The Euclid mission is to be launched in 2022 to survey during 6 years 15,000 degrees2 of the extragalactic sky in order to characterize the Dark Universe. The mission planning problem and drivers are exposed. The current status of the mission planning software system and infrastructure, its requirements, design, challenges and current implementation are also presented.
High precision measurements of the filters bandpass used on wide-field imagers mounted on large telescopes is critical for type Ia supernovae studies. A dedicated spectrophotometric bench is used to re-measure the now decommissioned ugriz filters used for the SNLS on CFHT-MegaCam. A full characterization of the optical response with respect to the location on the surface and the angle of incidence was performed for each filter. Strong variation over the filter surface is observed. The impact of the actual response on the observation is evaluated and we demonstrate an improvement with respect to the previous published results (SNLS1 and 2).
KEYWORDS: Signal to noise ratio, Signal to noise ratio, Sensors, James Webb Space Telescope, Point spread functions, Spectroscopy, Interference (communication), Imaging spectroscopy, Coronagraphy, Astronomy, Signal detection
In an effort to optimize the night time utilizing the exquisite weather on Maunakea, CFHT has equipped its dome with vents and is now moving its Queued Scheduled Observing (QSO)1 based operations toward Signal to Noise Ratio (SNR) observing. In this new mode, individual exposure times for a science program are estimated using a model that uses measurements of the weather conditions as input and the science program is considered completed when the depth required by the scientific requirements are reached. These changes allow CFHT to make better use of the excellent seeing conditions provided by Maunakea, allowing us to complete programs in a shorter time than allocated to the science programs.
Jean-Charles Cuillandre, Kanoa Withington, Patrick Hudelot, Yuliana Goranova, Henry McCracken, Frédéric Magnard, Yannick Mellier, Nicolas Regnault, Marc Bétoule, Hervé Aussel, J. J. Kavelaars, Pierre Fernique, François Bonnarel, Francois Ochsenbein, Olivier Ilbert
The Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) is a high impact scientific program which will
see its final official release open to the world in 2012. That release will seal the legacy aspect of the survey
which has already produced a large collection of scientific articles with topics ranging from cosmology to the
Solar system. The survey core science was focused on dark energy and dark matter: the full realization of the
scientific potential of the data set gathered between 2003 and 2009 with the MegaCam wide-field imager mounted
at the CFHT prime focus is almost complete with the Supernovae Legacy Survey (SNLS) team preparing its
third and last release (SNLS5), and the CFHTLenS team planning the release based around the cosmic shear
survey later this year. While the data processing center TERAPIX offered to the CFHTLS scientific community
regular releases over the course of the survey in its data acquisition phase (T0001-T0006), the final release took
three years to refine in order to produce a pristine data collection photometrically calibrated at better than the
percent both internally and externally over the total survey surface of 155 square degrees in all five photometric
bands (u*, g’, r’, i’, z’). This final release, called T0007, benefits from the various advances in photometric
calibration MegaCam has benefited through the joint effort between SNLS and CFHT to calibrate MegaCam
at levels unexplored for an optical wide-field imager. T0007 stacks and catalogs produced by TERAPIX will be
made available to the world at CADC while the CDS will offer a full integration of the release in its VO tools
from VizieR to Aladin. The photometric redshifts have been produced to be released in phase with the survey.
This proceeding is a general introduction to the survey and aims at presenting its final release in broad terms.
The ESPaDOnS spectrograph at the Canada-France-Hawaii Telescope was recently upgraded to use an E2V CCD42-90
deep-depletion CCD. While changing to this device from a standard silicon CCD42-90 had many benefits such as much
higher red QE and much lower fringing, it was also found that the new device exhibited persistence. After talking with
E2V, a solution to the persistence was found, but this resulted in reduced resolution on the spectrograph from charge
diffusion. This paper will describe the solution found to allow the detector to run with no persistence and with limited
charge diffusion.
