Sonntag, 15. Februar 2015 - 11:15 Uhr
Science Cases for DKIST
Spectral vs. Spatial Diagnostics The Sun sustains life on Earth and impacts human endeavors in space through variations in its radiative, magnetic and particle output as caused by magnetic activity. The solar atmosphere is controlled by magnetic fields. The Daniel K. Inouye Solar Telescope (DKIST) is the first major instrument designed by the astronomical community in all of its aspects as a tool for magnetic remote sensing. Its collecting area, spatial resolution, wavelength performance and integral focal plane instrumentation are all targeted for understanding how magnetic fields affect the physical properties of the Sun. DKIST will be the largest leap in ground-based solar capabilities since Galileo's telescope.
DKIST will be a four-meter off-axis reflecting telescope, which will have the spatial, temporal, spectral resolution and dynamic range that is needed to see and measure the basic magnetic structures (magnetic fibrils) at the solar surface and into the outer atmosphere. Currently much of the magnetic field is invisible. We therefore will depend on the DKIST for quantifying, understanding, and predicting the consequences of such magnetism on solar-terrestrial and astrophysical plasmas.
The DKIST addresses the basic questions: What is the nature of solar magnetism; how does that magnetism control our star; and how can we model and predict its changing outputs that affect the Earth? DKIST will observe solar plasma processes and magnetic fields with unprecedented resolution in space and time. It will provide critical information needed to solve the mysteries associated with the generation, structure, and dynamics of the surface magnetic fields, which govern the solar wind, solar flares, and short-term solar variability. Used in combination with space-based and other ground-based solar observing assets, DKIST will underpin a revolution in our understanding of the sun.
The following pages provide short descriptions of just some of the critical science topics scientists will use the DKIST to address and solve.
Flux Tubes: The Building Blocks of Solar and Stellar Magnetic Fields
Solar Granulation Observations have established that the photospheric magnetic field is organized in small fibrils or flux tubes (associated with the bright g-band points seen in the photo). These structures are mostly unresolved by current telescopes. Flux tubes are the most likely channels for transporting energy into the upper atmosphere, which is the source of UV and X-ray radiation from the Sun, which in turn affects the Earth's atmosphere. Detailed observations of these fundamental building blocks of stellar magnetic fields are crucial for our understanding not only of the activity and heating of the outer atmospheres of late-type stars, but also of other astrophysical situations such as the accretion disks of compact objects, or proto-planetary environments. The diffraction limited resolution of DKIST will be 0."03 at 500nm and 0."08 at 1.6 microns. At this resolution DKIST will provide the required spectroscopy and polarimetry at an angular resolution to explore the enigmatic flux tube structures.
Magnetic Field Generation, Local Dynamos and the Solar Cycle
Small Scale Dynamo To understand solar activity and solar variability, we need to understand how magnetic fields are generated and how they are destroyed. The 11-year sunspot cycle and the corresponding 22-year magnetic cycle are still shrouded in mystery. Global dynamo models that attempt to explain large-scale solar magnetic fields are based on mean field theories. Dynamo action of a more turbulent nature in the convection zone may be an essential ingredient to a complete solar dynamo model. Local dynamos may produce the small-scale magnetic flux tubes recently observed to cover the entire Sun. This "magnetic carpet" continually renews itself on a time scale of a few days at most and its flux may be comparable to that in active regions. The DKIST will make it possible to directly observe such local dynamo action at the surface of the Sun. The DKIST will measure the turbulent vorticity and the diffusion of small-scale magnetic fields and determine how they evolve with the solar cycle. The DKIST will address the following fundamental questions: How do strong fields and weak fields interact? How are both generated? How do they disappear? Does the weak-field component have global importance and what is its significance for the solar cycle? The DKIST will address these fundamental questions by resolving individual magnetic flux tubes and observing their emergence and dynamics. It will measure distribution functions of field strength, field direction and flux tube sizes and compare these with theoretical models. The DKIST will observe plasma motions and relate them to the flux tube dynamics.
