Author name code: jaeggli ADS astronomy entries on 2022-09-14 author:"Jaeggli, Sarah A." ------------------------------------------------------------------------ Title: A Publicly Available Multiobservatory Data Set of an Enhanced Network Patch from the Photosphere to the Corona Authors: Kobelski, Adam R.; Tarr, Lucas A.; Jaeggli, Sarah A.; Luber, Nicholas; Warren, Harry P.; Savage, Sabrina Bibcode: 2022ApJS..261...15K Altcode: 2022arXiv220501766K New instruments sensitive to chromospheric radiation at X-ray, UV, visible, IR, and submillimeter wavelengths have become available that significantly enhance our ability to understand the bidirectional flow of energy through the chromosphere. We describe the calibration, coalignment, initial results, and public release of a new data set combining a large number of these instruments to obtain multiwavelength photospheric, chromospheric, and coronal observations capable of improving our understanding of the connectivity between the photosphere and the corona via transient brightenings and wave signatures. The observations center on a bipolar region of enhanced-network magnetic flux near disk center on SOL2017-03-17T14:00-17:00. The comprehensive data set provides one of the most complete views to date of chromospheric activity related to small-scale brightenings in the corona and chromosphere. Our initial analysis shows a strong spatial correspondence between the areas of broadest width of the hydrogen-α spectral line and the hottest temperatures observed in Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 radio data, with a linear coefficient of 6.12 × 10-5Å/K. The correspondence persists for the duration of cotemporal observations (≍60 m). Numerous transient brightenings were observed in multiple data series. We highlight a single, well-observed transient brightening in a set of thin filamentary features with a duration of 20 minutes. The timing of the peak intensity transitions from the cooler (ALMA, 7000 K) to the hotter (XRT, 3 MK) data series. Title: Ground-based instrumentation and observational techniques Authors: Rimmele, Thomas; Kuhn, Jeff; Woeger, Friedrich; Tritschler, . Alexandra; Lin, Haosheng; Casini, Roberto; Schad, Thomas; Jaeggli, Sarah; de Wijn, Alfred; Fehlmann, Andre; Anan, Tetsu; Schmidt, Dirk Bibcode: 2022cosp...44.2507R Altcode: We'll review the current state-of-the-art for ground-based instrumentation and techniques to achieve high-resolution observations. We'll use the 4m Daniel K. Inouye Solar Telescope (DKIST), the European Solar Telescope (EST) and other ground-based instrumentation as examples to demonstrate instrument designs and observing techniques. Using adaptive optics and post-facto image processing techniques, the recently completed DKIST provides unprecedented resolution and high polarimetric sensitivity that enables astronomers to unravel many of the mysteries the Sun presents, including the origin of solar magnetism, the mechanisms of coronal heating and drivers of flares and coronal mass ejections. Versatile ground-based instruments provide highly sensitive measurements of solar magnetic fields, that in the case of DKIST, also include measurements of the illusive magnetic field of the faint solar corona. Ground-based instruments produce large and diverse data sets that require complex calibration and data processing to provide science-ready to a broad community. We'll briefly touch on ongoing and future instrumentation developments, including multi-conjugate adaptive optics. Title: Science Commissioning of the Diffraction-Limited Near-IR Spectropolarimter for the Daniel K. Inouye Solar Telescope Authors: Lin, Haosheng; Schad, Thomas; Kramar, Maxim; Jaeggli, Sarah; Anan, Tetsu; Onaka, Peter Bibcode: 2022cosp...44.2508L Altcode: The Diffraction-Limited Near-IR Spectropolarimeter (DL-NIRSP) is one of the first-generation facility instruments of the Daniel K. Inouye Solar Telescope (DKIST, or The Inouye Solar Telescope). It is a near-IR spectropolarimeter optimized to study the magnetism of the dynamic solar atmosphere, from the photosphere to the corona. DL-NIRSP is equipped with two integral field units (IFUs) coupled to a high-resolution grating spectrograph, and is capable of simultaneous measurements of the full polarized spectra of a 2-dimensional spatial field without scanning. Large field of view observations are supported by mosaicking. DL-NIRSP observes simultaneously at three spectral windows, enabling simultaneous coverage of different atmospheric layers with carefully selected spectral lines. It can also observe the Sun with three resolution modes, from diffraction-limited observations with a spatial sampling of 0.03" to wide-field mode covering a 32"x15" instantaneous FOV with 0.5" sampling. This paper will present results from science commissioning observations conducted in late 2021. Title: Thomson Scattering above Solar Active Regions and an Ad Hoc Polarization Correction Method for the Emissive Corona Authors: Schad, Thomas A.; Jaeggli, Sarah A.; Dima, Gabriel I. Bibcode: 2022ApJ...933...53S Altcode: 2022arXiv220509808S Thomson-scattered photospheric light is the dominant constituent of the lower solar corona's spectral continuum viewed off-limb at optical wavelengths. Known as the K-corona, it is also linearly polarized. We investigate the possibility of using the a priori polarized characteristics of the K-corona, together with polarized emission lines, to measure and correct instrument-induced polarized crosstalk. First we derive the Stokes parameters of the Thomson scattering of unpolarized light in an irreducible spherical tensor formalism. This allows forward synthesis of the Thomson-scattered signal for the more complex scenario that includes symmetry-breaking features in the incident radiation field, which could limit the accuracy of our proposed technique. For this, we make use of an advanced 3D radiative magnetohydrodynamic coronal model. Together with synthesized polarized signals in the Fe XIII 10746 Å emission line, we find that an ad hoc correction of telescope- and instrument-induced polarization crosstalk is possible under the assumption of a nondepolarizing optical system. Title: A Model-based Technique for Ad Hoc Correction of Instrumental Polarization in Solar Spectropolarimetry Authors: Jaeggli, Sarah A.; Schad, Thomas A.; Tarr, Lucas A.; Harrington, David M. Bibcode: 2022ApJ...930..132J Altcode: 2022arXiv220403732J We present a new approach for correcting instrumental polarization by modeling the nondepolarizing effects of a complex series of optical elements to determine physically realizable Mueller matrices. Provided that the Mueller matrix of the optical system can be decomposed into a general elliptical diattenuator and general elliptical retarder, it is possible to model the crosstalk between both the polarized and unpolarized states of the Stokes vector and then use the acquired science observations to determine the best-fit free parameters. Here we implement a minimization for solar spectropolarimetric measurements containing photospheric spectral lines sensitive to the Zeeman effect using physical constraints provided by polarized line and continuum formation. This model-based approach is able to provide an accurate correction even in the presence of large amounts of polarization crosstalk and conserves the physically meaningful magnitude of the Stokes vector, a significant improvement over previous ad hoc techniques. