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| Titel |
Solar off-limb line widths with SUMER: revised value of the non-thermal velocity and new results |
| VerfasserIn |
L. Dolla, J. Solomon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 9 ; Nr. 27, no. 9 (2009-09-25), S.3551-3558 |
| Datensatznummer |
250016649
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3551-2009.pdf |
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| Zusammenfassung |
| Alfvén waves and ion-cyclotron absorption of high-frequency waves are
frequently brought into models devoted to coronal heating and fast solar-wind
acceleration. Signatures of ion-cyclotron resonance have already been
observed in situ in the solar wind and in the upper corona. In the lower
corona, one can use the line profiles to infer the ion temperatures. But the
value of the so-called "non-thermal" (or "unresolved") velocity,
potentially related to the amplitude of Alfvén waves propagating in the
corona, is critical in firmly identifying ion-cyclotron preferential heating.
In a previous paper, we proposed a method to constrain both the Alfvén wave
amplitude and the preferential heating, above a polar coronal hole observed
with the SUMER/SOHO spectrometer. Taking into account the effect of
instrumental stray light before analysing the line profiles, we ruled out any
direct evidence of damping of the Alfvén waves and showed that ions with
the lowest charge-to-mass ratios were preferentially heated. We re-analyse
these data here to correct the derived non-thermal velocity, and we discuss
the consequences on the main results. We also include a measure of the
Fe VIII 1442.56 Å line width (second order), thus extending the
charge-to-mass ratio domain towards ions more likely to experience cyclotron
resonance. |
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