Measurements with STEREO/COR1 data of drag forces acting on small-scale blobs falling in the intermediate corona
1
INAF – Catania Astrophysical Observatory,
95040
Catania,
Italy
e-mail:
sdo@oact.inaf.if
2
INAF – Turin Astrophysical Observatory,
10025 Pino Torinese ( TO),
Italy
e-mail:
bemporad@oato.inaf.it
Received:
4
January
2013
Accepted:
20
December
2013
In this work we study the kinematics of three small-scale (0.01 R⊙) blobs of chromospheric plasma falling back to the Sun after the huge eruptive event of June 7, 2011. From a study of 3D trajectories of blobs made with the Solar TErrestrial RElations Observatory (STEREO) data, we demonstrate the existence of a significant drag force acting on the blobs and calculate two drag coefficients, in the radial and tangential directions. The resulting drag coefficients CD are between 0 and 5, comparable in the two directions, making the drag force only a factor of 0.45–0.75 smaller than the gravitational force. To obtain a correct determination of electron densities in the blobs, we also demonstrate how, by combining measurements of total and polarized brightness, the Hα contribution to the white-light emission observed by the COR1 telescopes can be estimated. This component is significant for chromospheric plasma, being between 95 and 98% of the total white-light emission. Moreover, we demonstrate that the COR1 data can be employed even to estimate the Hα polarized component, which turns out to be in the order of a few percent of Hα total emission from the blobs. If the drag forces acting on small-scale blobs reported here are similar to those that play a role during the CME propagation, our results suggest that the magnetic drag should be considered even in the CME initiation modelling.
Key words: Sun: corona / Sun: coronal mass ejections / magnetic fields
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