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE). II. Flares and Eruptions Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola; De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito, Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin, Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul; Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub, Leon; The Bibcode: 2022ApJ...926...53C Altcode: 2021arXiv210615591C Current state-of-the-art spectrographs cannot resolve the fundamental spatial (subarcseconds) and temporal (less than a few tens of seconds) scales of the coronal dynamics of solar flares and eruptive phenomena. The highest-resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by the Interface Region Imaging Spectrograph for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), subarcsecond-resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al., which focuses on investigating coronal heating with MUSE. Title: Probing the Physics of the Solar Atmosphere with the Multi-slit Solar Explorer (MUSE): II. Flares and Eruptions Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola; De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito, Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin, Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah; Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon Bibcode: 2021AGUFMSH51A..08C Altcode: Current state-of-the-art spectrographs cannot resolve the fundamental spatial (sub-arcseconds) and temporal scales (less than a few tens of seconds) of the coronal dynamics of solar flares and eruptive phenomena. The highest resolution coronal data to date are based on imaging, which is blind to many of the processes that drive coronal energetics and dynamics. As shown by IRIS for the low solar atmosphere, we need high-resolution spectroscopic measurements with simultaneous imaging to understand the dominant processes. In this paper: (1) we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne observatory to fill this observational gap by providing high-cadence (<20 s), sub-arcsecond resolution spectroscopic rasters over an active region size of the solar transition region and corona; (2) using advanced numerical models, we demonstrate the unique diagnostic capabilities of MUSE for exploring solar coronal dynamics, and for constraining and discriminating models of solar flares and eruptions; (3) we discuss the key contributions MUSE would make in addressing the science objectives of the Next Generation Solar Physics Mission (NGSPM), and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the Daniel K Inouye Solar Telescope (and other ground-based observatories) can operate as a distributed implementation of the NGSPM. This is a companion paper to De Pontieu et al. (2021, also submitted to SH-17), which focuses on investigating coronal heating with MUSE. Title: Chromospheric Heating Mechanisms in a Plage Region Constrained by Comparison of Magnetic Field and Mg II h & k Flux Measurements with Theoretical Studies Authors: Anan, Tetsu; Schad, Thomas; Kitai, Reizaburo; Dima, Gabriel; Jaeggli, Sarah; Tarr, Lucas; Collados, Manuel; Dominguez-Tagle, Carlos; Kleint, Lucia Bibcode: 2021AGUFMSH44A..05A Altcode: The strongest quasi-steady heating in the solar atmosphere from the photosphere through the corona occurs in plage regions. As many chromospheric heating mechanisms have been proposed, important discriminators of the possible mechanisms are the location of the heating and the correlation between the magnetic field properties in the chromosphere and the local heating rate. We observed a plage region with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation, the Interface Region Imaging Spectrograph (IRIS) obtained spectra of the ultraviolet Mg II h & k doublet emitted from the same region. In the periphery of the plage region, within the limited field of view seen by GRIS, we find that the Mg II radiative flux increases with the magnetic field in the chromosphere. The positive correlation implies that magnetic flux tubes can be heated by Alfvén wave turbulence or by collisions between ions and neutral atoms relating to Alfvén waves. Within the plage region itself, the radiative flux was large between patches of strong magnetic field strength in the photosphere, or at the edges of magnetic patches. On the other hand, we do not find any significant spatial correlation between the enhanced radiative flux and the chromospheric magnetic field strength or the electric current. In addition to the Alfvén wave turbulence or collisions between ions and neutral atoms relating to Alfvén waves, other heating mechanisms related to magnetic field perturbations produced by interactions of magnetic flux tubes could be at work in the plage chromosphere. Title: Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region Authors: Anan, Tetsu; Schad, Thomas A.; Kitai, Reizaburo; Dima, Gabriel I.; Jaeggli, Sarah A.; Tarr, Lucas A.; Collados, Manuel; Dominguez-Tagle, Carlos; Kleint, Lucia Bibcode: 2021ApJ...921...39A Altcode: 2021arXiv210807907A In order to investigate the relation between magnetic structures and the signatures of heating in plage regions, we observed a plage region with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation, the Interface Region Imaging Spectrograph obtained spectra of the ultraviolet Mg II doublet emitted from the same region. In the periphery of the plage region, within the limited field of view seen by GRIS, we find that the Mg II radiative flux increases with the magnetic field in the chromosphere with a factor of proportionality of 2.38 × 104 erg cm-2 s-1 G-1. The positive correlation implies that magnetic flux tubes can be heated by Alfvén wave turbulence or by collisions between ions and neutral atoms relating to Alfvén waves. Within the plage region itself, the radiative flux was large between patches of strong magnetic field strength in the photosphere or at the edges of magnetic patches. On the other hand, we do not find any significant spatial correlation between the enhanced radiative flux and the chromospheric magnetic field strength or the electric current. In addition to the Alfvén wave turbulence or collisions between ions and neutral atoms relating to Alfvén waves, other heating mechanisms related to magnetic field perturbations produced by interactions of magnetic flux tubes could be at work in the plage chromosphere. Title: The National Science Foundation's Daniel K. Inouye Solar Telescope — Status Update Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn, A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.; Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.; Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.; Mathioudakis, M.; Dkist Team Bibcode: 2021AAS...23810601R Altcode: The National Science Foundation's 4m Daniel K. Inouye Solar Telescope (DKIST) on Haleakala, Maui is now the largest solar telescope in the world. DKIST's superb resolution and polarimetric sensitivity will enable astronomers to unravel many of the mysteries the Sun presents, including the origin of solar magnetism, the mechanisms of coronal heating and drivers of flares and coronal mass ejections. Five instruments, four of which provide highly sensitive measurements of solar magnetic fields, including the illusive magnetic field of the faint solar corona. The DKIST instruments will produce large and complex data sets, which will be distributed through the NSO/DKIST Data Center. DKIST has achieved first engineering solar light in December of 2019. Due to COVID the start of the operations commissioning phase is delayed and is now expected for fall of 2021. We present a status update for the construction effort and progress with the operations commissioning phase. Title: Magnetic field structures associated with chromospheric heating in a plage region Authors: Anan, T.; Schad, T.; Kitai, R.; Dima, G.; Jaeggli, S.; Collados, M.; Dominguez-Tagle, C.; Kleint, L. Bibcode: 2021AAS...23821222A Altcode: The strongest quasi-steady heating in the solar atmosphere occurs in the active chromosphere and in particular within plage regions. Our aim is to investigate the relation between magnetic structures and the signatures of heating in the plage regions so as to clarify what mechanisms are at work. We observed a plage region in NOAA active region 12723 in the near infrared He I triplet and Si I 1082.7 nm on 2018 October 3 using the Integral Field Unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. At the same time, the Interface Region Imaging Spectrograph (IRIS) obtained spectra in the ultra-violet Mg II h & k doublet emitted from the same region. We applied the HAnle and ZEeman Light v2.0 inversion code (HAZEL v2.0) to the GRIS data to infer the photospheric and chromospheric magnetic field. We find that the radiative flux of the Mg II was large between patches of strong magnetic field strength in the photosphere, or at edges of the magnetic patches. On the other hand, the spatial correspondences between the Mg II flux and the magnetic field strength in the chromosphere and between the Mg II flux and the electric current are not so clear. In conclusion, chromospheric heatings in the plage region can be related to magnetic field perturbations produced by interactions of magnetic flux tubes. Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: Using Molecules to Investigate Cool Gas on the Sun with DKIST Authors: Jaeggli, Sarah Bibcode: 2021cosp...43E.970J Altcode: Simple molecules form in the solar atmosphere in regions of cool plasma. Molecules are physically interesting and provide critical diagnostics of cool plasma. They are sensitive to temperature and pressure, and some molecular lines are even magnetically sensitive. Strong absorption lines from molecules such as OH, CN, and CO are prominent in sunspot spectra. Molecular hydrogen, which has a noted absence of lines in the visible and infrared, may actually be the most abundant molecular species, comprising 10% of the total hydrogen population in very cool sunspot umbrae. CH, which is ubiquitous in the quiet-Sun, dissociates in hotter regions, revealing the features known as G-band bright points. The strongest lines of the fundamental band of CO at 4.6 um reveal what has been interpreted as a mix of hot and cool gas at the roots of the chromosphere. The U.S. National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will provide new observations of the Sun with unprecedented spatial and temporal resolution. DKIST instruments are designed to target atomic and molecular diagnostics to address a variety of science cases. Molecular diagnostics throughout the visible spectrum can be explored with the Visible Spectropolarimeter (ViSP). The Diffraction-Limited Near-Infrared Spectropolarimeter (DL-NIRSP) can be used to explore the dynamic behavior of OH in sunspots alongside sensitive magnetic field diagnostics of Fe I at 1565 nm using its integral field unit. The Cryogenic Near-Infrared Spectropolarimeter will provide the chance for detailed study of the 4.6 um CO lines on disk and at the limb. Title: The Daniel K. Inouye Solar Telescope - Observatory Overview Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode, Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.; McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich; von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn, Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.; Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang; Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian; Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard, Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross, Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit; Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon, Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer, Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.; Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer, Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes, Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag; Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik; Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis; Wampler, Stephen B.; Williams, Timothy R.; White, Charles Bibcode: 2020SoPh..295..172R Altcode: We present an overview of the National Science Foundation's Daniel 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. Title: Polarization modeling and predictions for Daniel K. Inouye Solar Telescope, part 6: fringe mitigation with polycarbonate modulators and optical contact calibration retarders Authors: Harrington, David M.; Jaeggli, Sarah A.; Schad, Tom A.; White, Amanda J.; Sueoka, Stacey R. Bibcode: 2020JATIS...6c8001H Altcode: Interference fringes are a major source of systematic error in astronomical spectropolarimeters. We apply the Berreman formalism with recent spatial fringe aperture averaging estimates to design and fabricate new fringe-suppressed polarization optics for several Daniel K. Inouye Solar Telescope (DKIST) use cases. We successfully performed an optical contact bond on a 120-mm-diameter compound crystal retarder for calibration with wavelength-dependent fringe suppression factors of one to three orders of magnitude. Special rotational alignment procedures were developed to minimize spectral oscillations, which we show here to represent our calibration stability limit under retarder thermal perturbation. We developed a fabrication technique to deliver low beam deflection for our large aperture polycarbonate (PC) retarders. Modulators are upgraded in two DKIST instruments with minimal beam deflection and bandpass-optimized antireflection coatings for fringe suppression factors of hundreds. We confirm that PC retarders do fringe as expected when low deflection is achieved. We show that increased retardance spatial variation from PC does not degrade modulation efficiency. Title: Observing Solar Plasma Environments with DKIST Authors: Jaeggli, Sarah Bibcode: 2020APS..DPPD02001J Altcode: The Sun displays diverse plasma environments structured by magnetic fields. The largely neutral photosphere is sprinkled with ∼1 kG magnetic fields rooted in the underlying convection zone. Just above this magneto-acoustic shocks and rapidly expanding magnetic fields create complex and dynamic structures interspersed with quiescent and eruptive phenomena in the chromosphere. The average temperature increases through the chromosphere abruptly jumps to >106 K in the solar corona. These different regimes are directly coupled by many processes that have been extensively studied using a combination of theory, simulations, and laboratory experiments: dynamos, waves, instabilities, and reconnection. The National Science Foundation's Daniel K. Inouye Solar Telescope is an unprecedented new facility that will allow for measurements of the highest spatial resolution and superb signal to noise on shorter timescales than ever before. First light instruments will provide simultaneous multi-wavelength observations with spectral and polarimetric capabilities on disk and above the limb. Coupled with radiative MHD modeling, this can provide 3D diagnosis of plasma parameters (e.g. magnetic field vector, temperature) over the plasma regimes found throughout the Sun's atmosphere. Title: Shock Heating Energy of Umbral Flashes Measured with Integral Field Unit Spectroscopy Authors: Anan, Tetsu; Schad, Thomas A.; Jaeggli, Sarah A.; Tarr, Lucas A. Bibcode: 2019ApJ...882..161A Altcode: 2019arXiv190710797A Umbral flashes are periodic brightness increases routinely observed in the core of chromospheric lines within sunspot umbrae and are attributed to propagating shock fronts. In this work we quantify the shock heating energy of these umbral flashes using observations in the near-infrared He I triplet obtained on 2014 December 7 with the SpectroPolarimetric Imager for the Energetic Sun, which is a novel integral field unit spectrograph at the Dunn Solar Telescope. We determine the shock properties (the Mach number and the propagation speed) by fitting the measured He I spectral profiles with a theoretical radiative transfer model consisting of two constant-property atmospheric slabs whose temperatures and macroscopic velocities are constrained by the Rankine-Hugoniot relations. From the Mach number, the shock heating energy per unit mass of plasma is derived to be 2 × 1010 erg g-1, which is insufficient to maintain the umbral chromosphere. In addition, we find that the shocks propagate upward with the sound speed and the Mach number does not depend on the temperature upstream of the shocks. The latter may imply suppression of the amplification of the Mach number due to energy loss of the shocks. Title: Optical Alignment of DL-NIRSP Spectrograph Authors: Jaeggli, Sarah A.; Anan, Tetsu; Kramar, Maxim; Lin, Haosheng Bibcode: 2019AAS...23410612J Altcode: The Diffraction-Limited Near-Infrared Spectropolarimeter (DL-NIRSP) will be delivered as part of the first light instrumentation for the Daniel K. Inouye Solar Telescope (DKIST) and is currently undergoing lab integration at the University of Hawai'i Institute for Astronomy's Advanced Technology Research Center on Maui. An off-axis hyperbolic mirror, with a focal length of 1250 mm, is used as both collimator and camera in the spectrograph, and makes this system particularly difficult to align. The optical axis, or vertex, of the parent