Seeing-Induced Errors in Solar Doppler Velocity Measurements |
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Authors: | Sreejith Padinhatteeri R Sridharan K Sankarasubramanian |
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Institution: | (1) Homer, IL, USA; |
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Abstract: | Imaging systems based on a narrow-band tunable filter are used to obtain Doppler velocity maps of solar features. These velocity
maps are created by taking the difference between the blue- and red-wing intensity images of a chosen spectral line. This
method has the inherent assumption that these two images are obtained under identical conditions. With the dynamical nature
of the solar features as well as the Earth’s atmosphere, systematic errors can be introduced in such measurements. In this
paper, a quantitative estimate of the errors introduced due to variable seeing conditions for ground-based observations is
simulated and compared with real observational data for identifying their reliability. It is shown, under such conditions,
that there is a strong cross-talk from the total intensity to the velocity estimates. These spurious velocities are larger
in magnitude for the umbral regions compared to the penumbra or quiet-Sun regions surrounding the sunspots. The variable seeing
can induce spurious velocities up to about 1 km s−1. It is also shown that adaptive optics, in general, helps in minimising this effect. |
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