63 research outputs found
A comprehensive examination of the Eps Eri system -- Verification of a 4 micron narrow-band high-contrast imaging approach for planet searches
Due to its proximity, youth, and solar-like characteristics with a spectral
type of K2V, Eps Eri is one of the most extensively studied systems in an
extrasolar planet context. Based on radial velocity, astrometry, and studies of
the structure of its circumstellar debris disk, at least two planetary
companion candidates to Eps Eri have been inferred in the literature (Eps Eri
b, Eps Eri c). Some of these methods also hint at additional companions
residing in the system. Here we present a new adaptive optics assisted
high-contrast imaging approach that takes advantage of the favourable planet
spectral energy distribution at 4 microns, using narrow-band angular
differential imaging to provide an improved contrast at small and intermediate
separations from the star. We use this method to search for planets at orbits
intermediate between Eps Eri b (3.4 AU) and Eps Eri c (40 AU). The method is
described in detail, and important issues related to the detectability of
planets such as the age of Eps Eri and constraints from indirect measurements
are discussed. The non-detection of companion candidates provides stringent
upper limits for the masses of additional planets. Using a combination of the
existing dynamic and imaging data, we exclude the presence of any planetary
companion more massive than 3 Mjup anywhere in the Eps Eri system.
Specifically, with regards to the possible residual linear radial velocity
trend, we find that it is unlikely to correspond to a real physical companion
if the system is as young as 200 Myr, whereas if it is as old as 800 Myr, there
is an allowed semi-major axis range between about 8.5 and 25 AU.Comment: 11 pages, 8 figures, A&A accepte
Electronic Bond Structure of Carbon Nitride Thin Film Deposited by HiPIMS and dc Magnetron Plasma
We report the difference in electronic bond structure and surface chemical property of amorphous carbon nitride (a-CNx) film as a function of N/C which has been deposited by high power impulse magnetron sputtering (HiPIMS) and DC magnetron (dc-MS) plasma. The spectroscopic analyses suggest that the presence of oxide layer is the major cause for the surface charging in the core level peak. The core electron peaks (C1s, N1s and O1s) in x-ray photoelectron spectroscopy (XPS) show higher surface charging in HiPIMS compare to the film deposited by dc-MS plasma. The core peaks are moved gradually toward its virgin position as the etching duration is increased from 1 min to 80 mins. The films deposited by HiPIMS retain a higher N/C ratio following ion etching as compared to those deposited by DC magnetron sputtering suggesting denser films with a higher degree of cross-linking
The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394
We combine new Lucky Imaging astrometry from NTT/AstraLux Sur with already
published astrometry from the AstraLux Large M-dwarf Multiplicity Survey to
compute orbital elements and individual masses of the 2MASS J10364483+1521394
triple system belonging to the Ursa-Major moving group. The system consists of
one primary low-mass M-dwarf orbited by two less massive companions, for which
we determine a combined dynamical mass of $M_{\rm{B}+\rm{C}}= 0.48 \pm 0.14\
M_\odot1.00 \pm 0.030.24 \pm 0.07\ M_\odot3.2 \pm 0.3\ 30\%20.1 \pm 2.08.41^{+0.04}_{-0.02}\ $years.Comment: 9 pages, 7 figures, accepted for publication in Astronomy &
Astrophysic
Analysis of the Release Characteristics of Cu-Treated Antimicrobial Implant Surfaces Using Atomic Absorption Spectrometry
New developments of antimicrobial implant surfaces doped with copper (Cu) ions may minimize the risk of implant-associated infections. However, experimental evaluation of the Cu release is influenced by various test parameters. The aim of our study was to evaluate the Cu release characteristics in vitro according to the storage fluid and surface roughness. Plasma immersion ion implantation of Cu (Cu-PIII) and pulsed magnetron sputtering process of a titanium copper film (Ti-Cu) were applied to titanium alloy (Ti6Al4V) samples with different surface finishing of the implant material (polished, hydroxyapatite and corundum blasted). The samples were submersed into either double-distilled water, human serum, or cell culture medium. Subsequently, the Cu concentration in the supernatant was measured using atomic absorption spectrometry. The test fluid as well as the surface roughness can alter the Cu release significantly, whereby the highest Cu release was determined for samples with corundum-blasted surfaces stored in cell medium
Near-infrared wavefront sensing for the VLT interferometer
The very large telescope (VLT) interferometer (VLTI) in its current operating
state is equipped with high-order adaptive optics (MACAO) working in the
visible spectrum. A low-order near-infrared wavefront sensor (IRIS) is
available to measure non-common path tilt aberrations downstream the high-order
deformable mirror. For the next generation of VLTI instrumentation, in
particular for the designated GRAVITY instrument, we have examined various
designs of a four channel high-order near-infrared wavefront sensor. Particular
objectives of our study were the specification of the near-infrared detector in
combination with a standard wavefront sensing system. In this paper we present
the preliminary design of a Shack-Hartmann wavefront sensor operating in the
near-infrared wavelength range, which is capable of measuring the wavefronts of
four telescopes simultaneously. We further present results of our design study,
which aimed at providing a first instrumental concept for GRAVITY.Comment: 10 pages, 7 figures, to appear in "Ground-based and Airborne
Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200
The GRAVITY Coud\'e Infrared Adaptive Optics (CIAO) system for the VLT Interferometer
GRAVITY is a second generation instrument for the VLT Interferometer,
designed to enhance the near-infrared astrometric and spectro-imaging
capabilities of VLTI. Combining beams from four telescopes, GRAVITY will
provide an astrometric precision of order 10 micro-arcseconds, imaging
resolution of 4 milli-arcseconds, and low and medium resolution
spectro-interferometry, pushing its performance far beyond current infrared
interfero- metric capabilities. To maximise the performance of GRAVITY,
adaptive optics correction will be implemented at each of the VLT Unit
Telescopes to correct for the effects of atmospheric turbulence. To achieve
this, the GRAVITY project includes a development programme for four new
wavefront sensors (WFS) and NIR-optimized real time control system. These
devices will enable closed-loop adaptive correction at the four Unit Telescopes
in the range 1.4-2.4 {\mu}m. This is crucially important for an efficient
adaptive optics implementation in regions where optically bright references
sources are scarce, such as the Galactic Centre. We present here the design of
the GRAVITY wavefront sensors and give an overview of the expected adaptive
optics performance under typical observing conditions. Benefiting from newly
developed SELEX/ESO SAPHIRA electron avalanche photodiode (eAPD) detectors
providing fast readout with low noise in the near-infrared, the AO systems are
expected to achieve residual wavefront errors of \leq400 nm at an operating
frequency of 500 Hz.Comment: to be published in Proc. SPIE vol. 8446 (2012
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