surface is located approximately 260 mm from the center of the off-axis section of the mirror, but there is no direct physical or optical reference for the location and orientation of the optical axis. We have made use of vendor data and a coordinate measuring machine (CMM) arm to transfer coordinates from the back and perimeter surfaces of the mirror to locate the optical axis focus and place the other optical components in reference to this mechanical model. In coordination, we have conducted tests of the optical quality at various points during the alignment to ensure that the mechanical tolerances maintain the optical quality of the system so that the instrument will be able to achieve excellent spectral resolution limited by the spectrograph slit width (λ/Δλ 250,000), and preserve the diffraction limited spatial resolution provided by the telescope and feed optics (0.06" at 1 μm). Title: Transient dynamics and energy transfer from the photosphere to the low corona: initial results from a coordinated ALMA, DST, Hinode, IRIS, and SDO observation campaign Authors: Kobelski, Adam; Tarr, Lucas A.; Jaeggli, Sarah A.; Savage, Sabrina Bibcode: 2019AAS...23430702K Altcode: We present initial results from a coordinated observation campaign to study transient dynamics and energy transfer in the low solar atmosphere. The observations ran from approximately 2017-03-21 from 13UT to 19UT, and include data from Hinode, IRIS, DST, and ALMA. The target, a small, magnetically bipolar active area associated with a coronal bright point, was chosen for showing reasonable dynamics in the chromosphere (as dictated by AIA 304 data from the day prior), and being near disk center to better facilitate magnetic field measurement. The campaign was designed to capture the dynamics of the target with as rapid a timescale as possible for each instrument. Photospheric dynamics are available from broadband IBIS data and the HMI. New to this dataset, the chromospheric dynamics were observed in radio frequencies using ALMA (Band 3: 92-108GHz) at a 2s cadence. Additional chromospheric data are spectral H-α from the IBIS instrument at the DST, spectropolarimetic HeI 10830 from the FIRS instrument at the DST, and the medium linelist from IRIS; coronal data includes imaging from XRT and spectral data from EIS. In this first set of results, we discuss the frequency of transient brightenings observed in each set of imaging data and how the spatial distribution relates across each data channel and to the regions magnetic topology. Title: Shock heating energy in an umbra of a sunspot with integral field unit spectroscopy Authors: Anan, Tetsu; Schad, Thomas A.; Jaeggli, Sarah A.; Tarr, Lucas A. Bibcode: 2019AAS...23421705A Altcode: On 2014 December 7 we used new integral field spectroscopy techniques to observe umbral flashes, which are periodic brightness increases routinely observed in the core of chromospheric lines within sunspot umbrae and are attributed to propagating shock fronts. In this work we quantify the shock heating energy of these umbral flashes using observations in the near infrared HeI triplet obtained with the SpectroPolarimetric Imager for the Energetic Sun (SPIES), which is novel integral field unit spectrograph at the Dunn Solar Telescope. We determine the shock properties (the Mach number and the propagation speed) by fitting the measured HeI spectral profiles with a theoretical radiative transfer model using two constant property atmospheric slabs whose temperatures and macroscopic velocities are constrained by the Rankine-Hugoniot relations. From the Mach number, the shock heating energy per unit mass of plasma is derived as 2 x 1010 erg/g. We conclude that the estimated shock heating energy rate is less than the amount required to maintain the umbral chromosphere. Title: Shock Heating Energy in an umbra of a sunspot Authors: Anan, Tetsu; Schad, Tom; Jaeggli, Sarah Bibcode: 2019EGUGA..2113543A Altcode: In December 7, 2014, umbral flashes, which are periodic brightness increases in chromospheric spectral lines of the umbrae due to shocks, were observed in near infrared He I triplet with an integral-field-unit spectrometer, SPIES (SpectroPolarimetric Imager for the Energetic Sun) on the Dunn Solar Telescope with a cadence of 14 seconds. The SPIES is a prototype instruments of a facility instrument of the Daniel K. Inouye Solar Telescope. In order to determine Mach number at upstream of shock waves, we fit the measured spectral profiles in the He I 1083 nm triplet with theoretical profiles computed with a radiative transfer equation using an atmospheric model based on two constant property slabs, of which temperatures and macroscopic velocities are constrained by the Rankine-Hugoniot relations. From the Mach number and the temperature, shock heating energy per unit mass of plasma is derived as 2.0 x 10 ^ {10} erg/g. Finding a positive correlation between a spatial variation of the chromospheric temperature and shock speed, we concluded that prominent heating mechanism can be related with the shock, although estimated shock heating energy rate is less than the required amount of energy to maintain the umbral chromosphere. Title: VizieR Online Data Catalog: UV spectrum of molecular hydrogen in the Sun (Jaeggli+, 2018) Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N. Bibcode: 2019yCat..18550134J Altcode: Ultraviolet (UV) lines of molecular hydrogen have been observed in solar spectra for almost four decades, but the behavior of the molecular spectrum and its implications for solar atmospheric structure are not fully understood. Data from the High-Resolution Telescope Spectrometer (HRTS) instrument revealed that H2 emission forms in particular regions, selectively excited by a bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models, sampling a broad range of temperature stratifications and radiation conditions. Stratification plays the dominant role in determining the population densities of H2, which forms in greatest abundance near the continuum photosphere. However, opacity due to the photoionization of Si and other neutrals determines the depth to which UV radiation can penetrate to excite the H2. Thus the majority of H2 emission forms in a narrow region, at about 650km in standard one-dimensional (1D) models of the quiet Sun, near the {tau}=1 opacity surface for the exciting UV radiation, generally coming from above. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can be satisfactorily reproduced in 1D stratified atmospheres, without including three-dimensional or time-dependent thermal structures. A detailed comparison to observations from 1205 to 1550Å is presented, and the success of this 1D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels in HRTS spectra.
(3 data files). Title: Instrument Calibration of the Interface Region Imaging Spectrograph (IRIS) Mission Authors: Wülser, J. -P.; Jaeggli, S.; De Pontieu, B.; Tarbell, T.; Boerner, P.; Freeland, S.; Liu, W.; Timmons, R.; Brannon, S.; Kankelborg, C.; Madsen, C.; McKillop, S.; Prchlik, J.; Saar, S.; Schanche, N.; Testa, P.; Bryans, P.; Wiesmann, M. Bibcode: 2018SoPh..293..149W Altcode: The Interface Region Imaging Spectrograph (IRIS) is a NASA small explorer mission that provides high-resolution spectra and images of the Sun in the 133 - 141 nm and 278 - 283 nm wavelength bands. The IRIS data are archived in calibrated form and made available to the public within seven days of observing. The calibrations applied to the data include dark correction, scattered light and background correction, flat fielding, geometric distortion correction, and wavelength calibration. In addition, the IRIS team has calibrated the IRIS absolute throughput as a function of wavelength and has been tracking throughput changes over the course of the mission. As a resource for the IRIS data user, this article describes the details of these calibrations as they have evolved over the first few years of the mission. References to online documentation provide access to additional information and future updates. Title: Predictions of DKIST/DL-NIRSP Observations for an Off-limb Kink-unstable Coronal Loop Authors: Snow, B.; Botha, G. J. J.; Scullion, E.; McLaughlin, J. A.; Young, P. R.; Jaeggli, S. A. Bibcode: 2018ApJ...863..172S Altcode: 