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  • 1
    Electronic Resource
    Electronic Resource
    Does the emission measure decrease during the start of a soft X-ray flare? (1978)
    Springer
    Solar physics 59 (1978), S. 373-376 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Soft X-ray flare observations, interpreted as the emission from a single temperature plasma, frequently indicate a significant decrease in the inferred emission measure. It is shown that this effect results naturally from the isothermal assumption, and is eliminated when the preflare contribution to the total emission is removed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00951842
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  • 2
    Electronic Resource
    Electronic Resource
    Trace — The transition region and coronal explorer (1994)
    Springer
    Space science reviews 70 (1994), S. 119-122 
    Details
    ISSN: 1572-9672
    Keywords: Sun ; Instrumentation ; Coronal Heating ; Coronal Structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract TRACE is a single-instrument solar mission that will be put into a Sunsynchronous polar orbit and will obtain continuous solar observations for about 8 months per year. It will collect images of solar plasmas at temperatures from 104 to 107 K, with 1-arcsec spatial resolution and excellent temporal resolution and continuity. With such data, we expect to gain a new understanding of many solar and stellar problems ranging from coronal heating to impulsive magnetohydrodynamic phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00777855
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  • 3
    Electronic Resource
    Electronic Resource
    Coronal survey in X-rays of O vii and Ne ix (1972)
    Springer
    Solar physics 26 (1972), S. 183-201 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report some results of a rocket experiment flown on 29 April, 1971. A survey of the solar corona was carried out with a pair of collimated Bragg spectrometers to study the resonance, intersystem and forbidden line emission from the helium-like ions O vii (22 Å) and Ne ix (13 Å). In the direction of dispersion the collimator provided a field of view of 1.7′. Also, the continuum radiation near 3 Å was monitored by a collimated proportional counter within a view angle of 4.2′. The observed X-ray emission came from the general corona, seven plage regions, and one dynamic feature- the late stage of a small flare. From the intensity of the O vii and Ne ix resonance lines the electron temperature and emission measure of the individual emitting regions are derived on the basis of two models, one (a) in which the region is assumed to be isothermal and another (b) in which the emission measure decreases exponentially with increasing temperature. The latter model, which is the most adequate of the two, yields for the electron temperature of the time-varying feature 2–3 × 106 K, for the other active regions 1.5–2.5 × 106 K, and for the general corona 1.3–1.7 × 106 K. The Ne ix emitting regions are about 1.5 times as hot as the O vii regions. The emission measure ranges from 0.4–2.3 × 1048 cm−3 for all active regions and is about 2 × 1049 cm−3 for one hemisphere of the general corona above 106 K. From an analysis of the ratio, R, of the forbidden and intersystem lines of O vii we conclude that none of the regions producing these lines at the time of the rocket flight had electron densities exceeding about 3 × 109 cm−3. Our data demonstrate a dependence of R upon temperature in agreement with the theory of Blumenthal et al. (1971). The wavelengths for the intersystem, the 1s 22s 2 S e−1s2p2s 2 P 0 satellite, and the forbidden transition show in the case of Ne ix improved agreement with predictions. The observed strength of the satellite lines for both O vii and Ne ix agrees with the predictions of Gabriel's (1972) theory, which attributes their formation to dielectronic recombination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00155119
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  • 4
    Electronic Resource
    Electronic Resource
    Early evolution of an X-ray emitting solar active region (1977)
    Springer
    Solar physics 55 (1977), S. 181-193 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The birth and early evolution of a solar active region has been investigated using X-ray observations from the Lockheed Mapping X-Ray Heliometer on board the OSO-8 spacecraft. X-ray emission is observed within three hours of the first detection of Hα plage. At that time, a plasma temperature of 4 × 106 K in a region having a density of the order of 1010 cm−3 is inferred. During the fifty hours following birth almost continuous flares or flare-like X-ray bursts are superimposed on a monotonically increasing base level of X-ray emission produced by plasma with a temperature of the order 3 × 106 K. If we assume that the X-rays result from heating due to dissipation of current systems or magnetic field reconnection, we conclude that flare-like X-ray emission soon after active region birth implies that the magnetic field probably emerges in a stressed or complex configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00150884
