104 research outputs found
Revisiting the transits of CoRoT-7b at a lower activity level
CoRoT-7b, the first super-Earth with measured radius discovered, has opened
the new field of rocky exoplanets characterisation. To better understand this
interesting system, new observations were taken with the CoRoT satellite.
During this run 90 new transits were obtained in the imagette mode. These were
analysed together with the previous 151 transits obtained in the discovery run
and HARPS radial velocity observations to derive accurate system parameters. A
difference is found in the posterior probability distribution of the transit
parameters between the previous CoRoT run (LRa01) and the new run (LRa06). We
propose this is due to an extra noise component in the previous CoRoT run
suspected to be transit spot occultation events. These lead to the mean transit
shape becoming V-shaped. We show that the extra noise component is dominant at
low stellar flux levels and reject these transits in the final analysis. We
obtained a planetary radius, , in agreement
with previous estimates. Combining the planetary radius with the new mass
estimates results in a planetary density of
which is consistent with a rocky composition. The CoRoT-7 system remains an
excellent test bed for the effects of activity in the derivation of planetary
parameters in the shallow transit regime.Comment: 13 pages, 13 figures, accepted to A&
A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability
Patsourakos et al. (Astrophys. J. 817, 14, 2016) and Patsourakos and
Georgoulis (Astron. Astrophys. 595, A121, 2016) introduced a method to infer
the axial magnetic field in flux-rope coronal mass ejections (CMEs) in the
solar corona and farther away in the interplanetary medium. The method, based
on the conservation principle of magnetic helicity, uses the relative magnetic
helicity of the solar source region as input estimates, along with the radius
and length of the corresponding CME flux rope. The method was initially applied
to cylindrical force-free flux ropes, with encouraging results. We hereby
extend our framework along two distinct lines. First, we generalize our
formalism to several possible flux-rope configurations (linear and nonlinear
force-free, non-force-free, spheromak, and torus) to investigate the dependence
of the resulting CME axial magnetic field on input parameters and the employed
flux-rope configuration. Second, we generalize our framework to both Sun-like
and active M-dwarf stars hosting superflares. In a qualitative sense, we find
that Earth may not experience severe atmosphere-eroding magnetospheric
compression even for eruptive solar superflares with energies ~ 10^4 times
higher than those of the largest Geostationary Operational Environmental
Satellite (GOES) X-class flares currently observed. In addition, the two
recently discovered exoplanets with the highest Earth-similarity index, Kepler
438b and Proxima b, seem to lie in the prohibitive zone of atmospheric erosion
due to interplanetary CMEs (ICMEs), except when they possess planetary magnetic
fields that are much higher than that of Earth.Comment: http://adsabs.harvard.edu/abs/2017SoPh..292...89
Transiting exoplanets from the CoRoT space mission I - CoRoT-Exo-1b: a low-density short-period planet around a G0V star
Context. The pioneer space mission for photometric planet searches, CoRoT,
steadily monitors about 12,000 stars in each of its fields of view; it is able
to detect transit candidates early in the processing of the data and before the
end of a run. Aims. We report the detection of the first planet discovered by
CoRoT and characterizing it with the help of follow-up observations. Methods.
Raw data were filtered from outliers and residuals at the orbital period of the
satellite. The orbital parameters and the radius of the planet were estimated
by best fitting the phase folded light curve with 34 successive transits.
Doppler measurements with the SOPHIE spectrograph permitted us to secure the
detection and to estimate the planet mass. Results. The accuracy of the data is
very high with a dispersion in the 2.17 min binned phase-folded light curve
that does not exceed 3.10-4 in flux unit. The planet orbits a mildly metal-poor
G0V star of magnitude V=13.6 in 1.5 days. The estimated mass and radius of the
star are 0.95+-0.15Msun and 1.11+-0.05Rsun. We find the planet has a radius of
1.49+-0.08Rjup, a mass of 1.03+-0.12Mjup, and a particularly low mean density
of 0.38 +-0.05g cm-3.Comment: A&A letters (in press) - 4 pages - 3 figure
Modeling photoelectron transport in the Martian ionosphere at Olympus Mons and Syrtis Major: MGS observations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95423/1/jgra20373.pd
TNFR1 inhibition with a nanobody protects against EAE development in mice
TNF has as detrimental role in multiple sclerosis (MS), however, anti-TNF medication is not working. Selective TNF/TNFR1 inhibition whilst sparing TNFR2 signaling reduces the pro-inflammatory effects of TNF but preserves the important neuroprotective signals via TNFR2. We previously reported the generation of a Nanobody-based selective inhibitor of human TNFR1, TROS that will be tested in experimental autoimmune encephalomyelitis (EAE). We specifically antagonized TNF/TNFR1 signaling using TROS in a murine model of MS, namely MOG(35-55)-induced EAE. Because TROS does not cross-react with mouse TNFR1, we generated mice expressing human TNFR1 in a mouse TNFR1-knockout background (hTNFR1 Tg), and we determined biodistribution of Tc-99m-TROS and effectiveness of TROS in EAE in those mice. Biodistribution analysis demonstrated that intraperitoneally injected TROS is retained more in organs of hTNFR1 Tg mice compared to wild type mice. TROS was also detected in the cerebrospinal fluid (CSF) of hTNFR1 Tg mice. Prophylactic TROS administration significantly delayed disease onset and ameliorated its symptoms. Moreover, treatment initiated early after disease onset prevented further disease development. TROS reduced spinal cord inflammation and neuroinflammation, and preserved myelin and neurons. Collectively, our data illustrate that TNFR1 is a promising therapeutic target in MS
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Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity
Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements
A global spectral library to characterize the world's soil
Soil provides ecosystem services, supports human health and habitation, stores carbon and regulates emissions of greenhouse gases. Unprecedented pressures on soil from degradation and urbanization are threatening agro-ecological balances and food security. It is important that we learn more about soil to sustainably manage and preserve it for future generations. To this end, we developed and analyzed a global soil visible-near infrared (vis-NIR) spectral library. It is currently the largest and most diverse database of its kind. We show that the information encoded in the spectra can describe soil composition and be associated to land cover and its global geographic distribution, which acts as a surrogate for global climate variability. We also show the usefulness of the global spectra for predicting soil attributes such as soil organic and inorganic carbon, clay, silt, sand and iron contents, cation exchange capacity, and pH. Using wavelets to treat the spectra, which were recorded in different laboratories using different spectrometers and methods, helped to improve the spectroscopic modelling. We found that modelling a diverse set of spectra with a machine learning algorithm can find the local relationships in the data to produce accurate predictions of soil properties. The spectroscopic models that we derived are parsimonious and robust, and using them we derived a harmonized global soil attribute dataset, which might serve to facilitate research on soil at the global scale. This spectroscopic approach should help to deal with the shortage of data on soil to better understand it and to meet the growing demand for information to assess and monitor soil at scales ranging from regional to global. New contributions to the library are encouraged so that this work and our collaboration might progress to develop a dynamic and easily updatable database with better global coverage. We hope that this work will reinvigorate our community's discussion towards larger, more coordinated collaborations. We also hope that use of the database will deepen our understanding of soil so that we might sustainably manage it and extend the research outcomes of the soil, earth and environmental sciences towards applications that we have not yet dreamed of
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