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The Daniel K. Inouye Solar Telescope (DKIST) is a ground-based observatory for observations of the solar atmosphere featuring an unprecedented entrance aperture of four meters. To address its demanding scientific goals, DKIST features innovative and state-of-the-art instrument subsystems that are fully integrated with the facility and designed to be capable of operating mostly simultaneously. An important component of DKIST’s first-light instrument suite is the Visible Broadband Imager (VBI). The VBI is an imaging instrument that aims to acquire images of the solar photosphere and chromosphere with high spatial resolution and high temporal cadence to investigate the to-date smallest detectable features and their dynamics in the solar atmosphere. VBI observations of unprecedented spatial resolution ultimately will be able to inform modern numerical models and thereby allow new insights into the physics of the plasma motion at the smallest scales measurable by DKIST. The VBI was designed to deliver images at various wavelengths and at the diffraction limit of DKIST. The diffraction limit is achieved by using adaptive optics in conjunction with post-facto image-reconstruction techniques to remove residual effects of the terrestrial atmosphere. The first images of the VBI demonstrate that DKIST’s optical system enables diffraction-limited imaging across a large field of view of various layers in the solar atmosphere. These images allow a first glimpse at the exciting scientific discoveries that will be possible with DKIST’s VBI.

This Conference Presentation, “The National Science Foundation’s Daniel K. Inouye Solar Telescope,” was recorded for the Astronomical Telescopes + Instrumentation 2020 Digital Forum.

The National Science Foundation’s (NSF) Daniel K. Inouye Solar Telescope (DKIST) is located on the island of Maui, Hawai'i. The DKIST is a 4-meter clear-aperture solar telescope nearing the end of its construction phase in 2021. Following construction there will be a one year Operations Commissioning Phase (OCP). The OCP allows for early observing opportunities, while at the same time, fine-tuning systems and procedures, in preparation for DKIST steadystate operations in 2022. During the OCP, the DKIST Science Operations Specialists (SOSs, a.k.a. Telescope Operators) will execute validated solar observing programs as instructed by Resident Scientists while coordinating with maintenance and engineering activities. DKIST maintenance and engineering tasks are performed by the technical operations staff sharing time during daylight with science operations, which is an entirely different scenario than for nighttime ground-based observatories. Presented here is a summary of the year leading up to the OCP from the perspective of the DKIST SOS group. We present the training planned for the current SOS group and how this folds into the DKIST’s still ongoing Integration, Testing and Commissioning phase. We are developing an efficient training program to reduce the overall training time. We also discuss the tools which assist the current SOS group in writing and generating shift schedules, procedures, checklists, and workflows.

We present an overview of the National Science Foundation’sDaniel K. Inouye Solar Telescope(DKIST), its instruments, and support facilities. The 4 m aperture DKIST provides the highest-resolution observations of the Sun ever achieved. The large aperture of DKIST combined with state-of-the-art instrumentation provide the sensitivity to measure the vector magnetic field in the chromosphere and in the faint corona, i.e. for the first time with DKIST we will be able to measure and study the most important free-energy source in the outer solar atmosphere – the coronal magnetic field. Over its operational lifetime DKIST will advance our knowledge of fundamental astronomical processes, including highly dynamic solar eruptions that are at the source of space-weather events that impact our technological society. Design and construction of DKIST took over two decades. DKIST implements a fast (f/2), off-axis Gregorian optical design. The maximum available field-of-view is 5 arcmin. A complex thermal-control system was implemented in order to remove at prime focus the majority of the 13 kW collected by the primary mirror and to keep optical surfaces and structures at ambient temperature, thus avoiding self-induced local seeing. A high-order adaptive-optics system with 1600 actuators corrects atmospheric seeing enabling diffraction limited imaging and spectroscopy. Five instruments, four of which are polarimeters, provide powerful diagnostic capability over a broad wavelength range covering the visible, near-infrared, and mid-infrared spectrum. New polarization-calibration strategies were developed to achieve the stringent polarization accuracy requirement of 5×10−4. Instruments can be combined and operated simultaneously in order to obtain a maximum of observational information. Observing time on DKIST is allocated through an open, merit-based proposal process. DKIST will be operated primarily in “service mode” and is expected to on average produce 3 PB of raw data per year. A newly developed data center located at the NSO Headquarters in Boulder will initially serve fully calibrated data to the international users community. Higher-level data products, such as physical parameters obtained from inversions of spectro-polarimetric data will be added as resources allow.