2018arXiv180704972S Synthetic intensity maps are generated from a 3D kink-unstable flux rope simulation using several DKIST/DL-NIRSP spectral lines to make a prediction of the observational signatures of energy transport and release. The reconstructed large field-of-view intensity mosaics and single tile sit-and-stare high-cadence image sequences show detailed, fine-scale structure and exhibit signatures of wave propagation, redistribution of heat, flows, and fine-scale bursts. These fine-scale bursts are present in the synthetic Doppler velocity maps and can be interpreted as evidence for small-scale magnetic reconnection at the loop boundary. The spectral lines reveal the different thermodynamic structures of the loop, with the hotter lines showing the loop interior and braiding and the cooler lines showing the radial edges of the loop. The synthetic observations of DL-NIRSP are found to preserve the radial expansion, and hence the loop radius can be measured accurately. The electron number density can be estimated using the intensity ratio of the Fe XIII lines at 10747 and 10798 Å. The estimated density from this ratio is correct to within ±10% during the later phases of the evolution; however, it is less accurate initially when line-of-sight density inhomogeneities contribute to the Fe XIII intensity, resulting in an overprediction of the density by ≈30%. The identified signatures are all above a conservative estimate for instrument noise and therefore will be detectable. In summary, we have used forward modeling to demonstrate that the coronal off-limb mode of DKIST/DL-NIRSP will be able to detect multiple independent signatures of a kink-unstable loop and observe small-scale transient features including loop braiding/twisting and small-scale reconnection events occurring at the radial edge of the loop. Title: Status of the Daniel K. Inouye Solar Telescope: unraveling the mysteries the Sun. Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini, Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich; Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt, Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka, Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin, Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team Bibcode: 2018AAS...23231601R Altcode: The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under construction on Haleakala, Maui will be the world’s largest solar telescope. Designed to meet the needs of critical high resolution and high sensitivity spectral and polarimetric observations of the sun, this facility will perform key observations of our nearest star that matters most to humankind. DKIST’s superb resolution and sensitivity will enable astronomers to address many of the fundamental problems in solar and stellar astrophysics, including the origin of stellar magnetism, the mechanisms of coronal heating and drivers of the solar wind, flares, coronal mass ejections and variability in solar and stellar output. DKIST will also address basic research aspects of Space Weather and help improve predictive capabilities. In combination with synoptic observations and theoretical modeling DKIST will unravel the many remaining mysteries of the Sun.The construction of DKIST is progressing on schedule with 80% of the facility complete. Operations are scheduled to begin early 2020. DKIST will replace the NSO facilities on Kitt Peak and Sac Peak with a national facility with worldwide unique capabilities. The design allows DKIST to operate as a coronagraph. Taking advantage of its large aperture and infrared polarimeters DKIST will be capable to routinely measure the currently illusive coronal magnetic fields. The state-of-the-art adaptive optics system provides diffraction limited imaging and the ability to resolve features approximately 20 km on the Sun. Achieving this resolution is critical for the ability to observe magnetic structures at their intrinsic, fundamental scales. Five instruments will be available at the start of operations, four of which will provide highly sensitive measurements of solar magnetic fields throughout the solar atmosphere - from the photosphere to the corona. The data from these instruments will be distributed to the world wide community via the NSO/DKIST data center located in Boulder. We present examples of science objectives and provide an overview of the facility and project status, including the ongoing efforts of the community to develop the critical science plan for the first 2-3 years of operations. Title: Solar UV Molecular Hydrogen Fluorescence Authors: Daw, Adrian Nigel; Jaeggli, Sarah Amelia; Judge, Philip G.; Roueff, Evelyne; Abgrall, Hervé Bibcode: 2018tess.conf21706D Altcode: Solar observations of ultraviolet molecular hydrogen lines indicate that H2 emission forms in particular regions, selectively excited by bright UV transition region and chromospheric lines. IRIS frequently observes numerous H2 lines during flares and smaller energetic events, but the diagnostic value of these lines for probing the structure of the solar atmosphere has heretofore remained largely unexploited. We present a synthesis method for H2 emission, using 1-D non-LTE models sampling a broad range of temperature stratifications and input radiation conditions from the atmosphere above, and compare the results to observations by IRIS, SUMER and HRTS from 1205 to 1550 Å. Because opacity due to photoionization of silicon and other neutrals determines the depth to which UV radiation can penetrate to excite the H2, the majority of H2 emission forms in a narrow region near the tau=1 opacity surface for the exciting UV radiation, generally coming from above. The success of this 1-D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels. Applications of the observed emission and implications for solar atmospheric structure are discussed. Title: Formation of the UV Spectrum of Molecular Hydrogen in the Sun Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N. Bibcode: 2018ApJ...855..134J Altcode: 2018arXiv180203779J Ultraviolet (UV) lines of molecular hydrogen have been observed in solar spectra for almost four decades, but the behavior of the molecular spectrum and its implications for solar atmospheric structure are not fully understood. Data from the High-Resolution Telescope Spectrometer (HRTS) instrument revealed that H2 emission forms in particular regions, selectively excited by a bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models, sampling a broad range of temperature stratifications and radiation conditions. Stratification plays the dominant role in determining the population densities of H2, which forms in greatest abundance near the continuum photosphere. However, opacity due to the photoionization of Si and other neutrals determines the depth to which UV radiation can penetrate to excite the H2. Thus the majority of H2 emission forms in a narrow region, at about 650 km in standard one-dimensional (1D) models of the quiet Sun, near the τ = 1 opacity surface for the exciting UV radiation, generally coming from above. