MegaCam image quality (IQ) data obtained with both the un-vented and vented dome of the Canada-France-Hawai’i Telescope are used to assess the impacts of venting the dome on the full width at half maximum intensity – FWHM (asec or ”) – of optics-corrected 500 nm zenith telescopic point spread function. Increasing the dome porosity from 5% with the slit alone to 11% with the vents open  reduces the median IQ from 0.66” to 0.50”, thereby removing a 0.37” contribution to image spread,  reduces IQ noise and the IQ deterioration downwind with the unvented dome but  still leaves a residual IQ contribution of 0.20”. Much of the IQ improvement is already had in near-zero wind speeds. The vents increase the diversity of free air currents and their efficiency at preventing local accumulations of thermal imbalances in the dome air. They lead to fewer significant thermal eddies in the telescope line of sight and better IQ.

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.

The Canada-France-Hawaii-Telescope Corporation (CFHT) plans to repurpose its observatory on the summit of Maunakea and operate a (60 segment) 11.25m aperture wide field spectroscopic survey telescope, the Maunakea Spectroscopic Explorer (MSE). The prime focus telescope will be equipped with dedicated instrumentation to take advantage of one of the best sites in the northern hemisphere and offer its users the ability to perform large surveys. Central themes of the development plan are reusing and upgrading wherever possible. MSE will reuse the CFHT site and build upon the existing observatory infrastructure, using the same building and telescope pier as CFHT, while minimizing environmental impact on the summit. MSE will require structural support upgrades to the building to meet the latest building seismic code requirements and accommodate a new larger telescope and upgraded enclosure. It will be necessary to replace the current dome since a larger slit opening is needed for a larger telescope. MSE will use a thermal management system to remove heat generated by loads from the building, flush excess heat from lower levels, and maintain the observing environment temperature. This paper describes the design approach for redeveloping the CFHT facility for MSE. Once the project is completed the new facility will be almost indistinguishable on the outside from the current CFHT observatory. Past experience and lessons learned from CFHT staff and the astronomical community will be used to create a modern, optimized, and transformative scientific data collecting machine.

Extensive series of DIMM and MASS seeing values from thirteen astronomical sites are used to examine the shapes of their statistical distributions and their evolutions with time. At all sites, the distributions of seeing values can be satisfactorily reproduced over densities that span more than four orders of magnitude by random combinations of seeing values from two independent equal-population log-normal seeing components. The seeing varies typically by a factor of 4 throughout a night. At good sites, it reaches sub-half-arc second on 80% of the night. It is most stable when near its modal value where the delays for a 10% change in DIMM seeing average ∼50 minutes. The average delays are ∼25 minutes at the 10th and 90th percentiles of the distributions. These lifetimes differ by a factor of 4 between the fastest and the slowest seeing sites. The MASS seeing evolves ∼7 times faster than the DIMM seeing. These characteristics make forecasting seeing a tall challenge.

The Canada France Hawaii Telescope operates a 3.6m Optical/Infrared telescope on the summit of Mauna Kea. As an effort to improve delivered image quality in a cost-effective manner, a dome venting project was initiated to eliminate local contributions to 'seeing' that exist along the optical path and arise to a large extent due to temperature gradients throughout the dome volume. The quality of images delivered by the telescope is adversely affected by variations in air temperature within the telescope dome. Air temperature differences are caused by the air’s contact with large structures. They are different from ambient as a result of their large thermal inertias and the consequent inability of these structures to follow rapid air temperature changes. The dome venting project is an effort to add a series of large openings, “vents”, in the skin of the dome with the purpose of allowing free stream summit winds to flush out “stagnant air”. The term, “stagnant air”, applies to thermally mixed air from the inside of the dome environment that, for one reason or another, has been heated or cooled by surfaces in the dome environment. The addition of vents to the CFHT dome is intended to facilitate the passive flushing of interior air by the local wind, thereby greatly reducing air temperature variations, a process that has been successfully demonstrated to improve image quality at other telescope facilities and supported by recent water tunnel tests conducted by CFHT staff.

Studies of astronomical seeing at the Canada France Hawaii Telescope (CFHT) site, from both inside and outside the dome, show that the full potential of the excellent seeing conditions at the CFHT site has never been fully exploited. These studies indicate that this is due to the classical unvented hemispherical CFHT dome. Tests have been performed to identify the causes of the "pathologies" revealed by these seeing studies and to find ways of mitigating them. In particular, we have investigated installing vents in the dome skin to improve air exchange between outside and inside the enclosure. A number of vent geometries were tested using water tunnel models at the University of Washington Aerodynamics Laboratory (UWAL). Relative flushing times for various dome slit to prevailing wind directions were compared for the different vent geometries. The general flow characteristics observed with these low Reynolds number tests were compared with computational fluid dynamics (CFD) simulations of the CFHT dome performed in collaboration with the Thirty Meter Telescope (TMT) project, as well as low-speed wind-tunnel tests and visualization of the flow around the actual observatory building.

