2,181 research outputs found
Slaving and disabling actuators with voice-coil adaptive mirrors
Adaptive mirrors based on voice-coil technology have force actuators with an
internal metrology to close a local loop for controlling its shape in position.
When actuators are requested to be disabled or slaved, control matrices have to
be re-computed. The report describes the algorithms to re-compute the relevant
matrixes for controlling of the mirror without the need of recalibration. This
is related in particular to MMT, LBT, Magellan, VLT, ELT and GMT adaptive
mirrors that use the voice-coil technology. The technique is successfully used
in practice with LBT and VLT-UT4 adaptive secondary mirror units.Comment: 12 pages, 1 figure, INAF Technical Report n.68 (2021),
http://hdl.handle.net/20.500.12386/2976
Optical calibration of large format adaptive mirrors
Adaptive (or deformable) mirrors are widely used as wavefront correctors in
adaptive optics systems. The optical calibration of an adaptive mirror is a
fundamental step during its life-cycle: the process is in facts required to
compute a set of known commands to operate the adaptive optics system, to
compensate alignment and non common-path aberrations, to run chopped or
field-stabilized acquisitions. In this work we present the sequence of
operations for the optical calibration of adaptive mirrors, with a specific
focus on large aperture systems such as the adaptive secondaries. Such systems
will be one of the core components of the extremely large telescopes.
Beyond presenting the optical procedures, we discuss in detail the actors,
their functional requirements and the mutual interactions. A specific emphasys
is put on automation, through a clear identification of inputs, outputs and
quality indicators for each step: due to a high degrees-of-freedom count
(thousands of actuators), an automated approach is preferable to constraint the
cost and schedule. In the end we present some algorithms for the evaluation of
the measurement noise; this point is particularly important since the
calibration setup is typically a large facility in an industrial environment,
where the noise level may be a major show-stopper.Comment: 50 pages. Final report released for the project "Development and test
of a new CGH-based technique with automated calibration for future large
format Adaptive-Optics Mirrors", funded under the INAF -TecnoPRIN 2010.
Published by INAF - Osservatorio Astrofisico di Arcetri. ISBN:
978-88-908876-1-
The Actuator Design and the Experimental Tests of a New Technology Large Deformable Mirror for Visible Wavelengths Adaptive Optics
Recently, Adaptive Secondary Mirrors showed excellent on-sky results in the
Near Infrared wavelengths. They currently provide 30mm inter-actuator spacing
and about 1 kHz bandwidth. Pushing these devices to be operated at visible
wavelengths is a challenging task. Compared to the current systems, working in
the infrared, the more demanding requirements are the higher spatial resolution
and the greater correction bandwidth. In fact, the turbulence scale is shorter
and the parameter variation is faster. Typically, the former is not larger than
25 mm (projected on the secondary mirror) and the latter is 2 kHz, therefore
the actuator has to be more slender and faster than the current ones. With a
soft magnetic composite core, a dual-stator and a single-mover, VRALA, the
actuator discussed in this paper, attains unprecedented performances with a
negligible thermal impact. Pre-shaping the current required to deliver a given
stroke greatly simplifies the control system, whose output supplies the current
generator. As the inductance depends on the mover position, the electronics of
this generator, provided with an inductance measure circuit, works also as a
displacement sensor, supplying the control system with an accurate feed-back
signal. A preliminary prototype, built according to the several FEA
thermo-magnetic analyses, has undergone some preliminary laboratory tests. The
results of these checks, matching the design results in terms of power and
force, show that the the magnetic design addresses the severe specifications
Optical calibration of large format adaptive mirrors
Adaptive (or deformable) mirrors are widely used as wavefront correctors in adaptive optics systems. The optical calibration of an adaptive mirror is a fundamental step during its life-cycle: the process is in facts required to compute a set of known commands to operate the adaptive optics system, to compensate alignment and non common-path aberrations, to run chopped or field-stabilized acquisitions. In this work we present the sequence of operations for the optical calibration of adaptive mirrors, with a specific focus on large aperture systems such as the adaptive secondaries. Such systems will be one of the core components of the extremely large telescopes.
