504 research outputs found
Discovery of a stellar companion to the nearby solar-analogue HD 104304
Sun-like stars are promising candidates to host exoplanets and are often
included in exoplanet surveys by radial velocity (RV) and direct imaging. In
this paper we report on the detection of a stellar companion to the nearby
solar-analogue star HD 104304, which previously was considered to host a
planetary mass or brown dwarf companion. We searched for close stellar and
substellar companions around extrasolar planet host stars with high angular
resolution imaging to characterize planet formation environments. The detection
of the stellar companion was achieved by high angular resolution measurements,
using the "Lucky Imaging" technique at the ESO NTT 3.5m with the AstraLux Sur
instrument. We combined the results with VLT/NACO archive data, where the
companion could also be detected. The results were compared to precise RV
measurements of HD 104304, obtained at the Lick and Keck observatories from
2001-2010.
We confirmed common proper motion of the binary system. A spectral type of
M4V of the companion and a mass of 0.21 M_Sun was derived. Due to comparison of
the data with RV measurements of the unconfirmed planet candidate listed in the
Extrasolar Planets Encyclopaedia, we suggest that the discovered companion is
the origin of the RV trend and that the inclination of the orbit of
approximately 35 degrees explains the relatively small RV signal.Comment: 4 pages, 4 PNG figures, use aa.cls, accepted for publication in
Astronomy & Astrophysic
Evidence for enhanced desorption of hydrogen atoms from a Si 100 surface induced by slow highly charged ions
We report evidence for an enhanced desorption of hydrogen atoms from a Si 100 surface bombarded by 30 keV Xeq q 6?22 ions. The measured desorption yield amounts to 0.76 and 2.2 hydrogen atoms per incident Xe10 and Xe18 ion, respectively. For understanding the behaviour of hydrogen desorption from Si, another experiment was carried out to see the hydrogen signals as a function of time for about 140 min after deliberately introducing hydrogen into the target chamber and then shut off the valve. The results are discussed in the light of potential sputtering which essentially dominates for ions at higher charge states and the interpretation is supported by theoretical estimates
Barrow and Kotzebue: an Exploratory Comparison of Acculturation and Education in Two Large Northwestern Alaska Villages
The State of Alask
From Village to Town: An Intermediate Step in the Acculturation of Alaska Eskimos
The State of Alask
Cavity-Enhanced Raman Spectroscopy of Natural Gas with Optical Feedback cw-Diode Lasers
We report on improvements made on our previously introduced technique of cavity-enhanced Raman spectroscopy (CERS) with optical feedback cw-diode lasers in the gas phase, including a new mode-matching procedure which keeps the laser in resonance with the optical cavity without inducing long-term frequency shifts of the laser, and using a new CCD camera with improved noise performance. With 10 mW of 636.2 nm diode laser excitation and 30 s integration time, cavity enhancement achieves noise-equivalent detection limits below 1 mbar at 1 bar total pressure, depending on Raman cross sections. Detection limits can be easily improved using higher power diodes. We further demonstrate a relevant analytical application of CERS, the multicomponent analysis of natural gas samples. Several spectroscopic features have been identified and characterized. CERS with low power diode lasers is suitable for online monitoring of natural gas mixtures with sensitivity and spectroscopic selectivity, including monitoring H2, H2S, N2, CO2, and alkanes
GRAVITY: The adaptive optics assisted, two object beam combiner for the VLTI
We present the adaptive optics assisted, near-infrared VLTI instrument -
GRAVITY - for precision narrow-angle astrometry and interferometric phase
referenced imaging of faint objects. Precision astrometry and phase-referenced
interferometric imaging will realize the most advanced vision of
optical/infrared interferometry with the VLT. Our most ambitious science goal
is to study motions within a few times the event horizon size of the Galactic
Center massive black hole and to test General Relativity in its strong field
limit. We define the science reference cases for GRAVITY and derive the top
level requirements for GRAVITY. The installation of the instrument at the VLTI
is planned for 2012.Comment: 9 pages, Advances in Stellar Interferometry, SPIE Proc. Vol. 6268,
626811 (2006
Polarization Diagnostics for Cool Core Cluster Emission Lines
The nature of the interaction between low-excitation gas filaments at ~104 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~107 K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields, and suprathermal particles. Under certain physical conditions, theoretical calculations predict of the order of 10% polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits ( 0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfacesPeer reviewe
Permeability evolution during progressive development of deformation bands in porous sandstones
[1] Triaxial deformation experiments were carried out on large (0.1 m) diameter cores of a porous sandstone in order to investigate the evolution of bulk sample permeability as a function of axial strain and effective confining pressure. The log permeability of each sample evolved via three stages: (1) a linear decrease prior to sample failure associated with poroelastic compaction, (2) a transient increase associated with dynamic stress drop, and (3) a systematic quasi-static decrease associated with progressive formation of new deformation bands with increasing inelastic axial strain. A quantitative model for permeability evolution with increasing inelastic axial strain is used to analyze the permeability data in the postfailure stage. The model explicitly accounts for the observed fault zone geometry, allowing the permeability of individual deformation bands to be estimated from measured bulk parameters. In a test of the model for Clashach sandstone, the parameters vary systematically with confining pressure and define a simple constitutive rule for bulk permeability of the sample as a function of inelastic axial strain and effective confining pressure. The parameters may thus be useful in predicting fault permeability and sealing potential as a function of burial depth and faul
Functional basis of electron transport within photosynthetic complex I
Photosynthesis and respiration rely upon a proton gradient to produce ATP. In photosynthesis, the Respiratory Complex I homologue, Photosynthetic Complex I (PS-CI) is proposed to couple ferredoxin oxidation and plastoquinone reduction to proton pumping across
thylakoid membranes. However, little is known about the PS-CI molecular mechanism and
attempts to understand its function have previously been frustrated by its large size and high
lability. Here, we overcome these challenges by pushing the limits in sample size and
spectroscopic sensitivity, to determine arguably the most important property of any electron
transport enzyme – the reduction potentials of its cofactors, in this case the iron-sulphur
clusters of PS-CI (N0, N1 and N2), and unambiguously assign them to the structure using
double electron-electron resonance. We have thus determined the bioenergetics of the
electron transfer relay and provide insight into the mechanism of PS-CI, laying the foundations for understanding of how this important bioenergetic complex functions
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