769 research outputs found
Ground-based follow-up observations of TRAPPIST-1 transits in the near-infrared
The TRAPPIST-1 planetary system is a favorable target for the atmospheric
characterization of temperate earth-sized exoplanets by means of transmission
spectroscopy with the forthcoming James Webb Space Telescope (JWST). A possible
obstacle to this technique could come from the photospheric heterogeneity of
the host star that could affect planetary signatures in the transit
transmission spectra. To constrain further this possibility, we gathered an
extensive photometric data set of 25 TRAPPIST-1 transits observed in the
near-IR J band (1.2 m) with the UKIRT and the AAT, and in the NB2090 band
(2.1 m) with the VLT during the period 2015-2018. In our analysis of these
data, we used a special strategy aiming to ensure uniformity in our
measurements and robustness in our conclusions. We reach a photometric
precision of (RMS of the residuals), and we detect no significant
temporal variations of transit depths of TRAPPIST-1 b, c, e, and g over the
period of three years. The few transit depths measured for planets d and f hint
towards some level of variability, but more measurements will be required for
confirmation. Our depth measurements for planets b and c disagree with the
stellar contamination spectra originating from the possible existence of bright
spots of temperature 4500 K. We report updated transmission spectra for the six
inner planets of the system which are globally flat for planets b and g and
some structures are seen for planets c, d, e, and f.Comment: accepted for publication in MNRA
Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST
The TRAPPIST-1 system is remarkable for its seven planets that are similar in
size, mass, density, and stellar heating to the rocky planets Venus, Earth, and
Mars in our own Solar System (Gillon et al. 2017). All TRAPPIST-1 planets have
been observed with the transmission spectroscopy technique using the Hubble or
Spitzer Space Telescopes, but no atmospheric features have been detected or
strongly constrained (Ducrot et al. 2018; de Wit et al. 2018; Zhang et al.
2018; Garcia et al. 2022). TRAPPIST-1 b is the closest planet to the system's M
dwarf star, and it receives 4 times as much irradiation as Earth receives from
the Sun. This relatively large amount of stellar heating suggests that its
thermal emission may be measurable. Here we present photometric secondary
eclipse observations of the Earth-sized TRAPPIST-1 b exoplanet using the F1500W
filter of the MIRI instrument on JWST. We detect the secondary eclipse in each
of five separate observations with 8.7-sigma confidence when all data are
combined. These measurements are most consistent with the re-radiation of the
TRAPPIST-1 star's incident flux from only the dayside hemisphere of the planet.
The most straightforward interpretation is that there is little or no planetary
atmosphere redistributing radiation from the host star and also no detectable
atmospheric absorption from carbon dioxide (CO) or other species.Comment: Submitted to Natur
Identification of target-specific bioisosteric fragments from ligand-protein crystallographic data
Bioisosteres are functional groups or atoms that are structurally different but that can form similar intermolecular interactions. Potential bioisosteres were identified here from analysing the X-ray crystallographic structures for sets of different ligands complexed with a fixed protein. The protein was used to align the ligands with each other, and then pairs of ligands compared to identify substructural features with high volume overlap that occurred in approximately the same region of geometric space. The resulting pairs of substructural features can suggest potential bioisosteric replacements for use in lead-optimisation studies. Experiments with 12 sets of ligand-protein complexes from the Protein Data Bank demonstrate the effectiveness of the procedure
Water Condensation Zones around Main Sequence Stars
Understanding the set of conditions that allow rocky planets to have liquid
water on their surface -- in the form of lakes, seas or oceans -- is a major
scientific step to determine the fraction of planets potentially suitable for
the emergence and development of life as we know it on Earth. This effort is
also necessary to define and refine the so-called "Habitable Zone" (HZ) in
order to guide the search for exoplanets likely to harbor remotely detectable
life forms. Until now, most numerical climate studies on this topic have
focused on the conditions necessary to maintain oceans, but not to form them in
the first place. Here we use the three-dimensional Generic Planetary Climate
Model (PCM), historically known as the LMD Generic Global Climate Model (GCM),
to simulate water-dominated planetary atmospheres around different types of
Main-Sequence stars. The simulations are designed to reproduce the conditions
of early ocean formation on rocky planets due to the condensation of the
primordial water reservoir at the end of the magma ocean phase. We show that
the incoming stellar radiation (ISR) required to form oceans by condensation is
always drastically lower than that required to vaporize oceans. We introduce a
Water Condensation Limit, which lies at significantly lower ISR than the inner
edge of the HZ calculated with three-dimensional numerical climate simulations.