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 seen in the quiet-Sun Solar Ultraviolet Measurement of Emitted Radiation atlas spectrum and HRTS light-bridge spectrum can be satisfactorily reproduced in 1D stratified atmospheres, without including three-dimensional or time-dependent thermal structures. A detailed comparison to observations from 1205 to 1550 Å is presented, and the success of this 1D approach to modeling solar UV H2 emission is illustrated by the identification of previously unidentified lines and upper levels in HRTS spectra. Title: Formation of the UV Spectrum of Molecular Hydrogen in the Sun Authors: Jaeggli, S. A.; Judge, P. G.; Daw, A. N. Bibcode: 2017AGUFMSH52B..01J Altcode: UV lines of molecular hydrogen in the Sun have been observed for almost four decades, but the behavior of the spectra and their implications for solar atmospheric structure are not fully understood. Data from the HRTS instrument revealed that H2 emission forms in particular regions, selectively excited by bright UV transition region and chromospheric lines. We test the conditions under which H2 emission can originate by studying non-LTE models with increasingly complex temperature stratification. Stratification plays the dominant role in determining the population densities of H2, which can form in abundance only within about 700 km of the continuum photosphere where 3D and dynamic structure generally play secondary roles to stratification. When irradiated from above using observed intensities of bright UV emission lines, detailed non-LTE calculations show that the spectrum of H2 can be satisfactorily modeled in 1D stratified atmospheric models, with no need to invoke unusual 3D or time dependent thermal structures. Title: Critical Infrared Science with the Daniel K. Inouye Solar Telescope Authors: Schad, Thomas A.; Fehlmann, Andre; Jaeggli, Sarah A.; Kuhn, Jeffrey Richard; Lin, Haosheng; Penn, Matthew J.; Rimmele, Thomas R.; Woeger, Friedrich Bibcode: 2017SPD....4811703S Altcode: Critical science planning for early operations of the Daniel K. Inouye Solar Telescope is underway. With its large aperture, all-reflective telescope design, and advanced instrumentation, DKIST provides unprecedented access to the important infrared (IR) solar spectrum between 1 and 5 microns. Breakthrough IR capabilities in coronal polarimetry will sense the coronal magnetic field routinely for the first time. The increased Zeeman resolution near the photospheric opacity minimum will provide our deepest and most sensitive measurement of quiet sun and active region magnetic fields to date. High-sensitivity He I triplet polarimetry will dynamically probe the chromospheric magnetic field in fibrils, spicules, and filaments, while observations of molecular CO transitions will characterize the coolest regions of the solar atmosphere. When combined with the longer timescales of good atmospheric seeing compared with the visible, DKIST infrared diagnostics are expected to be mainstays of solar physics in the DKIST era. This paper will summarize the critical science areas addressed by DKIST infrared instrumentation and invite the community to further contribute to critical infrared science planning. Title: Large Scale Coordination of Small Scale Structures Authors: Kobelski, Adam; Tarr, Lucas A.; Jaeggli, Sarah A.; Savage, Sabrina Bibcode: 2017SPD....4820005K Altcode: Transient brightenings are ubiquitous features of the solar atmosphere across many length and energy scales, the most energetic of which manifest as large-class solar flares. Often, transient brightenings originate in regions of strong magnetic activity and create strong observable enhancements across wavelengths from X-ray to radio, with notable dynamics on timescales of seconds to hours.The coronal aspects of these brightenings have often been studied by way of EUV and X-ray imaging and spectra. These events are likely driven by photospheric activity (such as flux emergence) with the coronal brightenings originating largely from chromospheric ablation (evaporation). Until recently, chromospheric and transition region observations of these events have been limited. However, new observational capabilities have become available which significantly enhance our ability to understand the bi-directional flow of energy through the chromosphere between the photosphere and the corona.We have recently obtained a unique data set with which to study this flow of energy through the chromosphere via the Interface Region Imaging Spectrograph (IRIS), Hinode EUV Imaging Spectrometer (EIS), Hinode X-Ray Telescope (XRT), Hinode Solar Optical Telescope (SOT), Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA), SDO Helioseismic and Magnetic Imager (HMI), Nuclear Spectroscopic Telescope Array (NuStar), Atacama Large Millimeter Array (ALMA), and Interferometric BIdimensional Spectropolarimeter (IBIS) at the Dunn Solar Telescope (DST). This data set targets a small active area near disk center which was tracked simultaneously for approximately four hours. Within this region, many transient brightenings detected through multiple layers of the solar atmosphere. In this study, we combine the imaging data and use the spectra from EIS and IRIS to track flows from the photosphere (HMI, SOT) through the chromosphere and transition region (AIA, IBIS, IRIS, ALMA) into the corona (EIS, XRT, AIA). Title: An Update on the Diffraction-Limited Near Infrared Spectropolarimeter for the Daniel K. Inouye Solar Telescope Authors: Jaeggli, Sarah A.; Lin, Haosheng; Onaka, Peter; McGregor, Helen; Yamada, Hubert Bibcode: 2017SPD....4811704J Altcode: DL-NIRSP is an integral field imaging spectropolarimeter for photospheric, chromospheric, and coronal magnetic field studies which is currently under development by the University of Hawaii’s Institute for Astronomy as part of the first light instrument suite for DKIST. DL-NIRSP pairs a multi-slit fiber-optic image slicer with narrow bandpass isolation filters and large format detectors to achieve very high cadence observations in three simultaneous wavelength channels in the Visible-IR. Planned diagnostics at first light include Fe XI 789.2 nm, Ca II 854.2 nm, Fe XIII 1074.7 nm, Si I/He I 1083.0 nm, Si X 1430.0 nm, and Fe I 1565.0 nm. More spectral lines will be added in the future. As the last stop in the DKIST light distribution system, DL-NIRSP will receive an AO corrected beam and will be able to operate simultaneously with the other visible light instruments. We provide an update on the current challenges and rewards yet to come with DL-NIRSP. Title: The Magnetic Classification of Solar Active Regions 1992-2015 Authors: Jaeggli, S. A.; Norton, A. A. Bibcode: 2016ApJ...820L..11J Altcode: 2016arXiv160302552J The purpose of this Letter is to address a blindspot in our knowledge of solar active region (AR) statistics. To the best of our knowledge, there are no published results showing the variation of the Mount Wilson magnetic classifications as a function of solar cycle based on modern observations. We show statistics for all ARs reported in the daily Solar Region Summary from 1992 January 1 to 2015 December 31. We find that the α and β class ARs (including all sub-groups, e.g., βγ, βδ) make up fractions of approximately 20% and 80% of the sample, respectively. This fraction is relatively constant during high levels of activity however, an increase in the α fraction to about 35% and and a decrease in the β fraction to about 65% can be seen near each solar minimum and are statistically significant at the 2σ level. Over 30% of all ARs observed during the years of solar maxima were appended with the classifications γ and/or δ, while these classifications account for only a fraction of a percent during the years near the solar minima. This variation in the AR types indicates that the formation of complex ARs may be due to the pileup of frequent emergence of magnetic flux during solar maximum, rather than the emergence of complex, monolithic flux structures. Title: Multi-wavelength Study of a Delta-spot. I. A Region of Very Strong, Horizontal Magnetic Field Authors: Jaeggli, S. A. Bibcode: 2016ApJ...818...81J Altcode: 2015arXiv151208463J Active region NOAA 11035 appeared in 2009 December, early in the new solar activity cycle. This region achieved a delta sunspot (δ spot) configuration when parasitic flux emerged near the rotationally leading magnetic polarity and traveled through the penumbra of the largest sunspot in the group. Both visible and infrared imaging spectropolarimetry of the magnetically sensitive Fe I line pairs at 6302 and 15650 Å show large Zeeman splitting in the penumbra between the parasitic umbra and the main sunspot umbra. The polarized Stokes spectra in the strongest field region display anomalous profiles, and strong blueshifts are seen in an adjacent region. Analysis of the profiles is carried out using a Milne-Eddington inversion code capable of fitting either a single magnetic component with stray light or two independent magnetic components to verify the field strength. The inversion results show that the anomalous profiles cannot be produced by the combination of two profiles with moderate magnetic fields. The largest field strengths are 3500-3800 G in close proximity to blueshifts as strong as 3.8 km s-1. The strong, nearly horizontal magnetic field seen near the polarity inversion line in this region is difficult to understand in the context of a standard model of sunspot magnetohydrostatic