The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly known as the Advanced Technology Solar Telescope (ATST) is currently under construction on Haleakalā (Maui, Hawai'i) projected to start operations in 2019. At the time of completion, DKIST will be the largest ground-based solar telescope providing unprecedented resolution and photon collecting power. The DKIST will be equipped with a set of first-light facility-class instruments offering unique imaging, spectroscopic and spectropolarimetric observing opportunities covering the visible to infrared wavelength range. This first-light instrumentation suite will include: a Visible Broadband Imager (VBI) for high-spatial and -temporal resolution imaging of the solar atmosphere; a Visible Spectro-Polarimeter (ViSP) for sensitive and accurate multi-line spectropolarimetry; a Fabry-Perot based Visible Tunable Filter (VTF) for high-spatial resolution spectropolarimetry; a fiber-fed Diffraction-Limited Near Infra-Red Spectro-Polarimeter (DL-NIRSP) for two-dimensional high-spatial resolution spectropolarimetry (simultaneous spatial and spectral information); and a Cryogenic Near Infra-Red Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field measurements and on-disk observations of, e.g., the CO lines at 4.7 μm. We will provide an overview of the DKISTs unique capabilities with strong focus on the first-light instrumentation suite, highlight some of the additional properties supporting observations of transient and dynamic solar phenomena, and touch on some operational strategies and the DKIST critical science plan. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The MCAO pathfinder Clear on the 1.6-meter Goode Solar Telescope has been enabling us to advance solar MCAO from early conceptual demonstrations to science grade wide-field image correction. We report on recent improvements to the control loop and we comment on issues such as the co-aligning of wavefront sensors and deformable mirrors and the sensitivity of wavefront sensor gains. Further, we comment on the challenges to wavefront sensing and the control system architecture faced when scaling up to a 4-meter aperture. Finally, we present an early concept of the future MCAO upgrade for the Daniel K. Inouye Solar Telescope.

The Wavefront Correction (WFC) system for the Daniel K. Inouye Solar Telescope (DKIST) is in its final stages of laboratory integration. All optical, mechanical, and software components have been unit tested and installed and aligned in our laboratory testbed in Boulder, CO. We will verify all aspects of WFC system performance in the laboratory before disassembling and shipping it to Maui for final integration with the DKIST in early 2019. The DKIST Adaptive Optics (AO) system contains a 1600-actuator deformable mirror, a correlating Shack- Hartmann wavefront sensor, a fast tip-tilt mirror, and an FPGA-based control system. Running at a nominal rate of 1975 Hz, the AO system will deliver diffraction-limited images to five of the DKIST science instruments simultaneously. The DKIST AO system is designed to achieve the diffraction limit (on-axis Strehl > 0.3) at wavelengths up to 500 nm in median daytime seeing (r0 = 7 cm). In addition to AO for diffraction-limited observing, the DKIST WFC system has a low-order wavefront sensor for sensing quasi-static wavefront errors, a context viewer for telescope pointing and image quality assessment, and an active optics engine. The active optics engine uses inputs from the low-order wavefront sensor and the AO system to actively correct for telescope misalignment. All routine alignment and calibration procedures are automated via motorized stages that can be controlled from Python scripts. We present the current state of the WFC system as we prepare for final integration with the DKIST, including verification test design, system performance metrics, and laboratory test data.

Construction of the Daniel K. Inouye Solar Telescope (DKIST) is well underway on the Haleakalā summit on the Hawaiian island of Maui. Featuring a 4-m aperture and an off-axis Gregorian configuration, the DKIST will be the world’s largest solar telescope. It is designed to make high-precision measurements of fundamental astrophysical processes and produce large amounts of spectropolarimetric and imaging data. These data will support research on solar magnetism and its influence on solar wind, flares, coronal mass ejections, and solar irradiance variability. Because of its large aperture, the DKIST will be able to sense the corona’s magnetic field—a goal that has previously eluded scientists—enabling observations that will provide answers about the heating of stellar coronae and the origins of space weather and exo-weather. The telescope will cover a broad wavelength range (0.35 to 28 microns) and operate as a coronagraph at infrared (IR) wavelengths. Achieving the diffraction limit of the 4-m aperture, even at visible wavelengths, is paramount to these science goals. The DKIST’s state-of-the-art adaptive optics systems will provide diffraction-limited imaging, resolving features that are approximately 20 km in size on the Sun. At the start of operations, five instruments will be deployed: a visible broadband imager (VTF), a visible spectropolarimeter (ViSP), a visible tunable filter (VTF), a diffraction-limited near-IR spectropolarimeter (DLNIRSP), and a cryogenic near-IR spectropolarimeter (cryo-NIRSP). At the end of 2017, the project finished its fifth year of construction and eighth year overall. Major milestones included delivery of the commissioning blank, the completed primary mirror (M1), and its cell. Commissioning and testing of the coude rotator is complete and the installation of the coude cleanroom is underway; likewise, commissioning of the telescope mount assembly (TMA) has also begun. Various other systems and equipment are also being installed and tested. Finally, the observatory integration, testing, and commissioning (IT&C) activities have begun, including the first coating of the M1 commissioning blank and its integration within its cell assembly. Science mirror coating and initial on-sky activities are both anticipated in 2018.

We explore the feasibility of adaptive optics for observations of prominences off the solar limb. We installed a wavefront sensor prototype on the GST at the Big Bear Solar Observatory. This sensor is used to conduct open and closed loop experiments to characterize the limitations of this application following up on first demonstrations at the DST. The sensor will enable us to optimize parameters and algorithms for a potential future implementation on NSF’s Daniel K. Inouye Solar Telescope. Unlike the granular structure of the solar photosphere that has served wavefront sensors in solar telescopes for decades with useful reference structures, prominences are much more challenging to use: they are faint and their fine structure is barely visible at the short exposures needed for an AO wavefront sensor.

