1,337 research outputs found
Extinction controlled adaptive phase-mask coronagraph
Context. Phase-mask coronagraphy is advantageous in terms of inner working
angle and discovery space. It is however still plagued by drawbacks such as
sensitivity to tip-tilt errors and chromatism. A nulling stellar coronagraph
based on the adaptive phase-mask concept using polarization interferometry is
presented in this paper. Aims. Our concept aims at dynamically and
achromatically optimizing the nulling efficiency of the coronagraph, making it
more immune to fast low-order aberrations (tip-tilt errors, focus, ...).
Methods. We performed numerical simulations to demonstrate the value of the
proposed method. The active control system will correct for the detrimental
effects of image instabilities on the destructive interference. The mask
adaptability both in size, phase and amplitude also compensates for
manufacturing errors of the mask itself, and potentially for chromatic effects.
Liquid-crystal properties are used to provide variable transmission of an
annulus around the phase mask, but also to achieve the achromatic {\pi} phase
shift in the core of the PSF by rotating the polarization by 180 degrees.
Results. We developed a new concept and showed its practical advantages using
numerical simulations. This new adaptive implementation of the phase-mask
coronagraph could advantageously be used on current and next-generation
adaptive optics systems, enabling small inner working angles without
compromising contrast.Comment: 7 pages, 6 figure
Extinction controlled Adaptive Mask Coronagraph Lyot and Phase Mask dual concept for wide extinction area
A dual coronagraph based on the Adaptive Mask concept is presented in this paper. A Lyot coronagraph with a variable diameter occulting disk and a nulling stellar coronagraph based on the Adaptive Phase Mask concept using polarization interferometry are presented in this work. Observations on sky and numerical simulations show the usefulness of the proposed method to optimize the nulling efficiency of the coronagraphs. In the case of the phase mask, the active control system will correct for the detrimental effects of image instabilities on the destructive interference (low-order aberrations such as tip-tilt and focus). The phase mask adaptability both in size, phase and amplitude also compensate for manufacturing errors of the mask itself, and potentially for chromatic effects. Liquid-crystal properties are used to provide variable transmission of an annulus around the phase mask, but also to achieve the achromatic π phase shift in the core of the PSF by rotating the polarization by 180°.A compressed mercury (Hg) drop is used as an occulting disk for the Lyot mask, its size control offers an adaptation to the seeing conditions and provides an optimization of the Tip-tilt correction
Imaging faint brown dwarf companions close to bright stars with a small, well-corrected telescope aperture
We have used our 1.6 m diameter off-axis well-corrected sub-aperture (WCS) on
the Palomar Hale telescope in concert with a small inner-working-angle (IWA)
phase-mask coronagraph to image the immediate environs of a small number of
nearby stars. Test cases included three stars (HD 130948, HD 49197 and HR7672)
with known brown dwarf companions at small separations, all of which were
detected. We also present the initial detection of a new object close to the
nearby young G0V star HD171488. Follow up observations are needed to determine
if this object is a bona fide companion, but its flux is consistent with the
flux of a young brown dwarf or low mass M star at the same distance as the
primary. Interestingly, at small angles our WCS coronagraph demonstrates a
limiting detectable contrast comparable to that of extant Lyot coronagraphs on
much larger telescopes corrected with current-generation AO systems. This
suggests that small apertures corrected to extreme adaptive optics (ExAO)
levels can be used to carry out initial surveys for close brown dwarf and
stellar companions, leaving followup observations for larger telescopes.Comment: accepted for publication in the Astrophysical Journa
Infrared Imaging of Capella with the IOTA Closure Phase Interferometer
We present infrared aperture synthesis maps produced with the upgraded IOTA
interferometer. Michelson interferograms on the close binary system Capella
(Alpha Aur) were obtained in the H-band between 2002 November 12 and 16 using
the IONIC3 beam combiner. With baselines of 15m < B < 38m, we were able to
determine the relative position of the binary components with milliarcsecond
(mas) precision and to track their movement along the approx. 14 degree arc
covered by our observation run. We briefly describe the algorithms used for
visibility and closure phase estimation. Three different Hybrid Mapping and
Bispectrum Fitting techniques were implemented within one software framework
and used to reconstruct the source brightness distribution. By dividing our
data into subsets, the system could be mapped at three epochs, revealing the
motion of the stars. The precise position of the binary components was also
determined with model fits, which in addition revealed I_Aa/I_Ab=1.49 +/- 0.10
and apparent stellar uniform-disk (UD) diameters of Theta_Aa=8.9 +/- 0.6 mas
and Theta_Ab=5.8 +/- 0.8 mas.
