The Atmospheric Imaging Assembly (AIA) provides multiple simultaneous high-resolution full-disk images of the corona and transition region up to 0.5 R ⊙ above the solar limb with 1.5-arcsec spatial resolution and 12-second temporal resolution. The AIA consists of four telescopes that employ normal-incidence, multilayer-coated optics to provide narrow-band imaging of seven extreme ultraviolet (EUV) band passes centered on specific lines: Fe xviii (94 A), Fe viii, xxi (131 A), Fe ix (171 A), Fe xii, xxiv (193 A), Fe xiv (211 A), He ii (304 A), and Fe xvi (335 A). One telescope observes C iv (near 1600 A) and the nearby continuum (1700 A) and has a filter that observes in the visible to enable coalignment with images from other telescopes. The temperature diagnostics of the EUV emissions cover the range from 6×104 K to 2×107 K. The AIA was launched as a part of NASA’s Solar Dynamics Observatory (SDO) mission on 11 February 2010. AIA will advance our understanding of the mechanisms of solar variability and of how the Sun’s energy is stored and released into the heliosphere and geospace.

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The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO)

We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution.

Standard Solar Composition

The Solar Optical Telescope (SOT) aboard the Hinode satellite (formerly called Solar-B) consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP). The OTA is a 50-cm diffraction-limited Gregorian telescope, and the FPP includes the narrowband filtergraph (NFI) and the broadband filtergraph (BFI), plus the Stokes Spectro-Polarimeter (SP). The SOT provides unprecedented high-resolution photometric and vector magnetic images of the photosphere and chromosphere with a very stable point spread function and is equipped with an image-stabilization system with performance better than 0.01 arcsec rms. Together with the other two instruments on Hinode (the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer (EIS)), the SOT is poised to address many fundamental questions about solar magnetohydrodynamics. This paper provides an overview; the details of the instrument are presented in a series of companion papers.

https://opensky.ucar.edu/islandora/object/articles%3A6218/datastream/PDF/view

The Solar Optical Telescope for the Hinode Mission: An Overview

The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 – 0.4 arcsec spatial resolution, two-second temporal resolution, and 1 km s−1 velocity resolution over a field-of-view of up to 175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332 – 1358 A, 1389 – 1407 A, and 2783 – 2834 A, including bright spectral lines formed in the chromosphere (Mg ii h 2803 A and Mg ii k 2796 A) and transition region (C ii 1334/1335 A and Si iv 1394/1403 A). Slit-jaw images in four different passbands (C ii 1330, Si iv 1400, Mg ii k 2796, and Mg ii wing 2830 A) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec × 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative–MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.

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The Interface Region Imaging Spectrograph (IRIS)

The photospheric-to-coronal iron abundance from X-ray lines observed by Yohkoh and other satellites

We present a study of the differential emission measure (DEM) of a `quiet Sun' area observed in the extreme ultraviolet at normal incidence by the Coronal Diagnostic Spectrometer (CDS) on the SOHO spacecraft. The data used for this work were taken using the NISAT_S observing sequence. This takes the full wavelength ranges from both the NIS channels (308-381 Angtr. and 513-633 Angst.) with the 2 arcsec by 240 arcsec slit, which is the narrowest slit available, yielding the best spectral resolution. In this work we contrast the DEM from subregions of 2 by 80 arcsec$^2$ with that obtained from the mean spectrum of the whole raster (20 by 240 arcsec$^2$). We find that the DEM maintains essentially the same shape in the subregions, differing by a constant factor between 0.5 and 2 from the mean DEM, except in areas were the electron density is below $2 \times 10^7$ cm$^{-3}$ and downflow velocities of 50 km/s are found in the transition region. Such areas are likely to contain plasma departing from ionisation equilibrium, violating the basic assumptions underlying the DEM method. The comparison between lines of Li-like and Be-like ions may provide further evidence of departure from ionisation equilibrium. We find also that line intensities tend to be lower where velocities of the order of 30 km/s or higher are measured in transition region lines. The DEM analysis is also exploited to improve the line identification performed by Brooks et al (1999) and to investigate possible elemental abundance variations from region to region. We find that the plasma has composition close to photospheric in all the subregions examined.

