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  • 1
    Electronic Resource
    Electronic Resource
    Multiwavelength analysis of a well observed flare from SMM (1985)
    Springer
    Solar physics 99 (1985), S. 167-188 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe and analyse observations of an M1.4 flare which began at 17: 00 UT on 12 November, 1980. Ground based Hα and magnetogram data have been combined with EUV, soft and hard X-ray observations made with instruments on-board the Solar Maximum Mission (SMM) satellite. The preflare phase was marked by a gradual brightening of the flare site in Ov and the disappearance of an Hα filament. Filament ejecta were seen in Ov moving southward at a speed of about 60 km s−1, before the impulsive phase. The flare loop footpoints brightened in Hα and the Caxix resonance line broadened dramatically 2 min before the impulsive phase. Non-thermal hard X-ray emission was detected from the loop footpoints during the impulsive phase while during the same period blue-shifts corresponding to upflows of 200–250 km s−1 were seen in Ca xix. Evidence was found for energy deposition in both the chromosphere and corona at a number of stages during the flare. We consider two widely studied mechanisms for the production of the high temperature soft X-ray flare plasma in the corona, i.e. chromospheric evaporation, and a model in which the heating and transfer of material occurs between flux tubes during reconnection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00157307
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  • 2
    Electronic Resource
    Electronic Resource
    Diagnostic application of highly ionized iron lines in the XUV spectrum of a solar flare (1984)
    Springer
    Solar physics 92 (1984), S. 199-216 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent atomic data have been used to analyze a solar flare spectrum obtained with the Goddard Space Flight Center's grating spectrometer on the OSO-5 satellite. There exist in the wavelength region 90–200 Å strong lines from each of the ions Fe xviii-Fe xxiv. The Fe xxi lines can be used as an electron density diagnostic for the 107 K plasma. From our analysis of a particular flare, we find a steep positive slope in the emission measure between 106.5 and 107.2 K and an electron density of ∼4 × 1011 cm−3 at 107 K. We emphasise the need for high spectral and spatial resolution observations of solar flares in this wavelength region, which has to date been largely neglected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00157246
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopic diagnostics in the VUV for solar and stellar plasmas (1994)
    Springer
    The astronomy and astrophysics review 6 (1994), S. 123-179 
    Details
    ISSN: 1432-0754
    Keywords: VUV spectra ; Plasma diagnostics ; Solar and stellar atmospheres
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary The VUV emission spectra from the solar atmosphere and stellar atmospheres have been intensively studied during the past 25 years with several major space programs. In this review we discuss the spectroscopic diagnostic techniques used to study astrophysical plasmas, the atomic processes involved, the recent observations and the plans for future space missions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01208253
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  • 4
    Electronic Resource
    Electronic Resource
    Nonthermal velocities in the solar transition zone observed with the high-resolution telescope and spectrograph (1993)
    Springer
    Solar physics 144 (1993), S. 217-241 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Data obtained during the first rocket flight of the NRL High Resolution Telescope and Spectrograph (HRTS) have been used to study nonthermal velocities for spectral lines primarily covering the temperature range 104 to 2 × 106 K. The high spectral and spatial resolution, combined with an enhanced dynamic intensity range of the reduced data, has enabled us to study the distribution of the nonthermal velocities for quiet and active regions. Average values of the nonthermal velocities peak at about 27 km s−1 at 105 K for the quiet regions, with a wide distribution of nonthermal velocities for each line. The active region nonthermal velocities have a narrower distribution which is weighted towards higher values. The SiIV and C IV line profiles are not well described by a single Gaussian, indicating that high-velocity components (above 30 km s−1) are present in the quiet-Sun spectra. The radiative losses for all plasma above l05 K have been calculated for the quiet Sun, an active region and a coronal hole. These have been compared with the acoustic wave flux inferred from the nonthermal line widths. There appears to be a sufficient flux of waves to heat these regions of the atmosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00627590
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    The Mg/Ne abundance ratio in a recently emerged flux region observed by CDS (1997)
    Springer
    Solar physics 175 (1997), S. 523-539 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Evidence for the existence of the FIP-effect in the transition region is presented here based on recent observations from the Coronal Diagnostic Spectrometer (CDS) on-board the Solar and Heliospheric Observatory (SOHO). Observations of an emerging flux region in lines of Mgv–vii and Nevi–vii reveal differences in the relative Mg/Ne abundance of a factor of 9.2 between two transition region brightenings separated by less than 1 arc min on the Sun. The lower abundance ratio is approximately equal to the photospheric Mg/Ne value and is associated with a small loop-like feature in the central, hottest part of the active region. The higher abundance ratio is found in spike-like structures at the edge of the active region. A density diagnostic of Oiv is used to derive an electron number density of 1011.3 cm-3 for the low Mg/Ne brightening, while a Mgvii diagnostic gives a density of 109.2 cm for the high Mg/Ne brightening.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004936106427
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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Observation of Transition Region Fine Structures with Soho/Sumer (1999)
    Springer
    Space science reviews 87 (1999), S. 241-244 
    Details
    ISSN: 1572-9672
    Keywords: UV spectral emission lines ; solar transition region
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a preliminary analysis of two quiet Sun transition region areas observed with the SOHO/SUMER spectrometer, using lines from oxygen, nitrogen and silicon. The average quiet Sun physical parameters are studied as a function of line intensity. Systematic variations of line position and width with increasing intensity are found. A large number of small-scale active points have been observed, and preliminary analysis of the physical properties and dynamics of these active features is presented. A jet-like structure, found in an active point, is also investigated and its velocity along the line of sight determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005160804176
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  • 10
    Electronic Resource
    Electronic Resource
    The interpretation of the spectral line intensities from the CHASE spectrometer on Spacelab 2 (1990)
    Springer
    Solar physics 129 (1990), S. 31-81 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we analyse the solar spectral intensities observed with the CHASE grazing incidence telescope and spectrometer flown on NASA's Spacelab 2 Mission in 1985. Our main purpose has been to investigate the sources of error that arise in the application of the differential emission measure technique used to analyse such data. We suggest methods by which these sources of error may be investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154365
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