Beyond presenting the optical procedures, we discuss in detail the actors, their functional requirements and the mutual interactions. A specific emphasys is put on automation, through a clear identification of inputs, outputs and quality indicators for each step: due to a high degrees-of-freedom count (thousands of actuators), an automated approach is preferable to constraint the cost and schedule. In the end we present some algorithms for the evaluation of the measurement noise; this point is particularly important since the calibration setup is typically a large facility in an industrial environment, where the noise level may be a major show-stopper
Numerical control matrix rotation for the LINC-NIRVANA Multi-Conjugate Adaptive Optics system
LINC-NIRVANA will realize the interferometric imaging focal station of the
Large Binocular Telescope. A double Layer Oriented multi-conjugate adaptive
optics system assists the two arms of the interferometer, supplying high order
wave-front correction. In order to counterbalance the field rotation,
mechanical derotation for the two ground wave-front sensors, and optical
derotators for the mid-high layers sensors fix the positions of the focal
planes with respect to the pyramids aboard the wave-front sensors. The
derotation introduces pupil images rotation on the wavefront sensors: the
projection of the deformable mirrors on the sensor consequently change. The
proper adjustment of the control matrix will be applied in real-time through
numerical computation of the new matrix. In this paper we investigate the
temporal and computational aspects related to the pupils rotation, explicitly
computing the wave-front errors that may be generated.Comment: 6 pages, 2 figures, presented at SPIE Symposium "Astronomical
Telescopes and Instrumentation'' conference "Adaptive Optics Systems
II'',Sunday 27 June 2010, San Diego, California, US
Modeling pyramidal sensors in ray-tracing software by a suitable user-defined surface
Following the unprecedented results in terms of performances delivered by the first light adaptive optics system at the Large Binocular Telescope, there has been a wide-spread and increasing interest on the pyramid wavefront sensor (PWFS), which is the key component, together with the adaptive secondary mirror, of the adaptive optics (AO) module. Currently, there is no straightforward way to model a PWFS in standard sequential ray-tracing software. Common modeling strategies tend to be user-specific and, in general, are unsatisfactory for general applications. To address this problem, we have developed an approach to PWFS modeling based on user-defined surface (UDS), whose properties reside in a specific code written in C language, for the ray-tracing software ZEMAXâ„¢. With our approach, the pyramid optical component is implemented as a standard surface in ZEMAXâ„¢, exploiting its dynamic link library (DLL) conversion then greatly simplifying ray tracing and analysis. We have utilized the pyramid UDS DLL surface-referred to as pyramidal acronyms may be too risky (PAM2R)-in order to design the current PWFS-based AO system for the Giant Magellan Telescope, evaluating tolerances, with particular attention to the angular sensitivities, by means of sequential ray-tracing tools only, thus verifying PAM2R reliability and robustness. This work indicates that PAM2R makes the design of PWFS as simple as that of other optical standard components. This is particularly suitable with the advent of the extremely large telescopes era for which complexity is definitely one of the main challenges
Marine Mesozoic Biostratigraphy of the Neuquén Basin
The marine Mesozoic of the Neuquen Basin in central west Argentina is characterized by ammonites and other invertebrates, especially bivalves, brachiopodes and calcareous microfossils. On that basis, Upper Triassic to Oxfordian, and Tithonian to Barremian have been divided in 39 and 18 ammonite assemblage / zones respectively, corresponding to 15 and 4 for bivalves, 15 and 2 for bra- chiopods and 11 and 9 for microfossils.El Mesozoico marino de la Cuenca de Neuquén, en el centro oeste argentino, se caracteriza por ammonites y otros invertebrados, tales como bivalvos, braquiópodos y microfósiles calcáreos. Sobre esta base, las unidades del Triásico Superior - Oxfordiano y la del Tithoniano - Barremiano, se han dividido en 39 y 18 zonas de grupos de ammonites, los que a su vez, corresponden respectivamente a 15 y 4 zonas de bivalvos, 15 y 2 de braquiópodos, y 11 y 9 zonas de microfósiles.Facultad de Ciencias Naturales y Muse
