1,720,987 research outputs found
Solar prominence polarimetry
No full textWe measure the resonance polarization in solar prominences in
Hα, Hβ and HeD3. A two-dimensional set-up with narrow-band
filter, polarization analyzer and CCD camera is used to take prominence images
in polarized light at high spatial resolution. Placed on a coudé telescope's
hour axis, the observations near the equinoxia are free from purely instrumental
polarization. Above the 0.1% noise limit, the Balmer lines do not show a
polarization in contrast to the HeD3 line. Here, we determine the complete
polarization profile after exchange of filter and CCD with the spectrograph,
keeping the polarization analyzer fixed. In most prominences the Stokes-U and
-Q profiles are not similar to Stokes-I: occasionally the blue and the red
components of the emission are equal or even show a reverse ratio. This
fits calculations for magnetic field strengths of the order of 50 Gauß
being markedly stronger than commonly assumed.
High spatial resolution solar polarimetry with interference filters
No full textA new type of two-dimensional polarimeter is used to measure
the center-to-limb variation of the scattering induced polarization in a
narrow continuum window up to the extreme limb. The polarimeter is set on
the Tenerife Gregory Coudé telescope's hour axis, where the two folding
flat mirrors cancel their polarizing effects for zero solar declination
at the equinox. The short CCD exposure of only 5 ms allows high spatial
resolution images in polarized light. A beam switching technique together
with an integration parallel to the solar limb over 20´´, yields a high
polarimetric accuracy with an rms noise of . Our results
for a continuum window at 4506–4508 Å agree with model calculations
down to limb distances of 0\farcs32 (i.e. )
Ionization memory of plasma emitters in a solar prominence
No full textAims. In the low-collisional, partially ionized plasma (PIP) of solar prominences, uncharged emitters might show different signatures of magnetic line broadening than charged emitters. We investigate if the widths of weak metal emissions in prominences exceed the thermal line broadening by a different amount for charged and for uncharged emitters.
Methods. We simultaneously observe five optically thin, weak metal lines in the brightness center of a quiescent prominence and compare their observed widths with the thermal broadening.
Results. The inferred nonthermal broadening of the metal lines does not indicate systematic differences between the uncharged Mg b2 and Na D1 and the charged Fe I
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Characterization of a thinned back illuminated MIMOSA V sensor as a visible light camera
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