The 4m Advance Technology Solar Telescope (ATST) is under construction on Maui, HI. With its unprecedented resolution and photon collecting power ATST will be an ideal tool for studying prominences and filaments and their role in producing Coronal Mass Ejections that drive Space Weather. The ATST facility will provide a set of first light instruments that enable imaging and spectroscopy of the dynamic filament and prominence structure at 8 times the resolution of Hinode. Polarimeters allow high precision chromospheric and coronal magnetometry at visible and infrared (IR) wavelengths. This paper summarizes the capabilities of the ATST first-light instrumentation with focus on prominence and filament science.

We provide an update on the construction status of the Daniel K. Inouye Solar Telescope. This 4-m diameter facility is designed to enable detection and spatial/temporal resolution of the predicted, fundamental astrophysical processes driving solar magnetism at their intrinsic scales throughout the solar atmosphere. These data will drive key research on solar magnetism and its influence on solar winds, flares, coronal mass ejections and solar irradiance variability. The facility is developed to support a broad wavelength range (0.35 to 28 microns) and will employ state-of-the-art adaptive optics systems to provide diffraction limited imaging, resolving features approximately 20 km on the Sun. At the start of operations, there will be five instruments initially deployed: Visible Broadband Imager (VBI; National Solar Observatory), Visible SpectroPolarimeter (ViSP; NCAR High Altitude Observatory), Visible Tunable Filter (VTF (a Fabry-Perot tunable spectropolarimeter); Kiepenheuer Institute for Solarphysics), Diffraction Limited NIR Spectropolarimeter (DL-NIRSP; University of Hawaii, Institute for Astronomy) and the Cryogenic NIR Spectropolarimeter (Cryo-NIRSP; University of Hawaii, Institute for Astronomy). As of mid-2016, the project construction is in its 4th year of site construction and 7th year overall. Major milestones in the off-site development include the conclusion of the polishing of the M1 mirror by University of Arizona, College of Optical Sciences, the delivery of the Top End Optical Assembly (L3), the acceptance of the Deformable Mirror System (Xinetics); all optical systems have been contracted and are either accepted or in fabrication. The Enclosure and Telescope Mount Assembly passed through their factory acceptance in 2014 and 2015, respectively. The enclosure site construction is currently concluding while the Telescope Mount Assembly site erection is underway. The facility buildings (Utility and Support and Operations) have been completed with ongoing work on the thermal systems to support the challenging imaging requirements needed for the solar research. Finally, we present the construction phase performance (schedule, budget) with projections for the start of early operations.

We provide a brief update on the construction status of the Daniel K. Inouye Solar Telescope, a $344M, 10-year construction project to design and build the world's largest solar physics observatory. We review the science drivers along with the challenges in meeting the evolving scientific needs over the course of the construction period without jeopardizing the systems engineering and management realization. We review the tools, processes and performance measures in use in guiding the development as well as the risks and challenges as the project transitions through various developmental phases. We elaborate on environmental and cultural compliance obligations in building in Hawai'i. We discuss the broad "lessons learned". Finally, we discuss the project in the context of the evolving management oversight within the US (in particular under the NSF).

Adaptive Optics (AO) that compensates for atmospheric turbulence is a standard tool for high angular resolution observations of the Sun at most ground-based observatories today. AO systems as deployed at major solar telescopes allow for diffraction limited resolution in the visible light regime. Anisoplanatism of the turbulent air volume limits the effectivity of classical AO to a small region, typically of order 10 seconds of arc. Scientifically interesting features on the solar surface are often larger thus multi-conjugate adaptive optics (MCAO) is being developed to enlarge the corrected field of view. Dedicated wavefront sensors for observations of solar prominences off the solar limb with AO have been deployed. This paper summarizes wavefront sensing concepts specific to solar adaptive optics applications, like the correlating Shack-Hartmann wavefront sensor (SH-WFS), multi-directional sensing with wide-field SH-WFSs, and gives a brief overview of recent developments.

When the Daniel K. Inouye Solar Telescope (DKIST) achieves first light in 2019, it will deliver the highest spatial resolution images of the solar atmosphere ever recorded. Additionally, the DKIST will observe the Sun with unprecedented polarimetric sensitivity and spectral resolution, spurring a leap forward in our understanding of the physical processes occurring on the Sun. The DKIST wavefront correction system will provide active alignment control and jitter compensation for all six of the DKIST science instruments. Five of the instruments will also be fed by a conventional adaptive optics (AO) system, which corrects for high frequency jitter and atmospheric wavefront disturbances. The AO system is built around an extended-source correlating Shack-Hartmann wavefront sensor, a Physik Instrumente fast tip-tilt mirror (FTTM) and a Xinetics 1600-actuator deformable mirror (DM), which are controlled by an FPGA-based real-time system running at 1975 Hz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r0 = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r0 = 20 cm). The DKIST wavefront correction team has completed the design phase and is well into the fabrication phase. The FTTM and DM have both been delivered to the DKIST laboratory in Boulder, CO. The real-time controller has been completed and is able to read out the camera and deliver commands to the DM with a total latency of approximately 750 μs. All optics and optomechanics, including many high-precision custom optics, mounts, and stages, are completed or nearing the end of the fabrication process and will soon undergo rigorous acceptance testing. Before installing the wavefront correction system at the telescope, it will be assembled as a testbed in the laboratory. In the lab, performance tests beginning with component-level testing and continuing to full system testing will ensure that the wavefront correction system meets all performance requirements. Further work in the lab will focus on fine-tuning our alignment and calibration procedures so that installation and alignment on the summit will proceed as efficiently as possible.

