Long-period oscillations in solar coronal bright points

¹ Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany e-mail: tian@mps.mpg.de
² Department of Geophysics, Peking University, Beijing, PR China
³ School of Space Science and Physics, Shandong Univ. at Weihai, Weihai, Shandong, PR China e-mail: xld@sdu.edu.cn
⁴ Department of Physics, Stanford University, Stanford, CA 94305, USA

Received: 7 May 2008
Accepted: 20 June 2008

Abstract

Aims. By analyzing TRACE (Transition Region and Coronal Explorer) data, we investigate intensity oscillations in coronal bright points (BPs) as well as the underlying chromosphere.

Methods. A Fourier analysis is applied to a sequence of images observed in the 195 Å and 1216 Å passbands of TRACE. We produce images of Fourier power in three different period ranges (4–16 min, 20–40 min, 42–75 min). The presence of periodic oscillations are further checked by applying a wavelet analysis to a selected rectangular region in each of the three BPs.

Results. We find a clear signature of oscillations with different periods dominating in different strands of BP loops in the 195 Å passband. The oscillatory power is stronger in BPs than in the surrounding quiet Sun. In the chromospheric 1216 Å passband, oscillations in these period ranges are found mainly above the magnetic network elements, which are not necessarily associated with the coronal BPs. The wavelet analyses reveal that oscillations with periods ranging from 8 to 64 min can last for several cycles in both the BPs and the underlying chromosphere.

Conclusions. It is still unclear whether these oscillations are caused by propagating magneto-acoustic waves in loop systems associated with the BPs, or result from recurrent magnetic reconnection powering the BPs.