<p>An explanation for the origin of asymmetry along the preferential axis of the point spread function (PSF) of an AO system is developed. When phase errors from high-altitude turbulence scintillate due to Fresnel propagation, wavefront amplitude errors may be spatially offset from residual phase errors. These correlated errors appear as asymmetry in the image plane under the Fraunhofer condition. In an analytic model with an open-loop AO system, the strength of the asymmetry is calculated for a single mode of phase aberration, which generalizes to two dimensions under a Fourier decomposition of the complex illumination. Other parameters included are the spatial offset of the AO correction, which is the wind velocity in the frozen flow regime multiplied by the effective AO time delay and propagation distance or altitude of the turbulent layer. In this model, the asymmetry is strongest when the wind is slow and nearest to the coronagraphic mask when the turbulent layer is far away, such as when the telescope is pointing low toward the horizon. A great emphasis is made about the fact that the brighter asymmetric lobe of the PSF points in the opposite direction as the wind, which is consistent analytically with the clarification that the image plane electric field distribution is actually the inverse Fourier transform of the aperture plane. Validation of this understanding is made with observations taken from the Gemini Planet Imager, as well as being reproducible in end-to-end AO simulations.</p>
The Gemini Planet Imager (GPI) is a near-infrared instrument that uses Adaptive Optics (AO), a coronagraph and advanced data processing techniques to achieve very high contrast images of exoplanets. The GPI Exoplanet Survey (GPIES) is a 600 stars campaign aiming at detecting and characterizing young, massive and self-luminous exoplanets at large orbital distances (>5 au). Science observations are taken simultaneously with environmental data revealing information about the turbulence in the telescope environment as well as limitations of GPI’s AO system. Previous work has shown that the timescale of the turbulence, τ<sub>0</sub>, is a strong predictor of AO performance, however an analysis of the dome turbulence on AO performance has not been done before. Here, we study correlations between image contrast and residual wavefront error (WFE) with temperature measurements from multiple locations inside and outside the dome. Our analysis revealed GPI’s performance is most correlated with the temperature difference between the primary mirror of the telescope and the outside air. We also assess the impact of the current temperature control and ventilation strategy at Gemini South (GS).
The Gemini Planet Imager Exoplanet Survey (GPIES) is a direct imaging campaign designed to search for new, young, self-luminous, giant exoplanet. To date, GPIES has observed nearly 500 targets, and generated over 30,000 individual exposures using its integral field spectrograph (IFS) instrument. The GPIES team has developed a campaign data system that includes a database incorporating all of the metadata collected along with all individual raw data products, including environmental conditions and instrument performance metrics. In addition to the raw data, the same database also indexes metadata associated with multiple levels of reduced data products, including contrast measures for individual images and combined image sequences, which serve as the primary metric of performance for the final science products. Finally, the database is used to track telemetry products from the GPI adaptive optics (AO) subsystem, and associate these with corresponding IFS data. Here, we discuss several data exploration and visualization projects enabled by the GPIES database. Of particular interest are any correlations between instrument performance (final contrast) and environmental or operating conditions. We show single and multiple-parameter fits of single-image and observing sequence contrast as functions of various seeing measures, and discuss automated outlier rejection and other fitting concerns. We also explore unsupervised learning techniques, and self-organizing maps, in particular, in order to produce lowdimensional mappings of the full metadata space, in order to provide new insights on how instrument performance may correlate with various factors. Supervised learning techniques are then employed in order to partition the space of raw (single image) to final (full sequence) contrast in order to better predict the value of the final data set from the first few completed observations. Finally, we discuss the particular features of the database design that aid in performing these analyses, and suggest potential future upgrades and refinements.
After more than 4 years of operation it’s expected that the Gemini Planet Imager (GPI) will move from Gemini South (GS) to the Gemini North (GN) telescope sometime in 2019. Though both telescopes are almost identical at a hardware and software level there are subtle differences. With the accrued knowledge from operations from both a software and hardware point of view we will be addressing the following subjects: Changes in software on the telescope control level to interface with the similar system at GN, changes in the user interface for both instrument operation, proposal management, and observation preparations by a PI. Adjustments and requirements to interface at a hardware level with cooling and power requirements, and changes in the hardware configuration of network interfaces. We also show the results from vibration measurements at both telescopes and these measurements indicate that the vibrations will not be an issues when moving from GS to GN. Using more than 600h of observations and performance measurements and weather conditions at GS, and correlating with several years of weather monitoring at Mauna Kea we show what improvements in performance we can expect. We expect a significant improvement in performance due to the less turbulent atmosphere at GN, with post-processed contrast improving by a factor of 1.3–2.6.
Over the last two decades, Optical Search for Extra-Terrestrial Intelligence experiments have been conducted to search for either continuous or pulsed visible-light laser beacons that could be used for interstellar communication or energy transmission. Near-infrared offers a compelling window for signal transmission since there is a decrease in interstellar extinction and Galactic background compared to optical wavelengths. An innovative Near-InfraRed and Optical SETI (NIROSETI) instrument has been designed and constructed to take advantage of a new generation of fast (> 1 Ghz) low-noise near-infrared avalanche photodiodes to search for nanosecond pulsed near-infrared (850 - 1650 nm) pulses. The instrument was successfully installed and commissioned at the Nickel (1m) telescope at Lick Observatory in March 2015. We will describe the overall design of the instrument with a focus on methods developed for data acquisition and reduction for near-infrared SETI. Time and height analyses of the pulses produced by the detectors are performed to search for periodicity and coincidences in the signals. We will further discuss our NIROSETI survey plans.