541 research outputs found
Pushing the precision limit of ground-based eclipse photometry
Until recently, it was considered by many that ground-based photometry could
not reach the high cadence sub-mmag regime because of the presence of the
atmosphere. Indeed, high frequency atmospheric noises (mainly scintillation)
limit the precision that high SNR photometry can reach within small time bins.
If one is ready to damage the sampling of his photometric time-series, binning
the data (or using longer exposures) allows to get better errors, but the
obtained precision will be finally limited by low frequency noises. To observe
several times the same planetary eclipse and to fold the photometry with the
orbital period is thus generally considered as the only option to get very well
sampled and precise eclipse light curve from the ground. Nevertheless, we show
here that reaching the sub-mmag sub-min regime for one eclipse is possible with
a ground-based instrument. This has important implications for transiting
planets characterization, secondary eclipses measurement and small planets
detection from the ground.Comment: Transiting Planets Proceeding IAU Symposium No.253, 2008. 7 pages, 4
figure
Planetary Phase Variations of the 55 Cancri System
Characterization of the composition, surface properties, and atmospheric
conditions of exoplanets is a rapidly progressing field as the data to study
such aspects become more accessible. Bright targets, such as the multi-planet
55 Cancri system, allow an opportunity to achieve high signal-to-noise for the
detection of photometric phase variations to constrain the planetary albedos.
The recent discovery that that inner-most planet, 55 Cancri e, transits the
host star introduces new prospects for studying this system. Here we calculate
photometric phase curves at optical wavelengths for the system with varying
assumptions for the surface and atmospheric properties of 55 Cancri e. We show
that the large differences in geometric albedo allows one to distinguish
between various surface models, that the scattering phase function cannot be
constrained with foreseeable data, and that planet b will contribute
significantly to the phase variation depending upon the surface of planet e. We
discuss detection limits and how these models may be used with future
instrumentation to further characterize these planets and distinguish between
various assumptions regarding surface conditions.Comment: 7 pages, 3 figures, accepted for publication in Ap
Measuring and processing in-cylinder measurements of NO and OH obtained by laser-induced fluorescence in a diesel rapid compression machine
A strong argument culture is characterized by at least five productive tensions, between: commitment and contingency, partisanship and restraint, personal conviction and sensitivity to the audience, reasonableness and subjectivity, and decision and non-closure. Differences in how communities manage these tensions explain why there are multiple argument cultures and, hence, why we need to understand arguing both within and among different cultures. The paper elaborates these five productive tensions, offers some examples of argument cultures that negotiate them in various ways, and considers what it means to argue across cultures in a world that is both increasingly diverse and increasingly atomized
Exploring hail and lightning diagnostics over the Alpine-Adriatic region in a km-scale climate model
The north and south of the Alps, as well as the eastern shores of the Adriatic Sea, are hot spots of severe convective storms, including hail and lightning associated with deep convection. With advancements in computing power, it has become feasible to simulate deep convection explicitly in climate models by decreasing the horizontal grid spacing to less than 4 km. These kilometer-scale models improve the representation of orography and reduce uncertainties associated with the use of deep convection parameterizations.
In this study, we perform km-scale simulations for eight observed cases of severe convective storms (seven with and one without observed hail) over the Alpine-Adriatic region. The simulations are performed with the climate version of the regional model Consortium for Small-scale Modeling (COSMO) that runs on graphics processing units (GPUs) at a horizontal grid spacing of 2.2 km. To analyze hail and lightning we have explored the hail growth model (HAILCAST) and lightning potential index (LPI) diagnostics integrated with the COSMO-crCLIM model.