The NST (New Solar Telescope), a 1.6 m clear aperture, off-axis telescope, is in its commissioning phase at Big Bear Solar Observatory (BBSO). It will be the most capable, largest aperture solar telescope in the US until the 4 m ATST (Advanced Technology Solar Telescope) comes on-line late in the next decade. The NST will be outfitted with state-of-the-art scientific instruments at the Nasmyth focus on the telescope floor and in the Coude Lab beneath the telescope. At the Nasmyth focus, several filtergraphs already in routine operation have offered high spatial resolution photometry in TiO 706 nm, Hα 656 nm, G-band 430 nm and the near infrared (NIR), with the aid of a correlation tracker and image reconstruction system. Also, a Cryogenic Infrared Spectrograph (CYRA) is being developed to supply high signal-to-noise-ratio spectrometry and polarimetry spanning 1.0 to 5.0 μm. The Coude Lab instrumentation will include Adaptive Optics (AO), InfraRed Imaging Magnetograph (IRIM), Visible Imaging Magnetograph (VIM), and Fast Imaging Solar Spectrograph (FISS). A 308 sub-aperture (349-actuator deformable mirror) AO system will enable nearly diffraction limited observations over the NST's principal operating wavelengths from 0.4 μm through 1.7 μm. IRIM and VIM are Fabry-Perot based narrow-band tunable filters, which provide high resolution two-dimensional spectroscopic and polarimetric imaging in the NIR and visible respectively. FISS is a collaboration between BBSO and Seoul National University focussing on chromosphere dynamics. This paper reports the up-to-date progress on these instruments including an overview of each instrument and details of the current state of design, integration, calibration and setup/testing on the NST (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-resolution studies of the Sun’s magnetic fields are needed for a better understanding of the fundamental processes responsible for solar variability. The generation of magnetic fields through dynamo processes, the amplification of fields through the interaction with plasma flows, and the destruction of fields are poorly understood. There is incomplete insight into physical mechanisms responsible for chromospheric and coronal structure and heating, causes of variations in the radiative output of the Sun, and mechanisms that trigger flares and coronal mass ejections. Progress in answering these critical questions requires study of the interaction of the magnetic field and convection with a resolution sufficient to observe scale fundamental to these processes. The planned 4 m aperture ATST will be a unique scientific tool, with excellent angular resolution, a large wavelength range, and low scattered light. With its integrated adaptive optics, the ATST will achieve a spatial resolution nearly 10 times better than any existing solar telescope. The ATST design and development phase began in 2001 and it is now ready to begin construction in 2009.

In this empirical study, we compare high-resolution observations obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO) in 2005 and with the Dunn Solar Telescope (DST) at the National Solar Observatory/Sacramento Peak (NSO/SP) in 2006. We measure the correction of the high-order adaptive optics (AO) systems across the field of view (FOV) using the spectral ratio technique, which is commonly employed in speckle masking imaging, and differential image motion measurements. The AO correction is typically much larger (10′′ to 25′′) than the isoplanatic angle and can be described by a radially symmetric function with a central core and extended wings. The full-width at half-maximum (FWHM) of the core represents a measure of the AO correction. The average FWHM values for BBSO and NSO/SP are 23.5′′ and 18.2′′, respectively. The extended wings of the function show that the AO systems still contribute to an improved speckle reconstruction at the periphery of the 80′′×80′′ FOV. The major differences in the level of AO correction between BBSO and NSO/SP can be explained by different contributions of ground-layer- and free-atmosphere-dominated seeing, as well as different FOVs of the wavefront sensors. In addition, we find an anisotropic spectral ratio in sunspot penumbrae caused by the quasi-one-dimensional nature of penumbral filaments, which introduces a significant error in the estimation of the Fourier amplitudes during the image restoration process.

In 2004 January, the Big Bear Solar Observatory (BBSO) was equipped with a high-order adaptive optics (AO) system built in collaboration with the National Solar Observatory (NSO) at Sacramento Peak. The hardware is almost identical to the AO system operated at the NSO Dunn Solar Tower (DST), incorporating a 97 actuator deformable mirror, a Shack-Hartmann wave-front sensor with 76 subapertures, and an off-the-shelf digital signal processor system. However, the BBSO optical design is quite different. It had to be adapted to the 65 cm vacuum reflector and the downstream postfocus instrumentation. In this paper, we describe the optical design, demonstrate the AO performance, and use image restoration techniques to illustrate the image quality that can be achieved with the new AO system.

Long-exposure spectro-polarimetry in the near-infrared is a preferred method to measure the magnetic field and other physical properties of solar prominences. In the past, it has been very difficult to observe prominences in this way with sufficient spatial resolution to fully understand their dynamical properties. Solar prominences contain highly transient structures, visible only at small spatial scales; hence they must be observed at sub-arcsecond resolution, with a high temporal cadence. An adaptive optics (AO) system capable of directly locking-on to prominence structure away from the solar limb has the potential to allow for diffraction-limited spectro-polarimetry of solar prominences. In this paper, the performance of the off-limb AO system and its expected performance, at the desired science wavelength {\CaII} 8542A, are shown.