Magnetic and Current Helicity and its Relevance to the Dynamo Problem
Twisted Magnetic Fields Helicity plays a fundamental role in evolution and topology of solar magnetic fields on different spatial and temporal scales. Helicity is essential for the effective operation of a dynamo. On the other hand, excessive helicity may suppress the dynamo action. To ensure efficient operation of the dynamo, helicity has to be removed from the dynamo region and transported to the coronal. On their way to the surface magnetic fields can accumulate addition helicity by interacting with turbulence in the convection zone.
Interaction of Magnetic Fields and Mass Flows
Sunspot Fine StructuresIn sunspots, the total magnetic field is large enough to completely dominate the hydrodynamic behavior of the local gas, a regime very different from that of the rest of the solar photosphere. Numerical simulations and theoretical models predict dynamical phenomena, such as oscillatory convection in the strong-field regions of sunspot umbrae, flows at the speed of sound along penumbral filaments and oscillations and wave phenomena. To verify the predictions of numerical simulations of sunspots and ultimately answer such fundamental questions as "Why do sunspots exist?" require an extremely capable instrument. High-resolution (<0.1 arcsec) vector polarimetry combined with high sensitivity (requires high photon flux) and low-scattering optics are required. Understanding the interaction of magnetic flux and mass flows is crucial for our understanding of the behavior of magnetic fields from the scales of planetary magnetospheres, to star-forming regions, to supernova remnants, to clusters of galaxies. Sunspots allow us to test those theories in a regime where magnetic fields dominate mass flows.
Flares and Mass Ejections
H-alpha FlareIt is commonly believed that solar flares represent a process of rapid transformation of the magnetic energy of active regions into the kinetic energy of energetic particles and plasma flows and heat. Detection of variations of magnetic field associated with solar flares has been one of the most important problems of solar physics for many years. Such detection would provide direct evidence of magnetic energy release in the flares. An important goal for the DKIST will be to study the small-scale processes in solar flares. The DKIST will also provide a new set of tools, in particular in the infrared, to measure magnetic fields at higher layers of the atmosphere. There is limited observational evidence that the distribution of electric currents and current helicity inside an active region varies with flares. Highly uniform sequences of high-resolution vector magnetograms of an active region before and after a flare are required to address this important issue.
Coronal mass ejections (CMEs) originate in large-scale magnetic arcades known as helmet streamers. These structures are known to contain twisted magnetic fields. According to the prevailing view, the arcade becomes dynamically unstable when its fields are twisted beyond some critical point. Field line footpoint motions in the photosphere have long been considered efficient ways to supply (or drain) magnetic shear and energy into (from) the coronal field. MHD simulations have identified critical magnetic shear conditions above which the arcade field will form current sheets, and magnetic reconnection processes will occur to cause active phenomena such as flares, CMEs, and prominence formation and eruption. It is thus important to measure field line footpoint motions and, if possible, the magnetic shear in active regions as well. Although measurements of the footpoint motion (in particular the horizontal plasma flow velocity) have improved considerably, the DKIST will offer unprecedented high spatial and temporal resolution in measuring the field line footpoint motion.
More recently this view has been challenged by models in which the arcade emerges as a twisted flux rope or models in which small-scale photospheric reconnection events inject helicity into the corona. These hypothesized reconnection events occur when small (0."1) photospheric flux elements cancel along the active region's magnetic neutral line. This model seems to contradict those models in which CMEs result from excessive twist in the arcade. Detailed observations of the flux emergence can reveal whether the emerging flux is introducing magnetic twist into the arcade, or changing the arcade's topology through footpoint cancellation. Only with higher spatial resolution vector measurements and good temporal resolution as will be provided by the DKIST, however, can it be established, for example, that the rate and orientation of these cancellations is consistent with an observed change in the twist of the overlying arcade. Such observations are critical to distinguishing between competing models.