Comparison with available high-resolution observations reveals good performance of the model in simulating total precipitation, hail, and lightning. By performing a detailed analysis of three of the case studies, we identified the importance of significant meteorological factors for heavy thunderstorms that were reproduced by the model. Among these are the moist unstable boundary layer and dry mid-level air, the topographic barrier, as well as an approaching upper-level trough and cold front. Although COSMO HAILCAST tends to underestimate the hail size on the ground, the results indicate that both HAILCAST and LPI are promising candidates for future climate research.</p
Adaptive Optics Images of Kepler Objects of Interest
All transiting planets are at risk of contamination by blends with nearby,
unresolved stars. Blends dilute the transit signal, causing the planet to
appear smaller than it really is, or produce a false positive detection when
the target star is blended with eclipsing binary stars. This paper reports on
high spatial-resolution adaptive optics images of 90 Kepler planetary
candidates. Companion stars are detected as close as 0.1 arcsec from the target
star. Images were taken in the near-infrared (J and Ks bands) with ARIES on the
MMT and PHARO on the Palomar Hale 200-inch. Most objects (60%) have at least
one star within 6 arcsec separation and a magnitude difference of 9. Eighteen
objects (20%) have at least one companion within 2 arcsec of the target star; 6
companions (7%) are closer than 0.5 arcsec. Most of these companions were
previously unknown, and the associated planetary candidates should receive
additional scrutiny. Limits are placed on the presence of additional companions
for every system observed, which can be used to validate planets statistically
using the BLENDER method. Validation is particularly critical for low-mass,
potentially Earth-like worlds, which are not detectable with current-generation
radial velocity techniques. High-resolution images are thus a crucial component
of any transit follow-up program.Comment: 9 pages, 4 figures, accepted to A
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Mean and extreme precipitation over European river basins better simulated in a 25km AGCM
Limited spatial resolution is one of the factors that may hamper applications of global climate models (GCMs), in particular over Europe with its complex coastline and orography. In this study, the representation of European mean and extreme precipitation is evaluated in simulations with an atmospheric GCM (AGCM) at different resolutions between about 135 and 25km grid spacing in the mid-latitudes. The continent-wide root-mean-square error in mean precipitation in the 25km model is about 25% smaller than in the 135km model in winter. Clear improvements are also seen in autumn and spring, whereas the model's sensitivity to resolution is very small in summer. Extreme precipitation is evaluated by estimating generalised extreme value distributions (GEVs) of daily precipitation aggregated over river basins whose surface area is greater than 50000km2. GEV location and scale parameters are measures of the typical magnitude and of the interannual variability of extremes, respectively. Median model biases in both these parameters are around 10% in summer and around 20% in the other seasons. For some river basins, however, these biases can be much larger and take values between 50% and 100%. Extreme precipitation is better simulated in the 25km model, especially during autumn when the median GEV parameter biases are more than halved, and in the North European Plains, from the Loire in the west to the Vistula in the east. A sensitivity experiment is conducted showing that these resolution sensitivities in both mean and extreme precipitation are in many areas primarily due to the increase in resolution of the model orography. The findings of this study illustrate the improved capability of a global high-resolution model in simulating European mean and extreme precipitation
Weak evidence for variable occultation depth of 55 Cnc e with TESS
55 Cnc e is in a 0.73 day orbit transiting a Sun-like star. It has been
observed that the occultation depth of this Super-Earth, with a mass of
8 and radius of 2, changes significantly over
time at mid-infrared wavelengths. Observations with Spitzer measured a change
in its day-side brightness temperature of 1200 K, possibly driven by volcanic
activity, magnetic star-planet interaction, or the presence of a circumstellar
torus of dust. Previous evidence for the variability in occultation was in the
infrared range. Here we aim to explore if the variability exists also in the
optical. TESS observed 55 Cnc during sectors 21, 44 and 46. We carefully
detrend the data and fit a transit and occultation model for each sector in a
Markov Chain Monte Carlo routine. In a later stage we use the Leave-One-Out
Cross-Validation statistic to compare with a model of constant occultation for
the complete set and a model with no occultation. We report an occultation
depth of 82.5 ppm for the complete set of TESS observations. In
particular, we measured a depth of 154 ppm for sector 21, while for sector
44 we detect no occultation. In sector 46 we measure a weak occultation of
85 ppm. The occultation depth varies from one sector to the next between
1.6 and 3.4 significance. We derive the possible contribution on
reflected light and thermal emission, setting an upper limit on the geometric
albedo. Based on our model comparison the presence of an occultation is
favoured considerably over no occultation, where the model with varying
occultation across sectors takes most of the statistical weight. Our analysis
confirms a detection of the occultation in TESS. Moreover, our results weakly
lean towards a varying occultation depth between each sector, while the transit
depth is constant across visits.Comment: 9 pages, 9 figures, accepted for publication on A&
Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star
Super-Earths transiting nearby bright stars are key objects that
simultaneously allow for accurate measurements of both their mass and radius,
providing essential constraints on their internal composition. We present here
the confirmation, based on Spitzer transit observations, that the super-Earth
HD 97658 b transits its host star. HD 97658 is a low-mass
() K1 dwarf, as determined from the Hipparcos
parallax and stellar evolution modeling. To constrain the planet parameters, we
carry out Bayesian global analyses of Keck-HIRES radial velocities, and MOST
and Spitzer photometry. HD 97658 b is a massive () and large ( at 4.5
m) super-Earth. We investigate the possible internal compositions for HD
97658 b. Our results indicate a large rocky component, by at least 60% by mass,
and very little H-He components, at most 2% by mass. We also discuss how future
asteroseismic observations can improve the knowledge of the HD 97658 system, in
particular by constraining its age. Orbiting a bright host star, HD 97658 b
will be a key target for coming space missions TESS, CHEOPS, PLATO, and also
JWST, to characterize thoroughly its structure and atmosphere.Comment: 8 figures, accepted to Ap
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