Ground-layer adaptive optics (GLAO) has the potential to dramatically increase the efficiency and capabilities of
existing ground-based telescopes over a broad range of astronomical science. Recent studies of the optical turbulence
above several astronomical sites (e.g. Mauna Kea, Paranal, and Antarctica) show that GLAO can be extended to fields of
view of several tens of arcminutes in diameter, larger than previously thought, with angular resolutions close to the freeatmosphere
seeing. This is a pivotal result since GLAO science cases benefit from the largest possible corrected fields
of view. The corrected areal field of a GLAO system is potentially 2-3 orders of magnitude larger than has been
demonstrated to date. The 'Imaka team is working toward an instrument that takes advantage of the one-degree field
afforded by Mauna Kea. In this paper we summarize the design/simulation work to date along with our plan to develop
an instrument that reaches for this wide field of view.
The IMAKA project is a ground layer corrected wide field visible imager proposed for CFHT. It consists of three
processes or components: The dome and local turbulence will be controlled by ventilation; the remaining ground layer
turbulence will be corrected by a GLAO system and the free atmosphere seeing will be locally reduced by using an
Orthogonal Transfer CCD to correct for tip-tilt within the isokinetic angle of field stars.
In designing the AO system, whether based on an adaptive secondary mirror or using pupil relay optics, it becomes
apparent that the conjugation of the deformable mirror is a difficult constraint to achieve given the large field. It turns
out this problem is not isolated to IMAKA, because the Lagrange Invariant for our project is in the same range as that of
EAGLE on the E-ELT for example. The effects of tilting the deformable mirror with respect to the pupil or
compensating for misconjugation of an adaptive secondary mirror using a tomographic reconstructor have been
investigated using Monte-Carlo simulation codes, including our code developed specifically for GLAO simulations.
We report on quantitative results from IMAKA simulations for a variety of realistic turbulence conditions for each
topical scheme, and allude to how these results are applicable to ELTs' adaptive optics.
The 'Imaka project is a high-resolution wide-field imager proposed for the Canada-France-Hawaii telescope
(CFHT) on Mauna Kea. 'Imaka takes advantage of two features of the optical turbulence above Mauna Kea:
weak optical turbulence in the free-atmosphere and boundary layer turbulence which is highly confined within a
surface layer tens of meters thick and or the telescope enclosures. The combination of the two allows a groundlayer
adaptive optics system (GLAO) to routinely deliver an extremely-wide corrected field of view of one-degree
at an excellent free-atmosphere seeing limit at visible wavelengths. In addition, populating the focal-plane with
orthogonal-transfer CCDs provides a second level of image improvement on the free-atmosphere seeing and the
residual GLAO correction. The impact of such an instrument covers a broad range of science and is a natural
progression of CFHT's wide-field expertise.
The goal of this project is to achieve exquisite image quality over the largest possible field of view, with a goal of a
FWHM of not more than 0.3" over a square degree field in the optical domain. The narrow PSF will allow detection of
fainter sources in reasonable exposure times. The characteristics of the turbulence of Mauna Kea, a very thin ground
layer with excellent free seeing allows very wide fields to be corrected by GLAO and would make such an instrument
unique. The Ground Layer AO module uses a deformable mirror conjugated to the telescope pupil. Coupled with a high
order WFS, it corrects the turbulence common to the entire field. Over such large fields the probability of finding
sufficiently numerous and bright natural guide sources is high, but a constellation of laser beacons could be considered
to ensure homogeneous and uniform image quality.
The free atmosphere seeing then limits the image quality (50% best conditions: 0.2" to 0.4"). This can be further
improved by an OTCCD camera, which can correct local image motion on isokinetic scales from residual high altitude
tip-tilt. The advantages of the OTCCD are not limited to improving the image quality: a Panstarrs1 clone covers one
square degree with 0.1" sampling, in perfect accordance with the scientific requirements. The fast read time (6 seconds
for 1.4 Gpixels) also leads to an improvement of the dynamic range of the images. Finally, the guiding capabilities of
the OTCCD will provide the overall (local and global) tip-tilt signal.
