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Spectrophotometric analysis of Ellerman Bombs in the Ca II, Hα and UV range View all abstracts by submitter

Etienne Pariat   Submitted: 2007-07-03 09:24

Even if Ellerman bombs have been observed in the Hα line withinemerging magnetic flux region since the early 20th century, their origin andthe mechanisms which lead to their formation has been strongly debated.Recently new arguments in favor of chromospheric magnetic reconnection havebeen advanced. Ellerman bombs seem to be the signature of reconnections thattake place during the emergence of the magnetic field. We have observed anactive region presenting emergence of magnetic flux. We detected and studiedEllerman bombs in two chromospheric lines: Ca II 8542 Å and Hα . Weinvestigated the link between Ellerman bombs and other structures andphenomena appearing in an emerging active region: UV Bright points, ArchFilament Systems and magnetic topology. On August 3rd, 2004, we performedmulti-wavelength observations of the active region NOAA 10655. This activeregion was the target of the SoHO Joint Observation Program 157. SoHO/MDIand TRACE (195 A & 1600 A) were used. Simultaneously, we observed in the CaII and Na D1 lines with the spectro-imager MSDP mode of THEMIS.Alternatively to the MSDP, we used the MTR spectropolarimeter on THEMIS toobserve in Hα and in the Fe I doublet at 6302 A. We derived themagnetic field vectors around some Ellerman Bombs. We presented the firstimages of EBs in the Ca II line. We confirmed that Ellerman bombs can indeedbe observed in the Ca II line, presenting the same `moustache'' geometryprofiles, as in the Hα line, but with a narrower central absorption inthe Ca II line, in which the peaks of emission are around ± 0.35 A. Wenoticed that the Ellerman bombs observed in the wings of Ca II line have anelongated shape - the length being about 50 % larger than the width. Wederived mean semi-axis lengths of 1.4'' x 2.0''. In the UV time profiles ofthe Ellerman bombs, we noticed successive enhanced emissions. Thedistribution of lifetimes of these individual impulses presents a strongmode around 210 s. Studying the magnetic topology we found that 9 out of the13 studied EBs are located on the inversion line of the longitudinal fieldand that some typical examples might be associated with a Bald Patchtopology. We provided new arguments in favor of the reconnection origin forEllerman bombs. The different individual impulses observed in UV may berelated to a bursty mode of reconnection. We also showed that this Ca II8542 Å chromospheric line is a good indicator to detect Ellerman bombs andcan bring new pieces of information about these phenomena.

Authors: E. Pariat, B. Schmieder, A. Berlicki, Y. Deng, N. Mein, A. Lopez Ariste & S. Wang
Projects: None

Publication Status: A&A (in press)
Last Modified: 2007-07-03 09:43
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