310 research outputs found
First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
To date, infrared interferometry at best achieved contrast ratios of a few
times on bright targets. GRAVITY, with its dual-field mode, is now
capable of high contrast observations, enabling the direct observation of
exoplanets. We demonstrate the technique on HR8799, a young planetary system
composed of four known giant exoplanets. We used the GRAVITY fringe tracker to
lock the fringes on the central star, and integrated off-axis on the HR8799e
planet situated at 390 mas from the star. Data reduction included
post-processing to remove the flux leaking from the central star and to extract
the coherent flux of the planet. The inferred K band spectrum of the planet has
a spectral resolution of 500. We also derive the astrometric position of the
planet relative to the star with a precision on the order of 100as. The
GRAVITY astrometric measurement disfavors perfectly coplanar stable orbital
solutions. A small adjustment of a few degrees to the orbital inclination of HR
8799 e can resolve the tension, implying that the orbits are close to, but not
strictly coplanar. The spectrum, with a signal-to-noise ratio of
per spectral channel, is compatible with a late-type L brown dwarf. Using
Exo-REM synthetic spectra, we derive a temperature of \,K and a
surface gravity of cm/s. This corresponds to a radius
of and a mass of , which is an independent confirmation of mass estimates from evolutionary
models. Our results demonstrate the power of interferometry for the direct
detection and spectroscopic study of exoplanets at close angular separations
from their stars.Comment: published in A&
High-throughput screening of metal-porphyrin-like graphenes for selective capture of carbon dioxide
Nanostructured materials, such as zeolites and metal-organic frameworks, have been considered to capture CO2. However, their application has been limited largely because they exhibit poor selectivity for flue gases and low capture capacity under low pressures. We perform a high-throughput screening for selective CO2 capture from flue gases by using first principles thermodynamics. We find that elements with empty d orbitals selectively attract CO2 from gaseous mixtures under low CO2 pressures (similar to 10(-3) bar) at 300 K and release it at similar to 450 K. CO2 binding to elements involves hybridization of the metal d orbitals with the CO2 pi orbitals and CO2-transition metal complexes were observed in experiments. This result allows us to perform high-throughput screening to discover novel promising CO2 capture materials with empty d orbitals (e.g., Sc- or V-porphyrin-like graphene) and predict their capture performance under various conditions. Moreover, these findings provide physical insights into selective CO2 capture and open a new path to explore CO2 capture materialsopen
Assignment of PolyProline II Conformation and Analysis of Sequence – Structure Relationship
International audienceBACKGROUND: Secondary structures are elements of great importance in structural biology, biochemistry and bioinformatics. They are broadly composed of two repetitive structures namely α-helices and β-sheets, apart from turns, and the rest is associated to coil. These repetitive secondary structures have specific and conserved biophysical and geometric properties. PolyProline II (PPII) helix is yet another interesting repetitive structure which is less frequent and not usually associated with stabilizing interactions. Recent studies have shown that PPII frequency is higher than expected, and they could have an important role in protein - protein interactions. METHODOLOGY/PRINCIPAL FINDINGS: A major factor that limits the study of PPII is that its assignment cannot be carried out with the most commonly used secondary structure assignment methods (SSAMs). The purpose of this work is to propose a PPII assignment methodology that can be defined in the frame of DSSP secondary structure assignment. Considering the ambiguity in PPII assignments by different methods, a consensus assignment strategy was utilized. To define the most consensual rule of PPII assignment, three SSAMs that can assign PPII, were compared and analyzed. The assignment rule was defined to have a maximum coverage of all assignments made by these SSAMs. Not many constraints were added to the assignment and only PPII helices of at least 2 residues length are defined. CONCLUSIONS/SIGNIFICANCE: The simple rules designed in this study for characterizing PPII conformation, lead to the assignment of 5% of all amino as PPII. Sequence - structure relationships associated with PPII, defined by the different SSAMs, underline few striking differences. A specific study of amino acid preferences in their N and C-cap regions was carried out as their solvent accessibility and contact patterns. Thus the assignment of PPII can be coupled with DSSP and thus opens a simple way for further analysis in this field
Rapid Sampling of Molecular Motions with Prior Information Constraints
Proteins are active, flexible machines that perform a range of different
functions. Innovative experimental approaches may now provide limited partial
information about conformational changes along motion pathways of proteins.
There is therefore a need for computational approaches that can efficiently
incorporate prior information into motion prediction schemes. In this paper, we
present PathRover, a general setup designed for the integration
of prior information into the motion planning algorithm of rapidly exploring
random trees (RRT). Each suggested motion pathway comprises a sequence of
low-energy clash-free conformations that satisfy an arbitrary number of prior
information constraints. These constraints can be derived from experimental data
or from expert intuition about the motion. The incorporation of prior
information is very straightforward and significantly narrows down the vast
search in the typically high-dimensional conformational space, leading to
dramatic reduction in running time. To allow the use of state-of-the-art energy
functions and conformational sampling, we have integrated this framework into
Rosetta, an accurate protocol for diverse types of structural modeling. The
suggested framework can serve as an effective complementary tool for molecular
dynamics, Normal Mode Analysis, and other prevalent techniques for predicting
motion in proteins. We applied our framework to three different model systems.
We show that a limited set of experimentally motivated constraints may
effectively bias the simulations toward diverse predicates in an outright
fashion, from distance constraints to enforcement of loop closure. In
particular, our analysis sheds light on mechanisms of protein domain swapping
and on the role of different residues in the motion
The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
The Astropy project supports and fosters the development of open-source and openly-developed Python packages that provide commonly-needed functionality to the astronomical community. A key element of the Astropy project is the core package Astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of inter-operable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy project
Multiple star systems in the Orion nebula
This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie Skłodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran
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