Mauna Kea (4200\,m elevation, Hawaii) is known for its pristine seeing
conditions, but sky transparency can be an issue for science operations:
25% of the nights are not photometric, a cloud coverage mostly due to
high-altitude thin cirrus. The Canada-France-Hawaii Telescope (CFHT) is upgrading
its real-time sky transparency monitor in the optical domain (V-band) into
a dual-color system by adding a B-band channel and redesigning the entire
optical and mechanical assembly. Since 2000, the original single-channel
SkyProbe has gathered one exposure every minute during each observing night
using a small CCD camera with a very wide field of view (35 sq. deg.)
encompassing the region pointed by the telescope for science operations,
and exposures long enough (30 seconds) to capture at least 100 stars of
Hipparcos' Tychos catalog at high galactic latitudes (and up to 600 stars
at low galactic latitudes). A key advantage of SkyProbe over direct thermal
infrared imaging detection of clouds, is that it allows an accurate absolute
measurement, within 5%, of the true atmospheric absorption by clouds affecting
the data being gathered by the telescope's main science instrument. This system
has proven crucial for decision making in the CFHT queued service observing
(QSO), representing today 95% of the telescope time: science exposures taken
in non-photometric conditions are automatically registered for being re-observed
later on (at 1/10th of the original exposure time per pointing in the observed
filters) to ensure a proper final absolute photometric calibration. If the absorption
is too high, exposures can be repeated, or the observing can be done for a lower
ranked science program. The new dual color system (simultaneous B & V bands) will
allow a better characterization of the sky properties above Mauna Kea and should enable
a better detection of the thinner cirrus (absorption down to 0.02 mag., i.e. 2%).
SkyProbe is operated within the Elixir pipeline, a collection of tools used for
handling the CFHT CCD mosaics (CFH12K and MegaCam), from data pre-processing to
astrometric and photometric calibration.
C. Juramy, E. Barrelet, K. Schahmaneche, P. Bailly, W. Bertoli, C. Evrard, P. Ghislain, A. Guimard, J.-F. Huppert, D. Imbault, D. Laporte, H. Lebbolo, P. Repain, R. Sefri, A. Vallereau, D. Vincent, P. Antilogus, P. Astier, J. Guy, R. Pain, N. Regnault, R. Attapatu, T. Benedict, G. Barrick, J.-C. Cuillandre, S. Gajadhar, K. Ho, D. Salmon
We present the first results of the SuperNova Direct Illumination Calibration Experiment (SNDICE), installed
in January 2008 at the Canada France Hawaii Telescope. SNDICE is designed for the absolute calibration of
the instrumental response of a telescope in general, and for the control of systematic errors in the SuperNova
Legacy Survey (SNLS) on Megacam in particular. Since photometric calibration will a critical ingredient for
the cosmological results of future experiments involving instruments with large focal planes (like SNAP, LSST
and DUNE), SNDICE functions also as a real-size demonstrator for such a system of instrumental calibration.
SNDICE includes a calibrated source of 24 LEDs, chosen for their stability, spectral coverage, and their power,
sufficient for a flux of at least 100 electron/s/pixel on the camera. It includes also Cooled Large Area Photodiode
modules (CLAPs), which give a redundant measurement of the flux near the camera focal plane. Before installing
SNDICE on CFHT, we completed a full calibration of both subsystems, including a spectral relative calibration
and a 3D mapping of the beam emitted by each LED. At CFHT, SNDICE can be operated both to obtain a
complete one-shot absolute calibration of telescope transmission in all wavelengths for all filters with several
incident angles, and to monitor variations on different time scales.
A project to upgrade PUEO, the CFHT AO system, was first proposed in 2002. As part of the upgrade effort, a
technology project was conceived to evaluate and characterize the backside-illuminated CCID-35 detector as suitable a
replacement for the array of avalanche photo diode modules (APDs) in the curvature wavefront sensor. The CCID-35
was envisioned to replace an array of expensive APDs thus providing a cost-effective means of upgrading PUEO to a
higher-order system. Work on the project, dubbed FlyEyes, occurred sporadically until Oct 2005 but substantial
progress has been made since. This paper was intended to report on the performance of FlyEyes in PUEO but
unfortunately the instrument was not ready for tests at the time of this writing. This paper summarizes the progress
made on the project thus far and touches upon some of the difficulties encountered.