Thanks to a rich legacy of more than 20 years, Canada is established as a strong leader in the eld of adaptive optics. Adaptive optics is absolutely critical for current and future ground based telescopes, and the key to maintaining Canada’s leadership in the coming decade and beyond will be a strong synergy between HIA, Canadian universities and Canadian industry. 1. PAST ACCOMPLISHMENTS AND CURRENT STATUS 1.1. AO instrumentation for current telescopes Canada’s leadership in AO started well before the beginning of the last decade, with the delivery to CFHT of HRCAM, a \simple tip-tilt corrector in 1988 that produced the highest-resolution images before HST, and PUEO (in collaboration with France, in 1995) { the most user-friendly and scientically productive AO system of its generation. That early investment in AO paid great dividends with the successful delivery of HIA-made Altair to Gemini North in 2002. Altair, which initially worked in natural guide star (NGS) mode, achieved an unprecedented level of automation (\one button operation) and of integration with the telescope, leading to a scientic productive instrument, very competitive with similar instruments being deployed at 8-meter class telescopes in the same time frame. In 2005, Gemini North was equipped with a laser guide star (LGS). This vastly increased Altair’s sky coverage, and, especially with the coupling in 2006 with the integral eld spectrograph NIFS (a desirable combination also favored at VLT and Keck), dramatically increased the scientic reach of AO,

As part of a program to measure and evaluate atmospheric turbulence on mountains at the most northerly tip of North America, we have deployed two SODARs and a lunar scintillometer at the Polar Environment Atmospheric Research Lab (PEARL) located on a 600m-high ridge near Eureka on Ellesmere Island, at 80° latitude. This paper discusses the program and presents a summary of ground-layer turbulence and seeing measurements from the 2009-10 observing season.

Optical turbulence is a key determinant of an astronomical telescope science performance. Forecasting optical turbulence at altitude is thus of paramount importance for astronomy. And so are the understanding and management of ground layer and locally induced turbulence. This paper presents an astronomer's view of both the futility and the utility of various site characterization activities, of the challenges they pose and of dreams one has about understanding and forecasting site qualities. It is pointed out that, for likely suitable sites, the average integrated optical turbulence can be calculated to good accuracy by a simple model and that turbulence profiles differ less between sites that between nights or times at a given site. The challenges therefore stem from the temporal and spatial variability of the turbulence. This variability is illustrated and briefly discussed. Collaboration between astronomers and atmospheric physicists must hold the key to the astronomers' dream of knowing in detail what the optical turbulence at the site will be tomorrow night, or next week, and which science program will then make best use of the facility.

We analyze stellar images on 36,520 exposures made in the u, g, r, i, and z bands with MegaCam at the focus of the 3.6 m Canada-France-Hawai'i Telescope between 2005 August and 2008 August. The effect on image quality (IQ) of temperature differences (Delta Ts) in the telescope environment and of wind speed and direction are first examined and discussed. The contributions of the optics to image spread are then estimated and the frequency distribution of the observatory-free site seeing is obtained. The main findings are: (1) In the convective mode, the thermally-induced image full width at half-maximum intensity (FWHM) grows with the temperature gradient and path length L at the rate of similar to 0.2 '' . (Delta T/L)(6/5) . L(3/5). (2) For a given |Delta T|, thermal convection is similar to 3 times more detrimental to image quality than thermal inversions. (3) The orientation of the dome slit with respect to the wind direction has important effects on IQ. (4) The median observatory induced seeing is 0.43 '' FWHM. (5) The FWHM caused by the optics and slight optomechanical imperfections ranges from 0.46 '' in u to 0.28 '' in i. (6) The median DIMM-scale zenith atmospheric seeing at a wavelength of 500 nm and an elevation of 17 m above ground at the CFHT site is 0.55 ''. (7) The characteristics value of the outer scale of turbulence is 30 m. The paper addresses various issues bearing on the management of facility seeing.

We examine the historical evolution of the image quality delivered by astronomical telescopes since the days of William Herschel. This is done by analyzing double-star discovery data from nine celebrated observers who used 12 telescopes at 11 sites. Complementary information is derived from errors in the separation measurements of the Sirius system between 1862 and 1960. The best delivered image quality steadily improved with time, from a full width at half maximum intensity of 5 ''. in 1780 to 0.5 ''. in 1970. This appears to have resulted largely from increasingly better optics. Selection effects and limitations that have affected these double-star surveys are briefly discussed, as is the driving role toward telescope improvement played historically by the study of double stars.

