122 research outputs found
Lightweight deformable mirrors for ground- and space-based imaging systems
The next generation of ground- and space-based astronomical observatories will generate an increased requirement for lightweight and robust deformable optics. In space ultra-lightweight actively controlled mirrors will enable a continuing increase of aperture sizes, whilst large adaptive mirrors will become increasingly standard features in the optical design of adaptive optics-optimised Extremely Large Telescopes on the ground. This thesis presents results from a project to design, manufacture and test a prototype active mirror in a nickel-carbon fibre reinforced polymer (CFRP), which has been suggested in the literature to be a promising candidate material for such applications. Extensive finite element analysis results from gravitational sag and thermal models, as well as finite element-based predictions of the central actuator influence function profile, are presented. The main problems were encountered as a result of the in-mold nickel coating process, which resulted in residual form errors, and poor design of the support structures, leading to deterioration of the mirror surface quality. No fundamental reason ruling this material out for the use of precision deformable optics was identified. The finite element analysis results show significant promise for increased use of the method in optical design, as well as in integrated optical simulations for Extremely Large Telescopes
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
Unproceedings of the Fourth .Astronomy Conference (.Astronomy 4), Heidelberg, Germany, July 9-11 2012
The goal of the .Astronomy conference series is to bring together
astronomers, educators, developers and others interested in using the Internet
as a medium for astronomy. Attendance at the event is limited to approximately
50 participants, and days are split into mornings of scheduled talks, followed
by 'unconference' afternoons, where sessions are defined by participants during
the course of the event. Participants in unconference sessions are discouraged
from formal presentations, with discussion, workshop-style formats or informal
practical tutorials encouraged. The conference also designates one day as a
'hack day', in which attendees collaborate in groups on day-long projects for
presentation the following morning. These hacks are often a way of
concentrating effort, learning new skills, and exploring ideas in a practical
fashion. The emphasis on informal, focused interaction makes recording
proceedings more difficult than for a normal meeting. While the first
.Astronomy conference is preserved formally in a book, more recent iterations
are not documented. We therefore, in the spirit of .Astronomy, report
'unproceedings' from .Astronomy 4, which was held in Heidelberg in July 2012.Comment: 11 pages, 1 figure, .Astronomy 4, #dotastr
The carbon footprint of large astronomy meetings
The annual meeting of the European Astronomical Society took place in Lyon,
France, in 2019, but in 2020 it was held online only due the COVID-19 pandemic.
The carbon footprint of the virtual meeting was roughly 3,000 times smaller
than the face-to-face one, providing encouragement for more ecologically minded
conferencing.Comment: Originated in a Twitter discussion
(https://twitter.com/sarahkendrew/status/1144186571538739202) at EWASS 2019;
followed up at the EAS 2020 conference sustainability session by
https://astronomersforplanet.earth - published in Nature Astronomy, September
202
A Direct Measurement of Atmospheric Dispersion in N-band Spectra: Implications for Mid-IR Systems on ELTs
Adaptive optics will almost completely remove the effects of atmospheric
turbulence at 10 microns on the Extremely Large Telescope (ELT) generation of
telescopes. In this paper, we observationally confirm that the next most
important limitation to image quality is atmospheric dispersion, rather than
telescope diffraction. By using the 6.5 meter MMT with its unique mid-IR
adaptive optics system, we measure atmospheric dispersion in the N-band with
the newly commissioned spectroscopic mode on MIRAC4-BLINC. Our results indicate
that atmospheric dispersion is generally linear in the N-band, although there
is some residual curvature. We compare our measurements to theory, and make
predictions for ELT Strehls and image FHWM with and without an atmospheric
dispersion corrector (ADC). We find that for many mid-IR applications, an ADC
will be necessary on ELTs.Comment: 22 pages, 8 figures, accepted to PAS
Correcting METIS spectra for telluric absorption to maximize spectral fidelity
METIS is a mid-infrared instrument proposed for the European Extremely Large
Telescope (E-ELT). It is designed to provide imaging and spectroscopic
capabilities in the 3 - 14 micron region up to a spectral resolution of 100000.
One of the novel concepts of METIS is that of a high-resolution integral field
spectrograph (IFS) for a diffraction-limited mid-IR instrument. While this
concept has many scientific and operational advantages over a long-slit
spectrograph, one drawback is that the spectral resolution changes over the
field of view. This has an impact on the procedures to correct for telluric
absorption lines imprinted on the science spectra. They are a major obstacle in
the quest to maximize spectral fidelity, the ability to distinguish a weak
spectral feature from the continuum. The classical technique of division by a
standard star spectrum, observed in a single IFS spaxel, cannot simply be
applied to all spaxels, because the spectral resolution changes from spaxel to
spaxel. Here we present and discuss possible techniques of telluric line
correction of METIS IFS spectra, including the application of synthetic model
spectra of telluric transmission, to maximize spectral fidelity.Comment: 11 pages, 3 figures; Copyright (2010) Society of Photo-Optical
Instrumentation Engineers. One print or electronic copy may be made for
personal use only. Systematic reproduction and distribution, duplication of
any material in this paper for a fee or for commercial purposes, or
modification of the content of the paper are prohibite
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
METIS - the Mid-infrared E-ELT Imager and Spectrograph
METIS, the Mid-infrared ELT Imager and Spectrograph (formerly called MIDIR),
is a proposed instrument for the European Extremely Large Telescope (E-ELT),
currently undergoing a phase-A study. The study is carried out within the
framework of the ESO-sponsored E-ELT instrumentation studies. METIS will be
designed to cover the E-ELT science needs at wavelengths longward of 3um, where
the thermal background requires different operating schemes. In this paper we
discuss the main science drivers from which the instrument baseline has been
derived. Specific emphasis has been given to observations that require very
high spatial and spectral resolution, which can only be achieved with a
ground-based ELT. We also discuss the challenging aspects of background
suppression techniques, adaptive optics in the mid-IR, and telescope site
considerations. The METIS instrument baseline includes imaging and spectroscopy
at the atmospheric L, M, and N bands with a possible extension to Q band
imaging. Both coronagraphy and polarimetry are also being considered. However,
we note that the concept is still not yet fully consolidated. The METIS studies
are being performed by an international consortium with institutes from the
Netherlands, Germany, France, United Kingdom, and Belgium.Comment: 15 pages, to be published in Proc SPIE 7014: Ground-based & Airborne
Instrumentation for Astronomy I
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