To improve the u, v-plane coverage, we compensated this orbital motion by
applying a rotation-compensating coordinate transformation. The resulting
model-independent map with a beam size of 5.4 x 2.6 mas allows the resolution
of the stellar surfaces of the Capella giants themselves.Comment: Accepted by the Astronomical Journal (2005-03-21
An infrared integrated optic astronomical beam combiner for stellar interferometry at 3-4 microns
Integrated-optic, astronomical, two-beam and three-beam, interferometric
combiners have been designed and fabricated for operation in the L band (3 - 4
microns) for the first time. The devices have been realized in
titanium-indiffused, x-cut lithium niobate substrates, and on-chip
electro-optic fringe scanning has been demonstrated. White light fringes were
produced in the laboratory using the two-beam combiner integrated with an
on-chip Y-splitter.Comment: This paper was published in Optics Express and is made available as
an electronic reprint with the permission of OSA. The paper can be found at
the following URL on the OSA website: http://www.opticsinfobase.org/oe.
Systematic or multiple reproduction or distribution to multiple locations via
electronic or other means is prohibited and is subject to penalties under la
Measurement of forward photon production cross-section in proton-proton collisions at = 13 TeV with the LHCf detector
In this paper, we report the production cross-section of forward photons in
the pseudorapidity regions of and ,
measured by the LHCf experiment with proton--proton collisions at =
13 TeV. The results from the analysis of 0.191 of data
obtained in June 2015 are compared to the predictions of several hadronic
interaction models that are used in air-shower simulations for
ultra-high-energy cosmic rays. Although none of the models agree perfectly with
the data, EPOS-LHC shows the best agreement with the experimental data among
the models.Comment: 21 pages, 4 figure
First astronomical unit scale image of the GW Ori triple. Direct detection of a new stellar companion
Young and close multiple systems are unique laboratories to probe the initial
dynamical interactions between forming stellar systems and their dust and gas
environment. Their study is a key building block to understanding the high
frequency of main-sequence multiple systems. However, the number of detected
spectroscopic young multiple systems that allow dynamical studies is limited.
GW Orionis is one such system. It is one of the brightest young T Tauri stars
and is surrounded by a massive disk. Our goal is to probe the GW Orionis
multiplicity at angular scales at which we can spatially resolve the orbit. We
used the IOTA/IONIC3 interferometer to probe the environment of GW Orionis with
an astronomical unit resolution in 2003, 2004, and 2005. By measuring squared
visibilities and closure phases with a good UV coverage we carry out the first
image reconstruction of GW Ori from infrared long-baseline interferometry. We
obtain the first infrared image of a T Tauri multiple system with astronomical
unit resolution. We show that GW Orionis is a triple system, resolve for the
first time the previously known inner pair (separation 1.4 AU) and
reveal a new more distant component (GW Ori C) with a projected separation of
8 AU with direct evidence of motion. Furthermore, the nearly equal (2:1)
H-band flux ratio of the inner components suggests that either GW Ori B is
undergoing a preferential accretion event that increases its disk luminosity or
that the estimate of the masses has to be revisited in favour of a more equal
mass-ratio system that is seen at lower inclination. Accretion disk models of
GW Ori will need to be completely reconsidered because of this outer companion
C and the unexpected brightness of companion B.Comment: 5 pages, 9 figures, accepted Astronomy and Astrophysics Letters. 201
PIONIER: a visitor instrument for the VLTI
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to see its
first fringes in 2010. It combines four ATs or four UTs using a pairwise ABCD
integrated optics combiner that can also be used in scanning mode. It provides
low spectral resolution in H and K band. PIONIER is designed for imaging with a
specific emphasis on fast fringe recording to allow closure-phases and
visibilities to be precisely measured. In this work we provide the detailed
description of the instrument and present its updated status.Comment: Proceedings of SPIE conference Optical and Infrared Interferometry II
(Conference 7734) San Diego 201
Hadron beam test of a scintillating fibre tracker system for elastic scattering and luminosity measurement in ATLAS
A scintillating fibre tracker is proposed to measure elastic proton
scattering at very small angles in the ATLAS experiment at CERN. The tracker
will be located in so-called Roman Pot units at a distance of 240 m on each
side of the ATLAS interaction point. An initial validation of the design
choices was achieved in a beam test at DESY in a relatively low energy electron
beam and using slow off-the-shelf electronics. Here we report on the results
from a second beam test experiment carried out at CERN, where new detector
prototypes were tested in a high energy hadron beam, using the first version of
the custom designed front-end electronics. The results show an adequate
tracking performance under conditions which are similar to the situation at the
LHC. In addition, the alignment method using so-called overlap detectors was
studied and shown to have the expected precision.Comment: 12 pages, 8 figures. Submitted to Journal of Instrumentation (JINST
Measurement of forward neutral pion transverse momentum spectra for = 7TeV proton-proton collisions at LHC
The inclusive production rate of neutral pions in the rapidity range greater
than has been measured by the Large Hadron Collider forward (LHCf)
experiment during LHC \,TeV proton-proton collision operation in
early 2010. This paper presents the transverse momentum spectra of the neutral
pions. The spectra from two independent LHCf detectors are consistent with each
other and serve as a cross check of the data. The transverse momentum spectra
are also compared with the predictions of several hadronic interaction models
that are often used for high energy particle physics and for modeling
ultra-high-energy cosmic-ray showers.Comment: 18 Pages, 10 figures, submitted to Phys. Rev.
- …