CFHT is planning to upgrade its adaptive optics system, PUEO, to a high order system with 104 elements, PUEO NUI. Currently PUEO uses a 19 element deformable mirror with the equivalent 19 avalanche photodiode (APD) detectors as its curvature wavefront sensor. PUEO NUI plans to implement the curvature wavefront sensor using back illuminated CCID-35 detectors developed by J. Beletic et al. instead of 104 APDs, which are prohibitively expensive under the present budget conditions. The CCID-35 detectors, developed at ESO and MIT/LL, were specifically designed to serve as direct replacements for APDs in curvature sensing. The first step in the upgrade is to build and test a system using two CCID-35 detectors, dubbed FlyEyes. These new detectors were successfully tested and integrated in the lab by R. Dorn at ESO but have yet to see sky time. FlyEyes will be their first opportunity. They will directly replace the 19 APDs in PUEO temporarily for a few engineering nights in January of 2005.
KEYWORDS: Charge-coupled devices, Telescopes, Spectroscopy, Spectrographs, Space telescopes, Astronomical imaging, Signal to noise ratio, Sensors, Galactic astronomy, Large telescopes
Back on several on-sky tests using the Multi-Object Spectrography at the Canada-France-Hawaii Telescope, we present refinements of the faint objects optical spectroscopy technique we proposed in 1994 (initially names "Va-et-Vient" = "Back-and-Forth"), a nod-and-shuttle technique that preserves a sky dominated photon noise regime. We validated schemes that allow 100% of the total telescope time used to integrate the light from the scientific objects. We also investigated how to optimize the configuration of the charge sifting in order to use minimal space on the detector. For typical distant galaxy fields (profile dominated by seeing), we demonstrated an increase by a factor of approximately 2 of the multiplex gain and even higher for more compact sources. The technique proves perfectly apt at eliminating all the systemic errors that may cause the saturation of the signal-to-noise ratio: slit defects, CCD fringing, and flat-field residuals. This technique is also the most efficient and unique approach to use curved slits.
High-z galaxies beyond redshift ~ 4 are essentially detected from ground based observations through their Lyα emission. The anticipated Lyα flux of galaxies at redshifts ~ 6 and beyond is a few times 0.1 10-17 ergs.s-1.cm-2 and its detection requires observations in low background conditions, when the observing wavelength is pushed into the near IR domain. We have carried out observations on 4-8 m telescopes to search for high z galaxies at 920 nm, 1060 and 1187 nm, resorting to various techniques: Narrow Band (NB) imaging and multi-slit windows. Observations, data reduction and preliminary results are described.
KEYWORDS: Adaptive optics, Stars, Planets, Asteroids, Satellites, High dynamic range imaging, Telescopes, Imaging spectroscopy, Point spread functions, Dynamical systems
Rethinking the efficient use of 4m-class telescopes in the dawning era of larger facilities is a timely but challenging debate. The extensive use of PUEO for imaging (and now spectroscopy) has kept CFHT at the forefront of scientific research with adaptive optics since its commissioning in 1996. Even though larger facilities are now starting to think about ways to implement high order AO systems, we believe the medium size of the CFHT and the excellent quality of the site on Mauna Kea is a perfect combination to reach the highest performances with a high order AO system.
The fields of application of high order adaptive optics are exciting: They include extremely high contrast imaging and coronography in the near-infrared and diffraction-limited imaging in the optical, with the corresponding gain in angular resolution. In this paper we present a quick description of a few specific astrophysical problems that would benefit from an upgraded AO system at the Canada-France-Hawaii Telescope.
More technical details about the upgrade of PUEO are presented by Lai et al. and Cuillandre et al. in these proceedings, see papers 4839-78 and 4839-31.
Until now, only avalanche photodiodes (APD) have been used as the detectors in curvature wavefront sensors in astronomy. This is due to the strict requirements of very short integration time and very low readout noise. In 1999, Beletic et al. invented a new CCD design which should achieve the same performance as APDs but with higher reliability and lower cost. In addition, this CCD has higher quantum efficiency than APD modules and larger dynamic range, eliminating the need for neutral density filters on bright objects. The CCD was designed and fabricated by MIT Lincoln Laboratory in collaboration with ESO and IfA. R. Dorn extensively tested the CCD in laboratory at ESO and proved that it achieves the predicted performance. CFHT is currently implementing this CCD on PUEO, CFHT’s Adaptive Optics system, to assess its performance for the first time in real conditions on the sky for a direct comparison with the current 19 APD detector system. In this article we present the current implementation scheme and discuss the upgrade we foresee for PUEO NUI, a 104-element high-order curvature AO system envisaged to replace the current AO system at Canada-France-Hawaii Telescope.