We present high-resolution observations of horizontal flow fields measured by local correlation tracking from intensity images in three wavelengths, i.e., G band (GB), white light (WL), and near-infrared (NIR). The observations were obtained on 2003 October 29 within the flaring super active region NOAA 10486, which was the source of several X-class flares, including an X10 flare that occurred near the end of the observing run. The data were obtained at National Solar Observatory/Sacramento Peak (NSO/SP) using the newly developed high-order adaptive optics (AO) system. We also use Dopplergrams and magnetograms from MDI on board SOHO to study the line-of-sight flow and magnetic field. We observe persistent and long-lived (at least 5 hr) strong horizontal and vertical shear flows (both in the order of 1 km s-1) along the magnetic neutral line (NL) until the X10 flare occurred. From lower photospheric level (NIR), the direction of the flows does not change up to the upper photosphere (GB), while the flow speeds in the shear motion regions decrease and, on the contrary, those in regions without shear motions increase with increasing altitude. Right after the X10 flare, the magnetic gradient decreased, while both horizontal and vertical shear flows dramatically enhanced near the flaring NL. Our results suggest that photospheric shear flows and local magnetic shear near the NL can increase after the flare, which may be the result of shear release in the overlying large-scale magnetic system or the reflection of a twisted or sheared flux emergence carrying enough energy from the subphotosphere.

The site survey for the Advanced Technology Solar Telescope concluded recently after more than two years of data gathering and analysis. Six locations, including lake, island and continental sites, were thoroughly probed for image quality and sky brightness. The present paper describes the analysis methodology employed to determine the height stratification of the atmospheric turbulence. This information is crucial because day-time seeing is often very different between the actual telescope aperture (~30 m) and the ground. Two independent inversion codes have been developed to analyze simultaneously data from a scintillometer array and a solar differential image monitor. We show here the results of applying them to a sample subset of data from May 2003, which was used for testing. Both codes retrieve a similar seeing stratification through the height range of interest. A quantitative comparison between our analysis procedure and actual in situ measurements confirms the validity of the inversions. The sample data presented in this paper reveal a qualitatively different behavior for the lake sites (dominated by high-altitude seeing) and the rest (dominated by near-ground turbulence)., To appear in the Publications of the Astronomical Society of the Pacific (PASP). Note: Figures are low resolution versions due to file size limitations

We present, for the first time, high-spatial-resolution observations combining high-order adaptive optics (AO), frame selection, and post-facto image correction via speckle masking. The data analysis is based on observations of solar active region NOAA 10486 taken with the Dunn Solar Telescope (DST) at the Sacramento Peak Observatory (SPO) of the National Solar Observatory (NSO) on 29 October 2003. The high Strehl ratio encountered in AO corrected short-exposure images provides highly improved signal-to-noise ratios leading to a superior recovery of the object’s Fourier phases. This allows reliable detection of small-scale solar features near the diffraction limit of the telescope. Speckle masking imaging provides access to high-order wavefront aberrations, which predominantly originate at high atmospheric layers and are only partially corrected by the AO system. In addition, the observations provided qualitative measures of the image correction away from the lock point of the AO system. We further present a brief inspection of the underlying imaging theory discussing the limitations and prospects of this multi-faceted image reconstruction approach in terms of the recovery of spatial information, photometric accuracy, and spectroscopic applications.

We present high spatial resolution observations of proper motions in the solar NOAA Active Region 10486 using a high-order adaptive optics system, frame selection, and speckle-masking image reconstruction. The data were obtained with the Dunn Solar Telescope of the National Solar Observatory/Sacramento Peak on 2003 October 29. The resolution of the images approaches the diffraction-limited resolution of the Dunn Solar Telescope of about 014 at 527 nm. We analyzed a 2 hr time series with a 1 minute cadence prior to an X10 white-light flare. Local correlation tracking was used to measure the photospheric proper motions. We find specific evidence of strong shear flows along the magnetic neutral line; these shear flows are well defined and correlated with white-light flare kernels in the visible and infrared. The speed along the flow channels can reach up to 1.6 km s-1, and the separation of channels with head-on flows can be less than 1''. Counterstreaming and complex flow patterns have been distinguishing characteristics of this extraordinarily flare-productive active region.

