76 research outputs found
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-
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
On the use of asymmetric PSF on NIR images of crowded stellar fields
We present data collected using the camera PISCES coupled with the Firt Light
Adaptive Optics (FLAO) mounted at the Large Binocular Telescope (LBT). The
images were collected using two natural guide stars with an apparent magnitude
of R<13 mag. During these observations the seeing was on average ~0.9". The AO
performed very well: the images display a mean FWHM of 0.05 arcsec and of 0.06
arcsec in the J- and in the Ks-band, respectively. The Strehl ratio on the
quoted images reaches 13-30% (J) and 50-65% (Ks), in the off and in the central
pointings respectively. On the basis of this sample we have reached a J-band
limiting magnitude of ~22.5 mag and the deepest Ks-band limiting magnitude ever
obtained in a crowded stellar field: Ks~23 mag.
J-band images display a complex change in the shape of the PSF when moving at
larger radial distances from the natural guide star. In particular, the stellar
images become more elongated in approaching the corners of the J-band images
whereas the Ks-band images are more uniform. We discuss in detail the strategy
used to perform accurate and deep photometry in these very challenging images.
In particular we will focus our attention on the use of an updated version of
ROMAFOT based on asymmetric and analytical Point Spread Functions.
The quality of the photometry allowed us to properly identify a feature that
clearly shows up in NIR bands: the main sequence knee (MSK). The MSK is
independent of the evolutionary age, therefore the difference in magnitude with
the canonical clock to constrain the cluster age, the main sequence turn off
(MSTO), provides an estimate of the absolute age of the cluster. The key
advantage of this new approach is that the error decreases by a factor of two
when compared with the classical one. Combining ground-based Ks with space
F606W photometry, we estimate the absolute age of M15 to be 13.70+-0.80 Gyr.Comment: 15 pages, 7 figures, presented at the SPIE conference 201
An active wavefront sensor to make feasible adaptive optics on 100m class telescopes
ABSTRACT Layer Oriented wavefront sensors can be made with a reasonable compact detector by the adoption of several stars enlargers, increasing only locally the focal ratio on the reference stars. The main opto-mechanical requirement in this kind of device is represented by the tolerances in tip and tilt of these star enlargers, which have to be moved over the Field Of View and aligned with the reference stars. A differential tip-tilt among the star enlargers leads to a mismatch between the different pupil images related to the reference stars. This misalignment eventually translates into a blurring of the measured wavefront, reducing the sensing quality. We describe a conceptual layout for an active control of the wavefront sensor, in order to reach the best mechanical positioning of these stars enlargers. In particular we discuss an algorithm to determine the effective pupils positions by simple movements and apply the requested displacement through commercially available piezoelectric actuators, shown in a preliminary opto-mechanical design of such wavefront sensor
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
New Extinction and Mass Estimates of the Low-mass Companion 1RXS 1609 B with the Magellan AO System: Evidence of an Inclined Dust Disk
We used the Magellan adaptive optics system to image the 11 Myr substellar
companion 1RXS 1609 B at the bluest wavelengths to date (z' and Ys). Comparison
with synthetic spectra yields a higher temperature than previous studies of
and significant dust extinction of
mag. Mass estimates based on the DUSTY tracks gives
0.012-0.015 Msun, making the companion likely a low-mass brown dwarf surrounded
by a dusty disk. Our study suggests that 1RXS 1609 B is one of the 25% of Upper
Scorpius low-mass members harboring disks, and it may have formed like a star
and not a planet out at 320 AU.Comment: 5 pages, 4 figures; accepted to ApJ
New Extinction and Mass Estimates from Optical Photometry of the Very Low Mass Brown Dwarf Companion CT Chamaeleontis B with the Magellan AO System
We used the Magellan adaptive optics (MagAO) system and its VisAO CCD camera
to image the young low mass brown dwarf companion CT Chamaeleontis B for the
first time at visible wavelengths. We detect it at r', i', z', and Ys. With our
new photometry and Teff~2500 K derived from the shape its K-band spectrum, we
find that CT Cha B has Av = 3.4+/-1.1 mag, and a mass of 14-24 Mj according to
the DUSTY evolutionary tracks and its 1-5 Myr age. The overluminosity of our r'
detection indicates that the companion has significant Halpha emission and a
mass accretion rate ~6*10^-10 Msun/yr, similar to some substellar companions.
Proper motion analysis shows that another point source within 2" of CT Cha A is
not physical. This paper demonstrates how visible wavelength AO photometry (r',
i', z', Ys) allows for a better estimate of extinction, luminosity, and mass
accretion rate of young substellar companions.Comment: Accepted for publication in ApJ; 6 figure
The crystal ball, the spider and other stories: a journey around the test tower of the M4 adaptive mirror
M4 is the adaptive mirror of ELT, currently at its FDR. It is composed by 6 thin shell mirror segments, controlled by 5136 voice coil actuators. Before its installation at the telescope, it will be optically calibrated on a test facility (OTT) in Italy. The calibration includes the computation of the flattening command and the segments co-phasing, i.e. the correction of the differential piston amongst them. Given the large complexity of the deformable mirror and the very tight requests on the measurement accuracy, we set-up a risk-mitigation activity based on the laboratory demonstration of some key elements within the test tower. In this paper we present the results of the experimentation. We measured at nanometer level the interferometric cavity; we investigated how the interferometer reacts in presence of spider arms dividing the test mirror into separated islands; we integrated and tested a multi wavelength sensor to measure the inter-segment absolute differential piston; we aligned and tested for stability the pupil relaying optical system to be installed on the OTT. Such activity is performed in the AO laboratory at INAF-Arcetri in Italy, in preparation of the M4 optical calibration on the OTT, scheduled to start in 2020. The M4 project is led by the Italian consortium AdOptica under an ESO contract
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