Rethinking the efficient use of 4m-class telescopes in the dawning era of larger facilities is a timely but challenging debate. The extensive use of PUEO for imaging (and now spectroscopy) has kept CFHT at the forefront of scientific research with adaptive optics since its commissioning in 1996. Even though larger facilities are now starting to think about ways of implementing high order AO systems, we believe the medium size of the CFHT and the excellent quality of our site on Mauna Kea is a perfect combination to reach the highest performances with a high order AO system.
The fields of application of high order adaptive optics are exciting: They include extremely high contrast imaging and coronography in the near-infrared and diffraction-limited imaging in the optical, with the corresponding gain in angular resolution. Specific science examples are described in and adjacent paper (Menard et al, these proceedings (4839-133)), and planned instrumentation in the form of four quadrant coronograph or existing dual (or triple) wavelength imagers (such as TRIDENT) would benefit tremendously from >90% Strehl ratios in the K band.
Simulations of a high order (104 electrodes) curvature system have been performed and produce the required performance and are presented in an adjacent paper (Lai & Craven-Bartle, (4860-28)). Technologically, the system is quite simple and re-uses most of the opto-mechanics of the existing PUEO. Deformable mirrors and real time computers are well within existing (and commercially available) specifications. An innovative solution of using a dedicated low read noise CCD camera (specifically for curvature systems) overcomes the potential cost drawbacks of using avalanche photo-diodes (APDs). This detector is described in detail in an adjacent paper (Cuillandre et al, these proceedings (4839-31)).
We have developed a system at the Canada-France-Hawaii Telescope (CFHT), SkyProbe, which allows for the direct measurement of the true attenuation by clouds once per minute, within a percent, directly on the field pointed by the telescope. It has been possible to make this system relatively inexpensively due to the low-cost CCD cameras from the amateur market. A crucial addition to this hardware is the quite recent availability of a full-sky photometry catalog at the appropriate depth: the Tycho catalog, from the Hipparcos mission. The central element is the automatic data analysis pipeline developed at CFHT, Elixir, for the improved operation of the CFHT wide-field imagers, CFH12K and MegaCam. SkyProbe’s FITS images are processed in real-time and the pipeline output (a zero point attenuation) provides the current sky transmission to the observers and helps immediate decision making. These measurements are also attached to the archived data, adding a key criteria for future use by other astronomers.
The Elixir system at CFHT provides automatic data quality assurance and calibration for the wide-field mosaic imager camera CFH12K. Elixir consists of a variety of tools, including: a real-time analysis suite which runs at the telescope to provide quick feedback to the observers; a detailed analysis of the calibration data; and an automated pipeline for processing data to be distributed to observers. To date, 2.4 × 1012 night-time sky pixels from CFH12K have been processed by the Elixir system.
The CFH12K is a 12K by 8K CCD mosaic camera for the Canada- France-Hawaii Telescope (CFHT), a 3.6 m telescope located on Mauna Kea, Hawaii. The CFH12K is comprised of twelve 4K by 2K thinned backside-illuminated CCDs, arrange din a close- packed array of two rows each containing six CCDs. Located at the CFHT Prime Focus, the CFH12K provides a 42 by 28 arcminute field-of-view, 0.206 arcsecond per pixel sampling, with a resulting data file of more than 200Mbytes per image. The camera has been designed to exploit the exceptional wide-field imaging capability provided by the CFHT. At the time of its commissioning in January 1999, the CFH12K is the largest thinned close-packed CCD mosaic in astronomy. This paper describes the system architecture, and some of the relevant issues associated with the construction, evaluation, and operation of very large mosaic cameras. Emphasis is given to system design issues, illustrating the CFHT12K as part of a larger system: the CFHT.