The Advanced Technology Solar Telescope (ATST) will perform high-resolution studies of the Sun's magnetic fields needed to understand their role in the fundamental processes responsible for solar variability. The generation of magnetic fields through dynamo processes, the amplification of fields through the interaction with plasma flows, and the destruction of fields remain poorly understood. There is incomplete insight as to what physical mechanisms are responsible for heating the corona, what causes variations in the radiative output of the Sun, and what mechanisms trigger flares and coronal mass ejections. Progress in answering these critical questions requires study of the interaction of the magnetic field and convection with a resolution sufficient to observe scales fundamental to these processes. The 4-m aperture ATST is designed as a unique scientific tool, with excellent angular resolution, a large wavelength range, and low scattered light. With its integrated adaptive optics, the ATST will achieve a spatial resolution nearly 10 times better than any existing solar telescope. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Sun is an ideal object for the development and application of multiconjugate adaptive optics(MCAO). An effort to develop solar MCAO is pursued by the National Solar Observatory (NSO) Adaptive OpticsProject. In developing solar MCAO, we bear in mind its possible implementation into the proposed 4 m AdvancedTechnology Solar Telescope (ATST). Two possible relay optical designs feeding an MCAO section and the coude´section of a 4 m off-axis solar telescope, such as the proposed ATST, are presented and discussed here.1. INTRODUCTIONExtending the size of the corrected field of view (FOV) withrespect to the classical adaptive optics (AO) system FOV isone of several new challenges to improving the performanceof astronomical telescopes. Atmospheric turbulence tomogra-phy, which measures the wave front produced by discreteatmo-spheric layers when receiving light beams from several ref-erence sources, has been one of the techniques proposed(Tallon& Foy 1990) to approach such a challenge. Assuming linearaddition (Roddier 1981) of the phase conjugation produced byeach weak turbulent layer, the configuration of guide sources,and the altitudes of the layers, the phase at any given turbulentlayer can be reconstructed. Foy & Labeyrie (1985) proposedto correct each discrete equivalent turbulent layer individuallyby using multiple deformable mirrors (DMs). Such a conceptwas called multiconjugate adaptive optics (MCAO). Many pa-pers have discussed the problem of turbulence tomography(Tallon & Foy 1990; Ragazzoni et al. 1999; Fusco et al. 1999).Tomographic wave-front retrieval (using wave-front measure-ments from several positions in the FOV) has been numericallysimulated by Ellerbroek (1994) and Fusco (1999). More re-cently, experimental closed-loop correction has been demon-strated in the laboratory (Knutsson & Owner-Petersen 2003;Wallace et al. 2003; Langlois et al. 2004c) and at telescopesfor solar observations (Langlois et al. 2004b). In the case ofsolar MCAO, several guiding regions are selected within asingle wave-front sensor with a large FOV (1 –2 ), and thewave front is evaluated using cross-correlation on the subi-mages. This technique has been sucessfully implemented usingboth sunspots and solar granulations as guiding regions, asdiscussed in Langlois et al. (2004b). Figure 1 shows the images

We use high-quality observations from the Dunn Solar Telescope at NSO/Sacramento Peak to study spatio-temporal co-location of acoustic flux events in the photosphere and internetwork grains in the chromosphere. The events are diagnosed as sites with excess upward-propagating five-minute waves measured from Dopplergrams. The grains are repetitive bright internetwork features in simultaneous Caii K2V filtergrams. We find that the largest-flux sites in the granulation have appreciably larger than random probability to co-locate with exceptionally bright chromospheric internetwork grains, at an average delay of about two minutes which is likely to represent sound travel time to the chromosphere. This finding strengthens the case for acoustic grain excitation.

The multi-conjugate adaptive optics (MCAO) pathfinder Clear on the New Solar Telescope in Big Bear Lake has provided the first-ever MCAO-corrected observations of the Sun that show a clearly and visibly widened corrected field of view compared to quasi-simultaneous observations with classical adaptive optics (CAO) correction. Clear simultaneously uses three deformable mirrors, each conjugated to a different altitude, to compensate for atmospheric turbulence. While the MCAO correction was most effective over an angle that is approximately three times wider than the angle that was corrected by CAO, the full 53′′ field of view did benefit from MCAO correction. We further demonstrate that ground-layer-only correction is attractive for solar observations as a complementary flavor of adaptive optics for observational programs that require homogenous seeing improvement over a wide field rather than diffraction-limited resolution. We show illustrative images of solar granulation and of a sunspot obtained on different days in July 2016, and present a brief quantitative analysis of the generalized Fried parameters of the images.

In this paper we present Big Bear Solar Observatory’s (BBSO) newest adaptive optics system – AO-308. AO-308 is a result of collaboration between BBSO and National Solar Observatory (NSO). AO-308 uses a 357 actuators deformable mirror (DM) from Xinetics and its wave front sensor (WFS) has 308 sub-apertures. The WFS uses a Phantom V7.3 camera which runs at 2000 Hz with the region of interest of 416×400 pixels. AO-308 utilizes digital signal processors (DSPs) for image processing. AO-308 has been successfully used during the 2013 observing season. The system can correct up to 310 modes providing diffraction limited images at all wavelengths of interest.

The DKIST wavefront correction system will be an integral part of the telescope, providing active alignment control, wavefront correction, and jitter compensation to all DKIST instruments. The wavefront correction system will operate in four observing modes, diffraction-limited, seeing-limited on-disk, seeing-limited coronal, and limb occulting with image stabilization. Wavefront correction for DKIST includes two major components: active optics to correct low-order wavefront and alignment errors, and adaptive optics to correct wavefront errors and high-frequency jitter caused by atmospheric turbulence. The adaptive optics system is built around a fast tip-tilt mirror and a 1600 actuator deformable mirror, both of which are controlled by an FPGA-based real-time system running at 2 kHz. It is designed to achieve on-axis Strehl of 0.3 at 500 nm in median seeing (r 0 = 7 cm) and Strehl of 0.6 at 630 nm in excellent seeing (r 0 = 20 cm). We present the current status of the DKIST high-order adaptive optics, focusing on system design, hardware procurements, and error budget management.

