179 research outputs found
Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations
We examine the implications for the distribution of extrasolar planets based
on the null results from two of the largest direct imaging surveys published to
date. Combining the measured contrast curves from 22 of the stars observed with
the VLT NACO adaptive optics system by Masciadri et al. (2005), and 48 of the
stars observed with the VLT NACO SDI and MMT SDI devices by Biller et al.
(2007) (for a total of 60 unique stars; the median star for our survey is a 30
Myr K2 star at 25 pc), we consider what distributions of planet masses and
semi-major axes can be ruled out by these data, based on Monte Carlo
simulations of planet populations. We can set this upper limit with 95%
confidence: the fraction of stars with planets with semi-major axis from 20 to
100 AU, and mass >4 M_Jup, is 20% or less. Also, with a distribution of planet
mass of dN/dM ~ M^-1.16 between 0.5-13 M_Jup, we can rule out a power-law
distribution for semi-major axis (dN/da ~ a^alpha) with index 0 and upper
cut-off of 18 AU, and index -0.5 with an upper cut-off of 48 AU. For the
distribution suggested by Cumming et al. (2007), a power-law of index -0.61, we
can place an upper limit of 75 AU on the semi-major axis distribution. At the
68% confidence level, these upper limits state that fewer than 8% of stars have
a planet of mass >4 M_Jup between 20 and 100 AU, and a power-law distribution
for semi-major axis with index 0, -0.5, and -0.61 cannot have giant planets
beyond 12, 23, and 29 AU, respectively. In general, we find that even null
results from direct imaging surveys are very powerful in constraining the
distributions of giant planets (0.5-13 M_Jup) at large separations, but more
work needs to be done to close the gap between planets that can be detected by
direct imaging, and those to which the radial velocity method is sensitive.Comment: 46 pages, 17 figures, accepted to Ap
The PHASES Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems
The Palomar High-precision Astrometric Search for Exoplanet Systems monitored
51 subarcsecond binary systems to evaluate whether tertiary companions as small
as Jovian planets orbited either the primary or secondary stars, perturbing
their otherwise smooth Keplerian motions. Six binaries are presented that show
evidence of substellar companions orbiting either the primary or secondary
star. Of these six systems, the likelihoods of two of the detected
perturbations to represent real objects are considered to be "high confidence",
while the remaining four systems are less certain and will require continued
observations for confirmation.Comment: 16 Pages, Accepted to A
Hard X-ray Emission Associated with White Dwarfs
We have used the WGACAT to search for hard X-ray sources associated with
white dwarfs (WDs) from the catalog of McCook & Sion (1999). We find 17 X-ray
sources coincident with WDs showing significant hard X-ray emission at energies
>0.5 keV. Twelve of these WDs are in known binary systems, in two of which the
accretion of the close companion's material onto the white dwarf produces the
hard X-ray emission, and in the other ten of which the late-type companions'
coronal activity emits hard X-rays. One WD is projected near an AGN which is
responsible for the hard X-ray emission. The remaining four WDs and two
additional white dwarfs with hard X-ray emission appear single. The lack of
near-IR excess from the apparently single WDs suggests that either X-ray
observations are more effective than near-IR photometry in diagnosing faint
companions or a different emission mechanism is needed. It is intriguing that
50% of the six apparently single WDs with hard X-ray emission are among the
hottest WDs. We have compared X-ray properties of 11 hot WDs with different
spectral types, and conclude that stellar pulsation and fast stellar winds are
not likely the origin of the hard X-ray emission, but a leakage of the
high-energy Wien tail of emission from deep in the stellar atmosphere remains a
tantalizing source of hard X-ray emission from hot DO and DQZO WDs. (This
abstract is an abridged version.)Comment: 35 pages, 8 figures, 4 tables, accepted for publication in AJ, April
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Do the Infrared Emission Features Need Ultraviolet Excitation
We present the results of imaging spectroscopy of the reflection nebula vdB
133, obtained with the infrared camera and circular variable filter wheel on
the Infrared Space Observatory (ISO). Our observations reveal the infrared
emission features (IEFs), at 6.2, 7.7, 8.6, 11.3, and 12.7 micron, and
associated 5 -- 15 micron continuum emission. The stellar system illuminating
vdB 133 has the lowest ratio of ultraviolet (shortward of 0.4 micron) to total
flux of any stars demonstrated to date to excite the IEFs and associated
continuum emission from adjacent interstellar dust, as opposed to circumstellar
dust. The low fraction of UV flux from this system poses a problem for existing
models for the emission mechanism and emitting material, which all require
substantial UV radiation for the excitation of the IEFs and associated
continuum.Comment: accepted for publication in ApJ
Association of KIR2DS1 and KIR2DS3 with fatal outcome in Ebola virus infection
Zaïre ebolavirus (ZEBOV) infection rapidly outruns the host's immunity and leads to death within a week. Fatal cases have been associated with an aberrant innate, proinflammatory immune response followed by a suppressed adaptive response leading to the rapid depletion of peripheral NK cells and lymphocytes. A critical role for NK cells has been suggested but not elucidated. In this genetic study, we investigated the association of KIR genotype with disease outcome by comparing genotypes of a Gabonese control population, IgG+ contacts, survivors, and fatalities of ZEBOV infection. We showed that the activating KIR2DS1 and KIR2DS3 genes associate with fatal outcome in Ebola virus infection. In addition, this study brings supplemental evidence in favor of the specificity of the IgG+ contact population. The outcome of fulminating Ebola virus infection could depend in part on the host's inherited KIR gene repertoire. This supports a key role for KIRs in disease susceptibility to infections
Speckle observations with PISCO in Merate - V. Astrometric measurements of visual binaries in 2006
