73 research outputs found
Evidence of a metal-rich surface for the asteroid (16) Psyche from interferometric observations in the thermal infrared
We describe the first determination of thermal properties and size of the
M-type asteroid (16) Psyche from interferometric observations obtained with the
Mid-Infrared Interferometric Instrument (MIDI) of the Very Large Telescope
Interferometer. We used a thermophysical model to interpret our interferometric
data. Our analysis shows that Psyche has a low macroscopic surface roughness.
Using a convex 3-D shape model obtained by Kaasalainen et al. (2002, Icarus
159, 369-395), we derived a volume-equivalent diameter for (16) Psyche of 247
+- 25 km or 238 +- 24 km, depending on the possible values of surface
roughness. Our corresponding thermal inertia estimates are 133 or 114
J.m-2.s-0.5.K-1, with a total uncertainty estimated to 40 J.m-2.s-0.5.K-1. They
are among the highest thermal inertia values ever measured for an asteroid of
this size. We consider this as a new evidence of a metal-rich surface for the
asteroid (16) Psyche.Comment: 45 pages (in referee and preprint format), 6 figure
Determination of physical properties of the asteroid (41) Daphne from interferometric observations in the thermal infrared
We describe interferometric observations of the asteroid (41) Daphne in the
thermal infrared obtained with the Mid-Infrared Interferometric Instrument
(MIDI) of the Very Large Telescope Interferometer (VLTI). We derived the size
and the surface thermal properties of (41) Daphne by means of a thermophysical
model (TPM), which is used for the interpretation of interferometric data for
the first time. From our TPM analysis, we derived a volume equivalent diameter
for (41) Daphne of 189 km, using a non-convex 3-D shape model derived from
optical lightcurves and adaptive optics images (B. Carry, private
communication). On the other hand, when using the convex shape of Kaasalainen
et al. (2002. Icarus 159, 369-395) in our TPM analysis, the resulting volume
equivalent diameter of (41) Daphne is between 194 and 209 km, depending on the
surface roughness. The shape of the asteroid is used as an a priori information
in our TPM analysis. No attempt is made to adjust the shape to the data. Only
the size of the asteroid and its thermal parameters (albedo, thermal inertia
and roughness) are adjusted to the data. We estimated our model systematic
uncertainty to be of 4% and of 7% on the determination of the asteroid volume
equivalent diameter depending on whether the non-convex or the convex shape is
used, respectively. In terms of thermal properties, we derived a value of the
surface thermal inertia smaller than 50 J m-2 s-0.5 K-1 and preferably in the
range between 0 and 30 J m-2 s-0.5 K-1. Our TPM analysis also shows that Daphne
has a moderate macroscopic surface roughness.Comment: 44 pages, 8 figures, 3 table
Evidence of a discontinuous disk structure around the Herbig Ae star HD 139 614
A new class of pre-main sequence objects has been recently identified as
pre-transitional disks. They present near-infrared excess coupled to a flux
deficit at about 10 microns and a rising mid-infrared and far-infrared
spectrum. These features suggest a disk structure with inner and outer dust
components, separated by a dust-depleted region (or gap). We here report on the
first interferometric observations of the disk around the Herbig Ae star HD
139614. Its infrared spectrum suggests a flared disk, and presents
pre-transitional features,namely a substantial near-infrared excess accompanied
by a dip around 6 microns and a rising mid-infrared part. In this framework, we
performed a study of the spectral energy distribution (SED) and the
mid-infrared VLTI/MIDI interferometric data to constrain thespatial structure
of the inner dust disk region and assess its possibly multi-component
structure. We based our work on a temperature-gradient disk model that includes
dust opacity. While we could not reproduce the SED and interferometric
visibilities with a one-component disk, a better agreement was obtained with a
two-component disk model composed of an optically thin inner disk extending
from 0.22 to 2.3 au, a gap, and an outer temperature-gradient disk starting at
5.6 au. Therefore, our modeling favors an extended and optically thin inner
dust component and in principle rules out the possibility that the
near-infrared excess originates only from a spatially confined region.