We report on the multi-conjugate adaptive optics (MCAO) system of the New Solar Telescope (NST) at Big Bear Solar Observatory which has been integrated in October 2013 and is now available for MCAO experiments. The NST MCAO system features three deformable mirrors (DM), and it is purposely flexible in order to offer a valuable facility for development of solar MCAO. Two of the deformable mirrors are dedicated to compensation of field dependent aberrations due to high-altitude turbulence, whereas the other deformable mirror compensates field independent aberrations in a pupil image. The opto-mechanical design allows for changing the conjugate plane of the two high-altitude DMs independently between two and nine kilometers. The pupil plane DM can be placed either in a pupil image upstream of the high-altitude DMs or downstream. This capability allows for performing experimental studies on the impact of the geometrical order of the deformable mirrors and the conjugate position. The control system is flexible, too, which allows for real-world analysis of various control approaches. This paper gives an overview of the NST MCAO system and reveals the first MCAO corrected image taken at Big Bear Solar Observatory.

A multi-conjugate adaptive optics (MCAO) system is being built for the world's largest aperture 1.6m solar telescope, New Solar Telescope, at the Big Bear Solar Observatory (BBSO). The BBSO MCAO system employs three deformable mirrors to enlarge the corrected field of view. In order to characterize the MCAO performance with different optical configurations and DM conjugated altitudes, the BBSO MCAO setup also needs to be flexible. In this paper, we present the optical design of the BBSO MCAO system.

The Daniel K. Inouye Solar Telescope is a 4-meter-class all-reflecting telescope under construction on Haleakalā mountain on the island of Maui, Hawai’i. When fully operational in 2019 it will be the world's largest solar telescope with wavelength coverage of 380 nm to 28 microns and advanced Adaptive Optics enabling the highest spatial resolution measurements of the solar atmosphere yet achieved. We review the first-generation DKIST instrument designs, select critical science program topics, and the operations and data handling and processing strategies to accomplish them.

We investigate seismic events, bursts of seismic waves that are generated locally just below the solar surface and that we detect traveling up through the photosphere. We identify a few thousand seismic events by their traveling wave character and —nd that they are associated with continuum darkening and down—ow and have an extent of on average about 10¨15 minutes and 1 Mm. Their birth rate is about 8 ) 10~16 m~2 s ~1. The observed upwardly traveling seismic —ux in the average event (as derived from velocities in the p-mode region of k-u space) is followed after about 3 minutes by some re—ected down- ward —ux. Only a small fraction of the energy generated in the hypocenter of the event below the surface travels straight up for us to see. The bulk of the generated energy is directed or re—ected downward, and is eventually transformed into p-modes. The seismic events at the surface contain about 1.5 ) 1019 Jo f seismic energy each, which corresponds to an average —ux level of about 8.5 kW m~2 over the whole surface. The total energy —ow is likely more than an order of magnitude greater, and is then in the same ballpark as the estimate of Libbrecht for the power required to sustain the p-mode spectrum. We —nd a roughly linear relation between the peak seismic —ux and the peak downward convective velocity associ- ated with each seismic event, which does not —t the highly nonlinear relations found theoretically by Lighthill and Goldreich & Kumar for stochastic excitation by turbulent convection, but does —t the monopole source deduced by Nigam & Kosovichev from a study of the p-mode spectrum. Subject heading: Sun: oscillationsSun: photospherewaves

We report new observations that combine high-precision infrared polarimetry and high-resolution imagery in the visible to demonstrate that most of the quiet solar surface contains a measurable magnetic field. We found that when observed at 1 arcsec2 resolution, 68% of the observed area contains magnetic flux higher than 5×1015 Mx (corresponding to an apparent average field of 1 G). The majority of these magnetic features have magnetic flux below 5×1016 Mx. Their magnetic field strengths range from below 200 to 1000 G, which means that their filling factors are on the order of 1%. The spatial distribution and time evolution of these magnetic features are closely associated with the solar granulation. The properties of these weak granular magnetic features we observed differ from those of the intranetwork fields described in earlier observations. We also observed the formation and disappearance of a kilogauss magnetic feature associated with the development of intergranular lanes, which may be evidence of convective collapse.

We made simultaneous high resolution observations of the solar granular field and the Sun‘s seismic events. We find that these events occur in the dark intergranular lanes. The events are preceded by the darkening of an already dark lane. On the leading edge of each event, there is a second more abrupt and precipitous darkening lasting a minute or two.

We study a time sequence of the velocity field measured in a sunspot light bridge classified as photospheric. The data provide clear evidence for a convective origin of the photospheric light-bridge phenomenon. Furthermore, the data strongly indicate that a form of oscillatory magnetoconvection is the physical process responsible for the formation of the observed light bridge. We observe umbral dots and find in them a very small upward velocity of order 50 m s-1. Both the intensity and the velocity signal vary in time. Some umbral dots fade over a period of about 15-20 minutes and then reappear at the same location. In the particular sunspot observed, umbral dots give the impression of being aligned in lanes that appear to separate individual flux fragments within the umbra.