equilibrium. Title: The Persistence of Apparent Non-Magnetostatic Equilibrium in NOAA 11035 Authors: Jaeggli, Sarah A. Bibcode: 2015IAUS..305...35J Altcode: 2015arXiv150401325J NOAA 11035 was a highly sheared active region that appeared in December 2009 early in the new activity cycle. The leading polarity sunspot developed a highly unusual feature in its penumbra, an opposite polarity pore with a strong magnetic field in excess of 3500 G along one edge, which persisted for several days during the evolution of the region. This region was well observed by both space- and ground-based observatories, including Hinode, FIRS, TRACE, and SOHO. These observations, which span wavelength and atmospheric regimes, provide a complete picture of this unusual feature which may constitute a force-free magnetic field in the photosphere which is produced by the reconnection of magnetic loops low in the solar atmosphere. Title: A very strong magnetic field region in NOAA 11035 Authors: Jaeggli, Sarah Amelia Bibcode: 2015TESS....111304J Altcode: NOAA 11035 was a fairly typical active region that emerged near the central meridian 13-14 December 2009, early in solar cycle 24. During the active region’s rapid emergence and evolution, a deeply-rooted magnetic bipole emerged into the pre-existing leading polarity with spectacular consequences. Multi-wavelength imaging and spectropolarimetry from FIRS, IBIS, Hinode, TRACE, and SOHO allow for a comprehensive investigation of the physical processes present in this region. Intrusion of the opposite polarity into the leading sunspot’s penumbra resulted in a region of highly concentrated horizontal magnetic field, with a peak field strength larger than 3600 G based on Milne-Eddington inversion of Fe I spectropolarimetry at 6302 and 15650 Å. Photospheric velocity measurements show blueshifts of 4 km/sec along the neutral line, which are coincident with a dark chromospheric structure in He I 10830 and H I 6563 Å. We conclude that these signatures are the result of continuous magnetic reconnection near photospheric heights. Title: Internetwork Chromospheric Bright Grains Observed With IRIS and SST Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson, Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt, Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan; Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean; Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli, Sarah; Kankelborg, Charles Bibcode: 2015ApJ...803...44M Altcode: 2015arXiv150203490M The Interface Region Imaging Spectrograph (IRIS) reveals small-scale rapid brightenings in the form of bright grains all over coronal holes and the quiet Sun. These bright grains are seen with the IRIS 1330, 1400, and 2796 Å slit-jaw filters. We combine coordinated observations with IRIS and from the ground with the Swedish 1 m Solar Telescope (SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H 3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å, Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.} 33), temporal, and spectral resolution. We conclude that the IRIS slit-jaw grains are the counterpart of so-called acoustic grains, i.e., resulting from chromospheric acoustic waves in a non-magnetic environment. We compare slit-jaw images (SJIs) with spectra from the IRIS spectrograph. We conclude that the grain intensity in the 2796 Å slit-jaw filter comes from both the Mg ii k core and wings. The signal in the C ii and Si iv lines is too weak to explain the presence of grains in the 1300 and 1400 Å SJIs and we conclude that the grain signal in these passbands comes mostly from the continuum. Although weak, the characteristic shock signatures of acoustic grains can often be detected in IRIS C ii spectra. For some grains, a spectral signature can be found in IRIS Si iv. This suggests that upward propagating acoustic waves sometimes reach all the way up to the transition region. Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode and Magnetic Modeling With Data-Driven Simulations Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.; Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner, P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint, L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.; Carlsson, M.; Hansteen, V. Bibcode: 2015ApJ...801...83C Altcode: 2015arXiv150101593C We report on observations of recurrent jets by instruments on board the Interface Region Imaging Spectrograph, Solar Dynamics Observatory (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21, recurrent coronal jets were observed to emanate from NOAA Active Region 11793. Far-ultraviolet spectra probing plasma at transition region temperatures show evidence of oppositely directed flows with components reaching Doppler velocities of ±100 km s-1. Raster Doppler maps using a Si iv transition region line show all four jets to have helical motion of the same sense. Simultaneous observations of the region by SDO and Hinode show that the jets emanate from a source region comprising a pore embedded in the interior of a supergranule. The parasitic pore has opposite polarity flux compared to the surrounding network field. This leads to a spine-fan magnetic topology in the coronal field that is amenable to jet formation. Time-dependent data-driven simulations are used to investigate the underlying drivers for the jets. These numerical experiments show that the emergence of current-carrying magnetic field in the vicinity of the pore supplies the magnetic twist needed for recurrent helical jet formation. Title: The 2014 March 29 X-flare: Subarcsecond Resolution Observations of Fe XXI λ1354.1 Authors: Young, Peter R.; Tian, Hui; Jaeggli, Sarah Bibcode: 2015ApJ...799..218Y Altcode: 2014arXiv1409.8603Y The Interface Region Imaging Spectrometer (IRIS) is the first solar instrument to observe ~10 MK plasma at subarcsecond spatial resolution through imaging spectroscopy of the Fe XXI λ1354.1 forbidden line. IRIS observations of the X1 class flare that occurred on 2014 March 29 at 17:48 UT reveal Fe XXI emission from both the flare ribbons and the post-flare loop arcade. Fe XXI appears at all of the chromospheric ribbon sites, although typically with a delay of one raster (75 s) and sometimes offset by up to 1''. 100-200 km s-1 blue-shifts are found at the brightest ribbons, suggesting hot plasma upflow into the corona. The Fe XXI ribbon emission is compact with a spatial extent of <2'', and can extend beyond the chromospheric ribbon locations. Examples are found of both decreasing and increasing blue-shift in the direction away from the ribbon locations, and blue-shifts were present for at least six minutes after the flare peak. The post-flare loop arcade, seen in Atmospheric Imaging Assembly 131 Å filtergram images that are dominated by Fe XXI, exhibited bright loop-tops with an asymmetric intensity distribution. The sizes of the loop-tops are resolved by IRIS at >=1'', and line widths in the loop-tops are not broader than in the loop-legs suggesting the loop-tops are not sites of enhanced turbulence. Line-of-sight speeds in the loop arcade are typically <10 km s-1, and mean non-thermal motions fall from 43 km s-1 at the flare peak to 26 km s-1 six minutes later. If the average velocity in the loop arcade is assumed to be at rest, then it implies a new reference wavelength for the Fe XXI line of 1354.106 ± 0.023 Å. Title: Venus' thermospheric temperature field using a refraction model at terminator : comparison with 2012 transit observations using SDO/HMI, VEx/SPICAV/SOIR and NSO/DST/FIRS Authors: Widemann, Thomas; Jaeggli, Sarah; Reardon, Kevin; Tanga, Paolo; Père, Christophe; Pasachoff, Jay M.; Vandaele, Ann Carine; Wilquet, Valerie; Mahieux, Arnaud; Wilson, Colin Bibcode: 2014DPS....4630206W Altcode: The transit of Venus in June 2012 provided a unique case study of the Venus' atmosphere transiting in front of the Sun, while at the same time ESA's Venus Express orbiter observed the evening terminator at solar ingress and solar egress.We report on mesospheric temperature at Venus' morning terminator using SDO/HMI aureole photometry and comparison with Venus Express. Close to ingress and egress phases, we have shown that the aureole photometry reflects the local density scale height and the altitude of the refracting layer (Tanga