1,690 research outputs found
Atmospheric refractivity effects on mid-infrared ELT adaptive optics
We discuss the effect of atmospheric dispersion on the performance of a
mid-infrared adaptive optics assisted instrument on an extremely large
telescope (ELT). Dispersion and atmospheric chromaticity is generally
considered to be negligible in this wavelength regime. It is shown here,
however, that with the much-reduced diffraction limit size on an ELT and the
need for diffraction-limited performance, refractivity phenomena should be
carefully considered in the design and operation of such an instrument. We
include an overview of the theory of refractivity, and the influence of
infrared resonances caused by the presence of water vapour and other
constituents in the atmosphere. `Traditional' atmospheric dispersion is likely
to cause a loss of Strehl only at the shortest wavelengths (L-band). A more
likely source of error is the difference in wavelengths at which the wavefront
is sensed and corrected, leading to pointing offsets between wavefront sensor
and science instrument that evolve with time over a long exposure. Infrared
radiation is also subject to additional turbulence caused by the presence of
water vapour in the atmosphere not seen by visible wavefront sensors, whose
effect is poorly understood. We make use of information obtained at radio
wavelengths to make a first-order estimate of its effect on the performance of
a mid-IR ground-based instrument. The calculations in this paper are performed
using parameters from two different sites, one `standard good site' and one
`high and dry site' to illustrate the importance of the choice of site for an
ELT.Comment: 11 pages, to be published in SPIE Proceedings vol. 7015, Adaptive
Optics Systems, eds. N. Hubin, C.E. Max and P.L. Wizinowich, 200
First Light with ALES: A 2-5 Micron Adaptive Optics Integral Field Spectrograph for the LBT
Integral field spectrographs are an important technology for exoplanet
imaging, due to their ability to take spectra in a high-contrast environment,
and improve planet detection sensitivity through spectral differential imaging.
ALES is the first integral field spectrograph capable of imaging exoplanets
from 3-5m, and will extend our ability to characterize self-luminous
exoplanets into a wavelength range where they peak in brightness. ALES is
installed inside LBTI/LMIRcam on the Large Binocular Telescope, taking
advantage of existing AO systems, camera optics, and a HAWAII-2RG detector. The
new optics that comprise ALES are a Keplerian magnifier, a silicon lenslet
array with diffraction suppressing pinholes, a direct vision prism, and
calibration optics. All of these components are installed in filter wheels
making ALES a completely modular design. ALES saw first light at the LBT in
June 2015.Comment: 13 pages, 9 figures, Proc. SPI
Mid-Infrared Instrumentation for the European Extremely Large Telescope
MIDIR is the proposed thermal/mid-IR imager and spectrograph for the European
Extremely Large Telescope (E-ELT). It will cover the wavelength range of 3 to
at least 20 microns. Designed for diffraction-limited performance over the
entire wavelength range, MIDIR will require an adaptive optics system; a
cryogenically cooled system could offer optimal performance in the IR, and this
is a critical aspect of the instrument design. We present here an overview of
the project, including a discussion of MIDIR's science goals and a comparison
with other infrared (IR) facilities planned in the next decade; top level
requirements derived from these goals are outlined. We describe the optical and
mechanical design work carried out in the context of a conceptual design study,
and discuss some important issues to emerge from this work, related to the
design, operation and calibration of the instrument. The impact of telescope
optical design choices on the requirements for the MIDIR instrument is
demonstrated.Comment: for publication in SPIE Proceedings vol. 6692, Cryogenic Optical
Systems and Instrumentation XII, eds. J.B. Heaney and L.G. Burriesci, San
Diego, Aug 200
The 2nd Generation VLTI path to performance
The upgrade of the VLTI infrastructure for the 2nd generation instruments is
now complete with the transformation of the laboratory, and installation of
star separators on both the 1.8-m Auxiliary Telescopes (ATs) and the 8-m Unit
Telescopes (UTs). The Gravity fringe tracker has had a full semester of
commissioning on the ATs, and a first look at the UTs. The CIAO infrared
wavefront sensor is about to demonstrate its performance relative to the
visible wavefront sensor MACAO. First astrometric measurements on the ATs and
astrometric qualification of the UTs are on-going. Now is a good time to
revisit the performance roadmap for VLTI that was initiated in 2014, which
aimed at coherently driving the developments of the interferometer, and
especially its performance, in support to the new generation of instruments:
Gravity and MATISSE.Comment: 9 pages, 6 figures, 1 table, Proc. SPIE 201
Development of a carbon fibre composite active mirror: Design and testing
Carbon fibre composite technology for lightweight mirrors is gaining
increasing interest in the space- and ground-based astronomical communities for
its low weight, ease of manufacturing, excellent thermal qualities and
robustness. We present here first results of a project to design and produce a
27 cm diameter deformable carbon fibre composite mirror. The aim was to produce
a high surface form accuracy as well as low surface roughness. As part of this
programme, a passive mirror was developed to investigate stability and coating
issues. Results from the manufacturing and polishing process are reported here.
We also present results of a mechanical and thermal finite element analysis, as
well as early experimental findings of the deformable mirror. Possible
applications and future work are discussed.Comment: Accepted by Optical Engineering. Figures 1-7 on
http://www.star.ucl.ac.uk/~sk/OEpaper_files
Wavelength calibration of the JWST-MIRI medium resolution spectrometer
We present the wavelength and spectral resolution characterisation of the
Integral Field Unit (IFU) Medium Resolution Spectrometer for the Mid-InfraRed
Instrument (MIRI), to fly onboard the James Webb Space Telescope in 2014. We
use data collected using the Verification Model of the instrument and develop
an empirical method to calibrate properties such as wavelength range and
resolving power in a portion of the spectrometer's full spectral range (5-28
microns). We test our results against optical models to verify the system
requirements and combine them with a study of the fringing pattern in the
instrument's detector to provide a more accurate calibration. We show that
MIRI's IFU spectrometer will be able to produce spectra with a resolving power
above R=2800 in the wavelength range 6.46-7.70 microns, and that the unresolved
spectral lines are well fitted by a Gaussian profile.Comment: 12 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
Mid-infrared astronomy with the E-ELT: Performance of METIS
We present results of performance modelling for METIS, the Mid-infrared
European Extremely Large Telescope (E-ELT) Imager and Spectrograph. Designed by
a consortium of NOVA (Netherlands), UK Astronomy Technology Centre (UK), MPIA
Heidelberg (Germany), CEA Saclay (France) and KU Leuven (Belgium), METIS will
cover the atmospheric windows in L, M and N-band and will offer imaging,
medium-resolution slit spectroscopy (R~1000-3000) and high-resolution integral
field spectroscopy (R~100,000). Our model uses a detailed set of input
parameters for site characteristics and atmospheric profiles, optical design,
thermal background and the most up-to-date IR detector specifications. We show
that METIS will bring an orders-of-magnitude level improvement in sensitivity
and resolution over current ground-based IR facilities, bringing mid-IR
sensitivities to the micro-Jansky regime. As the only proposed E-ELT instrument
to cover this entire spectral region, and the only mid-IR high-resolution
integral field unit planned on the ground or in space, METIS will open up a
huge discovery space in IR astronomy in the next decade.Comment: 13 pages, submitted to SPIE Proceedings vol. 7735, Ground-based and
Airborne Instrumentation for Astronomy III (2010). Simulation code available
at http://tinyurl.com/metis-sen
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