The CFHTIR is a large format near IR camera based on the Rockwell HAWAII Array. CFHTIR is designed for both direct imaging at the f/8 Cassegrain focus, as well as spectroscopy on the OSIS multiobject spectrograph. The camera provides 0.21 inch/pixel sampling in both applications with a single set cold transfer optics and pupil mask. The camera includes two eight-position filterwheels driven by cryogenic stepper motors with position control using a novel Hall effect sensor technique. CFHTIR also uses a novel dewar wiring technique employing flexible circuit vacuum feedthrus. CFHTIR is the second large format IR camera based on the Hawaii array constructed at CFHT, the first being the KIR camera for the CFHT Adaptive Optics Bonnette which was commissioned in 1997. This paper describes the system architecture of the CFHTIR highlighting key design concepts and detailing the physical elements.
CFH12K is a 12,228 by 8,192 pixel wide-field imaging camera in operation at the 3.6m Canada-France-Hawaii Telescope (CFHT) since January 1999. It still remains the largest close-packed array in use in astronomy today. The mosaic consists of twelve MIT Lincoln laboratories 2K by 4K thinned backside illuminated CCID-20 devices. The camera is used in broad-band and narrow-band filter direct imaging mode which constrains the devices' operating parameters to ensure the best data quality. Adaptation to the 20-year old CFHT prime focus environment included modifications to reduce the scattered light seen by the camera. Computer facilities have been upgraded and new software has been developed to handle the large amount of data generated. The two terabytes of scientific data taken by the camera in 1999 has proven the success of CFHT's new capability for 42 by 28 square arcminute imaging with high resolution subarcsecond seeing.
The CFH12K is a 12k X 8k CCD mosaic camera for the Canada-France-Hawaii Telescope (CFHT), a 3.6 m telescope located on Mauna Kea, Hawaii. The CFH12K is comprised of twelve 4k X 2k thinned backside-illuminated CCDs, arranged in a close-packed array of two rows each containing six CCDs. Located at the CFHT Prime Focus (f/4.2), the CFH12K provides a 42 by 28 arcminute field-of-view, 0.206 arcsecond per pixel sampling, with a resulting data file of more than 200 Mbytes per image. The camera has been designed to exploit the exceptional wide-field imaging capability provided by the CFHT. At the time of it's commissioning in January 1999, the CFH12K is the largest thinned close-packed CCD mosaic in astronomy. This paper describes the system architecture, and some of the relevant issues associated with the construction, evaluation, and operation of very large mosaic cameras. Emphasis is given to system design issues, illustrating the CFH12k as part of a larger system: the CFHT.
KIR is a 1024 by 1024 near-IR camera used with the adaptive optics Bonnette (PUEO) of the Canada-France-Hawaii Telescope. The camera houses a 1024 by 1024 HgCdTe and simple refractive optics providing diffraction-limited images with an image scale of 0.035 inch/pixel. First light was obtained in December 1997. The throughput of the camera, from the top of the atmosphere down to the atmosphere down to the detector including PUEO, is 19 percent, 20 percent and 21 percent at J, H and K, respectively. This project is a collaboration between the Universite de Montreal, the Observatoire Midi Pyrenees and the Canada-France-Hawaii Telescope. The design and performance of the instrument are presented in this paper.
The signal to noise ratio of very faint object spectroscopy is discussed in the context of the gain in limiting magnitude attainable on very large telescopes at low spectral resolution. It is shown that if the multiplicative errors resulting from the sky subtraction are not corrected, deeper spectroscopy will not be obtained by increasing the telescope size. A new CCD observing technique, which we call `Va et Vient' spectroscopy, is described in detail. This is a beam switching method where the elementary exposures are short enough to freeze the sky temporal fluctuations, and where the CCD is read only after a series of a few dozen of exposures. During the integration, the signals from the object field and the reference sky are separated by shifting the charges onto the CCD along the columns. Analytical evaluations are confirmed by laboratory tests and show that this technique is photon noise limited even at high flux and thus can lead to deeper spectroscopy. We give estimates of the results that can be achieved with the new generation of very large telescopes.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.