et al. 2012). The lightcurve of each spatially resolved aureole element is fit to a two-parameter model to constrain the meridional temperature gradient at terminator. Our measurements are in agreement with the VEx/SOIR temperatures obtained during orbit 2238 at evening terminator during solar ingress (46.75N - LST = 6.075PM) and solar egress (31.30N - LST = 6.047PM) captured from the Venus Express orbiter at the time Venus transited the Sun.We also performed spectroscopy and polarimetry during the transit of Venus focusing on extracting signatures of CO2 absorption. Observations were taken during the first half of the transit using the Facility InfraRed Spectropolarimeter (FIRS) on the Dunn Solar Telescope (DST). Although the predicted CO2 transmission spectrum of Venus was not particularly strong at 1565 nm, this region of the H-band often used in magnetic field studies of the Sun's photosphere provides a particularly flat solar continuum with few atmospheric lines. Sun-subtracted Venus limb observations show intensity distribution of vibrational CO2 bands 221 2v+2v2+v3 at 1.571μm and 141 v1+4v2+v3 at 1.606μm. Title: Hot explosions in the cool atmosphere of the Sun Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.; De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint, L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V. Bibcode: 2014Sci...346C.315P Altcode: 2014arXiv1410.5842P The solar atmosphere was traditionally represented with a simple one-dimensional model. Over the past few decades, this paradigm shifted for the chromosphere and corona that constitute the outer atmosphere, which is now considered a dynamic structured envelope. Recent observations by the Interface Region Imaging Spectrograph (IRIS) reveal that it is difficult to determine what is up and down, even in the cool 6000-kelvin photosphere just above the solar surface: This region hosts pockets of hot plasma transiently heated to almost 100,000 kelvin. The energy to heat and accelerate the plasma requires a considerable fraction of the energy from flares, the largest solar disruptions. These IRIS observations not only confirm that the photosphere is more complex than conventionally thought, but also provide insight into the energy conversion in the process of magnetic reconnection. Title: The unresolved fine structure resolved: IRIS observations of the solar transition region Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira, T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.; Martínez-Sykora, J. Bibcode: 2014Sci...346E.315H Altcode: 2014arXiv1412.3611H The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long-standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low-lying loops or loop segments at transition-region temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a long-standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle. Title: Evidence of nonthermal particles in coronal loops heated impulsively by nanoflares Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale, F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli, S. Bibcode: 2014Sci...346B.315T Altcode: 2014arXiv1410.6130T The physical processes causing energy exchange between the Sun’s hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High-resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60 seconds) of intensity and velocity on small spatial scales (≲500 kilometers) at the footpoints of hot and dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of nonthermal electrons, which are generated in small impulsive (≲30 seconds) heating events called “coronal nanoflares.” The accelerated electrons deposit a sizable fraction of their energy (≲1025 erg) in the chromosphere and TR. Our analysis provides tight constraints on the properties of such electron beams and new diagnostics for their presence in the nonflaring corona. Title: Prevalence of small-scale jets from the networks of the solar transition region and chromosphere Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.; Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves, K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber, M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W. Bibcode: 2014Sci...346A.315T Altcode: 2014arXiv1410.6143T As the interface between the Sun’s photosphere and corona, the chromosphere and transition region play a key role in the formation and acceleration of the solar wind. Observations from the Interface Region Imaging Spectrograph reveal the prevalence of intermittent small-scale jets with speeds of 80 to 250 kilometers per second from the narrow bright network lanes of this interface region. These jets have lifetimes of 20 to 80 seconds and widths of ≤300 kilometers. They originate from small-scale bright regions, often preceded by footpoint brightenings and accompanied by transverse waves with amplitudes of ~20 kilometers per second. Many jets reach temperatures of at least ~105 kelvin and constitute an important element of the transition region structures. They are likely an intermittent but persistent source of mass and energy for the solar wind. Title: On the prevalence of small-scale twist in the solar chromosphere and transition region Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.; Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.; Martinez-Sykora, J. Bibcode: 2014Sci...346D.315D Altcode: 2014arXiv1410.6862D The solar chromosphere and transition region (TR) form an interface between the Sun’s surface and its hot outer atmosphere. There, most of the nonthermal energy that powers the solar atmosphere is transformed into heat, although the detailed mechanism remains elusive. High-resolution (0.33-arc second) observations with NASA’s Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere and TR that are replete with twist or torsional motions on sub-arc second scales, occurring in active regions, quiet Sun regions, and coronal holes alike. We coordinated observations with the Swedish 1-meter Solar Telescope (SST) to quantify these twisting motions and their association with rapid heating to at least TR temperatures. This view of the interface region provides insight into what heats the low solar atmosphere. Title: An Interface Region Imaging Spectrograph First View on Solar Spicules Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen, V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli, S.; Kankelborg, C. Bibcode: 2014ApJ...792L..15P Altcode: 2014arXiv1407.6360P Solar spicules have eluded modelers and observers for decades. Since the discovery of the more energetic type II, spicules have become a heated topic but their contribution to the energy balance of the low solar atmosphere remains unknown. Here we give a first glimpse of what quiet-Sun spicules look like when observed with NASA's recently launched Interface Region Imaging Spectrograph (IRIS). Using IRIS spectra and filtergrams that sample the chromosphere and transition region, we compare the properties and evolution of spicules as observed in a coordinated campaign with Hinode and the Atmospheric Imaging Assembly. Our IRIS observations allow us to follow the thermal evolution of type II spicules and finally confirm that the fading of Ca II H spicules appears to be caused by rapid heating to higher temperatures. The IRIS spicules do not fade but continue evolving, reaching higher and falling back down after 500-800 s. Ca II H type II spicules are thus the initial stages of violent and hotter events that mostly remain invisible in Ca II H filtergrams. These events have very different properties from type I spicules, which show lower velocities and no fading from chromospheric passbands. The IRIS spectra of spicules show the same signature as their proposed disk counterparts, reinforcing earlier work. Spectroheliograms from spectral rasters also confirm that quiet-Sun spicules originate in bushes from the magnetic network. Our results suggest that type II spicules are indeed the site of vigorous heating (to at least transition region temperatures) along extensive parts of the upward moving spicular plasma. Title: Molecular absorption in transition region spectral lines Authors: Schmit, D. J.; Innes, D.; Ayres, T.; Peter, H.; Curdt, W.; Jaeggli, S. Bibcode: 2014A&A...569L...7S Altcode: 2014arXiv1409.1702S