Moreover, the outer disk is characterized by a very steep temperature profile
and a temperature higher than 300 K at its inner edge. This suggests the
existence of a warm component corresponding to a scenario where the inner edge
of the outer disk is directly illuminated by the central star. This is an
expected consequence of the presence of a gap, thus indicative of a
pre-transitional structure.Comment: 14 pages, 6 figure
HD139614: the interferometric case for a group-Ib pre-transitional young disk
The Herbig Ae star HD 139614 is a group-Ib object, which featureless SED
indicates disk flaring and a possible pre-transitional evolutionary stage. We
present mid- and near-IR interferometric results collected with MIDI, AMBER and
PIONIER with the aim of constraining the spatial structure of the 0.1-10 AU
disk region and assess its possible multi-component structure. A two-component
disk model composed of an optically thin 2-AU wide inner disk and an outer
temperature-gradient disk starting at 5.6 AU reproduces well the observations.
This is an additional argument to the idea that group-I HAeBe inner disks could
be already in the disk-clearing transient stage. HD 139614 will become a prime
target for mid-IR interferometric imaging with the second-generation instrument
MATISSE of the VLTI.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2014, 11 pages, 7 Figure
Parasitic Interference in Long Baseline Optical Interferometry: Requirements for Hot Jupiter-like Planet Detection
International audienceThe observable quantities in optical interferometry, which are the modulus and the phase of the complex visibility, may be corrupted by parasitic fringes superimposed on the genuine fringe pattern. These fringes are due to an interference phenomenon occurring from stray light effects inside an interferometric instrument. We developed an analytical approach to better understand this phenomenon when stray light causes cross talk between beams. We deduced that the parasitic interference significantly affects the interferometric phase and thus the associated observables including the differential phase and the closure phase. The amount of parasitic flux coupled to the piston between beams appears to be very influential in this degradation. For instance, considering a point-like source and a piston ranging from λ/500 to λ/5 in the L band (λ = 3.5 μm), a parasitic flux of about 1% of the total flux produces a parasitic phase reaching at most one-third of the intrinsic phase. The piston, which can have different origins (instrumental stability, atmospheric perturbations, etc.), thus amplifies the effect of parasitic interference. According to the specifications of piston correction in space or at ground level (respectively λ/500 ≈ 2 nm and λ/30 ≈ 100 nm), the detection of hot Jupiter-like planets, one of the most challenging aims for current ground-based interferometers, limits parasitic radiation to about 5% of the incident intensity. This was evaluated by considering different types of hot Jupiter synthetic spectra. Otherwise, if no fringe tracking is used, the detection of a typical hot Jupiter-like system with a solar-like star would admit a maximum level of parasitic intensity of 0.01% for piston errors equal to λ/15. If the fringe tracking specifications are not precisely observed, it thus appears that the allowed level of parasitic intensity dramatically decreases and may prevent the detection. In parallel, the calibration of the parasitic phase by a reference star, at this accuracy level, seems very difficult. Moreover, since parasitic phase is an object-dependent quantity, the use of a hypothetical phase abacus, directly giving the parasitic phase from a given parasitic flux level, is also impossible. Some instrumental solutions, implemented at the instrument design stage for limiting or preventing this parasitic interference, appear to be crucial and are presented in this paper
ZO-1 Guides Tight Junction Assembly and Epithelial Morphogenesis via Cytoskeletal Tension-Dependent and -Independent Functions
Formation and maintenance of tissue barriers require the coordination of cell mechanics and cell–cell junction assembly. Here, we combined methods to modulate ECM stiffness and to measure mechanical forces on adhesion complexes to investigate how tight junctions regulate cell mechanics and epithelial morphogenesis. We found that depletion of the tight junction adaptor ZO-1 disrupted junction assembly and morphogenesis in an ECM stiffness-dependent manner and led to a stiffness-dependant reorganisation of active myosin. Both junction formation and morphogenesis were rescued by inhibition of actomyosin contractility. ZO-1 depletion also impacted mechanical tension at cell-matrix and E-cadherin-based cell–cell adhesions. The effect on E-cadherin also depended on ECM stiffness and correlated with effects of ECM stiffness on actin cytoskeleton organisation. However, ZO-1 knockout also revealed tension-independent functions of ZO-1. ZO-1-deficient cells could assemble functional barriers at low tension, but their tight junctions remained corrupted with strongly reduced and discontinuous recruitment of junctional components. Our results thus reveal that reciprocal regulation between ZO-1 and cell mechanics controls tight junction assembly and epithelial morphogenesis, and that, in a second, tension-independent step, ZO-1 is required to assemble morphologically and structurally fully assembled and functionally normal tight junctions
