs can significantly improve limits on the nature of
dark energy.Comment: Accepted MNRAS, 27 Pages, 15 figures, matches published versio
Estimating the masses of extra-solar planets
All extra-solar planet masses that have been derived spectroscopically are
lower limits since the inclination of the orbit to our line-of-sight is unknown
except for transiting systems. It is, however, possible to determine the
inclination angle, i, between the rotation axis of a star and an observer's
line-of-sight from measurements of the projected equatorial velocity (v sin i),
the stellar rotation period (P_rot) and the stellar radius (R_star). This
allows the removal of the sin i dependency of spectroscopically derived
extra-solar planet masses under the assumption that the planetary orbits lie
perpendicular to the stellar rotation axis. We have carried out an extensive
literature search and present a catalogue of v sin i, P_rot, and R_star
estimates for exoplanet host stars. In addition, we have used Hipparcos
parallaxes and the Barnes-Evans relationship to further supplement the R_star
estimates obtained from the literature. Using this catalogue, we have obtained
sin i estimates using a Markov-chain Monte Carlo analysis. This allows proper
1-sigma two-tailed confidence limits to be placed on the derived sin i's along
with the transit probability for each planet to be determined. While a small
proportion of systems yield sin i's significantly greater than 1, most likely
due to poor P_rot estimations, the large majority are acceptable. We are
further encouraged by the cases where we have data on transiting systems, as
the technique indicates inclinations of ~90 degrees and high transit
probabilities. In total, we estimate the true masses of 133 extra-solar
planets. Of these, only 6 have revised masses that place them above the 13
Jupiter mass deuterium burning limit. Our work reveals a population of
high-mass planets with low eccentricities and we speculate that these may
represent the signature of different planetary formation mechanisms at work.Comment: 40 pages, 6 tables, 2 figures. Accepted for publication in the
Monthly Notices of the Royal Astronomical Society after editing of Tables 1 &
6 for electronic publication. Html abstract shortened for astro-ph submissio
Denoising Autoencoders for fast Combinatorial Black Box Optimization
Estimation of Distribution Algorithms (EDAs) require flexible probability
models that can be efficiently learned and sampled. Autoencoders (AE) are
generative stochastic networks with these desired properties. We integrate a
special type of AE, the Denoising Autoencoder (DAE), into an EDA and evaluate
the performance of DAE-EDA on several combinatorial optimization problems with
a single objective. We asses the number of fitness evaluations as well as the
required CPU times. We compare the results to the performance to the Bayesian
Optimization Algorithm (BOA) and RBM-EDA, another EDA which is based on a
generative neural network which has proven competitive with BOA. For the
considered problem instances, DAE-EDA is considerably faster than BOA and
RBM-EDA, sometimes by orders of magnitude. The number of fitness evaluations is
higher than for BOA, but competitive with RBM-EDA. These results show that DAEs
can be useful tools for problems with low but non-negligible fitness evaluation
costs.Comment: corrected typos and small inconsistencie
The XMM-Newton spectral-fit database
The XMM-Newton spectral-fit database is an ongoing ESA funded project aimed
to construct a catalogue of spectral-fitting results for all the sources within
the XMM-Newton serendipitous source catalogue for which spectral data products
have been pipeline-extracted (~ 120,000 X-ray source detections). The
fundamental goal of this project is to provide the astronomical community with
a tool to construct large and representative samples of X-ray sources by
allowing source selection according to spectral properties.Comment: Conference proceedings of IAU Symposium 304: Multiwavelength AGN
surveys and studie
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