Inhomogeneous Stellar Atmospheres
Limb Spectrum of Solar CO LinesMeasurements of CO absorption spectra near 4.7µm show surprisingly cool clouds that appear to occupy much of the low chromosphere. Only a small fraction of the volume apparently is filled with hot gas, contrary to classical static models that exhibit a sharp temperature rise in those layers. The observed spectra can be explained by a new class of dynamic models of the solar atmosphere. However, the numerical simulations indicate that the temperature structures occur on spatial scales that cannot be resolved with current solar infrared telescopes. A test of the recent models requires a large-aperture solar telescope that provides access to the thermal infrared. Such observations would further explore the dynamical basis of the thermal bifurcation process, a fundamental source of atmospheric inhomogeneities in late-type stars. Spicules, the forest of hot jets that penetrate from the photosphere into the chromosphere, are clearly a MHD phenomenon that is not understood nor adequately modeled. Their role in the mass balance of the atmosphere is uncertain. Combined with UV observations (like those of TRACE), the DKIST will allow us to resolve their nature.
Magnetic Fields and Stellar Coronae
Coronal LoopsThe origin and heating of the solar corona, and the coronae of late-type stars, are still mysteries. Most of the proposed scenarios are based on dynamic magnetic fields rooted at the 0.1-arcsec scale in the photosphere. However, none of the processes has been clearly identified by observations or theory. EUV and X-ray observations have gained in importance, but ground-based observations are still critical, not only to determine the forcing of the coronal fields by photospheric motions, but also for the measurement of the coronal magnetic field strength itself. This is important for developing and testing models of flares and coronal mass ejections, which propel magnetic field and plasma into inter-planetary space and induce geomagnetic disturbances. In particular, precise measurements of the coronal magnetic field strength and topology are needed in order to distinguish between different theoretical models. The DKIST with its large aperture, low scattered light characteristics, and the capability to exploit the solar infrared spectrum will provide these critical measurements.
Northumbria to help build world’s biggest solar telescope in £220 million project
Experts from Northumbria University, Newcastle are taking part in an international project to build the world’s biggest and most revolutionary solar telescope.
The $344 million (£220m) Daniel K Inouye Solar Telescope, to be known as DKIST, will be situated on Haleakala Mountain in Maui, Hawaii, and aims to unlock the secrets of the Sun. With a four-metre diameter primary mirror, the super-telescope will be able to pick up unprecedented detail on the Sun’s surface – the equivalent of being able to examine a £1 coin from a distance of 100km. It is hoped that DKIST will address fundamental questions at the core of contemporary solar physics. This will be achieved via high-speed spectroscopic and magnetic measurements of the solar photosphere, chromosphere and corona.
Northumbria’s Solar Physics research group will play a lead role in developing software to understand data from the telescope. Dr Richard Morton, Leverhulme Trust Early Career Research Fellow in the Department of Mathematics and Information Sciences, is the project lead at Northumbria.
He said: “DKIST is an exciting project that will revolutionise our understanding of the Sun and how it influences our lives. The Solar Physics research group at Northumbria will develop software to probe data from DKIST, providing key insight into the physical mechanisms responsible for energy transfer in the Sun's atmosphere and how this relates to solar variability and the generation of space weather, including solar flares, which can be hazardous to our technologically-advanced society.”
Northumbria University’s Pro Vice-Chancellor for Research and Innovation, Professor George Marston, said: “We are delighted to be one of eight UK universities helping to support the construction of the world’s most powerful solar telescope. Northumbria’s role in this international project clearly demonstrates the University’s ongoing commitment to driving scientific breakthroughs and technological innovation through the excellence of our world-class research and the expertise of our academics.” Professor Marston, who spent two years as a Resident Research Associate at NASA Goddard Space Flight Center near Washington DC, added: “The DKIST will address fundamental questions in contemporary solar physics; in addition, solar activity drives ‘space weather’ and has profound effects on Earth’s climate and global communications, highlighting the relevance of the research to important societal issues.”