https://arxiv.org/pdf/astro-ph/0412118.pdf

ADAS analysis of the differential emission measure structure of the inner solar corona. II. A study of the `quiet Sun' inhomogeneities from SOHO CDS-NIS spectra

The Bragg crystal spectrometer (BCS) is one of four instruments forming the scientific payload of the Solar-A mission. The spectrometer employs crystals that have been curved to diffract four wavelength ranges of importance for the study of high temperature plasma produced in solar flares. The ions involved and the related wavelength ranges are Fe XXVI(1.7636/~1.8404•), Fe XXV(1.8298/~1.8942/~), Ca XIX(3.1631A3.1912/~) and SXV(D.0160/~to 5.11432/~). The important emission lines in these ranges will be observed with resolving powers (A/AA) of between 3000 and 6000. The principle of operation of the instrument is illustrated schematically in Figure 1, while the layout of the spectrometer is given in Figure 2. Solar radiation enters the four apertures (labelled 1 to 4 and with the appropriate ion designations), encounters the crystals and is diffracted to one-dimensional position sensitive proportional counter detectors which register the spectra. This arrangement allows the four spectra to be obtained simultaneously and with good time resolution. The spectrometers are between 6 and 9 times more sensitive than those flown on the Solar Maximum Mission (Acton et al. 1980, Rapley et al. 1977). An instrument microcomputer allows the flexible organisation of the spectral data for transmission. In addtion, a large queue memory is available which allows preflare data to be stored at a rate which matches that of the spacecraft's flare mode telemetry format. The scientific goals of the investigation are concerned with clarifying the connection between the impulsive release of solar flare energy and the creation of high temperature plasma in the corona. The dynamics of the plasma will be examined by studying line broadening and wavelength shifts while temperatures and emission measures will be obtained from line ratios and intensities. The comparison of these observations with the images obtained with the Solar-A hard and soft X-ray

The Solar-A Bragg crystal spectrometer

Since the beginning of the SOHO (Solar and Heliospheric Observatory) mission an intercalibration programme was carried out which included simultaneous observations of the EUV instruments CDS (Coronal Diagnostic Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted Radiation) of common targets on the quiet Sun The observations in the chromospheric line of He i (584 A) and the two coronal lines of Mg x (609 A and 624 A) thus cover the long period of 4 years and provide a data set highly suitable not only for instrumental comparison but also for studies of the quiet Sun’s long term variability Up to the SOHO accident, both instruments show a very good temporal correlation and stability Even after the loss and recovery of the spacecraft, when the instruments had been exposed to extreme temperature conditions, the performance of the CDS and SUMER instruments is still good, as is the temporal correlation However, the ratio between the efficiencies of the two instruments, which remained constant with time until the SOHO accident seems to have changed afterwards In the coronal lines both instruments show an increase of average radiances towards the solar maximum

Comparison of Quiet-Sun Radiances Measured by CDS and SUMER on SOHO

Recent spectroscopic observations by the Solar and Heliospheric Observatory (SOHO) have revealed the dynamic nature of even the ‘quiet’ Sun. Spectral variability data clearly show that dynamics in the solar upper atmosphere take place on timescales shorter than those of ionisation relaxation. Accuracy in the interpretation of diagnostic spectral data can only be maintained through detailed quantitative modelling of the relevant atomic physics. In particular, dynamical plasma models of the solar plasma require matching dynamic atomic models to underpin conclusions drawn from the spectral reduction. The inclusion of important effects such as finite plasma electron density and the influence of metastable levels is essential to reduce the uncertainties associated with equilibrium assumptions.

J. Lang

Papers

The photospheric-to-coronal iron abundance from X-ray lines observed by Yohkoh and other satellites

ADAS analysis of the differential emission measure structure of the inner solar corona. II. A study of the `quiet Sun' inhomogeneities from SOHO CDS-NIS spectra

The Solar-A Bragg crystal spectrometer

Comparison of Quiet-Sun Radiances Measured by CDS and SUMER on SOHO

EUV Spectral Variability and Non-Equilibrium Ionisation in the ‘Quiet’ Sun