Magellan Adaptive Optics first-light observations of the exoplanet beta Pic b. II. 3-5 micron direct imaging with MagAO+Clio, and the empirical bolometric luminosity of a self-luminous giant planet
Young giant exoplanets are a unique laboratory for understanding cool,
low-gravity atmospheres. A quintessential example is the massive extrasolar
planet Pic b, which is 9 AU from and embedded in the debris disk of the
young nearby A6V star Pictoris. We observed the system with first light
of the Magellan Adaptive Optics (MagAO) system. In Paper I we presented the
first CCD detection of this planet with MagAO+VisAO. Here we present four
MagAO+Clio images of Pic b at 3.1 m, 3.3 m, , and
, including the first observation in the fundamental CH band. To
remove systematic errors from the spectral energy distribution (SED), we
re-calibrate the literature photometry and combine it with our own data, for a
total of 22 independent measurements at 16 passbands from 0.99--4.8 m.
Atmosphere models demonstrate the planet is cloudy but are degenerate in
effective temperature and radius. The measured SED now covers 80\% of the
planet's energy, so we approach the bolometric luminosity empirically. We
calculate the luminosity by extending the measured SED with a blackbody and
integrating to find log(/) . From our
bolometric luminosity and an age of 233 Myr, hot-start evolutionary tracks
give a mass of 12.70.3 , radius of 1.450.02 , and
of 170823 K (model-dependent errors not included). Our
empirically-determined luminosity is in agreement with values from atmospheric
models (typically dex), but brighter than values from the field-dwarf
bolometric correction (typically dex), illustrating the limitations in
comparing young exoplanets to old brown dwarfs.Comment: Accepted to ApJ. 27 pages, 22 figures, 19 table
On the Morphology and Chemical Composition of the HR 4796A Debris Disk
[abridged] We present resolved images of the HR 4796A debris disk using the
Magellan adaptive optics system paired with Clio-2 and VisAO. We detect the
disk at 0.77 \microns, 0.91 \microns, 0.99 \microns, 2.15 \microns, 3.1
\microns, 3.3 \microns, and 3.8 \microns. We find that the deprojected center
of the ring is offset from the star by 4.761.6 AU and that the deprojected
eccentricity is 0.060.02, in general agreement with previous studies. We
find that the average width of the ring is 14, also comparable to
previous measurements. Such a narrow ring precludes the existence of
shepherding planets more massive than \about 4 \mj, comparable to hot-start
planets we could have detected beyond \about 60 AU in projected separation.
Combining our new scattered light data with archival HST/STIS and HST/NICMOS
data at \about 0.5-2 \microns, along with previously unpublished Spitzer/MIPS
thermal emission data and all other literature thermal data, we set out to
constrain the chemical composition of the dust grains. After testing 19
individual root compositions and more than 8,400 unique mixtures of these
compositions, we find that good fits to the scattered light alone and thermal
emission alone are discrepant, suggesting that caution should be exercised if
fitting to only one or the other. When we fit to both the scattered light and
thermal emission simultaneously, we find mediocre fits (reduced chi-square
\about 2). In general, however, we find that silicates and organics are the
most favored, and that water ice is usually not favored. These results suggest
that the common constituents of both interstellar dust and solar system comets
also may reside around HR 4796A, though improved modeling is necessary to place
better constraints on the exact chemical composition of the dust.Comment: Accepted to ApJ on October 27, 2014. 21 pages, 12 figures, 4 table
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