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  • 1
    Electronic Resource
    Electronic Resource
    The Dependence of Chromospheric Ca II K Network Cell Sizes on Solar Latitude (1998)
    Springer
    Solar physics 180 (1998), S. 47-51 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Calcium K line spectroheliograms obtained during the solar minimum phases at Kodaikanal between 1913–1974 have been used to study the network cell sizes. The autocorrelation is calculated for two-dimensional strips at 5° interval up to ±50° latitude. The average size of the network cells was found to have a dependence on solar latitude with a maximum variation of about 7%. The pattern shows an apparent north–south symmetry with two minima at about 20° N and S.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005072907000
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The interfringe intensity in coronal interferograms (1994)
    Springer
    Experimental astronomy 5 (1994), S. 289-299 
    Details
    ISSN: 1572-9508
    Keywords: Astronomical Instrumentation ; Sun: corona
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The paper discusses the low contrast of the Fabry-Perot (FP) fringes observed in the interferograms of the solar corona. The various factors which affect the interfringe intensity of Fabry-Pérot line profiles are considered. The effect of continuum radiation on the interfringe intensity of Fabry-Pérot line profiles is calculated by assuming a coronal model. For the given FP, it was found that unless the ratio of line to continuum intensity (integrated line intensity to continuum per angström) is less than 10, continuum contribution has no significant effect on the fringe contrast. The analysis may be pertinent in the design aspects of a FP interferometer for astronomical observations. The excess interfringe intensity found in the coronal line profiles is interpreted as due to the presence of fast moving plasma components in corona along the line of sight. A detailed analysis qualitatively shows that the line excitation conditions existing in ambient corona and coronal loops are different in active regions while they are more similar in polar regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01583702
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The Correlation Lifetimes of Chromospheric Ca II K Network Cells (1998)
    Springer
    Solar physics 178 (1998), S. 251-257 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The lifetimes and spatial scales of emission network cells in the solar chromosphere were studied from a nearly continuous sequence of Caii K filtergrams, obtained from Antarctica. The temporal autocorrelation function (ACF) was calculated for spatially-aligned windows from the time sequence of filtergrams. The lifetime of network cells was found to be dependent on the activity of the region. The estimated lifetimes are 24–34 hours for quiet-region cells and 58–61 hours for active-region cells. The temporal ACF shows prominent undulations in some of the quiet-region windows. The spatial ACF reveals the periodicity of the emission network in quiet regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005094523212
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The excitation mechanism and the line-to-continuum intensity ratio of the [Fexiv] 5303 Å line in various coronal regions (1993)
    Springer
    Solar physics 147 (1993), S. 255-261 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The excitation mechanism of the coronal green line in various coronal regions is studied. The line-to-continuum intensity ratio is calculated using the model electron density values given by Newkirk (1961) and is compared with the observed values. Reasonably good agreement is found between the model calculations and observed values. The model calculations show that collisional excitation is more important in the innermost regions while radiative contribution progressively increases towards outer regions. The individual contributions depend strongly on the activity of the particular coronal region. An increased contribution from collisional excitation is seen in coronal active regions owing to the large electron density. A contour map of the line-to-continuum intensity ratio as derived from the observations, is plotted. At 1.10R⊙ the value is about 80 in active regions, 30–40 in coronal streamers, while it is less than 10 in polar regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00690716
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    A kinematic study of orion nebula in the emission line [S II] 6731 Å (1993)
    Springer
    Astrophysics and space science 204 (1993), S. 205-212 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fabry-Perot Interferometric observations were made on Orion Nebula in the forbidden emission line [S II] 6731 Å line. The observed field is about 6′ × 6′ on the face of the nebula and it covers the Orion Trapezium stars and the nearby regions. The relative line of sight velocities which denote the average deviations from the systematic velocities were derived at a large number of points in the nebula. Velocities were found to show a gradient towards the north of Trapezium stars. Large blue shifted velocities were found at the nebular boundaries, probably associated with the ionization fronts. The observed velocities, in general, show agreement with the flow model of Balick, Gull and Smith (1980).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00658025
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    Paper (German National Licenses)
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