Small-scale oscillations in a quiescent prominence observed by HINODE/SOT

Prominence oscillations

¹ Purple Mountain Observatory, Nanjing 210008, PR China e-mail: ningzongjun@pmo.ac.cn
² Center for Solar Terrestrial Research, New Jersey Institute of Technology, Newark, NJ 07102, USA e-mail: wcao@bbso.njit.edu
³ National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan e-mail: joten.okamoto@nao.ac.jp
⁴ Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto 607-8471, Japan e-mail: ichimoto@kwasan.kyoto-u.ac.jp
⁵ Yunnan Astronomy Observatory, Kunming 650011, PR China

Received: 25 August 2008
Accepted: 6 March 2009

Abstract

Context. Investigations of the behavior of small-scale threads can provide an alternative approach to studying prominence dynamics and understanding its origin and nature.

Aims. The behavior of threads are analyzed in a quiescent prominence, including drifting and both the horizontally and vertically oscillating motions. These indicate waves in the solar prominence.

Methods. We used the Hα images at a setting wavelength of +0.076 Å. A quiescent prominence was observed by HINODE/SOT on 2008 January 15 for about 3 h in total.

Results. Consistent with previous findings, prominences show numerous thread-like structures. Some threads clearly exhibit both vertically and horizontally oscillatory motions, while others are only drifting. Complicated cases show both drifting and oscillatory motions simultaneously. In the upper part of the prominence, the threads are oscillating independently of each other. We find that three threads oscillate with the same phase for at least two periods. The oscillations seem to be strongly damped since they disappear after a few periods. The maximum number of observed periods is 8 in our observations. In the lower part of the prominence, however, the different threads have a mixed character with the individual oscillatory motions unstable for one entire period. Most oscillatory motions will disappear after a half period or less, while the new oscillatory motions are excited nearby. A 5-min period is predominant, and the oscillating amplitudes show an average value of ±3.5 km s^-1. We find some upflows in the spicule layer, and they appear to transport the mass from photosphere (or spicules themselves) to the prominence. These upflows have an average velocity amplitude of 0.8 km s^-1.

Conclusions. The threads exhibit three distinct behaviors. The first is only drifting, the second is typically oscillating, and the third shows both characteristics. There are no substantial differences between the periods of horizontally and vertically oscillating threads in this prominence.