Other
Scientific paper
Sep 1964
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1964phdt........83b&link_type=abstract
Ph.D. Thesis, University of Utrecht (AFCRL-Environmental Research Paper, No.49), (1964), 131 pages
Other
108
Sun, Sun: Chromosphere
Scientific paper
The study of high-resolution solar disk spectroheliograms, or filtergrams, gives one an insight into the horizontal distribution of chromospheric fine structures which is hard to obtain from limb observations. The main part of this paper is concerned with such a study in the light of the Hydrogen Hα line (6562.8A) and of the Calcium K line (3933.7A).
Section 2 gives a description of the instrumentation used to secure the observations as well as some notes on observational techniques and experiences. It especially gives in detail some of the properties of the Sydney 1/8 A Hα birefringent filter.
Section 3 gives a description of the high-resolution H filtergrams obtained with this instrument and compares this description with those given by other authors. Details are given especially on (a) the morphology of the elongated fine mottles, which are the components of coarse mottles, (b) the spatial autocorrelation function and power spectrum for Hα +/- 0.5A filtergrams, and (c) the sytematic inflow of chromospheric matter into a sunspot (Evershed effect).
In Section 4 the elongated fine mottles are studied in more detail. The resulting properties are compared with those for spicules as studied on the limb. The following properties are found for fine mottling: (a) The width is 1.2 sec of arc, and the average length is 4.1 sec of arc. (b) The average orientation in space is vertical to the solar surface. The average angle to the vertical is 21O. (c) The average lifetime is 15 minutes. (d) The mottles are at first most visible at Hα - 0.5A, later at Hα + 0.5A, indicating a rising and falling. (e) The total number on the sun is 4 x 10^5, (f) Within the coarse mottle, the birth rate is equal to that of the solar granulation. All these properties agree with those for spicules, as far as known, except for the one under (d). There can be little doubt however that the elongated fine mottles are spicules.
Section 5 describes an attempt to measure the spectrum of such a spicule on the disk. Disk observations have the advantage of giving the source function and optical depth separately. Typical values for the optical depth and Doppler width are 1.5 and 0.5A while the source function is always lower than the intensity at the Hα - line center.
In Section 6, I computed the hydrogen spectrum of spicules under non-local thermodynamic equilibrium conditions for the Lyman α, β and γ lines, the Balmer α and β lines and the Paschen α line. At electron temperatures between 7500OK and 30,000OK, the Balmer-line emissions for limb spicules are nearly independent of electron temperature. The intensity observations give therefore a direct determination of the electron density. The Lyman-line intensities of the solar disk indicate the spicule temperature to be less than 9000OK.
Section 7 describes the appearance of K spectroheliograms. Spicules in K, as in Hα, are dark when seen on the solar disk. The Hα3 flocculi, the Hα1 grains, and the Hα3 vortex are recognized on these calcium images.
In Section 8, attention is drawn to the equality in birth rates for granules and spicules within the K flocculi, which indicates a physical relationship. Table 23 and Figure 47 summarize the terms used by the author in describing the chromospheric structures.
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