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Register a new userLarge Binocular Telescope Interferometer Adaptive Optics: On-sky performance and lessons learned
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The Large Binocular Telescope Interferometer is a high contrast imager and interferometer that sits at the combined bent Gregorian focus of the LBTs dual 8.4~m apertures. The interferometric science drivers dictate 0.1 resolution with $10^3-10^4$ contrast at $10~mu m$, while the $4~mu m$ imaging science drivers require even greater contrasts, but at scales $>$0.2. In imaging mode, LBTIs Adaptive Optics system is already delivering $4~mu m$ contrast of $10^4-10^5$ at $0.3-0.75$ in good conditions. Even in poor seeing, it can deliver up to 90% Strehl Ratio at this wavelength. However, the performance could be further improved by mitigating Non-Common Path Aberrations. Any NCPA remedy must be feasible using only the current hardware: the science camera, the wavefront sensor, and the adaptive secondary mirror. In preliminary testing, we have implemented an ``eye doctor grid search approach for astigmatism and trefoil, achieving 5% improvement in Strehl Ratio at $4~mu m$, with future plans to test at shorter wavelengths and with more modes. We find evidence of NCPA variability on short timescales and discuss possible upgrades to ameliorate time-variable effects
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The Large Binocular Telescope Interferometer (LBTI) is a versatile instrument designed for high-angular resolution and high-contrast infrared imaging (1.5-13 microns). In this paper, we focus on the mid-infrared (8-13 microns) nulling mode and present its theory of operation, data reduction, and on-sky performance as of the end of the commissioning phase in March 2015. With an interferometric baseline of 14.4 meters, the LBTI nuller is specifically tuned to resolve the habitable zone of nearby main-sequence stars, where warm exozodiacal dust emission peaks. Measuring the exozodi luminosity function of nearby main-sequence stars is a key milestone to prepare for future exoEarth direct imaging instruments. Thanks to recent progress in wavefront control and phase stabilization, as well as in data reduction techniques, the LBTI demonstrated in February 2015 a calibrated null accuracy of 0.05% over a three-hour long observing sequence on the bright nearby A3V star beta Leo. This is equivalent to an exozodiacal disk density of 15 to 30 zodi for a Sun-like star located at 10pc, depending on the adopted disk model. This result sets a new record for high-contrast mid-infrared interferometric imaging and opens a new window on the study of planetary systems.
MagAO is the new adaptive optics system with visible-light and infrared science cameras, located on the 6.5-m Magellan Clay telescope at Las Campanas Observatory, Chile. The instrument locks on natural guide stars (NGS) from 0$^mathrm{th}$ to 16$^mathrm{th}$ $R$-band magnitude, measures turbulence with a modulating pyramid wavefront sensor binnable from 28x28 to 7x7 subapertures, and uses a 585-actuator adaptive secondary mirror (ASM) to provide flat wavefronts to the two science cameras. MagAO is a mutated clone of the similar AO systems at the Large Binocular Telescope (LBT) at Mt. Graham, Arizona. The high-level AO loop controls up to 378 modes and operates at frame rates up to 1000 Hz. The instrument has two science cameras: VisAO operating from 0.5-1 $mu$m and Clio2 operating from 1-5 $mu$m. MagAO was installed in 2012 and successfully completed two commissioning runs in 2012-2013. In April 2014 we had our first science run that was open to the general Magellan community. Observers from Arizona, Carnegie, Australia, Harvard, MIT, Michigan, and Chile took observations in collaboration with the MagAO instrument team. Here we describe the MagAO instrument, describe our on-sky performance, and report our status as of summer 2014.
The performance of a wide-field adaptive optics system depends on input design parameters. Here we investigate the performance of a multi-conjugate adaptive optics system design for the European Extremely Large Telescope, using an end-to-end Monte-Carlo adaptive optics simulation tool, DASP. We consider parameters such as the number of laser guide stars, sodium layer depth, wavefront sensor pixel scale, number of deformable mirrors, mirror conjugation and actuator pitch. We provide potential areas where costs savings can be made, and investigate trade-offs between performance and cost. We conclude that a 6 laser guide star system using 3 DMs seems to be a sweet spot for performance and cost compromise.
The performance of a wide-field adaptive optics system depends on input design parameters. Here we investigate the performance of a multi-object adaptive optics system design for the European Extremely Large Telescope, using an end-to-end Monte-Carlo adaptive optics simulation tool, DASP, with relevance for proposed instruments such as MOSAIC. We consider parameters such as the number of laser guide stars, sodium layer depth, wavefront sensor pixel scale, actuator pitch and natural guide star availability. We provide potential areas where costs savings can be made, and investigate trade-offs between performance and cost, and provide solutions that would enable such an instrument to be built with currently available technology. Our key recommendations include a trade-off for laser guide star wavefront sensor pixel scale of about 0.7 arcseconds per pixel, and a field of view of at least 7 arcseconds, that EMCCD technology should be used for natural guide star wavefront sensors even if reduced frame rate is necessary, and that sky coverage can be improved by a slight reduction in natural guide star sub-aperture count without significantly affecting tomographic performance. We find that adaptive optics correction can be maintained across a wide field of view, up to 7 arcminutes in diameter. We also recommend the use of at least 4 laser guide stars, and include ground-layer and multi-object adaptive optics performance estimates.
We present new on-sky results for the Subaru Coronagraphic Extreme Adaptive Optics imager (SCExAO) verifying and quantifying the contrast gain enabled by key components: the closed-loop coronagraphic low-order wavefront sensor (CLOWFS) and focal plane wavefront control (speckle nulling). SCExAO will soon be coupled with a high-order, Pyramid wavefront sensor which will yield > 90% Strehl ratio and enable 10^6--10^7 contrast at small angular separations allowing us to image gas giant planets at solar system scales. Upcoming instruments like VAMPIRES, FIRST, and CHARIS will expand SCExAOs science capabilities.
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