The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field images of the corona and transition region on the solar disc and up to 1.5 R⊙ above the solar limb. Its normal incidence multilayer-coated optics will select spectral emission lines from Fe IX (171 A), Fe XII (195 A), Fe XV (284 A), and He II (304 A) to provide sensitive temperature diagnostics in the range from 6 × 104 K to 3 × 10 6 K. The telescope has a 45×45 arcmin field of view and 2.6 arcsec pixels which will provide approximately 5-arcsec spatial resolution. The EIT will probe the coronal plasma on a global scale, as well as the underlying cooler and turbulent atmosphere, providing the basis for comparative analyses with observations from both the ground and other SOHO instruments. This paper presents details of the EIT instrumentation, its performance and operating modes.

/pdf/eit-extreme-ultraviolet-imaging-telescope-for-the-soho-1nryma0pvk.pdf

EIT: Extreme-UltraViolet Imaging Telescope for the SOHO Mission

We compute in detail the rate at which energy injected by dark matter (DM) annihilation heats and ionizes the photon-baryon plasma at z{approx}1000, and provide accurate fitting functions over the relevant redshift range for a broad array of annihilation channels and DM masses. The resulting perturbations to the ionization history can be constrained by measurements of the CMB temperature and polarization angular power spectra. We show that models which fit recently measured excesses in 10-1000 GeV electron and positron cosmic rays are already close to the 95% confidence limits from WMAP. The recently launched Planck satellite will be capable of ruling out a wide range of DM explanations for these excesses. In models of dark matter with Sommerfeld-enhanced annihilation, where rises with decreasing WIMP velocity until some saturation point, the WMAP5 constraints imply that the enhancement must be close to saturation in the neighborhood of the Earth.

CMB constraints on WIMP annihilation: Energy absorption during the recombination epoch

Intergalactic space is filled with a pervasive medium of ionized gas, the intergalactic medium (IGM). A residual neutral fraction is detected in the spectra of quasistellar objects at both low and high redshifts, revealing a highly fluctuating medium with temperatures characteristic of photoionized gas. The statistics of the fluctuations are well reproduced by numerical gravity-hydrodynamics simulations within the context of standard cosmological structure formation scenarios. Thus, the study of the IGM offers an opportunity to probe the nature of the primordial density fluctuations on scales unavailable to other methods. The simulations also suggest that the IGM is the dominant reservoir of baryons produced by the Big Bang, and so the principal source of the matter from which galaxies formed. The detection of metal systems within the IGM shows that it was enriched by evolved stars early in its history, demonstrating an intimate connection between galaxy formation and the IGM. A comprehensive review of the current understanding of the structure and physical properties of the IGM and its relation to galaxies is presented, concluding with comments on prospects for furthering the study of the IGM using future ground-based facilities and space-based experiments.

/pdf/the-physics-of-the-intergalactic-medium-5d1z4a29rm.pdf

The physics of the intergalactic medium

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.

/pdf/hot-explosions-in-the-cool-atmosphere-of-the-sun-7eycl5p10t.pdf

Hot explosions in the cool atmosphere of the Sun.

X-ray and ultraviolet (UV) observations of the outer solar atmosphere have been used for many decades to measure the fundamental parameters of the solar plasma. This review focuses on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths, and discusses some of the diagnostic methods that have been used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances. We mainly focus on methods and results obtained from high-resolution spectroscopy, rather than broad-band imaging. However, we note that the best results are often obtained by combining imaging and spectroscopic observations. We also mainly focus the review on measurements of electron densities and temperatures obtained from single ion diagnostics, to avoid issues related to the ionisation state of the plasma. We start the review with a short historical introduction on the main XUV high-resolution spectrometers, then review the basics of optically thin emission and the main processes that affect the formation of a spectral line. We mainly discuss plasma in equilibrium, but briefly mention non-equilibrium ionisation and non-thermal electron distributions. We also summarise the status of atomic data, which are an essential part of the diagnostic process. We then review the methods used to measure electron densities, electron temperatures, the DEM, and relative chemical abundances, and the results obtained for the lower solar atmosphere (within a fraction of the solar radii), for coronal holes, the quiet Sun, active regions and flares.

/pdf/solar-uv-and-x-ray-spectral-diagnostics-38biavagbr.pdf

Solar UV and X-ray spectral diagnostics

We present a new evaluation of the ionization and recombination rates by electronic collision for astrophysically abundant elements. Our approach of the ionization rates relies on forty-two measured cross sections and on quantum mechanical calculations using the Coulomb-Born or distorted wave with exchange approximations. The direct ionization process and the excitation autoionization contribution, apparent in cross-sections of some sequences (Li-like, Na-like...) are separately estimated. We present a critical review of the dielectronic and radiative recombination rates and make some additions to existing compilations. All the material necessary to compute these rates (direct ionization, excitation autoionization, recombination) is given in tabular form or in appendices. We determine the equilibrium ionization of elements H, He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, Ni and discuss differences with previous calculations.

An updated evaluation of recombination and ionization rates. Commentary

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An updated evaluation of recombination and ionization rates. Commentary