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  • 5
    Electronic Resource
    Electronic Resource
    The soft X-ray polychromator for the Solar Maximum Mission (1980)
    Springer
    Solar physics 65 (1980), S. 53-71 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The 1.4–22.4 Å range of the soft X-ray spectrum includes a multitude of emission lines which are important for the diagnosis of plasmas in the 1.5–50 million degree temperature range. In particular, the hydrogen and helium-like ions of all abundant solar elements with Z 〉 7 have their primary transitions in this region and these are especially useful for solar flare and active region studies. The soft X-ray polychromator (XRP) is a high resolution experiment working in this spectral region. The XRP consists of two instruments with a common control, data handling and power system. The bent crystal spectrometer is designed for high time resolution studies in lines of Fe i-Fe xxvi and Ca xix. The flat crystal scanning spectrometer provides for 7 channel polychromatic mapping of flares and active regions in the resonance lines of O viii, Ne ix, Mg xi, Si xiii, S xv, Ca xix, and Fe xxv with 14″ spatial resolution. In its spectral scanning mode it covers essentially the entire 1.4–22.5 Å region. This paper summarizes the scientific objectives of the XRP experiment and describes the characteristics and capabilities of the two instruments. Sufficient technical information for experiment feasibility studies is included and the resources and procedures planned for the use of the XRP within the context of the Solar Maximum Mission is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151384
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  • 6
    Electronic Resource
    Electronic Resource
    Soft X-ray emission from active regions shortly before solar flares (1982)
    Springer
    Solar physics 76 (1982), S. 377-386 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Detailed examination of the variations in the intensity of soft X-ray emission prior to many solar flares are presented. In addition, these preflare intensity variations are contrasted with the variations typically observed for the same active regions in the absence of a flare. It is shown that a 5–20 min preflare brightening phase is not typically observed. These observations are discussed in context with other complimentary investigations and theoretical models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00170992
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  • 7
    Electronic Resource
    Electronic Resource
    TIME-DISTANCE HELIOSEISMOLOGY WITH THE MDI INSTRUMENT: INITIAL RESULTS (1997)
    Springer
    Solar physics 170 (1997), S. 63-73 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In time-distance helioseismology, the travel time of acoustic waves is measured between various points on the solar surface. To some approximation, the waves can be considered to follow ray paths that depend only on a mean solar model, with the curvature of the ray paths being caused by the increasing sound speed with depth below the surface. The travel time is affected by various inhomogeneities along the ray path, including flows, temperature inhomogeneities, and magnetic fields. By measuring a large number of times between different locations and using an inversion method, it is possible to construct 3-dimensional maps of the subsurface inhomogeneities. The SOI/MDI experiment on SOHO has several unique capabilities for time-distance helioseismology. The great stability of the images observed without benefit of an intervening atmosphere is quite striking. It has made it possible for us to detect the travel time for separations of points as small as 2.4 Mm in the high-resolution mode of MDI (0.6 arc sec pixel-1). This has enabled the detection of the supergranulation flow. Coupled with the inversion technique, we can now study the 3-dimensional evolution of the flows near the solar surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004907220393
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  • 8
    Electronic Resource
    Electronic Resource
    The Solar Oscillations Investigation - Michelson Doppler Imager (1995)
    Springer
    Solar physics 162 (1995), S. 129-188 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Solar Oscillations Investigation (SOI) uses the Michelson Doppler Imager (MDI) instrument to probe the interior of the Sun by measuring the photospheric manifestations of solar oscillations. Characteristics of the modes reveal the static and dynamic properties of the convection zone and core. Knowledge of these properties will improve our understanding of the solar cycle and of stellar evolution. Other photospheric observations will contribute to our knowledge of the solar magnetic field and surface motions. The investigation consists of coordinated efforts by several teams pursuing specific scientific objectives. The instrument images the Sun on a 10242 CCD camera through a series of increasingly narrow spectral filters. The final elements, a pair of tunable Michelson interferometers, enable MDI to record filtergrams with a FWHM bandwidth of 94 mÅ. Normally 20 images centered at 5 wavelengths near the Ni I 6768 spectral