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  • 1
    Electronic Resource
    Electronic Resource
    Soho Cds–nis in-flight intensity calibration using a plasma diagnostic method (1997)
    Springer
    Solar physics 175 (1997), S. 553-570 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) – Normal Incidence Spectrometer (NIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the CDS–NIS 1 and NIS 2 windows in a solar active region is analysed in order to determine the intensity calibration curve for both channels. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the preliminary CDS–NIS internal intensity calibration curves and the determination of the relative calibration between NIS 1 and NIS 2. A further correction factor of approximately three is found to be necessary for a correct intercalibration of the two wavelength windows. Also the NIS 2 second-order sensitivity is measured. The Arcetri diagnostic method proves to be a powerful tool for intensity calibration studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004984022356
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  • 2
    Electronic Resource
    Electronic Resource
    Euv Observations of a Macrospicule: Evidence for Solar Wind Acceleration? (1997)
    Springer
    Solar physics 175 (1997), S. 457-465 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a unique observation of a macrospicule, recorded in extreme ultraviolet light on 11 April 1996, using the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO). The observation was made by chance as part of a daily, large-area mapping sequence. Although the feature has some characteristics of the class of events which have become known as X-ray jets, we argue that the feature observed here is a macrospicule. This being the case, the observation demonstrates several new features of macrospicule observation. Emission is detected from the macrospicule to temperatures of 1 million degrees. In addition, some footpoint structure is detected at the root of the macrospicule, and the edges or sides of the macrospicule appear brighter than the central regions. A velocity analysis shows high speed flows within the macrospicule. Velocities are seen to increase with altitude until a plateau is achieved. Coincident with this, there is evidence for emission line narrowing. The significance of these observations for solar wind acceleration processes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004987505422
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  • 3
    Electronic Resource
    Electronic Resource
    Application of Spectroscopic Diagnostics to Early Observations with the SOHO Coronal Diagnostic Spectrometer (1997)
    Springer
    Solar physics 170 (1997), S. 143-161 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Coronal Diagnostic Spectrometer (CDS) has as a scientific goal the determination of the physical parameters of the solar plasma using spectroscopic diagnostic techniques. Absolute intensities and intensity ratios of the EUV spectral emission lines can be used to obtain information on the electron density and temperature structure, element abundances, and dynamic nature of different features in the solar atmosphere. To ensure that these techniques are accurate it is necessary to interface solar analysis programs with the best available atomic data calculations. Progress is reported on this work in relation to CDS observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004997003844
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  • 4
    Electronic Resource
    Electronic Resource
    The Coronal Diagnostic Spectrometer for the solar and heliospheric observatory (1995)
    Springer
    Solar physics 162 (1995), S. 233-290 
    Details
    ISSN: 1573-093X
    Keywords: Solar Atmosphere ; Extreme UV Spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Coronal Diagnostic Spectrometer is designed to probe the solar atmosphere through the detection of spectral emission lines in the extreme ultraviolet wavelength range 150 – 800 Å. By observing the intensities of selected lines and line profiles, we may derive temperature, density, flow and abundance information for the plasmas in the solar atmosphere. Spatial and temporal resolutions of down to a few arcseconds and seconds, respectively, allow such studies to be made within the fine-scale structure of the solar corona. Futhermore, coverage of large wavelength bands provides the capability for simultaneously observing the properties of plasmas across the wide temperature ranges of the solar atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00733431
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature structure of active regions deduced from the helium-like sulphur lines (1995)
    Springer
    Solar physics 157 (1995), S. 169-184 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Solar active-region temperatures have been determined from the full-Sun spectra of helium-like sulphur (Sxv) observed by the Bragg Crystal Spectrometer on board theYohkoh satellite. The average temperature deduced from Sxv is demonstrated to vary with the solar activity level: A temperature of 2.5 × 106 K is derived from the spectra taken during low solar activity, similar to the general corona, while 4 × 106 K is obtained during a higher activity phase. For the latter, the high-temperature tail of the differential emission measure of active regions is found most likely due to the superposition of numerous flare-like events (micro/nano-flares).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00680615
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  • 6
    Electronic Resource
    Electronic Resource
    Euv Spectroscopy of the Sunspot Region Noaa 7981 Using Soho – II. Velocities and Line Profiles (1998)
    Springer
    Solar physics 179 (1998), S. 279-312 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the dynamics in the sunspot transition region between the chromosphere and the corona and investigated the extension of the flow field into the corona. Based on EUV spectra of a medium size sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER on SOHO, we derive line-of-sight velocities and study the line profiles for a series of emission lines. The flow field in the low corona is found to differ markedly from that in the transition region. In the transition region the relative line-of-sight velocity shows an upflow in the umbra and relatively large areas with downflow that cover part of the penumbra. The spatial extent of these areas with upflow and downflow increases with increasing temperature in the transition region, but the whole flow field changes character as the temperature increases from the upper transition region to the low corona. Based on a calibration of the SUMER wavelength scale we find that the entire sunspot transition zone appears to be moving downwards towards the chromosphere. The relation between this finding and the general tendency for transition-region lines to show a net red shift is discussed. Several of the transition-region spectral line profiles are observed to show two line components with Gaussian shape and line-of-sight velocities that differ markedly. Several of the line profiles that are composed of two spectral line components occur close to the dividing line between up- and downflow. A discussion of this observation is presented. In small regions with spatial extent of a few arc sec we detect enhanced continuum emission underlying explosive events. The similarities between explosive events with continuum emission and the moustaches observed in Hα close to sunspots are so striking that we are tempted to introduce the notation ‘transition-region moustaches’.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005046111810
