Exploration of long-period oscillations in an H$alpha$ prominence. (arXiv:1903.00230v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zapior_M/0/1/0/all/0/1">M. Zapiór</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schmieder_B/0/1/0/all/0/1">B. Schmieder</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mein_P/0/1/0/all/0/1">P. Mein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mein_N/0/1/0/all/0/1">N. Mein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Labrosse_N/0/1/0/all/0/1">N. Labrosse</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Luna_M/0/1/0/all/0/1">M. Luna</a>
Context. In previous work, we studied a prominence which appeared like a
tornado in a movie made from 193 {AA} filtergrams obtained with the
Atmospheric Imaging Assembly (AIA) imager aboard the Solar Dynamics Observatory
(SDO). The observations in H$alpha$ obtained simultaneously during two
consecutive sequences of one hour with the Multi-channel Subtractive Double
Pass Spectrograph (MSDP) operating at the solar tower in Meudon showed that the
cool plasma inside the tornado was not rotating around its vertical axis.
Furthermore, the evolution of the Dopplershift pattern suggested the existence
of oscillations of periods close to the time-span of each sequence. Aims. The
aim of the present work is to assemble the two sequences of H$alpha$
observations as a full data set lasting two hours to confirm the existence of
oscillations, and determine their nature. Methods. After having coaligned the
Doppler maps of the two sequences, we use a Scargle periodogram analysis and
cosine fitting to compute the periods and the phase of the oscillations in the
full data set. Results. Our analysis confirms the existence of oscillations
with periods between 40 and 80 minutes. In the Dopplershift maps, we identify
large areas with strong spectral power. In two of them, the oscillations of
individual pixels are in phase. However, in the top area of the prominence, the
phase is varying slowly, suggesting wave propagation. Conclusions. We conclude
that the prominence does not oscillate as a whole structure but exhibits
different areas with their own oscillation periods and characteristics:
standing or propagating waves. We discuss the nature of the standing
oscillations and the propagating waves. These can be interpreted in terms of
gravito-acoustic modes and magnetosonic waves, respectively.
Context. In previous work, we studied a prominence which appeared like a
tornado in a movie made from 193 {AA} filtergrams obtained with the
Atmospheric Imaging Assembly (AIA) imager aboard the Solar Dynamics Observatory
(SDO). The observations in H$alpha$ obtained simultaneously during two
consecutive sequences of one hour with the Multi-channel Subtractive Double
Pass Spectrograph (MSDP) operating at the solar tower in Meudon showed that the
cool plasma inside the tornado was not rotating around its vertical axis.
Furthermore, the evolution of the Dopplershift pattern suggested the existence
of oscillations of periods close to the time-span of each sequence. Aims. The
aim of the present work is to assemble the two sequences of H$alpha$
observations as a full data set lasting two hours to confirm the existence of
oscillations, and determine their nature. Methods. After having coaligned the
Doppler maps of the two sequences, we use a Scargle periodogram analysis and
cosine fitting to compute the periods and the phase of the oscillations in the
full data set. Results. Our analysis confirms the existence of oscillations
with periods between 40 and 80 minutes. In the Dopplershift maps, we identify
large areas with strong spectral power. In two of them, the oscillations of
individual pixels are in phase. However, in the top area of the prominence, the
phase is varying slowly, suggesting wave propagation. Conclusions. We conclude
that the prominence does not oscillate as a whole structure but exhibits
different areas with their own oscillation periods and characteristics:
standing or propagating waves. We discuss the nature of the standing
oscillations and the propagating waves. These can be interpreted in terms of
gravito-acoustic modes and magnetosonic waves, respectively.
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