line are recorded each minute. MDI calculates velocity and continuum intensity from the filtergrams with a resolution of 4″ over the whole disk. An extensive calibration program has verified the end-to-end performance of the instrument. To provide continuous observations of the longest-lived modes that reveal the internal structure of the Sun, a carefully-selected set of spatial averages are computed and downlinked at all times. About half the time MDI will also be able to downlink complete velocity and intensity images each minute. This high rate telemetry (HRT) coverage is available for at least a continuous 60-day interval each year and for 8 hours each day during the rest of the year. During the 8-hour HRT intervals, 10 of the exposures each minute can be programmed for other observations, such as measurements in MDI's higher resolution (1.25″) field centered about 160″ north of the equator; meanwhile, the continuous structure program proceeds during the other half minute. Several times each day, polarizers will be inserted to measure the line-of-sight magnetic field. MDI operations will be scheduled well in advance and will vary only during the daily 8-hour campaigns. Quick-look and summary data, including magnetograms, will be processed immediately. Most high-rate data will be delivered only by mail to the SOI Science Support Center (SSSC) at Stanford, where a processing pipeline will produce 3 Terabytes of calibrated data products each year. These data products will be analyzed using the SSSC and the distributed resources of the co-investigators. The data will be available for collaborative investigations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00733429
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  • 9
    Electronic Resource
    Electronic Resource
    OSO-8 observations of the impulsive phase of solar flares in the transition-zone and corona (1981)
    Springer
    Solar physics 69 (1981), S. 373-389 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Several solar flares have been observed from their onset in C IV λ 1548.2 and 1–8 Å X-rays using instruments aboard OSO-8. In addition, microwave and Hα flare patrol data have been obtained for this study. The impulsive brightening in C IV is frequently accompanied by redshifts, interpreted as downflows, of the order of 80 km s-1. The maximum soft X-ray intensity usually arrives several minutes after the maximum C IV intensity. The most energetic C IV event studied shows a small blueshift just before reaching maximum intensity, and estimates of the mass flux associated with this upflow through the transition-zone are consistent with the increase of mass in the coronal loops as observed in soft X-rays. This event had no observable microwave burst, suggesting that electron beams did not play a major role in the chromospheric and transition-zone excitation. Lastly, our observations suggest that the frequent occurrence of violent dynamical processes at the onset of the flare are associated with the initial energy release mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00150001
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetohydrodynamic simulation of the coronal transient associated with the solar limb flare of 1980, June 29, 18∶21 UT (1983)
    Springer
    Solar physics 85 (1983), S. 351-373 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Soft X-ray data from the XRP experiment on SMM are used to generate the temperature and density in the flaring region of the 1980, June 29 (18∶21 UT) solar flare. The temporal data (T max ∼- 20 × 106 K and n max ∼- 4 × 1011 cm−3), together with an assumed velocity, are used to simulate mass injection as the input pulse for the MHD model of Wu et al. (1982a, 1983a). The spatial and temporal coronal response is compared with the ground-based, Mark III K-coronameter observations of the subsequent coronal transient. The simulation produces a spatially-wide, large amplitude, temporarily-steepened MHD wave for either of the two ‘canonical’ magnetic topologies (closed and open), but no shock wave. This result appears to be confirmed by the fact that a type II radio event was observed late in the event for only a few minutes, thereby indicating that a steepening wave with temporary, marginal shock formation, was indeed present. The density enhancements produced by the simulation move away from the Sun at the same velocity observed by the K-coronameter. However, the observation of the coronal transient included a rarefaction that does not appear in the simulation. A probable explanation for this discrepancy is the likelihood that the magnitude and temporal profile of the density of the soft X-ray emitting plasma should not have been used as part of the mass injection pulse. We believe that the temperature profile alone, as suggested by earlier simulations, might have been a necessary and sufficient condition to produce both the compression and rarefaction of the ambient corona as indicated by the K-coronameter data. Hence, the dense plasma observed by XRP was probably confined, for the most part, close to the Sun during the ∼ 17 min duration of the observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148659
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