International audienceWe present relative astrometric measurements of visual binaries made during the first semester of 2006, with the Pupil Interferometry Speckle camera and COronagraph at the 102-cm Zeiss telescope of the Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. We obtained 217 new measurements of 194 objects, with angular separations in the range 0.1-4.2arcsec, and an average accuracy of 0.01arcsec. The mean error on the position angles is 0.5°. About half of those angles could be determined without the usual 180° ambiguity by the application of triple-correlation techniques. We also present a revised orbit for ADS 277 for which the previously published orbit resulted in a large residual from our measurements
Long-term field metal extraction by pelargonium:phytoextraction efficiency in relation to plant maturity
The long length of periods required for effective soil remediation via phytoextraction constitutes a weak point that reduces its industrial use. However, these calculated periods are mainly based on short-term and/or hydroponic controlled experiments. Moreover, only a few studies concern more than one metal, although soils are scarcely polluted by only one element.In this scientific context, the phytoextraction of metals and metalloids (Pb, Cd, Zn, Cu,and As) by Pelargonium was measured after a long-term field experiment. Both bulk and rhizosphere soils were analyzed in order to determine the mechanisms involved in soil-root transfer. First, a strong increase in lead phytoextraction was observed with plant maturity, significantly reducing the length of the period required for remediation. Rhizosphere Pb, Zn, Cu, Cd, and As accumulation was observed (compared to bulk soil), indicating metal mobilization by the plant, perhaps in relation to root activity. Moreover, metal phytoextraction and translocation were found to be a function of the metals’ nature. These results, taken altogether, suggest that Pelargonium could be used as a multi-metal hyperaccumulator under multi-metal soil contamination conditions, and they also provide an interesting insight for improving field phytoextraction remediation in terms of the length of time required, promoting this biological technique
Mid-IR Observations of Mira Circumstellar Environment
This paper presents results from high-angular resolution mid-IR imaging of
the Mira AB circumbinary environment using the MIRAC3 camera at the NASA
Infrared Telescope Facility (IRTF). We resolved the dusty circumstellar
envelope at 9.8, 11.7 and 18 micron around Mira A (o Ceti), and measured the
size of the extended emission. Strong deviations from spherical symmetry are
detected in the images of Mira AB system, including possible dust clumps in the
direction of the companion (Mira B). These observations suggest that Mira B
plays an active role in shaping the morphology of the circumstellar environment
of Mira A as it evolves toward the Planetary Nebula phase.Comment: 11 pages, 2 PostScript figures, accepted for publication in the
Astrophysical Journal Letter
Production of CXC and CC chemokines by human antigen-presenting cells in response to Lassa virus or closely related immunogenic viruses, and in cynomolgus monkeys with lassa fever.
International audienceThe pathogenesis of Lassa fever (LF), a hemorrhagic fever endemic to West Africa, remains unclear. We previously compared Lassa virus (LASV) with its genetically close, but nonpathogenic homolog Mopeia virus (MOPV) and demonstrated that the strong activation of antigen-presenting cells (APC), including type I IFN production, observed in response to MOPV probably plays a crucial role in controlling infection. We show here that human macrophages (MP) produce large amounts of CC and CXC chemokines in response to MOPV infection, whereas dendritic cells (DC) release only moderate amounts of CXC chemokines. However, in the presence of autologous T cells, DCs produced CC and CXC chemokines. Chemokines were produced in response to type I IFN synthesis, as the levels of both mediators were strongly correlated and the neutralization of type I IFN resulted in an inhibition of chemokine production. By contrast, LASV induced only low levels of CXCL-10 and CXCL-11 production. These differences in chemokine production may profoundly affect the generation of virus-specific T-cell responses and may therefore contribute to the difference of pathogenicity between these two viruses. In addition, a recombinant LASV (rLASV) harboring the NP-D389A/G392A mutations, which abolish the inhibition of type I IFN response by nucleoprotein (NP), induced the massive synthesis of CC and CXC chemokines in both DC and MP, confirming the crucial role of arenavirus NP in immunosuppression and pathogenicity. Finally, we confirmed, using PBMC samples and lymph nodes obtained from LASV-infected cynomolgus monkeys, that LF was associated with high levels of CXC chemokine mRNA synthesis, suggesting that the very early synthesis of these mediators may be correlated with a favourable outcome
Design and analysis of low boom concepts at Langley Research Center
The objective of the sonic boom research in the current High Speed Research Program is to ultimately make possible overland supersonic flight by a high speed civil transport. To accomplish this objective, it is felt that results in four areas must demonstrate that such a vehicle would be acceptable by the general public, by the airframers, and by the airlines. It should be demonstrated: (1) that some waveform shape has the possibility of being acceptable to the general public; (2) that the atmosphere would not totally destroy such a waveform during propagation; (3) that a viable airplane could be built which produces such a waveform; and (4) that any performance penalty suffered by a low boom aircraft would be counteracted by the economic benefit of overland supersonic flight. The work being done at LaRC is in support of the third element listed above--the area of configuration design. The initial part of the paper will give a review of the theory being used for configuration designs and discuss two theory validation models which were built and tested within the past two years. Discussion of the wind tunnel and theoretical results (linear theory and higher order methods) and their implications for future designs will be included
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