We present the results of the Gemini Deep Planet Survey, a near-infrared adaptive optics search for giant planets and brown dwarfs around 85 nearby young stars. The observations were obtained with the Altair adaptive optics system at the Gemini North telescope, and angular differential imaging was used to suppress the speckle noise of the central star. Typically, the observations are sensitive to angular separations beyond 0.5'' with 5 σ contrast sensitivities in magnitude difference at 1.6 μm of 9.5 at 0.5'', 12.9 at 1'', 15.0 at 2'', and 16.5 at 5''. These sensitivities are sufficient to detect planets more massive than 2 MJ with a projected separation in the range 40-200 AU around a typical target. Second-epoch observations of 48 stars with candidates (out of 54) have confirmed that all candidates are unrelated background stars. A detailed statistical analysis of the survey results is presented. Assuming a planet mass distribution dn/dm ∝ m-1.2 and a semimajor-axis distribution dn/da ∝ a-1, the 95% credible upper limits on the fraction of stars with at least one planet of mass 0.5-13 MJ are 0.28 for the range 10-25 AU, 0.13 for 25-50 AU, and 0.093 for 50-250 AU; this result is weakly dependent on the semimajor-axis distribution power-law index. The 95% credible interval for the fraction of stars with at least one brown dwarf companion having a semimajor axis in the range 25-250 AU is 0.019, irrespective of any assumption on the mass and semimajor-axis distributions. The observations made as part of this survey have resolved the stars HD 14802, HD 166181, and HD 213845 into binaries for the first time.

The quality of astronomical images obtained with the 3 m liquid‐mirror telescope (LMT) of the NASA Orbital Debris Observatory (NODO) and with the University of British Columbia 6 m Large Zenith Telescope (LZT) is assessed and compared to that of conventional instruments. Analysis of star images in long‐exposure drift‐scan data indicates that the profile of the image core is primarily set by atmospheric turbulence. Defocused star images reveal the presence of low‐amplitude waves on the surface of the mercury, also seen in laboratory tests. The effect of these waves is to diffract light into the wings of the point‐spread function. Analysis of the intensity profiles of stellar images can therefore probe the structure of the mirror surface on scales smaller than the atmospheric coherence length, which is about an order of magnitude larger that the characteristic wavelengths of the surface waves. It is found that the rms surface height error produced by these waves was approximately 37 nm for the NODO LMT. Improvements to the rotational speed stability of liquid mirrors, reduction of the thickness of the mercury layer, and use of a protective Mylar cover have allowed the LZT to reduce this source of error to approximately 9 nm rms, thereby achieving an image quality approaching that of conventional telescopes.

Strehl ratios achieved on bright guide stars by 19 adaptive optics (AO) systems of various dimensions are examined. Both types of systems exhibit a similarly stronger attenuation of instrumental aberrations with smaller subapertures. With the same number of wave‐front sensor subapertures, curvature systems are generally found to be more efficient than Shack‐Hartmann systems at attenuating turbulence‐induced optical phase variance. Consequently, curvature systems use fainter guide stars to achieve the same performance as Shack‐Hartmann systems. The contrast is stronger for larger systems. Possible causes of these differences are discussed. Calibration errors of non–common‐path aberrations appear to be the most important. The compensation of the guide star image itself seems to be beneficial for large curvature systems. The likely performance of future very large systems are briefly discussed. A plea is made to encourage astronomical AO teams to uniformly and optimally characterize the on‐sky performance of their systems.

Direct exoplanet detections are limited by the speckle noise of the point spread function (PSF). This noise can be reduced by subtracting PSF images obtained simultaneously in adjacent narrow spectral bands using a multi-channel camera (MCC). Experiments have shown that speckle attenuation performances are severely degraded by differential optical aberrations between channels that decorrelate the PSFs of the different spectral bands. We present a new technique which can greatly alleviate this problem: the introduction of a holographic diffuser at the focal plane of the MCC. The holographic diffuser converts the PSF image into an incoherent illumination scene that is then re-imaged with the MCC. This imaging process is equivalent to a convolution of the scene with the PSF of each channel of the MCC. The optical aberrations in the MCC then affect only the convolution kernel of each channel and not the PSF globally, resulting in more correlated images. We report laboratory measurements with a dual channel prototype (1.575 mu m and 1.625 mu m) to validate this approach. We achieved a speckle noise suppression factor of 12-14, which is similar to 4-6 times better than what has been achieved by existing MCCs.

Seeing data from 41 campaigns at 23 sites ranging in altitude from 1130 to 5150 m and elevations between 1 and 30 m above grade are used to calibrate and test a simple seeing model that only involves altitude and elevation. The model is consistent with in situ studies of optical turbulence, reproducing measured median seeing values with a dispersion of 0.″096, while at multiple‐campaign sites the actual data show a dispersion of 0.″092. Surface‐layer turbulence is the characteristic that varies the most between campaigns and sites and is generally the dominant contribution to seeing at low elevations, the resulting image blur decreasing with a scale height of 3.5 m. The seeing distributions are lognormal at all sites, with quartile‐to‐median ratios of 4/5 and 5/4.