The 4m Advance Technology Solar Telescope (ATST) will be the world's leading ground-based resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. The project has entered its construction phase. Major subsystems have been contracted, designs are complete, and fabrication has started. As its highest priority science driver ATST shall provide high resolution and high sensitivity observations of the dynamic solar magnetic fields throughout the solar atmosphere, including the corona at infrared wavelengths. A high order adaptive optics system delivers a corrected beam to the initial set of state-of-the-art, facility class instrumentation located in the Coude laboratory facility. The initial set of five first generation instruments consists of imagers and spectro-polarimeters. Development and construction of a four-meter solar telescope presents many technical challenges, including thermal control of the enclosure, telescope structure and optics and wavefront control. A brief overview of the science goals and observational requirements of the ATST will be given, followed by a summary of the status of the telescope, its instrumentation, and the construction of the facility.

Long-exposure spectroscopy and spectro-polarimetry at near-infrared wavelengths is one of the preferred tools deployed to measure the physical properties of Solar Prominences, including the Prominence magnetic field. However, until now, it was not possible to observe Prominences in sufficient detail to allow us to understand their dynamical properties. In order to understand Solar prominences, we need to observe them at sub-arcsecond spatial resolution, with a temporal cadence sufficient to make highly transient structures visible. Adaptive Optics capable of locking-on to off-limb prominence structure has the potential of providing diffraction limited spectroscopy and polarimetry of prominence structure. Such an adaptive optics system will allow scientists to come one step closer to understanding the true nature of solar prominences. In this presentation, we will detail the design and construction of such a system.

This paper summarizes recent solar AO developments and new challenges, including conventional AO for large aperture telescopes, MCAO and adaptive optics for faint structure near the limb of the sun.

The RISE/PSPT (‘Radiative Inputs from the Sun to the Earth/Precision Solar Photometric Telescopes’) experiment will attain high differential photometric precision in full-disk solar images with 1 arc sec pixels. To achieve this spatial resolution it will be necessary to use frame selection techniques to minimize the effects of atmospheric ‘seeing’. We report here on experiments to use a simple scintillation monitor as a trigger or ‘veto’ for imaging observations.

The Advanced Technology Solar Telescope (ATST) requires active control of quasi-static telescope aberrations in order to meet image quality standards set by its science requirements. Wavefront control is managed by the Telescope Control System, with many telescope subsystems playing key roles. We present the design of the ATST quasi-static wavefront and alignment control architecture and the algorithms used to control its four active mirrors. Two control algorithms are presented, one that minimizes force on M1 actuators and another that employs a neutral-pointing constraint on M2 to reduce pointing error. We also present simulations that generate typical daily active mirror trajectories which correct optical misalignments due to changing gravitational and thermal loads.

The National Solar Observatory’s (NSO) Advanced Technology Solar Telescope (ATST) is the first large U.S. solar telescope accessible to the worldwide solar physics community to be constructed in more than 30 years. The 4-meter diameter facility will operate over a broad wavelength range (0.35 to 28 μm ), employing adaptive optics systems to achieve diffraction limited imaging and resolve features approximately 20 km on the Sun; the key observational parameters (collecting area, spatial resolution, spectral coverage, polarization accuracy, low scattered light) enable resolution of the theoretically-predicted, fine-scale magnetic features and their dynamics which modulate the radiative output of the sun and drive the release of magnetic energy from the Sun’s atmosphere in the form of flares and coronal mass ejections. In 2010, the ATST received a significant fraction of its funding for construction. In the subsequent two years, the project has hired staff and opened an office on Maui. A number of large industrial contracts have been placed throughout the world to complete the detailed designs and begin constructing the major telescope subsystems. These contracts have included the site development, AandE designs, mirrors, polishing, optic support assemblies, telescope mount and coude rotator structures, enclosure, thermal and mechanical systems, and high-level software and controls. In addition, design development work on the instrument suite has undergone significant progress; this has included the completion of preliminary design reviews (PDR) for all five facility instruments. Permitting required for physically starting construction on the mountaintop of Haleakalā, Maui has also progressed. This paper will review the ATST goals and specifications, describe each of the major subsystems under construction, and review the contracts and lessons learned during the contracting and early construction phases. Schedules for site construction, key factory testing of major subsystems, and integration, test and commissioning activities will also be discussed.

When completed, the Advanced Technology Solar Telescope (ATST) will be the largest and most technologically advanced solar telescope in the world. As such, it faces many challenges that have not previously been solved. One of these challenges is the high-order wavefront sensor (HOWFS) for the ATST adaptive optics system. The HOWFS requires a 960 x 960 detector array that must run at a 2 kHz frame rate in order for the adaptive optics to achieve its required bandwidth. This detector must be able to accurately image low-contrast solar granulation in order to provide usable wavefront information. We have identified the Vision Research DS-440 as an off-the-shelf solution for the HOWFS detector and demonstrate tests proving that the camera will be able to lock the adaptive optics loop on solar granulation in commonly-experienced daytime seeing conditions. Tests presented quantify the noise, linearity, gain, stability, and well depth of the camera. Laboratory tests with artificial targets demonstrate its ability to accurately track low-contrast objects and on-sky demonstrations showcase the camera's performance in realistic observing conditions.