Why Chromatic Imaging Matters
During the last two decades, the first generation of beam combiners at the
Very Large Telescope Interferometer has proved the importance of optical
interferometry for high-angular resolution astrophysical studies in the near-
and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v
coverage per pointing increases significantly, providing an opportunity to use
reconstructed images as powerful scientific tools. Therefore, interferometric
imaging is already a key feature of the new generation of VLTI instruments, as
well as for other interferometric facilities like CHARA and JWST. It is thus
imperative to account for the current image reconstruction capabilities and
their expected evolutions in the coming years. Here, we present a general
overview of the current situation of optical interferometric image
reconstruction with a focus on new wavelength-dependent information,
highlighting its main advantages and limitations. As an Appendix we include
several cookbooks describing the usage and installation of several state-of-the
art image reconstruction packages. To illustrate the current capabilities of
the software available to the community, we recovered chromatic images, from
simulated MATISSE data, using the MCMC software SQUEEZE. With these images, we
aim at showing the importance of selecting good regularization functions and
their impact on the reconstruction.Comment: Accepted for publication in Experimental Astronomy as part of the
topical collection: Future of Optical-infrared Interferometry in Europ
Parapatric speciation of Meiothermus in serpentinite-hosted aquifers in Oman
The factors that control the distribution and evolution of microbial life in subsurface environments remain enigmatic due to challenges associated with sampling fluids from discrete depth intervals via boreholes while avoiding mixing of fluids. Here, using an inflatable packer system, fracture waters were isolated and collected from three discrete depth intervals spanning >130 m in a borehole intersecting an ultramafic rock formation undergoing serpentinization in the Samail Ophiolite, Sultanate of Oman. Near surface aquifer waters were moderately reducing and had alkaline pH while deeper aquifer waters were reduced and had hyperalkaline pH, indicating extensive influence by serpentinization. Metagenomic sequencing and analysis of DNA from filtered biomass collected from discrete depth intervals revealed an abundance of aerobes in near surface waters and a greater proportion of anaerobes at depth. Yet the abundance of the putatively obligate aerobe, Meiothermus, increased with depth, providing an opportunity to evaluate the influence of chemical and spatial variation on its distribution and speciation. Two clades of Meiothermus metagenome assembled genomes (MAGs) were identified that correspond to surface and deep populations termed Types I (S) and II (D), respectively; both clades comprised an apparently Oman-specific lineage indicating a common ancestor. Type II (D) clade MAGs encoded fewer genes and were undergoing slower genome replication as inferred from read mapping. Further, single nucleotide variants (SNVs) and mobile genetic elements identified among MAGs revealed detectable, albeit limited, evidence for gene flow/recombination between spatially segregated Type I (S) and Type II (D) populations. Together, these observations indicate that chemical variation generated by serpentinization, combined with physical barriers that reduce/limit dispersal and gene flow, allowed for the parapatric speciation of Meiothermus in the Samail Ophiolite or a geologic precursor. Further, Meiothermus genomic data suggest that deep and shallow aquifer fluids in the Samail Ophiolite may mix over shorter time scales than has been previously estimated from geochemical data
The expected performance of nulling at the VLTI down to 5 mas
While VLTI offers the recombination of four 8-m telescopes with baselines of more than 100m, it has never hosted a dedicated high-contrast nulling beam-combiner. The SCIFY project aims to design, build and commission Hi- 5, the first nulling beam-combiner of the VLTI, optimized for the detection and characterization of young giant exoplanets near the snow line, with spectroscopy up to R=2000 in the L’ band. It will make use of advanced four-beam nulling combination schemes, like double-Bracewell and kernel-nulling implemented in a single-mode photonic device to produce differential nulled outputs with self-calibrating properties. In the wavelength range of interest, both instrumental errors and background noise are significant. In order to estimate the practical performance of these different configurations in the presence of instrumental errors and further optimize the instrumental design, we have developed SCIFYsim. SCIFYsim is an end-to-end simulator geared towards single- mode beam combiners with of a wide variety of instrumental errors, like optical path difference residuals from fringe tracking, wavefront error at the injection, longitudinal dispersion, chromaticity of the combiner chip, and more. In order to evaluate the performance of the combined spectral channels, we use statistical tests based on likelihood ratios, and account for the covariance in the data. In this paper, we present the expected performance of Hi-5 with a few examples and discuss the main technical limitations to reach the contrast required to image young giant exoplanets.SCIF
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