Eight UK institutes will be working as a consortium on DKIST. The project is led by Queen's University Belfast and includes Armagh Observatory, Northumbria University, University College London, and the Universities of Glasgow, Sheffield, St. Andrews and Warwick. The consortium will partner with Belfast-based company and Queen’s University spinout Andor Technology and the Science and Technology Facilities Council. It will oversee the development and delivery of the cameras, and take the lead in supporting the UK solar physics community in their use of DKIST by providing a set of processing tools for DKIST data, synthetic observations to validate diagnostic approaches, and support for developing observing proposals. DKIST is funded by the US National Science Foundation with £2.5m of funding for the cameras provided by the Science and Technology Facilities Council.Northumbria recently launched its Think Physics project to inspire more young people, especially girls and under-represented groups, to engage with Science, Technology, Engineering and Mathematics (STEM) from Early Years to Higher Education and into their careers. The University also recently announced an investment of £6.7 million in STEM facilities, co-funded by the Higher Education Funding Council for England (HEFCE), to help drive world-class research and teaching across STEM disciplines, and an increased flow of highly-employable graduates into industry. Northumbria University provides undergraduate and postgraduate courses in Physics and Physics with Astrophysics.
World’s biggest solar telescope to be built with Sheffield expertise
• New telescope will provide unprecedented insight into physics of the surface and atmosphere of the Sun
• A consortium of universities, including Sheffield, are building cameras for the ‘super telescope’ based in Hawaii
• Sheffield scientists will help UK solar physics community access facility
• Telescope will improve the forecasting of space weather hazards
The world’s biggest and most revolutionary solar telescope is being built with the help of researchers from the University of Sheffield.
Led by Queens University Belfast, the Sheffield team is building cameras for the £344 million super telescope which will be situated in Hawaii.
The Daniel K Inouye Solar Telescope (DKIST), which will be launched in 2019, is being constructed by the US National Solar Observatory on Haleakala mountain in Maui, Hawaii. With a four-metre diameter primary mirror, the telescope will be able to pick up unprecedented detail on the surface of the Sun – the equivalent of being able to examine a £1 coin from 100kms away.
It is hoped that DKIST will address fundamental questions at the core of contemporary solar physics via high-speed (sub-second timescales) spectroscopic and magnetic measurements of the solar photosphere, chromosphere and corona – the different layers of the Sun’s atmosphere. The project will be mainly funded by the US National Science Foundation.
Professor Michail Balikhin from the University of Sheffield said: “The development of this telescope provides great potential for us to make earlier forecasts of space weather hazards, such as identifying solar winds which can cause huge disruption to life on Earth.
Our Space System Laboratory in Sheffield has a well-established track record in space weather forecasting using a spacecraft situated about 1.5 million km from our planet. At the moment this enables us to identify space weather, such as solar wind velocities, approximately one hour before they reach Earth, but once this telescope is built we may be able to significantly extend this time.”
Dr Viktor Fedun from the University’s Solar Wave Theory Group added: “The new high-resolution cameras used by the telescope will provide an unprecedented amount of solar image data. Researchers at Sheffield will use their leading expertise in numerical modelling of plasma processes to develop new algorithms and numerical techniques to process the data observed from the new telescope which will be really impactful to the UK science community and beyond.”
Professor Robertus von Fay-Siebenburgen (a.k.a Erdelyi), Head of SP2RC (Solar Physics and Space Plasma Research Centre) at the University of Sheffield, said: “This is a fantastic opportunity to significantly improve the forecasting of Space Weather. In 1989 a particularly large amount of energetic solar plasma material was ejected from the Sun towards the Earth, which damaged satellites and electrical transmission facilities, as well as caused disruption to communications systems. The understanding and prediction of space weather is vitally important in the age of human exploration of the Solar System and the development of this new telescope will enable us to predict space weather events much earlier.
“It’s also a great facility for early career scientists in the UK and will pave the way for Sheffield to remain at the forefront of solar plasma research.”
The consortium will oversee the development and delivery of the cameras, and take the lead in supporting the UK solar physics community in their use of DKIST by providing a set of processing tools for DKIST data, synthetic observations to validate diagnostic approaches, and support for developing observing proposals.
Quelle: The University of Sheffield