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  • 7
    Electronic Resource
    Electronic Resource
    FLOWS AND DYNAMICS IN THE CORONA OBSERVED WITH THE CORONAL DIAGNOSTIC SPECTROMETER (CDS) (1997)
    Springer
    Solar physics 170 (1997), S. 163-177 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) show significant flows of plasma in active region loops, both at coronal and transition region temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and Mgx 624 Å corresponding to upflows in the plasma reaching velocities of 50 km s-1 have been observed in an active region. Smaller velocities are detected in the coronal lines Fexvi 360 Å and Sixii 520 Å. Flows reaching 100 km s-1 are observed in spectral lines formed at transition region temperatures, i.e., Ov 629 Å and Oiii 599 Å, demonstrating that both the transition region and the corona are clearly dynamic in nature. Some high velocity events show even higher velocities with line profiles corresponding to a velocity dispersion of 300–400 km s-1. Even in the quiet Sun there are velocity fluctuations of 20 km s-1 in transition region lines. Velocities of the magnitude presented in this paper have never previously been observed in coronal lines except in explosive events and flares. Thus, the preliminary results from the CDS spectrometer promise to put constraints on existing models of the flows and energy balance in the solar atmosphere. The present results are compared to previous attempts to observe flows in the corona.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004945702259
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  • 8
    Electronic Resource
    Electronic Resource
    Yohkoh observations of the creation of high-temperature plasma in the flare of 16 December 1991 (1994)
    Springer
    Solar physics 153 (1994), S. 307-336 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Yohkoh observations of an impulsive solar flare which occurred on 16 December, 1991 are presented. This flare was a GOES M2.7 class event with a simple morphology indicative of a single flaring loop. X-ray images were taken with the Hard X-ray Telescope (HXT) and soft X-ray spectra were obtained with the Bragg Crystal Spectrometer (BCS) on board the satellite. The spectrometer observations were made at high sensivity from the earliest stages of the flare, are continued throughout the rise and decay phases, and indicate extremely strong blueshifts, which account for the majority of emission in Caxix during the initial phase of the flare. The data are compared with observations from other space and ground-based instruments. A balance calculation is performed which indicates that the energy contained in non-thermal electrons is sufficient to explain the high temperature plasma which fills the loop. The cooling of this plasma by thermal conduction is independently verified in a manner which indicates that the loop filling factor is close to 100%. The production of ‘superhot’ plasma in impulsive events is shown to differ in detail from the morphology and mechanisms appropriate for more gradual events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712508
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  • 9
    Electronic Resource
    Electronic Resource
    Active Regions Observed in Extreme Ultraviolet Light by the Coronal Diagnostic Spectrometer on Soho (1997)
    Springer
    Solar physics 175 (1997), S. 487-509 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present observations of five active regions made by the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO). CDS observes the Sun in the extreme ultraviolet range 150–780 Å. Examples of active region loops seen in spectral lines emitted at various temperatures are shown. Several classes of loops are identified: those that are seen in all temperatures up to 2 x 106 K; loops seen at 106 K but not reaching 1.6 x 106 K; those at temperatures 2– 4 x 10-5 K and occasionally at 6 x 10-5 K but not reaching 106 K. An increasing loop size with temperature and the relationship between the cool and hot structures is discussed. CDS observations reveal the existence of loops and other unresolved structures in active regions, at temperatures between 1.5– 4 x 10-5 K, which do not have counterparts in lines emitted above 8 x 10-5 K. Bright compact sources only seen in the transition region lines are investigated. These sources can have lifetimes of up to several days and are located in the vicinity of sunspots. We study the variability of active region sources on time scales from 30 sec to several days. We find oscillatory behaviour of Hei and Ov line intensities in an active region on time scales of 5–10 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004933209773
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  • 10
    Electronic Resource
    Electronic Resource
    Euv Spectroscopy of the Sunspot Region Noaa 7981 Using Soho – I. Line Emission and Time Dependence (1998)
    Springer
    Solar physics 179 (1998), S. 43-74 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981, were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer (CDS) and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral lines formed in the transition region and corona show considerable structure and large deviations from a uniform spatial distribution over the active region. Enhanced EUV emissions in transition region lines are concentrated in small regions outside the umbra of the sunspot throughout most of the observing sequence. Only during a short, active period do we find an enhanced line emission that reaches into the umbra. Preliminary values for the umbral intensity are given. Marked changes are detected between the spatial distribution of line emission in the transition region and the low corona. The difference is not limited to cool and hot non-flaring loops not being cospatial, but includes differences both regarding the time variability and the orientation and size of the emission features. Whereas both rapid (≈ 4 and 2 min) and slow (≈ 10 and 12 h) temporal variations are found in the chromosphere (Hei 584 Ú) and transition region (Ov 629 Ú), the response in the low corona (Mgix 368 Ú) is slow (≈ 5 h). Furthermore, marked differences between the spatial distributions in the Mgviii 315 Ú, Mgix 368 Ú lines formed in the low corona and the coronal Fexiv 334 Ú, Fexvi 360 Ú lines are detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005003407826
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