This difference is due to a behavior change of water clouds, from low-altitude
dayside convective clouds to high-altitude nightside stratospheric clouds.
Finally, we calculated transit spectra, emission spectra and thermal phase
curves of TRAPPIST-1b, c and d with H2O-rich atmospheres, and compared them to
CO2 atmospheres and bare rock simulations. We show using these observables that
JWST has the capability to probe steam atmospheres on low-mass planets, and
could possibly test the existence of nightside water clouds.Comment: Accepted for publication in Astronomy & Astrophysic
Accumulating discursive capital, valuating subject positions. From Marx to Foucault
Whenever people use language, they participate in valuation practices, i.e. they give value to themselves as well as to others. To account for the construction of social inequality through discursive valuation practices, discourse theorists need Marxist theory and Marxists need discourse theory. By going from the early Marx to the late Foucault, I will revisit Marx?s value theory in light of practice-oriented approaches to social inequality. I will discuss examples from two distinct arenas, the monopolization of attention by populist leaders and the academic star system, both of which are accounted for in terms of the accumulation of discursive capital. This perspective asks how the value of subject positions is constructed and hierarchies between them are established in discursive practices. Investigating the construction of valuable subject positions in discourse communities, this perspective attempts to overcome the traditional division between language, the economic and the social. Discourse not only represents value and the social order but, through representation, it also contributes to constituting the social as a hierarchical world of more or less valued subject positions
Rationality and the experimental study of reasoning
A survey of the results obtained during the past three decades in some of the most widely used tasks and paradigms in the experimental study of reasoning is presented. It is shown that, at first sight, human performance suffers from serious shortcomings. However, after the problems of communication between experimenter and subject are taken into account, which leads to clarify the subject's representation of the tasks, one observes a better performance, although still far from perfect. Current theories of reasoning, of which the two most prominent are very briefly outlined, agree in identifying the load in working memory as the main source of limitation in performance. Finally, a recent view on human rationality prompted by the foregoing results is described
Fancine 2003, n. 08
Abstract not availabl
Predicting impacts of chemicals from organisms to ecosystem service delivery: A case study of endocrine disruptor effects on trout
We demonstrate how mechanistic modeling can be used to predict whether and how biological responses to chemicals at (sub)organismal levels in model species (i.e., what we typically measure) translate into impacts on ecosystem service delivery (i.e., what we care about). We consider a hypothetical case study of two species of trout, brown trout (Salmo trutta; BT) and greenback cutthroat trout (Oncorhynchus clarkii stomias; GCT). These hypothetical populations live in a high-altitude river system and are exposed to human-derived estrogen (17α‑ethinyl estradiol, EE2), which is the bioactive estrogen in many contraceptives. We use the individual based model in STREAM to explore how seasonally varying concentrations of EE2 could influence male spawning and sperm quality. Resulting impacts on trout recruitment and the consequences of such for anglers and for the continued viability of populations of GCT (the state fish of Colorado) are explored. in STREAM incorporates seasonally varying river flow and temperature, fishing pressure, the influence of EE2 on species-specific demography, and inter-specific competition. The model facilitates quantitative exploration of the relative importance of endocrine disruption and inter-species competition on trout population dynamics. Simulations predicted constant EE2 loading to have more impacts on GCT than BT. However, increasing removal of BT by anglers can enhance the persistence of GCT and offset some of the negative effects of EE2. We demonstrate how models that quantitatively link impacts of chemicals and other stressors on individual survival, growth, and reproduction to consequences for populations and ecosystem service delivery, can be coupled with ecosystem service valuation. The approach facilitates interpretation of toxicity data in an ecological context and gives beneficiaries of ecosystem services amore explicit role in management decisions. Although challenges remain, this type of approach may be particularly helpful for site-specific risk assessments and those in which trade offs and synergies among ecosystem services need to be considered
SPECULOOS: a network of robotic telescopes to hunt for terrestrial planets around the nearest ultracool dwarfs
We present here SPECULOOS, a new exoplanet transit search based on a network
of 1m-class robotic telescopes targeting the 1200 ultracool (spectral
type M7 and later) dwarfs bright enough in the infrared (-mag )
to possibly enable the atmospheric characterization of temperate terrestrial
planets with next-generation facilities like the . The ultimate goals of the project are to reveal the frequency of
temperate terrestrial planets around the lowest-mass stars and brown dwarfs, to
probe the diversity of their bulk compositions, atmospheres and surface
conditions, and to assess their potential habitability.Comment: 21 pages, 13 figures, 1 table. Proceedings of SPI
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